Krell KSA 100mkII Clone

[Mark A. Gulbrandsen]

The two negative MOSFETS read 1.48 volts each and the two positive MOSFETS are unbalanced. One is reading 1.2 volts and the other is 1.5 volts. I am going to replace the one that reads low and see if that does it.

Mark

[Flodstroem]

Check voltage across R7 and R8, should be ca 15V across each of them, could be some error in differential pair Q1, Q2 (or R3, R4) ?

Regards

[Mark A. Gulbrandsen]

So far I have replaced all the MOSFETS and Q-1&2 but still the same problem. Am gouing to replace Q-3&4 next then the current diodes if it isn't the A970's. Resistors everywhere all measure well within 1%. I will see what R-7 & 8 have to say....

Mark

[Mark A. Gulbrandsen]

Looks ok to me...

R-4 7.8

R-8 7.6

R-9 7.7

R-10 7.6

Also across....

R-3 .250

R-4 .241

R-5 .240

R-6 .244


Its not the current diodes either, just changed those.

I give up... I will get a another set of resistors and trimpots tommrrow and build another board up.

Mark

[jacco vermeulen]

Mark,

You're sure you have the right values for R37/R38, not switched them maybe ?

The source voltage difference of Q5/Q6 looks like there's plenty current through Q9, +10mA, Q11/Q12 work fine too.

[Flodstroem]

Then measure the amp in "on" position.
If neg:
Check for Q13 is a 15030 device.
Also, shift Q13 to a new one (seems to work but could be a bad transistor)

If neg:
measure voltage drop across:
R30 and R35 (equal)
also:
R31 and R33
R32 and R34
equal on pos and neg sides?

The two negative MOSFETS read 1.48 volts each and the two positive MOSFETS are unbalanced. One is reading 1.2 volts and the other is 1.5 volts. I am going to replace the one that reads low and see if that does it.

That one measuring 1.2V is this Q6? If yes, Q9 could be bad (to low Hfe value)

Regard

[loek]

I think those base-emitter voltages are high with 1,1 V....
Hope you find the needle.
Loek

[Flodstroem]

if I'm reading right you have made output boards for your amps? If so, would you mind sharing at all? I hate doing these thing point to point and would prefer a proper board. That should be a simple board that I could easily have made locally, or maybe we could inlcude this in the GB?

I wouldnt mind to share the idea with you and other who wants boards like this in GB.

I havnt made boards, only design the boards on my computer. I can send all files that is necessary for a PCB production.

If this is of interests I would like to suggest that we share the idea in this forum and that we can have a beneficial discussion regarding the layout for to optimize the board construction.

Also I dont know any cheap way to order a small series of boards for us. Maybe you could step in here and help finding one?

I will post pictures of the design here soon. Must convert it to pdf and small enough files for the porpose.

I give up... I will get a another set of resistors and trimpots tommrrow and build another board up.

Mark

Come on Mark, find the error! This experience could be beneficial when thinking of what can go wrong when members start building this amp, dont you think?

Regards

[Mark A. Gulbrandsen]

Come on Mark, find the error! This experience could be beneficial when thinking of what can go wrong when members start building this amp, dont you think?

I have boight more parts today... more sets of resistors, pots and capacitors.

Are you not happy with the present board design?

Mark

[Mark A. Gulbrandsen]

Ok, I found the problem... The big dummie that stuffed the parts in the board switched positions of R-36 and R-37 so JAcco who suggested this wins the turkey. All is fine now....
Thnanks to everyone for all their suggestions!! Now I get to hear this play in STEREO!

Mark