My amp is picking up noise ...

... mostly from the transformer.
I think that there could be something related to the PCB design, so can you suggest improvements in my layout? it is attached to this post

putting a steel panel between the transormer and the board greatly reduce the noise

Thank You,
Mauro
 

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Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Hi Mambo, sounds like magnetic field from transformer inducing currents into signal wiring. Just going off your P.C.B. layout disconect inputs at C1 both the ground and signal and apply short across the input. Any change ? Next with the short in place reconnect your signal earth. Again any change ? If yes try a low value (2.2 ohm or similar) in series with the input ground. Hum and noise can be very hard to eradicate and may require a rethink on your wiring layout.
Regards Karl
 
HI Mambo,


Ive encountered this problem in the past, almost always has been a case of the wiring from input jacks to the board picking up magnetic fields from the transformer. My fix is to use very fine solid copper conductor coaxial cable, eliminates all noise picked up. Not Rg59, but much thinner with copper conductor and copper braided shield. Worse case scenario its a ground loop, which can be insanely difficult to find.

Tryi moving input wiring around to see if it changes the amount of hum.
Colin
 
Shorting the input at the input connector doesn't produce any change: also removing the short track between the signal GND and the power GND and running a cable from the signal GND to the Start Ground does not produce any improvement.

Physical distance seem to cure: the other board, which is the second channel of a bridge configuration is placed side by side of the first, and it is at a greater distance from the trafo.
From that board it is impossible to distinguish circuit intrinsic noise from that picked up by the transformer.

Moreover, putting a ear near the transformer allow me to ear what seems to be same noise coming form the speaker

I think i'll ask to encapsulate the trasformer where I asked to build it ... if this could be of some help
 

Mooly

Administrator
Paid Member
2007-09-15 8:14 am
Mambo, If it really is induced currents causing problem, which from what you say it could well be, try if possible rotating the transformer slightly. The stray field is not constant, there are peaks and troughs. An encapsulated trx may be physically quiter but it will not eliminate stray field.
Karl