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Old 4th July 2011, 04:00 PM   #2361
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Joachim,

A nice servo trick is to connect both the sense and force connections of the servo to the same point, the output. It's like the servo nulls it's own input and there is no impact on the rest of the circuit.
I've used it a few times and even if it looks funny it works great!
I'll put a small diagram together for later.

Edit: attached

jan
Joachim,

I looked again at the circuit I and think I made a mistake. I thought the output was a current output but it is a source follower. That means that my clever servo will not work at that point. It needs a high impedance point. It would work on the input to your RIAA network (R17 in the circuit I saw).

jan didden
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Old 4th July 2011, 04:14 PM   #2362
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Thanks Jan. Sure, you are right. I will try it out. I already tried my version and the time constant influences the RIAA. That can be corrected by changing the values in the RIAA. I will try if your version has the same effect.
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Old 4th July 2011, 04:22 PM   #2363
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new company
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Old 4th July 2011, 06:58 PM   #2364
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Thanks.
Here is the "Problem Child". It is basically an MPP Summer 2011 2 Stage with two Salas regulators with yet another output buffer. Curiously it worked with only one regulator. With two it gets hot and the sound is sharp. See my humble effort to damp with series resistors.
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Old 4th July 2011, 08:36 PM   #2365
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Can you post the shunt schematic ?
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Old 4th July 2011, 09:13 PM   #2366
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Quote:
Originally Posted by Joachim Gerhard View Post
Thanks.
Here is the "Problem Child". It is basically an MPP Summer 2011 2 Stage with two Salas regulators with yet another output buffer. Curiously it worked with only one regulator. With two it gets hot and the sound is sharp. See my humble effort to damp with series resistors.
That one is special V1 for DCB1, has 100uF lytic cap as output termination. Has plenty of phase margin, and uses its output cap's ESR as damping. If the rails at the load side have small fast caps across to grounds shorting the outputs ESR, series inductors, reactive whatever, margin could have been eaten out, maybe one could just take it, but two could have formed some damping impedance drop path beyond their phase margin handling. Hot and sharp is tell tale oscillating. Try higher ESR output caps on the PSU boards, see what can be adding complexity on the load's rails, have nothing in series on the rails. What can be common and suspect between channels on the rails? Keep the scope on the rails looking for a flat line when AC coupled scope input is selected while trying. This one you got its very seldom it oscillates, had been used widely by people with very diverse circuits, surely you will find a way to apply it better even in an odd situation I trust. One working solo properly already is a good sign.
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Old 4th July 2011, 09:48 PM   #2367
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Too much low impedance shunting on board. Desolder that ! i feel guilty.
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Old 4th July 2011, 10:30 PM   #2368
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Originally Posted by Joachim Gerhard View Post
Thanks.
Here is the "Problem Child". It is basically an MPP Summer 2011 2 Stage with two Salas regulators with yet another output buffer. Curiously it worked with only one regulator. With two it gets hot and the sound is sharp. See my humble effort to damp with series resistors.
Crazy mousebox, can't believe its "sharpness" ...
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Old 4th July 2011, 10:32 PM   #2369
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It is sleeping ! Do not weak it.
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Old 4th July 2011, 10:44 PM   #2370
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Thanks.
Here is the "Problem Child". It is basically an MPP Summer 2011 2 Stage with two Salas regulators with yet another output buffer. Curiously it worked with only one regulator. With two it gets hot and the sound is sharp. See my humble effort to damp with series resistors.
Hi Joachim,

I think I see a blue and a black mouse, IMO they are the culprit !
Please be gentle and kind to them. I love animals

Tjuus,

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