Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: oguinn on November 11, 2018, 07:54:48 AM
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After grounding issues I saw in this thread (https://bottlehead.com/smf/index.php?topic=11161.0), I ran a new pair of orange twisted wire parallel to the CAT5 already in place from the right input jack to the potentiometer which seemed to resolve the issue. Then I went away for two weeks for work, came back, and had an even worse sound problem on the right hand side.
I ran all the resistance checks. Everything was fine except the middle pin of the RCA jack. I reflowed that joint, which didn't solve the problem. I replaced the other orange pair from the tube to the pot and that didn't solve it either. At this point I'm wondering whether it's the pot or RCA jack itself, or if I've had a run of broken CAT5, or if I am truly garbage at soldering or what.
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Here's a SoundCloud link (https://soundcloud.com/user-652549496/right-channel/s-ldGwV) to the sound that was coming out of the right channel. This was a cheap set of headphones with nothing plugged into the amp's input recorded by my iPhone. The noise started right after the LEDs on the C4S lit.
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What is the resistance reading that you are getting that's concerning?
Some of your joints could indeed use a little extra solder/heat.
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At the center pin on the right RCA the reading was over limit.
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What reading do you get between the outer pair of lugs on the volume pot where the orange wires land?
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On the A side: 1 ohm. On the B side: over limit
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1 ohm is not really a possibility for what I'm asking for. Maybe this will help.
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Ah, ok. Sorry.
96.7K on the top lugs, over limit on the bottom (orange) lugs.
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That indicates that your pot is damaged and needs to be replaced. It is very difficult to damage a potentiometer, but occasionally crud can get inside and destroy the wiper or excessive tugging on the lugs can disconnect them from the carbon track.
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Thanks, PB.
I’ve had weird balance issues from day one - including a tube that was damaged. What are the chances all of those things are due to the pot being damaged?
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That's very difficult to say. Tubes are incredibly resilient and will often tolerate issues like this without any complaining.
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Got it. Ordered a replacement.
In the meantime, does the Stereomour stock kit use the same pot? Could I scavenge that while waiting on the replacement to ship?
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Yes, just be sure to use the pot that says "A100K", not "B100K".
-PB
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Thanks, PB.
If I make it out to Seattle I owe you a nice bottle of something.
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Alright, well... I'm still seeing issues. The left channel is fine, but the right channel sounds like it's under water. Very muffled. If I poke around, the only thing that is making noise is the pins toward the front of the chassis.
Here's what I've done so far.
- I scavenged the A100K pot from my Stereomour kit and installed it.
- Replaced the orange striped pair from the pot to the tube and the terminal strip.
- Reheated the joints on any pin that made noise when I poked it, specifically A8, A9 and A10.
I'm kind of at a loss at this point. Am I missing any potential causes? Should I just rip out the right side around the tube and start over?
Also - I emailed the replacements address a couple of times and haven't gotten a response. Not really in a hurry, but I want to make sure my emails aren't getting sent to spam.
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Recheck your voltages and resistances.
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Jameson, sorry if this is obvious but did you try swapping the tubes from left to right? Also, I've had a few 6FJ7's with steel pins that were kind of cruddy. Sometimes removing and replacing the tube solves this. Other times I've used Doc B's' "Cotton Swab chucked into an electric drill with a little metal polish trick" to clean up the nastier oxide examples.
I wouldn't go "ripping anything out" at this point if I were you. A more systematic troubleshooting approach like PB has been helping you with makes more sense.
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Resistances were all good. Right input pin was 93.2K, left was 94.8K.
Voltages were also good:
| Terminal | Manual | Observed |
| 2 | 65-95 | 80.2 |
| 3 | 15-18 | 18.8 |
| 4/5 | 0 | 0 |
| 6 | 385 | 378 |
| 7 | 400 | 406 |
| 10 | 380 | 383 |
|
| 16 | 65-95 | 79.5 |
| 17 | 15-18 | 16.8 |
| 18/19 | 0 | 0 |
| 20 | 385 | 384 |
| 21 | 400 | 410 |
| 24 | 380 | 390 |
|
| H2, H5 | +/-2.8-3.2 | 3.3, 3.31 |
| H4, H7 | +/-2.8-3.2 | -3.13, -3.14 |
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Jameson, sorry if this is obvious but did you try swapping the tubes from left to right? Also, I've had a few 6FJ7's with steel pins that were kind of cruddy. Sometimes removing and replacing the tube solves this. Other times I've used Doc B's' "Cotton Swab chucked into an electric drill with a little metal polish trick" to clean up the nastier oxide examples.
I wouldn't go "ripping anything out" at this point if I were you. A more systematic troubleshooting approach like PB has been helping you with makes more sense.
I was a slight bit dramatic. I’m a little frustrated after having been at this a few hours.
