Bottlehead Forum
Bottlehead Kits => Stereomour II => Topic started by: denti alligator on December 18, 2021, 05:36:36 PM
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I’ve had my Stereomour II (w/ shunt regulator) for about 6 years now. Almost no issues. Lately I’ve been so swamped at work that I haven’t had the chance to listen to much music at all. It’s been 2 or maybe even 3 weeks since I turned it on. Today I turned it on and got a scratchiness (slight pops, too) in the right channel and no sound at all in the left channel. I have swapped tubes. No change. Tomorrow I’ll put it on the bench. What should I look for as a possible cause?
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The first thing to check is that the input and output cables are connected and the source(s) and speakers are working - it happens more often that you would think! (Just last week I lost a channel; it took me a good hour to determine that one of the banana plugs to the crossover had fallen out of its connector :^\ - it should have taken 30 seconds!)
The most common cause is (of course) an unreliable connection. Somewhere. But don't just go looking for one, there are too many possibilities, and it might be something else anyhow. Check the resistances and voltages, which will point to many fewer probable causes.
Post some pictures too. High resolution and good focus helps, since one can then zoom in on individual connections, solor codes, etc. The more information, the faster the diagnosis. It's difficult, but try not to make any premature changes, since they often invalidate the list of symptoms and confuse the thread.
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I checked the sources and speaker connections already. Forgot to mention that. I’ll double check again this morning to be sure. I find it odd that everything was working fine for over 6 years. I didn’t move it, either. Can this really be from a solder joint that went bad after this much time?
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What's the passcode for the manual archive? I have misplaced my digital copy and need to re-download.
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resistance:
1. 1.1m (and rising)
2. 1.1m (and rising)
4. 248.7k
5. 1
6. 1284
7. 3.26m
8. 00.9
9. .303m
10. 8.3k
11. 7.71k
12. .303m
13. 00.8
14. 3.28m
15. 2907
16. .008
17. 248.5k
18. .009
19. 1.1m (and rising)
20. 1.1m (and rising)
21. 1494
22. 1298
24. 1298
25. 1284
26. 1.0
27. 1.03m (and rising)
28. 0.8
29. 0.8
30. 1m (and rising)
31. 1m (and rising)
32. 0.9
33. 0.8
34. 1m (and rising)
35. 0.8
36. 2908
37. 2921
39. 2921
40. 3117
These already show some issues. What other terminals should I check? Should I move on to voltages?
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15. 2907
There's a 2K and a 3K resistor in parallel in this region. Your 2K resistor is likely loose.
When you post a list of resistances, it's a good idea just to post the ones that don't align with the manual.
What are your voltages?
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When you post a list of resistances, it's a good idea just to post the ones that don't align with the manual.
What are your voltages?
Sorry, I can't locate my manual :(
I'll post voltages soon.
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I would deal with the 2K resistor issue before messing with voltages.
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1. 370
2. 389
6. 52.6
7. 241.8
9. 305.3
12. 303.8
14. 301.4
15. 64
19. 394
20. 380
21. 53.2
22. 53.8
24. 53.9
25. 53.6
27. 388
30. 395
31. 397
34. 391
36. 63.7
37. 63.8
39. 64
40. 63.6
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I would deal with the 2K resistor issue before messing with voltages.
I flowed the terminals on either side of that resistor. Same readings after. Above are the voltages. I can try flowing and adding some solder to 16/36. I nicked the cap on 20/30 in do this, unfortunately. I hope it isn't damaged.
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15 is a bit "dirty." Not sure what this black stuff is...
... cleaned it up with the rubbing alcohol, swipes, and a toothpick.
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Again, terminal 15 (and the others that should read 1.2K) get that resistance from a 2K and 3K resistor that are wired in parallel. You are seeing a 3K resistance here meaning the 2K resistor isn't connected. This resistance issue would be the most important thing to resolve at the moment.
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How would you recommend going about it? Should I de- and re-solder both joints? I have reflowed and added solder twice now to both 16 and 36, top and bottom (where that resistor is connected). Should I try reflowing 15?
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Can you use your meter probes to verify that the 2K resistor is reading 2K?
If the 2K resistor is reading 2K but those terminals read 3K, the 2K resistor is not properly connected.
Looking at your solder joints, more heat and a clean tip would be helpful.
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Can you use your meter probes to verify that the 2K resistor is reading 2K?
If the 2K resistor is reading 2K but those terminals read 3K, the 2K resistor is not properly connected.
Looking at your solder joints, more heat and a clean tip would be helpful.
That resistor is reading 2909. Does this mean it’s damaged?
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Why don't you heat up the solder joint that holds one end in and pop one lead out, then measure the resistor that way.
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I’m not getting a reading at all now (having detached one end).
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OK, I would replace that part then. One possible reason this could happen is inserting the 2A3 tube on that side without the fat pins on the tube aligned with the fat pins on the socket, which could allow a direct connection between B+ and the cathode resistors, which would also possibly cause some swelling of the top of the 220uF cap mounted in that area. Otherwise it would be very abnormal for a part like that to just randomly open up.
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I haven’t switched out (let alone taken out) the tubes in over a year. And it was working fine just a few weeks ago. Strange. Does it matter what brand I use? I can get some TOUHIA ones on amazon by Tuesday, which would be nice.
https://www.amazon.com/TOUHIA-Wirewound-Ceramic-Resistor-Inductionless/dp/B07VRBRTVX/ref=sr_1_3?crid=2ZG6I62U7OBAR&keywords=Resistor+2k+5w&qid=1639934974&sprefix=resistor+2k+5w%2Caps%2C84&sr=8-3
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Sure, those will work. If the leads don't reach the terminal strips you can just wrap them around the remaining 3K resistor.
The brand isn't so important because the AC signal current is almost completely handled by the cathode bypass cap.
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Great, thanks. So I won’t need to replace the right channel resistor to match?
Here’s the cap I nicked. Will this be a problem?
Actually, I have a pair of Solen 3.30uF/700V and another pair of Solen 0.10uF 630V caps. I forget where these were supposed to go (and without the manual this is hard to tell). I assume the former could replace the nicked cap and its pair? And the other would go on the PC board where the Daytons are?
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I would replace that Solen, yes. You do not need to replace the other 2K resistor, as I said before, these are almost entirely out of the signal path.
