amp buzzing

[kzeprf22]

Hi I have a problem concerning an amplifier of mine. More specificaly there is a slight periodic buzz comming out of the speaker. The buzz exists with or without connected to the input by the same amount. Is permanent. The amp is monoblock, hast the mains earth connected to the chassi, and I use a 10 ohm resistor with 100nf cap for connecting the chassi to PSU ground. I disconected the mains earth and the noise is the same. Has the point connected the mains earth to be exactly the same withe the end of the loop braker? Total cpacitance is 150mf in a symmetric PSU +/-32v with a 7Hz low pass filter cap-resistor-cap.
I have done the same amp before without this problem, but now I have this problem. There are two different thing though. The first is that in this I have more output devices (mosfets) and the second I noticed a slight difference in the secondaries of the transformer (400VA) in voltages, is about half voltage different. Can this be the root of cause? Also another question is about the orientation of the main connected to the primaries of the transformer. Can the orientation create this buzz. I am asking this because inside my amp I have a second auxiliary transformer with its primary connected (parallel) to the primary of the big one. If I change the "polarities" makes a difference?
Any help it will be welcome.
Thnx

[kzeprf22]

Originally Posted by kzeprf22

Hi I have a problem concerning an amplifier of mine. More specificaly there is a slight periodic buzz comming out of the speaker. The buzz exists with or without connected to the input by the same amount. Is permanent. The amp is monoblock, hast the mains earth connected to the chassi, and I use a 10 ohm resistor with 100nf cap for connecting the chassi to PSU ground. I disconected the mains earth and the noise is the same. Has the point connected the mains earth to be exactly the same withe the end of the loop braker? Total cpacitance is 150mf in a symmetric PSU +/-32v with a 7Hz low pass filter cap-resistor-cap.
I have done the same amp before without this problem, but now I have this problem. There are two different thing though. The first is that in this I have more output devices (mosfets) and the second I noticed a slight difference in the secondaries of the transformer (400VA) in voltages, is about half voltage different. Can this be the root of cause? Also another question is about the orientation of the main connected to the primaries of the transformer. Can the orientation create this buzz. I am asking this because inside my amp I have a second auxiliary transformer with its primary connected (parallel) to the primary of the big one. If I change the "polarities" makes a difference?
Any help it will be welcome.
Thnx

Currently I use two bridge rectifiers for the Positive and negative. Do you think that i I use only one with the center tapp as ground will be better?
Any opinions?

[AndrewT]

tell us what transformer you are using?
Show us how you have wired the transformer.
What type of rectifier are you using?
Show us how you have wired the rectifier.
Show us the PSU schematic.

[kzeprf22]

Here it the schematic I use?

[kzeprf22]

Also I read in this article
Ground loops, speaker hum and buz from Nico Ras that the voltage differentiation of the two secondaries may lead to buzzin is that correct? And if yes is a way to cure it except buying new transformer?
Anyone with any ideas?
Thnx