It hadn’t followed the tube when I checked yesterday, but I didn’t try again yet. I’m give it another go tomorrow
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If that doesn't resolve it, let us know and I can write up a set of instructions for installing jumpers through the amp. This should at least narrow down the problem area. I can also give instructions for tracing a 60Hz AC signal through your amp with your multimeter.
-PB
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Ok, confirmed that the issue does not follow the tube. What are my next set of options?
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Play a 60Hz tone into your SEX at full volume from your phone. Measure the AC voltage between ground and the center pin on each level of the pot with the pot all the way up, then half way up. Report those values here. The SEX does not need to be on for this set of measurements.
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Alright. This is where we start to see the seams of what I know.
I took a series of measurements because I was unsure how to get at what you're looking for. It's possible my multimeter might not be up to snuff. Attached is a picture of the dial.
See the attached photo for a key of the multimeter settings.
Setting 1 (I believe this to be AC volts, but the lowest setting I have is 200V):
| Reading | Right | Left |
| 50% | 00.1 | 00.2 |
| 100% | 00.1 | 00.2 |
Setting 2 (I believe this isn't what you're looking for; this seems like DC amperage):
| Reading | Right | Left |
| 50% | 2.7 | 5.2 |
| 100% | 2.7 | 5.2 |
Setting 3 (This is DC voltage, again not what you asked for):
| Reading | Right | Left |
| 50% | Ranged from 0 to 0.4 | 1.5 |
| 100% | Ranged from 0 to 0.4 | 1.5 |
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Attaching the photo again here. It didn't work last time.
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While your meter is totally accurate for checking DC voltages in our kits, that AC scale doesn't go down low enough. The ~$20 meter at Hazard Fraught is going to be really helpful for this debugging:
Meter (https://www.harborfreight.com/11-function-digital-multimeter-with-audible-continuity-61593.html)
This meter with a set of $30 Fluke probes is the best meter you can get for $50.
While the probes aren't so wonderful, the actual meter is excellent. On the 2V AC setting, you should get a much clearer reading of those levels.
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I was definitely fearing/anticipating that response when I saw AC only went to 200V. I'll get a new one ordered and chalk it up to lack of experience. Thanks!
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Alright, ordered a new multimeter from Amazon that goes down to 600mv AC. Picked the Amazon one (and some new leads) because of overnight shipping. We'll kick this pig tomorrow. Thanks, PB.
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Which one did you get? I like to try to have a few recommendations when people ask.
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This multimeter (https://www.amazon.com/gp/product/B071JL6LLL/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1) (AstroAI WH5000A) and these leads (https://www.amazon.com/gp/product/B06XYNF47M/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1) (AstroAI leads with alligator clips and others).
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Ok. Got the new multimeter. With the black lead clipped to the ground buss and the red lead clipped to the middle pin of the output jacks, I get:
Right: 403.5 mV
Left: 402.6 mV
I did not notice a difference when changing the pot position.
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The middle pin of each level of the pot should give you a different AC voltage reading as you turn the pot.
-PB
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One of these days I'll read slowly and thoroughly enough get your meaning the first time around. I was measuring at the RCA output level instead of the pot lugs. Here are the updated readings.
Right 50%: 36mV
Left 50%: 34.5mV
Right 100%: 403.4mV
Left 100%: 402.7mV
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OK, that is good, you have a working pot.
The next test is to check for channel balance at G1 on each 12 pin socket. Again, you can do this without the amp on. This is the AC signal voltage at pin 10 on each 12 pin tube socket.
If those balance, power up the amp and turn the pot all the way up. With the tone playing check and compare AC voltages at:
Terminal 4 vs. 18
Terminal 3 vs. 17
It also came to my mind that a 1000uF/35V cap that wasn't well connected would give you some pretty terrible performance out of one channel.
-PB
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A10 - 403.6
B10 - 402.7
4 - 6.53
18 - 7.5
3 - 59.2
17 - 89.5
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I also went ahead and touched up that 1000uf/35v cap, which didn’t make a difference.
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Swap the tubes and repeat the AC tone voltage checks on those last 4 terminals I listed.
-PB
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4 - 7.53
18 - 7.15
3 - 87.6
17 - 107.4
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Now measure the AC across the binding posts.
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Well. Something’s gone haywire now. The right side is making no noise, and the left side is making a god awful buzzing sound. Voltages were 3.4mv on the right and 402.4 on the left. I assume something is now definitely broken and I should repeat the voltage and resistance checks?
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Yes, you may have a loose connection somewhere that you've disturbed enough to now be able to locate.
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Voltages and resistances all checked out. A couple of the zero terminals had millivolts, but I assume that's ok and that I am just now noticing them because my meter is more sensitive.
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In essence, you have a decent amount of signal at terminals 3 and 17. This signal is stepped down through your output transformers to your speaker posts. If it isn't getting through, I would focus on the output transformer wiring.
