buzzing transformers....

[rtate]

I have 8 leach super amp mono blocks all built with toroid transformers, 10 amp with 80,000uf supplies
Some of the trannies have developed a hum or buzz that is audible during quiet passages.

Is there any solution to this problem??

[Nordic]

tighten nuts
possibly add absorbent foam or rubber layer under fixing point
submerge in transformer varnish...

[rtate]

The transformers are "potted" and insulated and mounted on
1/4' high density rubber.

I have read that there can be stray dc voltage in the ac mains that would cause this??

[astouffer]

I have read that there can be stray dc voltage in the ac mains that would cause this??

Are all 8 of them running from the same breaker? Toroids have a low DC resistance to begin with so all 8 in parallel would be super low.

[gareth]

Hi,
Try turning the toroids, there may be a point where the hum is minimised. They will also hum if there isn't enough load on the transformer.
Thanks
Gareth

[rtate]

All 8 are on one dedicated 20 amp breaker ran with 10 gauge wire.
I don't understand what you mean by "lo DC resistance"
Is there something I can do about this?

[Mooly]

Hi, I take it you mean mechanical hum. I have heard, but never tried this myself, that you can connect a large value electolytic in series with live and neutral connections BUT YOU MUST INCLUDE a pair of inverse connected diodes across each cap to limit the D.C. across each to around 0.7 volts. If you are at all unsure DONT TRY THIS. I can draw what you need but as to it's effectivness I don't know. This is to prevent D.C. component that may be superimposed on mains causing a problem. Do you have an oscilloscope ?
Regards Karl

[Dan2]

If the buzz is coming through the speakers it could be the rectifier

[rtate]

it is deffenitly a mechanical noise from the transformers.
I would like to fond some suggestions for building some sort of "trap" circuit that i can put on the supply side of the 115 vac feed.
Each amp has a 1000va transformer with 80,000uf cap.

[fotios]

Originally posted by rtate
I have 8 leach super amp mono blocks all built with toroid transformers, 10 amp with 80,000uf supplies
Some of the trannies have developed a hum or buzz that is audible during quiet passages.

Is there any solution to this problem??

I had the same problem as you with toroid xformer. Not the tightening - up to death! - and not the rotation resolved the buzz problem. After a discussion with my supplier, he told with each sincerity that the noise caused from the core if it is not tightened very strongly. The core of the toroid constructed from a soft iron flat plate which is formed by turning a piece of it around a cylinder for example 5 times. One secret it is there. The cylindrical folded core it is not absolutelly compact, and thus can cause crackling noise even without load. Most constructors use the tightening of the copper wires during the winding process to tight simultaneously the core. But this method it is not the better. A such maden xformer even if it is encapsulated with epox. rosin can cause buzz noise. After examining the problem with my supplier, now we have resolved it, with an additional cost of 10Euros per piece, for: After the forming of core and before the winding, the core is dipped on varnish first and stay for 2 days tightened for good drying. Then it follows a carefull winding proccess, and before the final winding of the mylar insulating tape, it is dipped again in the varnish and stays again to dry for another 2 days. Then the encapsulation it is useless. The only additions it is the filling of the centre hole of xformer with epoxy rosin with the mounting bolt fixed into (thus there is not need for use an upper plate for mounting), and an external metal foil around the xformer for electromagnetic shielding.
Finally, a little secret from my experience. After delivering the xformer, i leave it on the shelf (in room temperature) for two weeks at least so to i feel secure that the varnishes dryied absolutelly. Never i connect it in the mains before this. Thus, the xformer after all these it becames a compact device.

Fotios