Small humming, but want's to get rid of it ! - diyAudio
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Old 6th March 2004, 10:53 AM   #1
2Bak is offline 2Bak  Denmark
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Default Small humming, but want's to get rid of it !

I read is this post the below quote from Alcaid: Please comment my Inverted Gainclone PCB

Quote:
Originally posted by Alcaid
...And another thing; the OUT-GND must go to power-ground not signal-ground.
Should signal ground and pwr-ground not be connected in an IGC...??

I my pcb (poweramps only) I have a little bit of humming, and I can't figure out where comes from. The amp doesn't hum at all, when interconnects' are not plugged in. Complete silence
I have two wires (the grey ones) to connect pwr-ground and signal-ground to common starground.
At the moment those two grey wires are of same thickness, perhaps I should make the wire from the signal thinner, however this doesn't make sence to me, cause no current runs in ground...?

I've read many places that out-gound and in-ground should be connected....?

Please give me a hint where I should look for the cause of my humming.

Thread with my pcb's

/Jan
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Old 6th March 2004, 11:51 AM   #2
matjans is offline matjans  Netherlands
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does it hum with all interconnects? If so, it might be a ground loop between your CDP and amp.
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Old 6th March 2004, 12:07 PM   #3
2Bak is offline 2Bak  Denmark
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Quote:
Originally posted by matjans
does it hum with all interconnects? If so, it might be a ground loop between your CDP and amp.
It's a four channel gainclone pwr-amp, e.i. two sets of interconnects, and input comes from a Thule surround preamplifier's output, and hum is there with all kinds of sources in the preamp - dvd, cd, tuner, etc.

If I disconnect the one set of interconnects (only two channels running), no difference....still humming in the two channels which have signal in.

And if I don't use the preamp at all, and instead connect a cd-player with variable output directly to the GC I still have humming.

I've tried everything. Connecting grounds between all four RCA's inside the CG, connecting starground between all four channels, doing chassis ground with 100R's, and much more combinations... But unsuccessfully.

How would one cure a ground loop between source and amp?

/Jan
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Old 6th March 2004, 01:15 PM   #4
2Bak is offline 2Bak  Denmark
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...what I haven't tried is to use shielded cables from the amp's phono sockets to the pcb's input terminals.
At the moment I use twisted Stripline 2000 cable:

Stripline

Could this be worth trying?
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Old 6th March 2004, 02:18 PM   #5
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this may seem like a strnage connection, but can you try and disconect the ground sheild on the RCA inputs, so that only the signal pin is conected to anything, as there may be significant currents trying to flow through the screen if your amp and pre's chasis are at different potentials.
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Old 6th March 2004, 07:29 PM   #6
2Bak is offline 2Bak  Denmark
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Quote:
Originally posted by bigparsnip
this may seem like a strnage connection, but can you try and disconect the ground sheild on the RCA inputs, so that only the signal pin is conected to anything, as there may be significant currents trying to flow through the screen if your amp and pre's chasis are at different potentials.
Would there be any danger to my GC/speakers trying this experiment? FYI none of my equipment use AC ground.
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Old 7th March 2004, 06:42 AM   #7
2Bak is offline 2Bak  Denmark
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...my rca's are isolated, so this experiment wouldn't make sence..?
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