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separating PSU for preamp

Hi all

I am considering pulling the PS out of my 24V aikido preamp. There is a low level underlying hum from it ( I have managed to knock most of the noise out of it by grounding etc) and I think the PSU may have something to do with it. This is because the hum on one channel is a bit higher than the other and it is the channel nearest the PS. Now the hum isn't that high - for example the fridge about 15' away in my open plan room is much louder than the hum through the speakers. However, I would like to get it a bit quieter if I could - even as a learning exercise.

The set up is 2 aikido boards which run from a powerone linear 24v supply all mounted in a standard full width case. The heaters are wired in series so both heaters and B+ are all at 25.2V. Each supply goes through its own choke before getting to the PCBs.

Now before I do this I will pull out the supply and just jumper it in to try out. But if it was to work what would be the best way to arrange the PS and chokes? Should I leave the chokes in the preamp case and just separate the PSU, or should I put the chokes in a separate box with the PSU and then run directly to the boards? Am I mad?

Link to the PS: power one

What do you all think?
 
Nope, you're not mad. I'm quite familiar with the Power One series of linear supplies cause I've used them. The power transformers are not shielded and removing the unit from the amp will probably cure the problem. Reorienting it's position may also do the trick if you have the extra room. Removing it for a test will tell you if the chokes need to be moved also. I say they can probably stay. The aluminum L frame that Power One uses is isolated and should not be causing a ground loop.

Victor
 
OK,

more on this: It seems that its not the PS.

If I only connect one source, its pretty quiet. As I add more sources, it gets noisier - doesn't really matter which ones and in what order, just the more thats connected the noisier it gets. The CDP was making the biggest contribution and I swapped in its balanced outputs instead and the noise is well down overall.

So my grounding scheme is basically star, all circuit grounds are tied together with a bus bar all along the back across all the inputs and outputs, circuit grounds, etc all tied together at one point and then brought back the PS ground - which are also together at one point.

I had this then connected to ground via diode/cap breaker, but have left that disconnected at the moment - will need to reconnect this for safetly alone.

So, anyone have any other tips? Should I bring each input/output ground to the star separately instead of together?

Fran
 
woodturner-fran said:
OK,

more on this: It seems that its not the PS.

If I only connect one source, its pretty quiet. As I add more sources, it gets noisier - doesn't really matter which ones and in what order, just the more thats connected the noisier it gets. The CDP was making the biggest contribution and I swapped in its balanced outputs instead and the noise is well down overall.

So my grounding scheme is basically star, all circuit grounds are tied together with a bus bar all along the back across all the inputs and outputs, circuit grounds, etc all tied together at one point and then brought back the PS ground - which are also together at one point.

I had this then connected to ground via diode/cap breaker, but have left that disconnected at the moment - will need to reconnect this for safetly alone.

So, anyone have any other tips? Should I bring each input/output ground to the star separately instead of together?

Fran

The sources you connect are also grounded. The RCA cables you use to connect them may be creating ground loops. Maybe use an RCA cable with a disconnected ground?