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Old 16th December 2006, 09:17 AM   #11
Netlist is offline Netlist  Belgium
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Imagine a wire between the two white clips.
Don't pay attention to the resistor in the picture.
Connect as shown.
Now your one input is shorted to ground.
Short the humming channel, then the other, then both and listen if you hear any difference.

/Hugo
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Old 17th December 2006, 12:24 AM   #12
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Quote:
Originally posted by Pass lover
Final question, there is only hum noise from the right channel, so I just ground only one right RCA interconnect?
Yes, you can do this one channel at a time. The point is to
evaluate the noise not connected to a source. At the same time,
an open input will pick up stray noise, and so is shorted to ground
to avoid that.
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Old 16th May 2009, 12:00 PM   #13
mercc is offline mercc  Slovakia
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Hi,

I have the same problem, lots of hum from right channel and smaller amount from left channel. When I short rca inputs, very small portion of hum disappears, I would say the grainy part but big smooth remaining part of hum stays. So which components have to be replaced to lower the hum?
Also I read that inner noise of the amplifier can be lowered by lowering the output gain by 6 db, how can this be done?

Thanks
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Old 17th May 2009, 11:28 AM   #14
mercc is offline mercc  Slovakia
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From audio analyzer output, the hum seems to have peak mostly at 100 Hz, lower peaks are around 200, 150, 300 and 50 Hz.
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Old 17th May 2009, 03:01 PM   #15
mercc is offline mercc  Slovakia
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After shorting rca inputs, the hum peaks seems to be (in descending order): little over 150Hz, then 250, 100, 50 and 550 Hz.
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Old 17th May 2009, 08:59 PM   #16
mercc is offline mercc  Slovakia
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After removing cables and shorting rca inputs with short wire has the hum peak at 100Hz and lower peak at 200 Hz. Measurement of zener diodes with digital multimeter show values 780 for left and 782 (mv?) for right channel. So maybe replacing the diodes will lower the hum.
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Old 18th May 2009, 08:05 PM   #17
cfcubed is offline cfcubed  United States
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If the noise came about w/no other changes to setup, and is confirmed not in source or due to faulty cable, I'd be inclined to think PS cap. Especially if the caps are 10/15 yrs older or more, live in a hot box and rated 85 deg.

Just my thoughts as a place to start if thinking component failure.
But others that know far than I have spoken & I'm speaking from quite limited experience.

Edit: And if its a design that has a series of large power supply caps in parallel per rail, it might be easy to see if one is faulty... Possibly pull one at a time, test for hum, then replace it & pull another one.
Not sure if that's a sanctioned form of testing, but...
In a NAD w/this problem I was able to confirm it was indeed PS caps by pulling the pair & replacing with a set w/equal (or higher) voltage rating. IIRC, the test replacement caps were only 1000uf, where origs where 4700uf, but the test was good enough to confirm them the culprit.
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Old 19th May 2009, 02:11 PM   #18
mercc is offline mercc  Slovakia
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Thank you for your response. Can you tell me why there is more hum in the right channel? Somewhere i read that its design property of Aleph, but the wiring seems to be symmetrical for both channels. And capacitors are likey to wear out evenly for both channels in time.
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Old 19th May 2009, 02:17 PM   #19
cfcubed is offline cfcubed  United States
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Quote:
Originally posted by mercc
Thank you for your response. Can you tell me why there is more hum in the right channel?
No, I know nothing about this design in particular. But if the design has a PS common to both channels, this would work against the PS cap at fault idea.

Quote:
Originally posted by mercc
And capacitors are likey to wear out evenly for both channels in time. [/B]
I'd be surprised if this were the case. Of the 1000s of hours the caps are rated for, having 2 or more go in the same week would not seem likely to me. BUT if I found any caps at fault in a section I'd replace them all of course.

Although it seems an idea that's easy to try, if problem is only in 1 channel & design does not have fully independent PSs/channel, perhaps not the thing to try.
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