I would do the least possible amount of messing around until you get the amp up and running properly again. If you go to put the 0.1uF Solen caps on the regulator board and that modification causes new problems, it will make debugging a lot more difficult.
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OK, but just to confirm (sorry, again, I don’t have the manual on me), the 3.3uF would go to where that nicked cap is?
I’ll wait off on the regular board cap upgrade.
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If you twist the melted cap over, it should say 3.3uF on it, and yes, that's where that part goes.
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If you twist the melted cap over, it should say 3.3uF on it, and yes, that's where that part goes.
Sorry, I have Clarity Caps here and the markings have faded.
Thanks for all your help! I’ll report back when I get the replacement resistor in Tuesday.
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New resistor installed.
Terminal 15 now reads 1176. Not balanced with the right side, but should this be okay?
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That is in spec.
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Thought so. But now I’m not getting sound out of either channel. Will post voltages in a moment.
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I was hoping to get the manual first, but Dan accidentally sent me the manual for the filament upgrade. While I’m waiting I’ll just check the voltages anyway. Which of the ones listed above are off? Maybe I can compare to that list and post just the problem readings.
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Just posting the voltages on each 4 pin socket would provide a lot of information.
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A1. 56.8
A2. 366
A3. [no reading]
A4. 57
B1. 51.4
B2. [no reading]
B3. 51.6
B4. 51.6
Clearly there’s a problem.
I was over hasty and added those new caps after the resistance checked out. So that’s most likely where the problem is. I can put the Daytons back if you think that will help.
The one terminal with an off reading is 14, which has 301
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The 4 pin socket readings you have at B would have me wondering if that tube is properly installed, but at the same time seeing 366 and A2 tells me that you haven't done this on the B socket, but rather you likely need to remeasure.
The [no reading] should be around 0V, and 0V is a reading.
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Yes, sorry. 0 for A2/B2.
That 14 terminal is a problem, though, right? Must be related to the resistor I replaced, no?
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Pin 2 is the plate and will carry the high voltage. Pin 3 is the grid and will be approximately at 0V.
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Sorry, for A3/B3 I am getting about -0.17
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OK, that is correct.
I would recheck pin 2. It is highly improbable that you have ~60V on either of those.
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Let me do it again. Sorry, I did mix up the pins.
A1. 53
A2. 366
A3. 0
A4. 53.1
B1. 54.7
B2. 356
B3. 0
B4. 54.8
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OK, the 2A3s are working properly. What are the voltages on the metal tabs of the C4S driver boards?
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OK, the 2A3s are working properly. What are the voltages on the metal tabs of the C4S driver boards?
Which tabs? All of them?
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Sure, you can list them as big board and small board.
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Big board
bA 0
bB 0
A +reg 310 and dropping
B + reg 305 steady
A1 384
B1 382
OA 303.8
OB 305
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Little board
OA 239.5
OB 301.5
1A 304.9
1B. 303.8
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Ok, that narrows things down a bit. The regulator seems to be doing its job, but the OB on the small board tells us that the driver half of one 12AT7 isn't drawing any current. This could be a loose resistor on pin 3 of the 9 pin socket under the small board, a bad solder joint on the small board (it doesn't matter if it has been working for x many months/years, it can still happen), a broken wire, or a loose resistor going to pin 2 on that same socket.
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OK, I reflowed 2 and 3 on the 9-pin. The LEDs for B on the small board are not lit up. What else can I try?
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I tried switching the 12AT7 tubes. Now the LEDs all light up. Maybe one of them wasn’t in right?
Voltages for small board are not even:
1A 354
1B 303.7
OA: 285.7
OB: 244.4
I also reflowed all connections on the small board
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If plugging and unplugging the tubes is causing huge changes, you have loose socket connections (or something connected to a socket is not well connected at its other end).
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Sockets are very very tight.
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It's not the sockets, it's that something connected to the socket pins is loose or not well soldered.
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I’ll reflow all the pins. But here’s something weird. I switched the tubes again and the LEDs, went out. So I switched them back and they’re back on. ??
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I reflowed all the pins. Can you tell me what readings I’m supposed to get on the boards? I’ve still got a discrepancy between A and B.
(And I’m starting to despair.)
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OA and OB on the big board should be just a bit over 300V.
OA and OB on the small board should be around 200V.
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Readings on the big board have changed:
OA: 380
OB: 348
Small board
OA: 289
OB: 246
Does the odd reading at 14 not tell us anything?
Also, the consistency with which those B LEDs go out when I switch the tubes has me troubled. If it were a matter of something loose, wouldn’t it not be coinsistent? Again, the B LEDs only light up with one of the tubes—the same tube.
Could it be that one of the tubes is bad?
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14 is wired to OB on the small board.
The pair of high voltages on the big board indicate loose connections and/or broken wires.
You have loose connections or broken wires.
The high voltage at OA on the small board are a different loose connection or broken wire that's likely unrelated to the bigger regulator board's issue.
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OK, thanks. How would suggest trying to track this down? Systematically reflowing all connections on the left side? I did the board, but not the resistors and transistors on it. I guess I can reflow those, too.
Can you explain why switching the tubes makes the LEDs lights not light up?
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Well, I’m leaving town for a week and won’t be able to work on this till I return. A little tomorrow morning, if you have any last-minute suggestions.
Here’s what I’ve done:
Reflowed (and in some cases added new solder) to
- All 9 pins of left channel tube, including center pin.
- Terminals 14 (top), 16 (top and bottom), 36 (top and bottom), 12 (bottom), 11 (top), 34 (top and bottom), and probably more.
- All wire connections to small board
- reflowed transistor leads on B side of small board
- all wired connections to big board
Checked all wires and leads going to left 9-pin socket. No nicks or breaks or interferences.
I don’t know what else to do.
Note that I get different readings when I switch the tubes, and I also get LEDs lit up with ones but not the other. This goes *with the tube*, but doesn’t affect the LEDs when I move it to the other side. The readings, though, are consistent.
ONE WAY:
Small board:
No B LEDs
OA 233
1A 305
1B 304
OB 301
Big board:
OB 305
1B. 389
OA 303
1A 388
OTHER WAY:
Small board:
B LEDs are lit up
OA 291
1A. 347
OB 242
1B 304
Big board:
OB 325
1B 387
OA 303
1A 389
If I didn’t know better (and I don’t!) I’d say there’s a problem with one of these tubes.
