power supply switching noise help

[smuel]

Hi,

I've just finished building a guitar amp, and its all working fine, except there is a horrible 100khz signal leaking through the valve pre-amp swiching power supply and appearing at the output.

is there a simple way to filter this noise at the dc outputs of the psu? the outputs are 12v and 260v.

will some kind of low pass filter do the trick?

I've put a fair bit of sheilding in around the psu, but i could probably put more in if this would help.

thanks,

Sam

 

[rmathur]

Put bypass capacitors that should take care of it. I w'ld put a 10 uF and .1uF capacitor to gnd to filter out the noise from the power supply.

 

[VVV]

First try some decoupling capacitors or better RC filters on the low voltage supply.

If that does not cure it, then it's possible the noise is picked up somehow. So you need to identify the path. You can then short to GND the input of the preamp and see if that gets rid of it. Continue with other stages.

 

[IanP]

More effective then just capacitor or even RC network are LC low pass filters.
In your case you should use inductor of around 1mH and then 2 capacitors: one 100nF ceramic and one 10µF tantalum.
Also, you can try to use inductors on both: positive and negative lines. This will ensure, that no noise is comming from GND line ..
Regards,
IanP

 

[mohamedtaha]

Put an LC filter on the output of the power supply, this will greatly reduce the output voltage ripple.

 

[marshel]

use full differantial amp