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soundslave 20th March 2018 07:32 PM

1 Attachment(s)

soundslave 20th March 2018 07:39 PM

I'm having as much success with the photos as I'm having with the amp

Dennis Hui 20th March 2018 10:07 PM

Are P3 and P4 at minimium and are you getting around 4.3V between T7-T10 and T12-T9?
If so, what happens when you slightly start adjusting P3/ P4? (Actually start with P3) Can you
get The T18-G voltage to drop closer to 0?

soundslave 20th March 2018 10:47 PM

Yes p3 and p4 are counterclockwise and I get 4.78v at both T7-T10 andT9-T12. I can adjust p3 to get less than 1v

Dennis Hui 20th March 2018 10:55 PM

OK. That sounds good. I would now try the bias procedure.
Start at page 8 (Adjust P1 for T16....):

jaab6 2nd April 2018 07:41 PM

3 Attachment(s)
After I changed the FQP3n0 and FQP3P30 from the BOM by matched 2SJ313 an 2SK2013
my problems are gone!
The voltage test point are fine. my problem right now is the vgs wrote
on one of the Sony vfet pair. One pair are readable 9.9 but the second pair I can just identify the 9, the second digit can be 1 4 7 or 9 .
I don't know whom to ask !
Attachment 672671

Attachment 672672

Attachment 672673

Dennis Hui 2nd April 2018 09:28 PM

You can be conservative and pretend it's 10V so set initial bias voltage at 11V.

jaab6 3rd April 2018 12:50 AM

Doesn't matter if it's 9.1 and I set to 10?

Dennis Hui 3rd April 2018 07:59 AM


Originally Posted by jaab6 (
Doesn't matter if it's 9.1 and I set to 10?

If it's actually 9.1 and you pretend it's 10 and set the initial bias voltage
at 11, all that should happen is you will have to turn the bias pots more
to get current to flow during your installing vfet and adjustment procedure.

Since the vfet conducts more current as you decrease the bias voltage,
the idea of setting the initial bias voltage based the measured value of
the vfet is to make sure the current is low. If you know your parts are
9.X then setting the voltage at 11 is safe.

jaab6 4th April 2018 07:12 PM

I took to much time writing my post and all have been lost!
we have similar values in g-t6 g-t8 and I changed r15 r16 to 46.4k but it's perhaps not necessary!
I would check again the resistors perhaps a 47.5k 47.5 has been inverted if not check the values of the trimers two are 500 ohms and two are 5k ohms. check if they are fully turned

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