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You can certainly put a new pair of tubes on order, but I wouldn't be super convinced that this will take care of all the issues. Still, it would be helpful to reduce some variables in the process.
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Alright, I’ve ordered a new pair which should be here when I get back home in a week.
Assuming the problem persists in some fashion:
Is there anything I can do to narrow down the source? See the list of what I’ve done above.
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I may be way off base here, and I don't own a Stereomour II. But I seem to remember reading something PJ wrote about the 12AT7 in the amp. I think he said one triode in the tube was the voltage amplifier. So being the efficient engineer he is the left triode is used in the left tube and the right triode is used in the right tube, or visa versa. So on the base amp without shunt regulation when you wear out the 12AT7 you could swap left for right and start using the fresh triode in each tube.
If this really is the case maybe one triode in one of your 12AT7s is bad and swapping them put the working triode in the gain position. Of course if you do have the shunt regulation upgrade it would also mean the bad triode is now doing SR duty and that is not working properly. If that is the case a new tube or pair of tubes should fix the problem.
Paul, if this is totally wrong and would only confuse others who read it please delete this post.
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...
Paul, if this is totally wrong and would only confuse others who read it please delete this post.
I don't think that is totally wrong, though there are some indications of further issues. Trying some fresh tubes will help answer that question.
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Thanks, Ken. I do have the shunt regulator installed. I’m curious to see what happens when I try the new tubes. I’ll report back in about a week.
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New tubes in. Voltages look to be normal now. I guess it was a bad tube after all. Maybe even explains how that resistor got shot?
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ONe major problem solved. Next one predates this and I thought it was related, but it persists:
Intermittent scratchiness in right channel
Switching tubes does not change this
Selecting different input does not change this
Balance control does not eliminate (so even if I move the balance all the way to the left channel, I still hear the scratchiness in the right channel)
Hum pot doesn’t change it
Volume doesn’t affect it.
I tried reflowing some of the pins of the 9-pin socket and some terminals on the right side. Nothing yet.
I assume this is a loose wire or bad solder joint. Any suggestions for which terminals I should attend to first?
Thanks!
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Hook up a really cheap pair of speakers to the Stereomour while it's running and use a wooden chopstick to poke around in the circuit. When you poke at the problematic connection, you should get a nice pop through one or both speakers.
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Hook up a really cheap pair of speakers to the Stereomour while it's running and use a wooden chopstick to poke around in the circuit. When you poke at the problematic connection, you should get a nice pop through one or both speakers.
I tried all over the place, but nothing. Couldn’t even determine a connection between my poking and the scratchiness. How hard should I be doing this? I was poking on every terminal and pin.
It’s quiet now. It can be totally quiet for several minutes and then start up again.
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Are you 100% sure this isn't noise from a wireless device getting into your Stereomour? This kind of noise sounds more like a Morse Code pulse with somewhat irregular periodicity.
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No. That might be it. Let me move things about a bit and see what happens.
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I unplugged all other transmitting devices nearby. No difference.
I moved the amp to the other side of the house, into a room where there are no electronic devices at all. Same problem. Right channel only.
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Try cleaning the tube sockets and pins?
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Try cleaning the tube sockets and pins?
Busting out the Deoxit! Though Paul is right that the intermittent nature of this points to some external interference. But a) why only the right channel and b) why no change in other parts of house?
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Throwing up my hands!
Still scratchy. Pretty quiet. Maybe I have to learn to live with it?
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Is it possible it’s not a connection but something in the transformer?
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No, it's not a transformer or a part that's doing that. This issue sounds a lot like a contact problem like a cold/loose solder joint or tube pin corrosion, though you ruled that out with some new tubes.
Did your DC voltage issues disappear completely?
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Yes. The only discrepancy is the terminals that are supposed to read 58 are 51.6 on the left and 56.6 on the right.
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I’m continuing to prod the circuits with a chopstick. Nothing. I’m trying every terminal, every wire, every socket, every resistor and capacitor, every connection on the PC boards. Nothing.
Last time I turned it on the scratchiness started before the LEDs lit up. Not sure if that tells you anything.
However, for the last 2-3 minutes it has been quiet. ??
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It’s back. Have we exhausted troubleshooting options?
Again:
- volume is turned all the way down
- balance doesn’t change the scratchiness
- it’s very intermittent (sometimes stops for minutes at a time)
- but I turned off my router, all close by electronics and shut off phones (no difference)
- prodded every single terminal and connection while on with no increases in sound.
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You said you replaced the tubes, did you replace all tubes or just the 2a3's?
My money is still on the 12at7 on the offending side. a thorough cleaning / scraping of the pins and socket may help.
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Last time I turned it on the scratchiness started before the LEDs lit up. Not sure if that tells you anything.
That tells me it's most likely that your issue is in the power supply and/or output stage, so 4 pin sockets and power supply wiring, not the C4S boards and 9 pin sockets.
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That tells me it's most likely that your issue is in the power supply and/or output stage, so 4 pin sockets and power supply wiring, not the C4S boards and 9 pin sockets.
OK, I’ll go and reflow those. Which are the main terminals for the power supply on the right channel?
I replaced the 12AT7s. The 2a3s are not an issue I don’t think. At the least, when I switch them the scratchiness stays in the right channel.
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The SM2 uses a pseudo dual power supply, check/reflow the 130 ohm resistors and the 100uf caps on the offending side and also the connections where it connects to B+
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I reflowed and added a little solder to the right side 4-pins and terminals connected to it and to the terminals where the 100uF caps are and to the tabs on the chokes.
Turned it on: scratchy.
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I think I’m ready to send this in. Paul, can you tell me which terminals I should reflow besides the 4 pins, and I’ll try one more time. If that doesn’t do it, I think I’ll let you take over.
I decided to tighten the socket brackets on the 4-pin R. This has significantly reduced the amount of scratchiness. I’m getting a short pop here and there, at most. So these pins are clearly the culprit. I had already reflowed them carefully. The 2a3 was a bit too easily wobbled in place, hence the idea. Now, granted, the L side is about the same (in terms of looseness). And again, I’m still hearing a little scratch or pop every 30 seconds or so. Aaaand, as I write it’s starting to make the noise again steadily…. So never mind!!
