Pass Aleph P1.7 Help needed

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#24
Re: something wrong...

Klaus said:
Hi,

my hint: read the service manual carefully – the P1.7 of course runs perfect, once built correct.

This tread gave some hints about the testing and measuring on the circuit. Good luck with finding the mistakes in the setup!
http://www.diyaudio.com/forums/showthread.php?s=&threadid=39844&highlight=

Regards

Klaus
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Hi Klaus,


thanks for your hint. I messure 14 V across the input and 28 V across the output caps.
The voltage over R 44/59/70/55 is 0,65 V. Do you have an idea why my voltage are higher ?

Thanks and Best Regards
 
#25
Hi,

as far as I understand your Aleph P1.7 is just amplifying signal voltage some times, but not +20dB. But at least the bias – and so the basic function – of the circuit seems to be ok. The voltages are not higher, but just ok within normal tolerances. I got one idea...

What is hanging at the output of your P1.7 as volume attenuator?

Regards

Klaus
 
#26
Klaus said:
Hi,

as far as I understand your Aleph P1.7 is just amplifying signal voltage some times, but not +20dB. But at least the bias – and so the basic function – of the circuit seems to be ok. The voltages are not higher, but just ok within normal tolerances. I got one idea...

What is hanging at the output of your P1.7 as volume attenuator?

Regards

Klaus
Click to expand...


Hi Klaus,

you are absolutely right.
I tried without an out attenuator (pure 47k Resistor) and with the attenuator ladder (like in the original Pass Design). I can not meassure any difference in the amplification between both.
Probably the MOSFETs are gone, although I have already replaced them in one channel. I just orderd new ones today.
What do you think.

Any idea is highly appreciated.

Thanks
 
#27
Hi,

no, 47k pot is not supporting my idea of a possible mistake. My idea was that you could have used a low resistance pot, e.g. 1k or so at the output from signal to ground. This very low output work resistor would have killed the amplification factor.

But now I have no more idea... If the bias is right the FETs will be ok. You must have a mistake somewhere in your set... Good luck with finding!

Regards

Klaus
 
#28
Klaus said:
Hi,

no, 47k pot is not supporting my idea of a possible mistake. My idea was that you could have used a low resistance pot, e.g. 1k or so at the output from signal to ground. This very low output work resistor would have killed the amplification factor.

But now I have no more idea... If the bias is right the FETs will be ok. You must have a mistake somewhere in your set... Good luck with finding!

Regards

Klaus
Click to expand...


Hi Klaus,

thanks for your help. I will try with new MOSFETS next week. I will keep you posted.

Thanks for your assistance
 
#29
Hi fschlenk,

have you found some solution in the meanwhile?
I'm afraid, I have a similar problem. My P1.7 shows the same behaviour an both channels and both polarities. I will check again tomorrow, maybe I mixed input attenuator settings 1,2 with 3,4. (Yes, hope dies last....)

Regards
Thomas
 
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