Krell KSA 100mkII Clone

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#2,445
Can someone explain what the top-rear white resistor on the output board does? I ask because it is soldered with both ends on the same copper track. Page 228 has the pcb-layout photos showing this detail better.
Any comment Fix???

3429413415_53d00a42c4_o.jpg
 
#2,446
samoloko said:
can be used 600VA 2 x 40VAc per ch
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i would say no, because the 600VA 40+40Vac is effectively a 7.5Aac transformer.

The extra rail voltage from a 40Vac transformer will require extra output bias for ClassA, maybe 3Adc rather than 2.6Adc. The extra voltage and extra bias will require more output dissipation capability.
Secondly the maximum DC current I would draw from the 600VA transformer would be 1.9Adc continuous (bias+quiescent) and this matches the KSA50 bias current.

The 900VA 37+37Vac used in the KSA100 can give a maximum continuous DC current of 3Adc and this is comfortably more than the 2.6Adc of bias.
 
#2,447
Pure Class A?

Hi,
Sorry to interrupt but I just bought this original KSA 100 where the fans have been replaced to somewhat strong (and noisy) ones (you can hear them in the next room when no music is played).
I'm very surprised by how cool this amp runs. I play low levels of volume and the amp is basically cold.
Is this normal? Could it be that the amp has been tweaked and no longer runs pure Class A or is it just that the very strong fans are keeping it cool?
Thanks
.
 
#2,450
I think the procedure might be in the owners manual.

If not then start posting pics of the inside particularly around the output stages.

There are a number of KSA threads and at least one website that already have pics of partially dismantled KSA shown.
You should be able to compare your version to some of these and from there identify the outputs and the emitter resistors.
 
#2,453
thanks Andrew.
I'll try to find the time to open up the amp and verify this point among my three running baby girls, work, visitng parents in law, etc.
Can the measure of the voltage that the amp is pulling in idle be an indication to it running class A or not?
have a great day and thanks again for your help.
 
#2,454
yes,
the voltage measurement across the output emitter resistors allows you to calculate the bias current passing through each output device.
For this push pull output stage, the maximum ClassA output current is ~2*bias current

The KSA100 is a 4pair output stage.
If you have 600mV across all 16 emitter resistors then you know you have each output device is passing 600mA.
4devices in parallel pass 2.4A and from there the maximum ClassA current is 4.8Apk. This is equivalent to 92W of ClassA output into 8r0. 600mV is underbiased. Krell should tell you what the correct bias is for you model.
 
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