… aaaaand now it’s quiet again, with the occasional scratch/pop. So annoying. I’ve done nothing in the meantime but sit here. I’m not even playing music.
(And if it is these pins, why wouldn’t I get a reaction from gently rocking the tube in place while turned on, which I tried?)
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You could try a replacement socket. If there's any possibility that the fat pins were ever inserted into the wrong holes, or even just attempted for that matter, that can stretch things out a bit.
Otherwise just follow all the wiring that leaves the 4 pin socket to the 12 or to terminals closest to those sockets and reflow those joints.
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It was pretty quiet for about an hour, then I left the house. I’ll test it again tomorrow. I don’t think I ever put the tube in wrong. I’ll report back. Do you think replacing the socket is the way to go?
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If you wiggle the 2A3 around in that channel and hear the noise, I would either replace the socket or be sure that both ends of everything connected to each socket pin is well connected.
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Well, maybe it’s not those pins after all. I woke up this morning, flipped on the amp, and the scratchiness started worse than ever. Moving the tube in the socket *does not* affect the noise. There is zero connection. Sometimes I wiggle the tube and it’s totally quiet. Sometimes it makes noise when I’m not touching it.
I cleaned the socket with Deoxit again. Nothing. But now as I’m writing it has stopped. Maybe warming up has an effect on it?
Nah, it just started again. If I didn’t know better, I’d say this is interference from a wireless signal or something. It’s so erratic.
At this point I think I’ll contact Eileen and get it sent out to you. Not sure what else to do.
P.S. Yeah, I’m done. If anything, it’s gotten worse. I tried tightening the sockets again. No difference. I’m very curious what you find, Paul! Coming your way soon.
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Can you post a recording of the noise?
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Can you post a recording of the noise?
Sure. Gimme a minute or two.
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Here is about 1:30 from the moment I turned on the amp.
https://www.dropbox.com/s/swy8l1cuzyluszc/New%20Recording.m4a?dl=0
Just so you know: I left the amp on and it’s quiet now. Won’t last more than 30 seconds, though.
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Hum balance pot, maybe?
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Hum balance pot, maybe?
I reflowed the connections there and have adjusted it to see if it has any effect. None.
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Again, I’m giving up. I can’t see where this is coming from. If I jab every single terminal, plus some of the wires, plus some of the resistors and capacitors and it makes no difference; if I re-flow almost every connection and the right side and it makes no difference; I don’t see what else to do. I guess I could switch out the sockets for the 2A3 tubes and see if it changes channels. I’m getting to the point of frustration—and also totally bummed to be throwing a small NYE party with no music.
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Happy New Year!
I’ve got my PayPal invoice to send this to you, Paul, but want to give you a chance to weigh in one last time after hearing the recording (posted on previous page). Let me know if there’s any last-minute tests you think might help locate the source of this problem. Otherwise, I’ll pay the invoice and initiate the repair shipment. Thanks!
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I still believe it's a loose connection with the realistic possibility that when it gets here it makes no noise in my workshop.
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And most likely it is, but damned if I can’t locate it. Would you suggest trying to swop out the tube sockets? If the noise moves channels, we’d at least know it’s something there.
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I think if you tried to remove the tube sockets, you'd probably damage one in the process to the point where it would no longer be useful, so you'd be worse off than you are now.
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Too late, unfortunately. And I have to say, the socket on the right doesn’t look good. One of the pins drops down into the socket all the way. The other socket looks good. I’ve done the desoldering and hardware exchange. I’ll resolder
after dinner and report back. If the noise moves channels I might as well start by replacing the socket.
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That was a bunch of work for nothing! Switched out the sockets and the noise is still in the same right channel.
There’s no way you won’t hear this, Paul. I’m very curious to know the source and am very happy for your help on the way and your repair expertise!
Thank you. I’m paying for the shipping box now.
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I appreciate your willingness to spend some time on your end before sending it out.
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I’m very grateful for your patience troubleshooting with me, especially during the holiday week.
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I finally had some bench time to explore this repair. The noise was absolutely there, so Denti isn't crazy. I ended up shorting stages to chase the noise and it was present even with the 2A3 grid shorted on the channel, so that localized it to a very specific spot. When I was looking around there, I noticed this crazy green corrosion on the tube socket, and I could poke around with my meter and measure some substantial DC voltage crawling around on the surface of the ceramic, so out that went and in went a new tube socket and all is well.
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Paul,
This doesn’t make sense, because one of the things I did during troubleshooting is to switch out the L and R tube sockets! The sound was still there, but only in the right channel.
I’m totally confused. Though I also have no idea what that green stuff is.
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Did you perhaps use alcohol to clean the contacts at some point? I could imagine the water content of rubbing alcohol creating the corrosion.
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No, I only used DeOxit.
And to clarify: I *swopped* the sockets (I didn't replace one). I wanted to see if the noise would travel with the socket. It didn't! Which is why Paul's solution doesn't make sense to me (though if it's quiet, who am I to complain?).
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The noise was absolutely there, so Denti isn't crazy.
I'm starting to think I am crazy! Seriously. The only thing I can imagine is that I somehow mixed up L and R speaker wires after I swapped the sockets. In fact, if Paul is only hearing noise in the left channel then this *must* be what happened. There is no other logical explanation. The socket was the issue and when I swapped them the noise went with it, but I didn't notice because I had mixed up the speaker wires...
The thing is: I'm pretty sure I didn't mix up the wire. In fact, I tried it on a couple speakers, so I would have had to mix up the wiring twice. Actually three times, because I tested right before packaging it up to send to Paul.
Paul, can you definitely reassure me there was only noise in one channel?
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I only heard the noise in one channel. I also mix up speaker wires and RCA plugs when trying to sort stuff like this out, so what you're experiencing is not that inconceivable.
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If this is the case it kills me, because that means I actually had figured out the problem (I even contemplated buying a new socket), but screwed up my testing. Talk about face palm!
Still, I simply cannot understand how I could have mixed up the wires...
Oh well, at least I'm also getting the right shunt regulator resistors installed. :)
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So, as I suspected, the source of this noise could not have only been that tube socket that Paul replaced. I received the amp back from him and there is still noise in the right channel. Only the right channel. Same as before.
