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Old 23rd March 2002, 08:00 AM   #1
BrianGT is offline BrianGT  United States
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Default Matching Aleph input devices as a part of the complete amplifier?

I was reading the volksamp aleph 60 manual and I noticed this:

"The input devices are the same as the originals, but significant improvement is to be found in the manner of matching the input devices. Previously the input differential transistors were merely matched to each other, but beginning with the Aleph 30 and 60 they are now matched both to each other and to the rest of the amplifier circuit. We select the input devices as part of the complete amplifier, swapping them in and out until the best performance is achieved. Tweaking the input stage in this manner and with other adjustment techniques we have been able to significantly lower the noise floor and improve the power supply noise rejection of the amplifier."

Would this help the performance of the Aleph 2 amplifiers that I am making?

If so, how exactly is it done, the matching of the devices?

Also, of those who build an aleph amplifier, how many IRF9610 devices should I buy to match them properly?

One more thing, I am planning on buying 100 IRFP240 transistors, and matching sets. Would anyone here be interested in buying matched sets for their alephs, assuming I get good matching. I am planning on using the expensive hp curve tracers that they have here at Georgia Tech.

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Old 25th March 2002, 12:09 AM   #2
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If you get 10 9610s that will be enough to get 2 pairs closely matched.

Having 100 IRFP240s will be plenty. I matched to within 0.01V on 4 sets of 6 using a starting population of 50.
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Old 25th March 2002, 03:30 AM   #3
Asen is offline Asen  Bulgaria
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My sugestion is that you should look for lower DC offset at the output when changing the input devices. But I'm noy sure in what I'm saying. I hope Mr. Pass will give us his explanation. I'm also interested in the working of the resistors marked with *, and their approximative values.

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Old 25th March 2002, 11:42 AM   #4
UrSv is offline UrSv  Sweden
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Several threads deal with the resistors. Try:

Aleph 30 unmarked resistors?
or
Aleph 30

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Old 28th March 2002, 02:54 PM   #5
BrianGT is offline BrianGT  United States
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Asen- I guess that would be what was described in the manual, swapping matched pairs in the final design to optimize for lowest dc offset. I will have to try that.

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Old 28th March 2002, 07:11 PM   #6
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Actually, we swap them until we get lowest distortion
and noise. DC we don't worry about much.
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