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Old 28th August 2004, 05:14 PM   #1
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Default Aleph P oscilating or something else!!!

Hi guys,
My Aleph P 1.7 worked just fine until today. Today I've changed gain resistor (2K pot on the Nelson's schematics) from 810R to 300R. It is a Caddock resistor and everything is OK with it (I measured it). So I plugged it in and the music was far more open and dynamic compared to lower gain setting (810R). But, after some listening I heard pretty strange shhhh sounds in left speaker in some tracks I've listened to. It's not a buzz or hum. What is it?????
I switched the outputs of the preamplifier and the shhhh sound moved to the other speaker, so it's not the speaker problem. Can I solve that problem without an osciloscope?
All the measured voltages are OK. Output caps ~27V, input caps ~ 13V.

Any suggestions are welcome!
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Old 28th August 2004, 09:34 PM   #2
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It looks like my preamp picked up some radio frequencies in one channel. Now I've covered it with a grounded aluminum plate and everything seems to be OK.
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Old 29th August 2004, 10:02 PM   #3
Blues is offline Blues  United States
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Could it be that the added gain uncovered ambient noise in the recorded material? Is the noise present in all music you play? Do you hear it without music or at idle?
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Old 30th August 2004, 10:05 AM   #4
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You are right Blues. That is exactly what happened. Aleph P circuit was picking up RFI even before I increased the bias, but it wasn't so obvious. Same thing with the ambient noise from the music, especially from bad recordings. I can hear all the noise in tracks that I've heard hundreds of times. So, everything is more amplified with more gain. Noise is not present at idle, I can hear it only with some CDs.
The sound overall is awesome. Completely unexpected. Completely opened and transparent. Nelson is a genius.
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Old 30th August 2004, 04:17 PM   #5
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Congratulations and great job! Mine will be done by Friday. I can't wait!
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