Silly question! :-)

[zerokelvin99]

Hi everyone!

I have a basic question that I am a little embarassed about!

I am currently designing a class A, fully balanced phono stage and am having issues with the 100hz hum after rectification.

We currently have a large amount of AC after filtering caps (sufficient capacitance) with our linear power supply. The 0v rail bypasses this and goes straight into the circuit. While the positive rails feed into our voltage regulater circuits.

The problem is that while +ve / -ve rails to 0v rails show 0v AC (as they reference and track the 0v rail in the regulation stage) we are having substantial problems with this 100hz hum after full bridge rectificaiton. Is it okay for the rails to contain AC components, if they all match each other? So, measuring the rails to ground shows this AC component but not to each other.

Can anyone advise on this situation? I have some inductors and capacitors on order for a parallel LC circuit between the smoothing capacitors and the regulators, but am skeptical of the results :-). Targetting F=100hz, Lcrit is double minimum value, I=90mA, etc

Many, many thanks for any help!

Sincerely,

Andrew

[AndrewT]

go and read
Audio Component Grounding and Interconnection - diyAudio

[zerokelvin99]

Thanks!