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Should I just reflow the right channel output transformer joints and then try again? Are there any voltage or resistance checks to tell me whether there's something wrong with the output transformer itself?
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You did the voltage checks...
You can measure the AC voltage between terminals 5 and 10 on each OT-2 if you like with the signal generator on.
It is incredibly unlikely that there is an issue with the output transformer (you would be the first person ever to have a defective OT-2).
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Got it. I'll give it a shot.
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Alright, reheated the OT terminals. Right channel is still completely out, left channel is very staticky. Swapped the tubes and the problems persist. Should I just ship it to you guys? I feel like I’m making things worse.
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You could definitely take advantage of the repair service. You might also want to post photos of the OT wiring on each side.
-PB
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I found a broken orange wire (I break those Cat 5 wires constantly - any tips on how to strip them without cutting too deep and breaking them?) but it didn’t make a difference. All voltages still look good. Here (https://imgur.com/a/ym4OZxL) are photos of the OT
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You could try an Ideal Stripmaster with 16 to 26 ga. jaws. Some people don't like them but I get very consistent results with them.
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Thanks, Doc. I’ll give it a shot.
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Jameson,
I use an Exacto blade, I lay the blade on the insulation with light pressure and roll the wire under the blade. This will cut almost through the insulation, then use your finger nail to strip off the cut end of insulation. A little practice to get the pressure right and you can strip that CAT 5 wire without any nicks.
Jamie
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I’ll give that a shot also. Thanks, Jamie.
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Paul - Here is the wiring (https://imgur.com/a/ym4OZxL) for the right side output terminal.
The current status after a little prodding around over the weekend is:
- Right channel is completely out
- Left channel is working but staticky
- Voltages and resistances are all within regular parameters
You'd mentioned previously about installing jumpers to troubleshoot. Would that be my next course of action?
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If you don't have one perfectly operating channel, then the jumper tests won't provide any conclusive results.
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Ok. Hopefully I’ll get some time in the next couple weeks to devote to getting the left channel back. The only thing that’s changed there is the pot, so it should be easy enough to isolate. I picked up an extra foot of Cat 5 just in case.
I’m kind of baffled that everything was working reasonably well for a month and then just imploded. Doesn’t inspire a ton of confidence that I can pull off the builds for the Stereomour, Smash, and Reductor that I have boxed up and waiting to start.
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Sometimes just purchasing some tools that are slightly better suited for the job will make the build process a ton easier.
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For sure - and to be clear, I'm blown away by the support you all are providing. My lack of confidence is in my skills.
Just wanted to make sure you all don't think I'm blaming Bottlehead for my clumsy build.
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You could try an Ideal Stripmaster with 16 to 26 ga. jaws. Some people don't like them but I get very consistent results with them.
These showed up last night. I tried them on a couple spare pieces of 24 gauge wire I had laying around… Wow! Really nice stripping. Thanks for the recommendation!
Our fiscal year ends tonight (thank god), so I shoul hopefully get some bench time on the amp this weekend.
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Alright, I’m calling it. I reheated a bunch of joints on the right channel and nothing changed. Paid for the repair service since I’m basically just beating my head against the wall.
After you’ve done the repair, will you let me know what my error was?
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That costs extra.
Just messing with you. We put a note in with the repaired gear that explains what was fixed.
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Awesome. I’m looking forward to a harsh critique of my soldering technique.
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Hey Doc,
Just received my repaired SEX. It works great! Thanks to the team.
I didn't see any notes on what was repaired, however. Could whoever fixed let me know what they did to get it running right so I can be on the lookout in future builds?
Thanks!
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I think maybe Terry did that one. He is primarily our Nagra tech and thus not usually doing the Bottlehead repairs, so he may have forgotten to include a note. I want to say he replaced the headphone jack, but I could be thinking of another repair. I will ask him when he is in tomorrow.
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Holy crap, if it was just the headphone jack I’m going to cry. I never even considered testing through speakers as well.
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I could have the wrong info. Let me get the story tomorrow.
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Thanks, Doc.
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Wanted to follow up with the conclusion of the story here to provide a cautionary tale to anyone troubleshooting an amp.
I finished my Crack amp today and gave the first listen with my old, shitty headphones just in case I had messed something up so I didn't blow my HD-650s. Fired everything up and got no sound out of the right ear. Turned the amp off, checked all the connections. Then I remembered that I'd used this set of headphones to test my non-functional SEX before sending it in.
I switched to an old pair of Sennheiser 598s I had laying around and everything's fine. Turns out that my Crack's right channel issue, and probably my SEX's right channel issue, were due to a blown set of headphones.
Two takeaways:
- Always troubleshoot with a shitty set of headphones. I blew the right channel in the bad headphones when troubleshooting. Better those than my 650s.
- Get two sets of shitty headphones.