Aleph P oscilating or something else!!!

bbakota2000 · 28th August 2004, 06:14 PM

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!

bbakota2000 · 28th August 2004, 10:34 PM

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.

Blues · 29th August 2004, 11:02 PM

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?

bbakota2000 · 30th August 2004, 11:05 AM

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.

kilowattski · 30th August 2004, 05:17 PM

Congratulations and great job! Mine will be done by Friday. I can't wait!

28th August 2004, 06:14 PM	#1
bbakota2000 diyAudio Member Join Date: Jan 2004 Location: Croatia	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!

30th August 2004, 05:17 PM	#5
kilowattski diyAudio Member Join Date: Aug 2003 Location: Long Island, New York	Congratulations and great job! Mine will be done by Friday. I can't wait! __________________ ----------------------------------------------- Kilowattski

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28th August 2004, 10:34 PM	#2
bbakota2000 diyAudio Member Join Date: Jan 2004 Location: Croatia	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.

29th August 2004, 11:02 PM	#3
Blues Lightning In A Bottle diyAudio Member Join Date: Sep 2003 Location: Bremerton, WA	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?

30th August 2004, 11:05 AM	#4
bbakota2000 diyAudio Member Join Date: Jan 2004 Location: Croatia	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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