Quad 909 transformer sheilding

[steevo]

Hi I have a quad 909 and it uses quite a large torroidal transformer which
produces stray magnetic fields that affect the amplifier boards. rotationg the
transformer affects the SNR of the amp and in its worst case when the amp was connected to a preamp it produced a buzz throught the tweeters on my speakers when connected to the amp. This was noticable. when only 1 channel was connected the buzz dissapeared nut when both were connected the buzz came back. Has anyone any ideas why this onyl occurs when both channels are connected???.I am not sure.

To fix it the transformer was rotated and this seems to eliminate the buzz. A better solution I think is to make enclose the transformer with a thin metal sheet steel to block any stray magnetic fields from reaching the boards. This should improve the SNR even more. If I do this how should I connect the cylindrical sheet to the case.At one point only
Anyone have any recomendations on the best way to sheild the transformer???.

Steevo

[nigelwright7557]

If your only getting the buzz with both amps connected then it sounds more like an earth loop problem between the amps.

Enclosing the transformer could cause it to overheat.

But of course i could be completely wrong !

[steevo]

It could be an earth loop problem but then why would twisting the transformer eliminate it just about. I would not enclose the transformer completely, it would still be open top and bottom, also I could use a fine mesh sheet steel to allow air flow inwhich case I could enclose it completely.

Steevo

[nigelwright7557]

It could be a combination of lack of shielding and an earth loop.

I have seen a few threads on here where poeple had problems with two amps running off the same power supply.

[steevo]

I dont see how, If it was an earth loop then twisting the transformer would not
eliminite it, it might make it slightly better, but the noise due to the earthloop would still be there.

Steevo

[nigelwright7557]

I have numerous power amps right next to the transformer and never get any hum.
One is a 1000VA transformer.

There is clearly something not quite right with your wiring or the input to your amp is floating and very sensitive.

[steevo]

plus the quad amps run of seperate secondary windings per channel that should eliminate earth loop between channels

Steevo

[steevo]

Here is the quad circuit diagram for the 909. Tell me what you think.

Steevo

[sakis]

a loose ground contat or any other of this type of mistake will makeyour amp boards sensitive topick up noises ....

your estimation is wrong and repositioning of the trafo will only reduce the problem ...so the cause is not there

either a computer is conected to the amp and produces some earth loops or somthing is wrong with plugs cables and ground contacts

regards sakis

[bobodioulasso]

Has anyone any ideas why this onyl occurs when both channels are connected???.I am not sure.

Hum or buzz when 2 channels are connected only means an earth loop.