Krell KSA 100mkII Clone

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#602
Yep, thats what I measured on the working channel, the negative side Q-7, Q-8 measures the same. The non working channel measures about the same on those devices. There is not any real difference till I measure the collectors of Q-9 and 10... those are a volt lower than the good board.

Those readiings taken are in this order...... Drain Gate Source

Mark
 
#604
do you have same readings on R24,25,26 and R27 on good and bad board?
Click to expand...

Yes, both boards measure within one or two tenths of a volt of each other on the MOSFETS. I had not mreasure across the resistors though and will do that in a little while. Am re-mounting the drovers after testing and am screwing heatsink and board together to make it easier to mount the drivers. Holding the heatsink, board, and hardware at same time is a bit difficult while keeping it aligned.

I will get back in an hour or so on the reading across those resistors.

Thanks
Mark
 
#616
Check C7 for shorts (desolder and lift one leg)

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.
Click to expand...

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

Regard 😎
 
#618
Gert,

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?
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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
Click to expand...

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 😎
 
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