Paul says the green residue is the source. However, I don’t see any of it on the right channel (now that the offending tube socket was replaced—however, remember that that socket was until the very last minute in the left socket and I never heard noise there). In fact, I see a tiny bit of this green residue on the left channel right now, but there is no noise in that channel. Never has been.
All I have ever used on this amp was 60/40 rosin core solder and deoxit. I’ve used solder wick (the copper ribbon kind), but that shouldn’t leave a residue. And I’ve used a Radio Shack solder tip cleaner. That’s it.
Suffice it to say I am very frustrated. I just spent over $300 for a repair, and while Paul fixed some things for me, the problem for which I sent it in has not gone away. Paul can chime in here. But I don’t understand his explanation, which does not account for how the noise is isolated to the right channel only.
At this point I’m going to have to live with it. Most of the music I listen to will drown it out. But I needed to vent a little and was hoping someone else might have some ideas or insights.
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We are just going to refund you since I was unable to successfully repair your kit.
-PB
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I am going to try and clean the offending area. Paul, could you please tell me what that area is. You said you had a narrowed it down to a specific area (power output). Knowing exactly which terminals to focus on would help.
First I’ll clean these. Suggestions: deoxit? Rubbing alcohol? Toothbrush? Cotton swabs?
If that doesn’t work I will remove solder and resolder.
If that doesn’t work I’ll try the dishwasher method.
Again, I cannot determine the source of this green contaminant. I’ve only ever used rosin core solder, deoxit to clean, desoldering wick, brass solder tip ‘scrubber’, and solder tip cleaning paste.
The cleaning paste contains tin and ammonium phosphate. Could these be at fault?
The desoldering wick is of course copper, so maybe it is to blame?
Google led me to some discussions of flux causing issues. I have rarely (if ever) cleaned off flux while soldering. Should I be? I will play around with my basic materials and an unneeded white ceramic socket I have and see if I can replicate the green contaminant.
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We are just going to refund you since I was unable to successfully repair your kit.
-PB
You don’t need to do that, especially if I can count on further guidance from you on this matter (see previous post). I do really want to get to the bottom of this.
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In our lengthy e-mail exchange, I posited a likely next step. Do I also need to post that here?
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Paul contacted me about this and I agreed with him that it is appropriate to give you a refund since you still have the noise issue. We were away from the business this weekend but you should see it today. And we will continue to support you here to try to resolve the issue.
It is frustrating when we send something in for a repair and the thing we wanted to get fixed is not fixed. I could tell you stories of my own from both sides. After experiencing this a few times over the years it seems to me that sometimes the issue is elusive enough that it doesn't manifest itself very often. That can make it difficult for the tech to verify resolution absolutely in the time they can allot to the project. What Paul did find - conductive tracks of corrosion across the one tube socket - is certainly something I would have assumed to be a red flag and his replacing that socket was the appropriate course of action whether it was the source of the noise or not. It is unfortunate that it did not resolve the noise but it was imperative to fix from the standpoint of functionality.
Not sure if ammonium phosphate could cause the corrosion issue but I had experiences in the past with corrosion appearing after a while on terminals when I used a sal ammoniac block - ammonium chloride - for tip cleaning. The dishwasher cleaning method can be a pretty effective means of removing stuff that you don't want to be on the connections whether it be flux or other contaminants. Just make sure the components are completely dry before testing and powering up.
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OK, I guess I will try the dish washer method. Is a heat dry cycle safe or should I just take it out an air dry when it’s done?
I inspected the amp again yesterday and could not find any traces of the green residue, except on the other tube socket. But I’m not getting any noise on that channel! Is it possible that something is allowing for the interference from this green stuff to move channels? That would explain, in part, how replacing the right socket (that was on the left for most of the troubleshooting) mitigated the noise but didn’t eliminate it.
Also, I tried playing around with an unused socket: soldering, desoldering with wick, using the tip cleaner, etc. No green residue. I don’t know where it came from.
I looked at the old Sovtek 2A3s, since one of these failed on me a few years ago, and there’s no trace of anything on them. But the Shuguang tubes I have in there now look different. One of them has a tiny speck of green on it and it looks like there may be (very hard to tell without magnification) green underneath the pins (where the pins meet the ceramic base). Could this stuff be “leaking†from the tube? (Note that switching tubes from channel to channel makes no difference.)
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My logic flow for this
1) we don't know the exact cause of the noise problem
2) we've seen corrosion on the amp somewhere and we know that corrosion can cause similar problems
3) there might be corrosion somewhere in the noisy channel that is hidden - maybe under solder joints, maybe up inside the gap between the tube pin terminals and the ceramic, maybe elsewhere.
4) dishwashing might solve the problem based upon our past experience, and it is less intrusive than replacing parts until the noise subsides
I don't feel I can offer any other useful speculation until that has been attempted. The best bet is probably to try the dishwasher method, make sure the amp is absolutely bone dry, check all the resistance readings and then check all the voltages. Then run the amp and see if it has resolved the issue. At that point we can regroup and see where we are at.
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Great, thanks. A couple more questions before I proceed:
1. Is the heat dry cycle of the dishwasher going to be safe (it gets awfully hot).
2. I'm assuming I take out the tubes and don't include them in the wash.
3. There is some weird black gunk on parts of the amp that wasn't there before. Looks like it could melt (further). Should I try and remove this? Paul, can identify this?
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if your dishwasher's dry cycle gets hot enough to melt plastic kitchenware then it's probably not a good idea.
Yes please remove the tubes
The black material is a high temp adhesive that has been applied to the capacitors to keep them from getting knocked around in shipping. It can stay.
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Non-dishwasher safe plastic can get warped/melted, especially if put on the bottom. I could put it on the top and minimize the dry cycle? I just want to be sure I don’t inflict more damage.
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Can't really speak to this with any certainty but that probably makes sense. Might be a good idea to let the amp sit for some time afterwards too, to be sure all the nooks and crannies get dry. It couldn't hurt to blow a fan on the chassis for a while.
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Thanks, Dan. I looked into it and apparently my dishwasher reaches 150 degrees (Fahrenheit). So long as that’s not too hot, I will run it. Paul mentioned the possibility of discoloration. Is this from the heat or the water? What if I put a cover on the top and leave the bottom open to get the majority of the direct water spray?
