Bottlehead Forum
Bottlehead Kits => Eros Phono => Topic started by: harv-e on December 14, 2011, 08:53:10 AM
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Decided to ressurect my turntable and record collection. I took great care of them and they sound great (for the most part). So then, time to upgrade my preamp, wandered across the Bottlehead site, was impressed, and here I am with my completed EROS. No difficulty with construction, though I have some difficulty stripping wires, even though I bought a new wire stripper just for this project. I followed the testing procedures throughout. First problem was with ground to one of the tube sockets. Close inspection showed that I had soldered the insulation covering the wire, actually missing the wire completely! After final completion, all voltages/resistances checked. Fired it up - horrendous noise in left channel only when attached to the turntable. Switched plugs. No effect. Took it all apart, including circuit boards, and resoldered everything I could see. No luck. Somehow I moved the input wire from the phone IN jack with my finger as I was becoming frustrated........and the noise stopped. Close inspection showed that the ground wire was broken inside the insulation from the ground lug on the jack! UGH.
OK. Now it's working! Next two issues. There is a distinct hum when I turn up the amp. But I am reading that I need to burn things in a bit more, so I am not too concerned about it. However, there is a definite "motorboating" sound that I cannot isolate by changing tubes or inputs, that seems to be coming from both channels. Power supply issues? I cannot find anything in the forum searching for "motorboating," but I don't know what else to look for.
So any help would be appreciated!
Thanks from the newbie!
Harvey
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First thing is to get or make some shorting plugs - RCA plugs that are internally shorted, either with wire or a low-value resistor (100 to 1000 ohms?). Cheap plugs from Rat Shak will do, and they will come in handy for years to come. Plug them into the input, thus removing the turntable and its wiring from the equation. If the hum goes away, then you've found the problem; otherwise you've at least eliminated one possibility.
Checking the connection between Eros and the preamp is more difficult, depending on what the preamp is and how it's powered (2- or 3-prong plug? Can it be reversed? Are they on the same power circuit?)
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Does the oscillation occur with no turntable plugged in?
Does the oscillation occur with the inputs shorted?
Do all the voltages and resistances measure properly? (I'm wondering if you're not getting 0 Ohms in certain places where you should)
Also, if you have any power conditioning ahead of your preamp and/or Eros, try plugging them both straight into the wall.
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Thanks guys for your input. I have had to resurrect this thread as I just cannot live with this sound!
So I have completed all tasts to no avail.
I disconnected the turntable.
I shorted input plugs
I bypassed the power scrubber.
I even disconnected to output to see if the issue was behind the EROS.
I tapped the tubes to see if they make a noise (nope)
I must admit that I have not rechecked the voltages, as I checked them after unit construction and there were no issues then and this motorboating sound was immediate. There was an early hum that I noted in my initial post......that has resolved.
The issue of motorboating still persists.
Frustrating!
H
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Motorboating is typically due to a problem with the filter caps. It's most usually due to filter caps having been damaged or resistors between the caps having been damaged. Are the caps in the proper orientation and are the correct cap values in the correct places? FWIW I think this is the first time I have heard of one of our kits having this problem.
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I'd be extra cautious with those little silver capacitors mounted to the front PC boards. I put some in backwards in a BeePre prototype and they took a very, very long time to give out.
I'd be very interested in the voltages, especially those coming off the power supply board on the power transformer.
-PB
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Harvey,
I hear the frustration in your post. Where are you? If you are near an experienced Bottlehead you might seek out some assistance.
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So I went to test the voltages. My Bottlehead Manual CD case.....was empty. I had version 5-26-09. Can't find it! More frustration.......Is there a link to download this....or do I have to wait for snail mail and order one?
BTW, I live in Erie, PA
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I should have posted this earlier....because as soon as I did....I found the CD!
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Voltages:
Left board looking from underneath: kreg 0.6 b reg 80.1 OB 80.8 OA 124.4
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Incomplete last post.
Voltages in the boards looking from underneath (all four LEDs are lit on all boards).
LEFT Kreg 0.6 breg 80.1 OB 80.8 OA 124.4 bA 0 1A 200
RIGHT Kreg 0.6 breg 80.7 OB 80.4 OA 128.6 bA 0 1A 200
Hope this helps
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Can you double check that those silver caps across Kreg are properly oriented?
