PSU for MV 810/2 preamps

[Malte]

Here is what it sounds like at the moment:

First without any input connected, then with music.

https://dl.dropbox.com/u/5370185/mv%...blem%20hum.mp3

When I turn up the volume on the MV 810/2 I hear some kind of "knocking" sound. Something oscillates in the low frequency range (when I turned up the gain to the max, you hear it with quite a lot of distortion).

[Matt Syson]

Hi
It certainly appears to be a positive earth design so you should link pin A3a to ground.
Seeing the other half of the schematic may be of assistance.
Since it calls for 20 Volts it may be worth turning your supply down to that but many modules are pretty tolerant and 4 Volts is not wildly high. I have not come across the supply you mention but if it is a 'switchmode' it could upset the module with HF switching noise or as the module may not draw much current, a high powered switcher may not be entirely happy regulating such a low current, certainly not 'quietly' and it could be 'pulsing'. Putting an extra load, say a resistor that draws 200mA may stop it messing about if this what is wrong.
Matt S

[Malte]

Hi Matt,

thank you!!! I did as you said and now it works! Without 60Hz hum and the extra load took care of the pulsating noise. You are a genius!