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Old 6th December 2002, 06:41 AM   #1
Jean is offline Jean  United States
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Question I have a slight problem, need some suggestions

So here is my little problem that I would like fix 100%. My amplifier is dead silent when a) nothing is connected to it b) only one rca cable is connected to it. It has low freq. noise present if both rca jacks are connected to the amplifier and the other end to a source.

This is what I tried so far to try and narrow down the problem. I moved my amp and the source (cd player) to another room and its doing the same thing. I tried it with another source and the same thing happens. Finally I tried connected the rca ground ends together with a jump wire , still same thing.

The way that I have everything wired is as follows. Single transformer, and two bridge rectifiers (one per secondary). They meet at the cap bank which is fairly simple. This is the center point , from this point I have ground wire going to the speaker output jacks and the power to the two amplifier boards. The rca jacks on the chassis are connected via shielded cable directly to the pcboard (not the capacitor bank). Also, DC ground is not connnected to the chassis or AC ground.

Would my next step be to lift one of the rca jack grounds, or lift both and connect them together and then run a single wire to the capacitor bank ground point ?

Tia,

Jean
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Old 6th December 2002, 10:23 AM   #2
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'Would my next step be to lift one of the rca jack grounds, or lift both and connect them together and then run a single wire to the capacitor bank ground point ?'

Hello, I am new here.
You can try to connect ground together at rca jacks (without discinnecting from any of rca). It'll reduce the ground loop.
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Old 6th December 2002, 10:32 AM   #3
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I'd lift the ground from one of the RCAs. Shielding is not broken since it's still connected at the output of the preamplifier and this way you only have a single connection between the grounds of pre and amp.

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Old 6th December 2002, 02:12 PM   #4
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jarek, have already tried that (with jumper wire) and it didn't help.
Andypairo, thanks I will try lifting one of the ground wires to see if it helps .
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Old 6th December 2002, 02:54 PM   #5
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Ok, let us know..

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Old 6th December 2002, 07:26 PM   #6
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Sorry Jean, I didn't read carefully. Andypairo is right, it will do the job (I think), but I don't like losing a symmetry.
I'd also try lift both rca and then run a single wire to the central ground point. Maybe you should disconnect small signal ground from supply ground on the pcb. Then you will be able to run small signal ground to the central ground separately.

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Old 7th December 2002, 04:03 AM   #7
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Success Lifting one rca ground solved the problem. I did it on the passive volume control side, and noticed if the ground connections of left and right channels are connected the noise is present (even w/o connecting the amp to the source).

I will try also rewiring it inside to preserve its symmetry.
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Old 9th December 2002, 12:55 PM   #8
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I am happy it worked!


Cheers

Andrea
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