Everything looks a little low, I suspect there may be a pair of swapped resistors, or a miswire.
-PB
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Voltages at the Power supply board are as follows:
T4/5 = 7 T6/7 = 106.1 6.3 VDC pins measures 5.46 275VDC pins measures 234
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Silver caps at Kreg - blue side is at the -kreg, per the instructions
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The fact that both regulated voltages are low by the same percentage (16%, more or less) suggests either you meter is bad (worn battery?) or perhaps you are measuring DC with an AC voltage setting.
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I considered that. It could be that the battery needs to be changed. The meter is made in China and that might be a factor too. And I noticed that the manual states the AC mains voltage at which the figures were obtained from the circuit board duirng testing. I didn't check my wall voltage. But if all the figures are low by the same percentage, doesn't that mean that they're all OK? For instance, the voltages on the Left and Right boards may be low, but they're pretty close to one another.
I'll change the battery tonight and post again, but after all, it's a $10 meter from Harbor Freight.
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IA and IB are regulated, as is the 6.3V supply on the power supply PC board. When you put in a fresh battery, measure that 6.3V pad to be sure that the meter is working properly.
-PB
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New battery installed in meter. Voltages seem worse!
Power Supply Board
T4/5 = 6.4 T6/7 = 95.5 6.3vdc pins measures 4.9vdc 275vdc pins measure 216vdc
LEFT Board Kreg 1.02 breg 80.2 OB 78.8 OA 122.5 bA 0 1A 187
RIGHT Board Kreg 0.83 breg 80.2 OB 79.4 OA 126.2 bA 0 1A 187
Harvey
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Hey Harvey,
With the amp on, put the black probe on the "-" pad on the 6.3V corner of the board, and the red probe on the "+" pad on that same corner, then see what that DC voltage is.
Though this may seem annoyingly redundant, any differences here will provide useful information.
-PB
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When I listed the voltages on the power supply, they were all taken directly from the pads on the board.
I compared the DC voltages with the neg lead on the pad with the negative lead on the chasis and they were the same.
Harvey
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The voltage checks are typically from a point, terminal or PCB pad, to ground. PB is asking you to measure from one PCB pad to another. It just might be different.
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OK. Maybe I'm not understanding. The lower right hand corner of the power supply board, next the the nut on the screw, has a + and a - "pad" just under the 6.3vDC stencil. I checked this voltage with the two probes from the meter. Then moved the negative probe to pin 23 of the terminal strip, leaving the positive probe at the + on the power supply PC board. These two voltages were the same.
Is this what is being asked?
Harvey
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That is good. The measurement on the board says that it is producing the right voltage, the measurement to a ground lug says that the circuit is grounded as it should be. (I'm assuming you are saying that the voltage is right.)
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Unfortunately, that's not true. The voltages both read 5.1vDC, not 6.3vDC....regardless of where they are measured.
I will borrow another meter from a friend and see if there is any difference in the readings. Stay tuned......
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Do let us know about the other meter, getting anything that is lower than about 6.25V or higher than 6.35V is very suspicious there, and getting the same voltage with your black probe in the two different places tells us that your grounds are wired in.
On the other hand, if you do end up finding that you have that very low voltage there, you have have found the entire problem with your Eros (but good to double check before we go further).
-PB
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OK. Borrowed a friends GB meter. Here are the voltages with this meter.
Line 119.1
Power Supply: T4/5 8.5vAC T6/7 126.7vAC 6.3vDC measures 6.21 to pads (6.22 to ground pin 23) 275vAC measures 299vAC
LEFT Board Kreg 1.1 breg 95.4 OB 93.2 OA 158.5 bA 0 1A 297
RIGHT Board Kreg 1.1 breg 97.3 OB 96.6 OA 160.5 bA 0 1A 298
Hope this gives better information for you.
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Just a reminder about the underlying issue. The music sound and quality is terrific. But there is an underlying low frequency motorboating putt-putt noise coming out of both speakers that can be heard during quiet music passages and even with the turntable unplugged. Switching the tubes and tapping them has no effect.
Just a reminder about what this is all about.
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We are getting somewhere now!
Measure the pads on the power supply board, specifically IA/IB, OA/OB, and Kreg.
-PB
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There is a smaller board under the power supply board with the following markings and voltages (I cannot find OA OB or IA IB pads on this board:
LEFT A side: bA 0 breg 1 +reg 1 Kreg 9.0
RIGHT B side: bB 0 breg 1 +reg 1 Kreg 8.9
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Yes, sorry, the regulator board just under the power supply board.
