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Old 2nd December 2012, 04:50 PM   #341
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Joachim, the offset is fluctuating within a range of more than a 100mV every second - it is not steady and is too fast for the servo to correct. Finally took a listen using a DL103: there is a very prominent hiss, completely against expectations. Bad batch of electrolytics at the input stage? Oscillations?
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Old 2nd December 2012, 04:52 PM   #342
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And it is definitely not related to the servo. Also took a listen without the servo - same fluctuations at output and same hiss. Granted the 103 is a bit low in output but i have carts with 3 times lower output...
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Old 2nd December 2012, 04:55 PM   #343
pdul is offline pdul  Denmark
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My opamps came in original sealed bags, from RS, anyway i tried to use some AD711 with same result.
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Old 2nd December 2012, 04:57 PM   #344
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I had a short discussion with MiiB. He is in Hong-Kong at the moment preparing to sleep.
That is what we came up :
Preforming the Elcaps, especially the ones in the input. Load them up to the rated voltage with a battery or a lab PSU. Let them soke up the voltage for some hours so that they form. Then put them in the circuit.
Thermo couple the input transistors with a piece of metal. The circuit has a lot of gain in the lower frequency region so thermal drift can challenge the servo.
Decouple the mirrors locally with ceramic caps, that can take away oscillation.
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Old 2nd December 2012, 05:01 PM   #345
beetle is offline beetle  Germany
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Quote:
Originally Posted by FdW View Post
That's easy done!
It seems not to be. Still the same issue. I bet there is something oscillating at the negative side. Will fire up the scope..
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Old 2nd December 2012, 05:01 PM   #346
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What brand of Elcaps do you use ? I use Panasonic, a long life version of the FM. I think they are part of the group buy and should be good. I also tried Rubicon ZL and ZY without problem. Elna should be good too.
Another option is to make the servo faster by reducing the 1uF cap. It will still reach down low enough.
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Old 2nd December 2012, 05:08 PM   #347
pdul is offline pdul  Denmark
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I use Panasonic FR like you, and i already tried to reduce the cap in the servo to 220nf, but with no result?
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Old 2nd December 2012, 05:14 PM   #348
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The only way then is to use a scope and check for oscillation.
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Old 2nd December 2012, 05:26 PM   #349
pdul is offline pdul  Denmark
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It is cheaper for me right now to be without paradise, than to buy a scope
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Old 2nd December 2012, 05:29 PM   #350
pdul is offline pdul  Denmark
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I guess it will be solved, since we are already two with the same problem, and there are probably more to come.
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