I’ll probably try it tonight and then let it dry overnight.
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Electronic components are typically rated for 85C which is 185F. Darkening of the raw aluminum panel can occur if you use detergent containing phosphates. If the top is covered I would guess that water will get trapped inside. But I have not covered the top so I don't know what the result would be.
Instead of using the dishwasher's dry cycle you can put the chassis in an oven set to 170F after cleaning.
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I have no idea what causes the discoloration I sometimes get on the bare metal. When I've done this, I always do it with no detergent and the silver aluminum plate will often take on mild gold hues here and there.
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OK, I ran it through the dishwasher today. That cleaned it up nice! The green discoloration on the left socket is now gone. Resistance and voltage check out fine. Same noise is present in the right channel. Where do we go from here?
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You replace the remaining tube sockets and potentially any terminal strips that could have been affected by the green goo.
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I don’t know what that was and the last time I saw it it was on the left socket (no noise in left channel). Is there any way to isolate the source of the noise more precisely? Seems like a lot of work for something that may not be the cause.
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You can ground the grid of the 2A3 on the noisy channel to see if that makes the noise go away. That is how I isolated the noise on the output stage when I had your amp on the bench.
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You can ground the grid of the 2A3 on the noisy channel to see if that makes the noise go away. That is how I isolated the noise on the output stage when I had your amp on the bench.
Can you tell me how to do that?
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You can wrap a piece of bare wire around the 249K resistor.
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You can wrap a piece of bare wire around the 249K resistor.
Can you be a little more detailed. What kind of wire? Anything? How much? Wrap around what part? The body? How many times? (Sorry for all the questions)
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Since you are trying to create a short, you are connecting one end of the 249K resistor to the other end of the 249K resistor. A clip lead would work fine.
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Since you are trying to create a short, you are connecting one end of the 249K resistor to the other end of the 249K resistor. A clip lead would work fine.
Got it, thanks. I’ll try this a bit later. If I still hear the noise, what does this mean? If I don’t, what does it mean?
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It splits the circuit in half. Noise present means it's related to the 2A3 output stage. No noise means it's back around the 9 pin socket area.
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Well, it was not easy to attach a wire there. The lead on one side was practically non-existent. But I think I got it and the noise still persists. (Though I guess it’s possible I didn’t attach the wire well enough. Can I just connect terminals 4 and 5 instead of trying to get at the resistor leads?)
If I have to systemically replace the parts, I’d rather go one at a time. What are the terminals, parts that this narrows it down to?
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Yes, connecting 4 and 5 is the same as connecting the resistor leads.
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Yes, connecting 4 and 5 is the same as connecting the resistor leads.
Alright, I’ll try it one more time to be sure.
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This time very securely connected 4 and 5. Noise immediately audible upon turning on the amp.
So, where should I start? Terminals 1-5 and 21-25? Could it be one of the PC boards? Should I take out the shunt regulator to eliminate that as a possible source?
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If the noise is there with terminals 4 and 5 connected, that indicates the PC boards are fine and that you should not remove the shunt regulator.
I would swap 2A3s just to rule out the most obvious possibility. You can leave the jumper in for now.
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OK, 2A3s swopped. Same noise. Same channel. It’s immediate now when I turn it on.
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Now try it with no 2A3 at all.
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Now try it with no 2A3 at all.
No noise.
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Is there any green staining around the hum pot?
Do the DC voltages wander around when the noise creeps in?
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I don’t see any.
I haven’t tested the voltage with speakers attached. I can try that tomorrow. But I’m assuming I would have seen the wandering when I did the voltage test earlier, and I didn’t.
I did notice, though, that the voltages were slightly lower on the right channel. I think. I can double check tomorrow. Nothing dramatically different, but still.
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Just a thought, run the hum pot on that side back and forth a number of times and reset for lowest noise, can't hurt....John
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I tried turning the hum pot when I first was troubleshooting. Made no difference. I can try again.
Paul, when I test the voltages again later today do you want me to leave the jumper in or remove it first.
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You can leave the jumper there.
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OK, no obvious fluctuation in voltages when the noise comes in. No green visible anywhere.
Here are the voltages:
1:382
2: 399
6: 53.8
7:216.2
21: 54
22: 54.6
24: 54.7
25: 54.1
For comparison (the left channel, which works fine):
14: 210
15:56.5
19: 398
20: 370
36: 56.8
37: 57.4
39: 57.4
40: 56.7
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At this point I would suggest running the amp for a week straight without turning it off, then revisiting the issue. If there is some partially conductive goo still in there somewhere, it may burn out over time or make itself more obvious if the amp is allowed to run for a considerable time period.
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At this point I would suggest running the amp for a week straight without turning it off, then revisiting the issue. If there is some partially conductive goo still in there somewhere, it may burn out over time or make itself more obvious if the amp is allowed to run for a considerable time period.
Will do. I’ll report back next week. Or sooner, if it somehow disappears before then.
(It’s quiet now … was noisy a few minutes ago… )
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Quick update: nothing definitive yet, but it’s been on for 16+ hours now and although I can’t right now sit next to the speaker (or even in the same room), I was just downstairs and sat there for about 5 minutes (it’s rarely silent for more than a minute) and it was completely silent.
I remember when I first got it back from you, Paul, I turned it on and immediately put music on, so I didn’t hear the noise right away (I was listening to LPs, so easy to take the noise for static on the record). That night I accidentally left it on and in the morning I did not notice any sound. It wasn’t until I turned it off and then later back on that I heard the noise.
Also, you said you ran it for 40 hours straight with no noise. So maybe it goes away as the amp gets really warm?
Does this helps identify the possible source?
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This would be consistent with the contaminant hypothesis. If the contaminant makes semi conductive pathways in the amp but these burn off as the amp runs, you may be able to just cook this off by leaving the amp running continuously for a week.
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Fingers crossed
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I've been sitting here now for about 15 minutes or so, maybe slightly more. And it's been totally silent, until a second ago, when there was one brief burst of noise. Now it's quiet again. So I doubt it has been totally quite the whole time.