This board is the same board placed up front over the EF86 tubes, it has the "IA", "OA", "IB", and "OB" pads in all the same places.
breg and +reg can't be 1 with everything else you've told us, perhaps you need to turn the range up on the meter?
-PB
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OK. Found OA and 1A....they were blocked by the heat sinks and I missed them. And the scale was incorrect on breg and +reg. The readings are as follows:
LEFT OA 224 1A 273 breg 224 +reg 225
RIGHT OA 224 1A 273 breg 224 +reg 224
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Putting it all in one place for you:
Line 119.1
Power Supply Board
T4/5 8.5vAC T6/7 126.7vAC 6.3vDC measures 6.21 to pads (6.22 to ground pin 23) 275vAC measures 299vAC
Regulator Board
LEFT A side: bA 0 Kreg 9.0 OA 224 1A 273 breg 224 +reg 225
RIGHT B side: bB 0 Kreg 8.9 OA 224 1A 273 breg 224 +reg 224
LEFT lower Board Kreg 1.1 breg 95.4 OB 93.2 OA 158.5 bA 0 1A 297
RIGHT lower Board Kreg 1.1 breg 97.3 OB 96.6 OA 160.5 bA 0 1A 297
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Hi. Just curious about suggestions for the next step since all suggestions have been followed through and things have been quiet here since my last post with all voltages a few weeks ago. Thanks.
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I'd pop up a couple of photos of the underside if you can. This is very odd, generally motorboating is a ground connection that's missing or a failing cap, but you appear to have neither.
-PB
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There is another cause of motorboating that I discovered the hard way. But it doesn't apply to the Eros. I got the poles of my coupling and output caps too close together in a PAS 3 rebuild and it made the woofers pump back and fourth a good 2".
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Photo 1
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Photos 2
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The things that jump out at me are:
1. Long resistor leads, I'd go back and look at how they are installed in the manual, tightening them up a bit for consistency.
2. Non-factory 47K resistors at the inputs (Were they missing? Have any other parts been substituted?)
3. Ground wires everywhere. Look at the 6922 socket in the manual, all the black wires are laid against the chassis and tucked away nicely. I would try to mimic this as much as possible.
4. Similar to #3, wire routing between boards is up in the air, not tucked away as the manual shows.
5. Be sure the foil on the STP heater wires do not touch anything. I am looking at the 6922 socket, and wondering if the foil is contacting any parts? This is dealt with in the manual by stripping the black insulation back a fair amount, leaving a good length of exposed twisted pair so that the larger body and its foil can be positioned further away.
Let me know if any of these checks reveal anything. The layout stuff may seem nitpicky, but it can add up to an unstable circuit.
-PB
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Good advice on the layout stuff. I'll go through it and see what I can "tighten up."
There were four resistors missing that I did make substitutes for. But with the issue persistent with the inputs shorted I negated this as the source of the trouble.
Harvey
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Putting it all in one place for you:
Line 119.1
Power Supply Board
T4/5 8.5vAC T6/7 126.7vAC 6.3vDC measures 6.21 to pads (6.22 to ground pin 23) 275vAC measures 299vAC
Regulator Board
LEFT A side: bA 0 Kreg 9.0 OA 224 1A 273 breg 224 +reg 225
RIGHT B side: bB 0 Kreg 8.9 OA 224 1A 273 breg 224 +reg 224
LEFT lower Board Kreg 1.1 breg 95.4 OB 93.2 OA 158.5 bA 0 1A 297
RIGHT lower Board Kreg 1.1 breg 97.3 OB 96.6 OA 160.5 bA 0 1A 297
The lower board IA (input to the A-side C4S) should be connected to the regulated voltage from the regulator board, so they can't be different - you are showing 225v on one, and 297v on the other. I assume this is a measurement error, since the highest voltage available anywhere off the PSU board is 273v (IA, IB on the regulator board) is 273v. Other than that, these all look quite good.
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Hello. I finally got around to taking the preamp out and resoldering the connections. Tested it......and found a new issue that I can't seem to solve. Looking at the kit from the back, the lower left light on the middle board is out and all the lights are out on the right lower board. I can't seem to find the broken connection on the middle board. Can you steer me towards the right direction? Thanks.
