Gainclone picking up buzz/whine/high pitched noise from TV power supply

[altie]

Thanks for all the resources here that helped me put my Gainclone together. It's running great for the most part. Ran into a kinda funny problem with it though. There's a high pitched hum or whine present when it's connected to my computer via analog RCA, or my Kenwood receiver's preamp outputs. I was going to try to look at this hum with my oscilloscope when I was short a power cord. I unplugged my TV to use that cord and... the hum stopped.

The TV is not in this signal path at all, but is plugged into the same set of outlets as the receiver and Gainclone. It's a 42" Dynex LCD. This sounds similar to problems people describe with TV and laptop switched mode power supplies. The TV's "off" state is really more like "standby" where it's still drawing a very small amount of current to power the remote control receiver.

My question is: what's my first step to diagnose further (besides buying more power cords )? Is this more likely to be solved by better power line isolation, or better shielding on the line level cabling?

[djoffe]

noise could be coming in either path...via the power supply (e.g. conducted), via the "ether" (radiated), or both.

Here's a series of experiments:

1. Plug in power amp and TV, but no input cords on the power amp? Is it noisy? then the problem is conducted through the power supply. If it's quiet, then...

2. Add cords to amp input, but keep them away from the TV...is it quiet? does it get noisier as you bring the cords near the TV? Does shorting the far end of the cords help?

it expands a bunch from there, but these two might get you usefully started.

[gootee]

This should help:

Audio Component Grounding and Interconnection

[jaycee]

Badly behaved SMPS's can often cause this. Is your Gainclone in a metal case, and is that grounded to safety ground?