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Woke up this morning and it’s noisier than ever. :(
(Edit: it’s pretty chilly in the morning. Heat kicked in and since then it’s been silent…)
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Little over half way through the week. It’s been running non-stop. Sadly the hope I had around days 2-3 has vanished. It’s been pretty consistently noisy for the last couple days. It does sometimes go for longer without any noise at all, but rarely for more than a minute or two. 3 days to go. Maybe it will burn through whatever contaminant is in there after all. I’m not counting on it, though.
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OK, so it’s been a week that the amp has been on. This morning it is still making that same noise. Where do we go from here? I am willing to begin replacing parts on the right channel, if that’s what it takes. But it would be good to know where to begin. I’d rather move slowly and replace one part at a time to see if it makes a difference. I have wire. I would need new resistors and capacitors, if these might be the culprits. I could order these myself or if possible I would happily buy them from you.
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Since grounding the grid of the 2A3 allowed the noise to remain, you would want to replace:
4 pin tube socket (if it isn't the one I already replaced)
Both terminal strips bolted to the 4 pin socket
The 2K and 3K resistors
The 220uF bypass cap
The hum pot
The 22 ohm resistors
That would be my next step based on the information provided; it is not necessarily the solution.
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Thanks. What about the
220ohm carbon film resistor (red, red, brown, gold)
and
0.15ohm 3W (brown, green,
silver, gold, violet)
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Those are parts are unlikely to create noise problems if there's semi-conductive residue on them. The grid stoppers because there's no current flowing through them, and the 0.15 ohm resistors because they are already such low resistance that they are unlikely to be influenced by anything short of a dead short.
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OK, thanks. I'm getting the parts from Eileen. The socket is new (the one you put in) and I have extra 2K wirewound resistors. I'll start by replacing the 2k resistor, which I have on hand.
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I would suggest doing it all at once if at all possible.
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I would suggest doing it all at once if at all possible.
OK, will do. Though it would be kind of nice to know what, exactly, was at fault—if indeed any of these replacements fixes it.
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I’m replacing the parts Paul recommended to replace on the right side. As I’m doing so I’m seeing something that seems to me the obvious source of that green stuff: the 0.15ohm 3 resistors on the socket. They have a primarily green color, are right there where the green stuff was found, and I’m seeing that tiny bits of the outer green part of the resistors has chipped off. It’s the same green color that was there. Could I be that I put too much heat on those and the outer part (what’s it made of) “melted†down onto the socket?
Could these resistors be damaged in some way? They are not among the parts you told me to replace.
I’ll report back later, once I’ve switched everything out.
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OK, everything has been replaced. I flipped it on and it was noisy. Damn. But that only lasted about 10-15 seconds. Like it needed to clear its throat first. Mind you, this is only happening on the right channel, not the left, so this isn’t the usual slight sound of turning the amp on. But now it’s been quiet for about 5 minutes with only very, very, very tiny little pops every now and then. Fingers crossed. This might be the end.
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Right, spoke too soon. It’s definitely quieter. But those pops and scratchy sounds still come in every now and then. I’m keeping track of it.
By the way, with the balance turned all the way to the left channel I still hear the noise in the right channel. Not sure that helps identify anything.
In setting the hum pot I noticed that the right channel also has more hum than the left. And if I put my ear up to the mid range speaker I can hear a constant low-level scratchiness. So it’s still there, all the time, but it only gets loud enough to hear from listening distance about once every minute or so, then it quiets down. Certainly better than it was before, but not totally gone.
What other parts might I try replacing?
(Note that I didn’t replace the wiring, just the parts Paul listed above.)
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I’m seeing something that seems to me the obvious source of that green stuff: the 0.15ohm 3 resistors on the socket.
What about the hundreds and hundreds of other 0.15 ohm resistors in everyone else's Stereomour kits? How about the tens of thousands of these resistors that have been sold over the last decade and installed in consumer electronics? A little bit of critical thinking in situations like this can go a long way.
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Look, no need to get snarky. I’ve told you over and over that I have not used anything besides the products recommended on this forum and I’m trying to figure out the source. The same critical thinking would have me believe that whatever was there on the socket should be elsewhere, but I found no evidence of it. Not in any of the six or so other Bottlehead kits I’ve built. So I’m desperately trying to think where it may have come from. Maybe I overheated those resistors or something, I don’t know. It seems more likely than that this stuff came from the solder or iron or whatever. I was asking “might it be†the source since there is something green there with missing green parts. Doesn’t seem that outlandish. And you could have simply answered “no, that’s not possible†instead of insulting me.
Anyway, if the noise is still there, what am to do now?
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Next you'd want to put a clip lead back across the 249K resistor from 2A3 grid to ground on the noisy channel to see if the noise is still present. When you performed this experiment previously, the noise was unchanged, and it would help to know if that's still the case or if this eliminates the noise.
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OK, I clipped a lead across that resistor as before and the noise is still there. Note, however, that it is significantly less constant and loud.
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Now swap the 2A3s to see if the nature of the noise changes.
Also if you have to press your ears up against your speakers to hear what you're hearing, that would suggest that the amp is quiet enough.
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Yes, same noise with tubes swapped. I can hear the noise from 10 feet away. It is quieter, though, and less frequent. But then again, when I left it on for a week I had a day or two when it was similarly less constant and less loud. My comment about putting my ear up to the speaker was just to confirm that the low-level noise is indeed constant, unlike in the left channel, which is dead silent.
I’m happy to replace the remaining wiring and resistors in the right channel output stage, if these might be responsible. What about the other tube socket? Or, what parts could I swap with the other channel to see if the noise moves?
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Unless you think it’s a waste of time, I will swap these parts from one channel to the other to see if the noise moves: .15ohm resistors on 4-pin socket, .1uf. Capacitor (4U to 7U), 220ohm resistor (A3 to 4U).
Should I replace the wiring near the R channel 4-pin socket?
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How about you swap output transformers.
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How about you swap output transformers.
I may do that just to rule them out. I mean, it has to be coming from somewhere, and it’s not in the left channel. Having replaced most of the output stage of the right channel I might as well keep going.
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It does sound like you have come to the point of swapping transformer or other major components. If nothing else it gives you a chance to scrutinize each wire for something like a break under the insulation or something insidious, hold it in your hand and able to look from all angles.
And sometimes just taking it apart and putting it back together can make it magically start to work; gotta believe in magic...John
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This is a tough one! I've been following the thread, but I'm not as familiar with the layout of the 2.0 so I've not been posting.
