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Old 11th June 2013, 05:15 PM   #31
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OK, I sat down this morning and took new measurements, one board at a time. I have tried posting them on a schematic I'm not sure how well it will all show up on here but here goes.

I was surprised to find that most of the numbers were very close, especially given that the rails changed slightly. However, everything looks good side to side except for the collectors for Q12 and Q16 on the red board. They are both over 58V. Any idea where this is coming from? I replaced Q12 and Q22 and still no change. Haven't touched Q16 since the other change made no difference.

Also I have about 1.5V drop across the 100ohm 1/4W resistors in place of the fuses. Leach says it should be less than .5V

Thanks, Terry
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Old 11th June 2013, 07:43 PM   #32
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Do you have an oscilloscope and signal generator? If things aren't smoking, I trace out waveforms to see how far the signal is getting and observe if oscillation is present.

Haven't attempted to build a Superamp, but I'm hoping you'll get your's running and we can study the results. Documenting the proper working voltages would be very useful. I'm intrigued by the cascoded VAS stage.

If you get really stuck, I could try testing one of your boards here with a single output quad.
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Old 11th June 2013, 09:26 PM   #33
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I do have a scope and a signal generator. Unfortunately, I misplaced the probes. I have a couple coming. Should be here this week. I will probably need help since it's been so long since I did it.

I will happily mark up a schematic with voltages once I get it working. I agree, it would be very useful to folks wanting to build one of these.

Blessings, Terry
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Old 11th June 2013, 09:39 PM   #34
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your Q26 base emitter is reverse biased, that is the problem...so with your Q22, Q23......
voltage between base and emitters of small trannies must be around 0.6v...
or that you inserted them correctly into the board..
first make sure that you got the right trannie inserted in those spots..

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Old 11th June 2013, 10:51 PM   #35
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Quote:
Originally Posted by AJT View Post
your Q26 base emitter is reverse biased, that is the problem...so with your Q22, Q23......
voltage between base and emitters of small trannies must be around 0.6v...
or that you inserted them correctly into the board..
first make sure that you got the right trannie inserted in those spots..

Click the image to open in full size.
Rats, I was hoping you onto something but no such luck, the parts are right and in the right orientation.
As I said, I don't really understand how the voltages are produced other than know that a resistor will reduce it. I see 58V and I have no idea how that got there. If there are any other readings you need to help get to bottom of this I will be happy to check for them. I have spent a bit of time checking both boards to look for anything different but I can't see anything.

Thanks, Terry
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Old 12th June 2013, 01:41 AM   #36
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there's your problem right there, get the voltages right and you'll get a working amp...
incorrect voltages is a clue that something is wrong, you have to find out...
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Old 12th June 2013, 01:48 AM   #37
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I agree. Now if someone can tell me what is causing the voltage offset I will be a happy camper.
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Old 12th June 2013, 02:44 AM   #38
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Disable or isolate VI limiter...It seems it affects the circuit operation..

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Old 12th June 2013, 02:52 AM   #39
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Quote:
Originally Posted by still4given View Post
I agree. Now if someone can tell me what is causing the voltage offset I will be a happy camper.
if you can solve the wrong voltage readings, i believe the output offset will solve itself...so first things first....that output offset is far from my mind looking at your readings...
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Old 12th June 2013, 06:31 AM   #40
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Quote:
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Disable or isolate VI limiter...It seems it affects the circuit operation..

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Are you saying to disconnect where the red X's are?

Edit; After looking at the board, R37-R40 aren't attached. They go to the outlets for the power devices which are on another board which is not connected. I can disconnect the 4 diodes. I will do that and take another reading.

Quote:
if you can solve the wrong voltage readings, i believe the output offset will solve itself...so first things first....that output offset is far from my mind looking at your readings...
I didn't mean the offset at the output. I was talking about the -43V on the one side and the 58V on the other. Ricdelros may be onto somethng. I remember that either D7 or D8 was fluctuating so much I couldn't get a reading.

Thanks Guys!

Last edited by still4given; 12th June 2013 at 06:45 AM.
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