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Old 8th September 2008, 05:38 PM   #1
oblerum is offline oblerum  Norway
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Default Aleph1.2 clone trouble

I just finished aleph1.2 clones and am getting nearly no sound at all from it. I measure the same values when I measure left and right channel, see schematics.

Everything is as the schematics say except the MPSA 18 are replaced with BC 550 (yes I do know about the reversed pins, so they are turned 180 degrees)

Her are some facts/measures:

- amp built as per schematics (KK-PCB)
- hear very low signal trough amps
- The mosfets are matched within 0,015V, but will not heat up
- I measure 69 Volts over mosfets (no voltage drop at all), but no volts over R40-51
- Powersupply with testload measured 58V
- BC 550 used (not MPSA 18), otherwise original parts
- Q1, Q2 and Q3 are hot (but not to hot)

any help would be MUCH appreciated,
cheers,
Ole Bjørn
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Old 8th September 2008, 05:50 PM   #2
Zen Mod is offline Zen Mod  Serbia
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for start - instead R11 put 100R resistor in series with 100R pot ,then try to set pot to have nearer to 4V across R14 , chasing 0,5V across source resistors of output mosfets

to my eyes - you don't have enough current through input LTP (Q1,Q2) , so not enough current through R14 , so not enough voltage across it to open enough lower bank of output mosfets ;

one thing you didn't measured - output DC voltage ; I can bet that you have there near +55V
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Old 8th September 2008, 10:16 PM   #3
oblerum is offline oblerum  Norway
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Thank you!

I shall try this over the weekend, and post the answer when I tried it.

cheers
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Old 8th September 2008, 10:20 PM   #4
Manu is offline Manu  Europe
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Quote:
Originally posted by Zen Mod

I can bet that you have there near +55V
Thats normal you're pita, sorry pithia of BaC afterall...


Naaah, just sincerely admirative how you can do ferndiagnose ...
You know what I mean...

I am always fascinated how some issues (when then solved) can bring so much understanding in a given matter...

Manu
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Old 9th September 2008, 02:55 AM   #5
john65b is offline john65b  United States
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I had a similar issue on a Zen v5 - one of may rails was not "on"
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