I can't say I remember every trial that's been made, but it seems the noise is determined to be in the output stage or power supply. It occurs to me that the power supply is "pseudo dual mono," that is there are two stages of RC filter for each tube (130 ohm/100uF). You should be able to swap the power supply outputs between channels to test them.
I think you've already tried swapping speakers, in case it's a fault in one of them or the cables or connections. But I may be mis-remembering, so worth a try if you haven't.
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This is a tough one! I've been following the thread, but I'm not as familiar with the layout of the 2.0 so I've not been posting.
I can't say I remember every trial that's been made, but it seems the noise is determined to be in the output stage or power supply. It occurs to me that the power supply is "pseudo dual mono," that is there are two stages of RC filter for each tube (130 ohm/100uF). You should be able to swap the power supply outputs between channels to test them.
I think you've already tried swapping speakers, in case it's a fault in one of them or the cables or connections. But I may be mis-remembering, so worth a try if you haven't.
Thanks, Paul. I have tried swapping speakers. Even tried different speakers to be doubly sure.
I’m not following you on the RC filter: how would I swap the power supply outputs between channels?
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Changed the misleading subject heading of this thread, since the left channel issue was resolved early on.
Yesterday I swapped out the 0.15ohm 3W resistors. Noise still in R channel.
Today I'm going to swap the 0.1uf 630V cap on 4U/7U and 14U/17U and the 220ohm resistor on A3/4U and D3/17U.
After that I guess I'll swap the transformers.
What else is in the path that I could check?
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Thanks, Paul. I have tried swapping speakers. Even tried different speakers to be doubly sure.
I’m not following you on the RC filter: how would I swap the power supply outputs between channels?
I'll get back to you, but it will take me a while since I don't know the v.2.0 layout well.
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There is a blue wire coming off each plate choke that eventually connects to pin 2 of one of the 2A3s. One side side it is attached at 1L. On the other side it is attached at 20L. Just swap the blue wires connected at those terminals. I'm guessing you may need jumpers/clip leads. Be very careful not to short the jumper connections to anything.
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Thanks, Dan! Too late, though. I already removed both transformers. Oh well, fun times. I'm really, really hoping the noise travels channels, otherwise I feel like we've hit a dead end. Fingers crossed.
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Might as well do both. Swapping output transformers will tell you if the output transformer or its connections are making noise. Swapping the final power supply nodes will tell you if the noise is coming from the power supply filter components that are unique to a channel. I would lean towards the power supply final node being more a likely culprit than the OT.
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Great, thanks. I’ve remounted the transformers. I’ll wire them standard first and check, then try swapping the blue wire.
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We have the source of the noise!! It’s the transformer! I swapped them L/R and indeed the noise went from the R channel to the L channel. Phew!
Doc, can I get a replacement from you guys? I am happy to pay for it.
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Best bet is to do this thru the [email protected] email. We can certainly replace the noisy transformer but I'm not sure what the stock situation is on that part as I sit here. Transformers have been one of our biggest hangups supply-wise and Eileen can check inventory status and let you know via that email.
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I’m assuming I need the plate chokes, too? Do they come as a pair?
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I don't see any reason to replace the plate choke if the output transformer is the part that the noise followed.
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Sorry, my bad. I replaced swopped both parts. I just assumed they went together. So actually, I don’t know for sure if it’s the transformer or plate choke that is causing the noise. Is there a way to tell without stopping one part back?
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Not that I can think of. Always change one thing at a time.
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Alright, back to the bench!
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Perhaps just disconnect the choke inputs and outputs and temporarily extend the wires to put the chokes back to their original sides. This is not foolproof but may be telling.
Scientific method states only one variable change at a time.
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Not that I can think of. Always change one thing at a time.
Swapping the blue wires will swap plate chokes and power supply filters - but the output transformer exchange you just did says it isn't the power supply, so that's an OK way to test the chokes.
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That was a PITA, but it’s done and a good thing, too. So it’s NOT the transformer but the plate choke that is causing the noise. Swapping chokes moved the noise back to the right channel. Any idea what might have caused this part to fail?
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Following this thread with great interest
My Stereomour (I) also making noise as described here; also only right channel
Maybe I'll try to swap the B+ connection to plate choke (red wire in my case since its configure for 45 tube)
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I think you will probably be disappointed. This case is way an outlier. We have not ever had another noisy plate choke that I can recall. So it seems unlikely that lightning will strike twice in the same spot. Best to check the more likely culprits like bad solder joints first. Once the more likely things like tubes, solder joints, pin contacts, resistors and capacitors have been eliminated you could move on to more unlikely causes.
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Maybe Doc,
But this noise problem had going for a while and I have tried and eliminate the usual suspect : tubes, speaker, reflow soldier joint etc.
Since this check only involve swapping 2 wires, I might try it anyway.
I'll report back
Thanks
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Hi
I swapped the choke by swapping the blue wires connected to 4pin socket from left to right.
The result : noise is moved from right to left. I think the choke has some problem.
I guess I will need to order replacement
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If you swap just the blue wires, you are changing the current loop for the output stage to include the other half of the pseudo dual mono power supply.
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Thanks Paul
Yes, by swapping the blue wires, this swapped the choke, the 1.2k resistor, and the final filter Caps
Maybe I will try also to swap the choke's red wires and if noise still in the same channel, then definitely its the choke
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Hi all,
Update : I swapped the choke red wires and it still in the same channel/choke. So its not the resistor and filter caps in the PSU. I guess I have a bad choke?
Thanks guys
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Received my plate choke replacement today (thanks, Eileen!), swapped out the defective one and the amp, at first, had no sound in the right channel. I checked voltages, which were slightly low around 6, 21, 22 (51.7V compared to 56.something on the other side), but all else well, so I plugged it back in and …
… it works! And it sounds great! And there is no more noise!!
Thanks so much for helping me get to the bottom of this!
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That's great news.
I'm ordering my replacement now. Hope same result as yours
Thanks for this thread, I would have not expected that the choke are the source of the noise
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Hi all
Just an update :
Received plate chokes sometimes ago but was too busy. Finally this week I manage install them.
Noise all gone (for now, cross finger). Will have marathon music next weekend to further see if noise comes back and also break-in the chokes
As bonus, the new chokes also look better with end bells !!
Thanks guys