the Buzz (Hummmmm)

[catwink]

O.K. Here's the problem.....
After listening to my G.C.'s happily for a while I put the guts in new cases. Now when I connect the amps to pre-amp I get buzz from the speakers, even with no sources connected. I've tried grounding everything. Funny thing is that if I pull one I.C. the buzz goes away and one channel is fine. If I disconnect power from G.C.'s , no buzz... but of course no music either.
I can't figure out if it's power supply, gainclones, or pre....
Any advice would be appreciated.

Jamie

[carlmart]

Originally posted by catwink
O.K. Here's the problem.....
After listening to my G.C.'s happily for a while I put the guts in new cases. Now when I connect the amps to pre-amp I get buzz from the speakers, even with no sources connected. I've tried grounding everything.

This is easy to say but not easy to solve. If it worked fine outside the case, then you did something wrong when you put it inside. Your humm looks like a ground loop.

1) Are you grounding the case onto the star?

2) Are you isolating the input jacks from the case?


Carlos

[carlosfm]

Typical of people testing only one channel each time before making the amp and fitting the whole thing in the box.
I said this a million trillion times, but here it goes again:

With ONE tranformer for both channels you MUST have the two chips close from each other.
Run a thick wire, as short as possible, from the power ground of one chip to the power ground of the other chip.
On the middle point of that wire solder the ground cable that comes from the PSU.
No HUM!

[soundNERD]

If Carlosfm's suggestion doesn't work, then also try your preamp with another amp and see if it is the problem. Then, connect an input directly to the amp with no preamp. Remember that the equipment producting the input signal MUST have some form of volume control (like a portable CD player) or it will be on max...

[catwink]

I am using two transformers so that shouldn't be the problem. I will try isolating the I.C.'s. I did try a different amp and no buzz, so I guess It's in the p.s. or g.c.'s. Any chance one of the chips is bad???
Thanks for your responses.

Jamie

[soundNERD]

are the trafos and PS components the same? and are both amps identical? Also, do both share a common ground? If not, try that, and if so, try not connecting the grounds.

[2Bak]

Originally posted by carlosfm
Typical of people testing only one channel each time before making the amp and fitting the whole thing in the box.
I said this a million trillion times, but here it goes again:

With ONE tranformer for both channels you MUST have the two chips close from each other.
Run a thick wire, as short as possible, from the power ground of one chip to the power ground of the other chip.
On the middle point of that wire solder the ground cable that comes from the PSU.
No HUM!

Carlos, does this also apply if humming is non-existing when interconnects are not connected?
I have one transformer for two channels, and I have some small humming when I put my ear to the woofer. However if I disconnect my interconnects, the amp is dead silent with no hum at all.
I did not use your recommendation above, but seperated grounds from bridges until meet at star ground.

/Jan

[carlmart]

Originally posted by 2Bak

I have one transformer for two channels, and I have some small humming when I put my ear to the woofer. However if I disconnect my interconnects, the amp is dead silent with no hum at all.

More reasons to think of a miswiring on the input connectors, which only gets active when you plug in an external source.

Did you check those wirings as I described above?

Why don't you try disconnecting one of the RCA grounds altogether? That is leave only the RCA end on one channel or the signal end within the amp, but only one end. That maybe the loop.

By leaving just one end connected you will still shield the signal wire but severe the ground loop.


Carlos (the other)

[carlosfm]

Originally posted by 2Bak

Carlos, does this also apply if humming is non-existing when interconnects are not connected?
I have one transformer for two channels, and I have some small humming when I put my ear to the woofer. However if I disconnect my interconnects, the amp is dead silent with no hum at all.
I did not use your recommendation above, but seperated grounds from bridges until meet at star ground.

/Jan

Can you post a picture?
That may help.
It's much better to do as I said than to drive a ground cable from each channel (chip) to a star ground.
It's really a question of centimeters.
The two chips have to be close one to the other.
Absolutely no humm, with or without the source connected.
You have a ground loop there.

[2Bak]

Originally posted by carlosfm



Can you post a picture?
That may help.
It's much better to do as I said than to drive a ground cable from each channel (chip) to a star ground.
It's really a question of centimeters.
The two chips have to be close one to the other.
Absolutely no humm, with or without the source connected.
You have a ground loop there.

pictures here: http://2bak.homepage.dk/gainclone.htm

/Jan