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Old 16th April 2003, 06:30 PM   #1
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Default Gainclone trouble

Ok...my gainclone works BEAUTIFULLY...but I have this tiny hum in it. Sounds like the television hum. I know these things are supposed to be silent. I tried a resistor from input ground to ground...doesn't help. I can UNPLUG the input ground to ground and there is NO CHANGE in hum or fuction...weird huh? Everything is fairly simplistic....Peter Daniels schema etc. Its not a 60 hz hum...but sounds like a harmonic...like 120 hz or 240 or something. I have an IEC receptical which has a "filter" in it for the power input. I have star ground...two chassis...star ground in the amp chassis. Any ideas?

-Matthew K. Olson

ps...the hum goes away basically if I unplug the source...discman or regular cd player makes same amount of hum

pps...I have a 50k to ground resistor instead of a pot...its after the caps 2.1uF but before my 10k resistor on the input ...hope that helps
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Old 16th April 2003, 10:27 PM   #2
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Ok...I've been fighting this stupid hum all day long. Its more like a buzz...sounds exactly like a flourescent light, and exactly as loud. I removed my 50k input resistors to ground....no difference. W/ or w/o input ground attached doesn' t seem to matter. This is too weird. I've got power ground attached to power grounds, speaker ground and input ground...all mounted to the chassis...I've tried different configs....still no change...it only gets worse. The buzz does NOT go up and down w/ volume change. ...and worse...now my toroid is humming. Plitron 18-0-18 225va. Please help!

-Matthew K. Olson
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Old 16th April 2003, 10:40 PM   #3
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Default Shooting the hum

Can you try two 12v batteries in series, as a +/-12v supply, and see what happens?

Can you get two big capacitors, at least 10000uF each, switch everything on, and then see if the hum goes away when you turn the AC off?

Is the gainclone inside a metal box which is also grounded?

Have you tried disconnecting the amp ground from the wall ground?



Carlos
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Old 16th April 2003, 10:43 PM   #4
moamps is offline moamps  Croatia
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Hi,

maybe your amp oscillate. Is heatsink warm without signal?
Have you zobel on output?

regards
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Old 16th April 2003, 10:47 PM   #5
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Ok...I don't have car batteries...but that is an idea.

I have almost 15kuf on the rails of capacitance right now. yes, the hum goes away when I turn the ac off. again, the hum though is not being amplified...I can turn up my discman to whatever level...actually I can't...gets too loud! :-D but anyway, the hum isn't amplified...the ps case is not grounded, and the wall ground is not attached. I tried messing w/ that...no difference. Yeah, the ps case is not grounded...but I think I've tried w/ a jumper wire to ground it...gets worse I think.

Also...when I jumper the inputs to ground...ie...so there is for sure no signal...I still get hum. BUT...if I have nothing plugged into the inputs...no hum. Wish it was like that when I plugged stuff in! doesn't matter what I plug in though...whether its a test RCA that shorts input to ground or my discman or a regular cdplayer or a preamp...120hz hum...audible in a quiet room.

-Matthew K. Olson
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Old 16th April 2003, 10:48 PM   #6
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No I don't have a zobel on the output...I have pretty big heatsinks on the thing. I was thinking of it oscillating, and that still could be, but the heatsinks are not even warm. What are the values for the zobel on the output? Thanks!

-Matthew K. Olson
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Old 16th April 2003, 10:58 PM   #7
moamps is offline moamps  Croatia
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Quote:
Originally posted by Mattyo5
Ok...I don't have car batteries...but that is an idea.

Also...when I jumper the inputs to ground...ie...so there is for sure no signal...I still get hum. BUT...if I have nothing plugged into the inputs...no hum. Wish it was like that when I plugged stuff in! doesn't matter what I plug in though...whether its a test RCA that shorts input to ground or my discman or a regular cdplayer or a preamp...120hz hum...audible in a quiet room.

-Matthew K. Olson
Where is ground of RCA connected?

Quote:
Originally posted by Mattyo5
No I don't have a zobel on the output...I have pretty big heatsinks on the thing. I was thinking of it oscillating, and that still could be, but the heatsinks are not even warm. What are the values for the zobel on the output? Thanks!

-Matthew K. Olson
R can be from 1 to 10ohms 2W min
C can be 100nF or 220nF/50 or 100V MKT min

But, from your answers I dont think that your problem is with oscillating.
Problem is somewere with grounding.
Have you any pictures?

regards
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Old 16th April 2003, 11:04 PM   #8
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Whether the RCA ground is connected or not the hum is there...weird huh? RCA grounds are connected w/ everything else at star ground. I kind have this sinking feeling that when I cranked down the RCA's there was a shard of aluminum that went through the teflon and is grounding the RCA to the case ...ie...away from star ground. But ....I'd have to have done that at both spots. Lemme get some pics and post em. Hang on

-Matthew K. Olson
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Old 16th April 2003, 11:12 PM   #9
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Heres the Power supply
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File Type: jpg power supply.jpg (78.4 KB, 1054 views)
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Old 16th April 2003, 11:31 PM   #10
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Heres the guts of the amp...you can see my connector that isn't connected...thats from the RCA ground...strange huh? Other than that, I used 3 caps in parallel for the input caps...is that my problem? hmm...what else could go wrong?

-Matthew K. Olson
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File Type: jpg p4160087.jpg (57.3 KB, 1029 views)
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