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Hello. I finally got around to taking the preamp out and resoldering the connections. Tested it......and found a new issue that I can't seem to solve. Looking at the kit from the back, the lower left light on the middle board is out and all the lights are out on the right lower board. I can't seem to find the broken connection on the middle board. Can you steer me towards the right direction? Thanks.
Voltages?
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Here are the voltages:
Line 125
Power Supply Board
T4/5 8.6 T6/7 134 6.3vDC measures 6.22 275vAC measures 318
Regulator Board
Left A side: bA 0 Kreg 0.7 OA 0 IA 316 breg 0 +reg 0
Right B side: bB 0 Kreg 8.8 OA 224 IA 317 breg 224 +reg 223
Left lower board: Kreg 1.36 breg 99.6 OB 98.1 OA 145.5 bA 0 IA 224
Right lower board: kreg 0 breg 0 OB -.02 OA 0 bA 0 IA 0
Thanks. Any help would be GREATLY appreciated.
H
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Your regulator board is not passing any voltage through on one side. I'd do your best to reheat all the "A" side joints.
-PB
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I tried reheating the joints.....no joy.
Could you please be a little more specific as to where the issue might be? I can read schematics, so that is not a problem for me. Oddly, now that I have gone over the schematic, D1 on the A side is out but D2 is working. The only way I can see this happening is if R1 is shorted. Yet with D2 lit, power should be getting to V2.
Any ideas from this point?
Thanks.
H
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The single lit LED is generally a poor ground connection from the bias string, or a funky solder joint on a transistor in that C4S. (The 0V at the output supports a bad transistor solder joint)
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OK. That's fixed. I cleaned off the board with some alcohol and found a tiny solder bridge shorting that transistor. So the regulator board and been completely "resoldered." All lights work. Audio from both speakers.
And so now I am back to the original problem - motorboating sound coming out of both speakers even with the inputs shorted. I am OK with hiss. But not this constant putt putt puttering. To my mind, this is a power supply problem since it is coming from both speakers.....and I do not believe it is a solder connection as I have gone over these on the regulator board (I have not redone the joints on the power supply board). I have to believe that it is a bad component.....but I do not have a clue as to which one it is.
The voltages before the "resolder all the joints" issue seem to be within specs......and that's why I was advised to resolder the joints.
This is very annoying. I have been patient trying to fix this, but I don't know what else to do.
Thanks.
Harvey
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Could it be interference from something nearby?
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Nope. I replaced the EF86 tubes and the problem is GONE. Actually, I replaced all the tubes, one at a time. No change until I got to the EF86s
FINALLY
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Wellllll, so much for that. An hour of use.....and the motor boating is back.
Sad. Really thought this was going to be it. I'm going to have to go elsewhere for product. No reliable answers here. Disappointing.
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We do offer repair services if you would like us to get it up and running for you.
-PB
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I've experienced the motor boating phenomenon before with an old pair of Boston Acoustic computer speakers, traced the problem to a dodgy power supply cap right after the diode bridge.
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I understand that you are frustrated. The suggestions may not have solved your original problem, but that does not mean our answers to questions are unreliable as you seemed to have had other issues come up that you were coached on fixing. I can't think of any other Eros that we have heard of having this motorboating problem and thus we don't have any previous experience dealing with it. You could just send it to us and let us fix it for you. If the issue is a bad part there will be no charge. If the issue is a construction error you will get a very nice preamp for a reasonable repair fee.
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Hello Harv-e,
I got into your repair yesterday afternoon and this morning, and I found that a couple of resistors may have been damaged on the 12BH7 socket, so I replaced them with more robust parts.
I also found some other parts that may have been a bit loose, and I tightened them all down to prevent any further contact issues.
Also, the ground wire from one of the input RCA jacks to the terminal strip was loose in the terminal strip and not soldered down. This presented us with significant hum while running the amp in until I was able to find it by poking around with a pencil. This is most likely to be the primary issue you were facing, and when you ended up replacing the tubes, the physical jarring of the Eros would have temporarily re-established this connection for you for a while.
I did end up replacing one of the C4S boards in the process of debugging, but in retrospect it wasn't at all necessary.
We'll keep running the amp for a few days with the inputs shorted and the outputs driving speakers so we can be sure that you won't have any additional noise issues.
Sincerely,
PB