Hum loop in chain from single PSU

[Jahloon]

Hum loop in chain from single PSU:
I'm using a Voluum followed by a Wahoo in a signal chain. If I power them from the same 9v PSU (Have tried 2 different ones) I get a hum loop.
Powering the pedals from separate 9v PSUs eliminates the problem, as does powering both pedals from a single USB port, or powering either from the 9volt source and the other from USB.
I suspect the Voluum is generating the hum initially.
Is there any way I could power both units from one 9v PSU without this problem?

[james]

Are the power supplies chained? In other words it goes from PSU to Voluum to Wahoo?

A lot depends on the PSU, but generally if you are able to run 2 separate leads back to the PSU you will get better results. So you have PSU to the Voluum and a separate lead from PSU to the Wahoo. This helps avoid ground hum going between different pedals. It's not as good as separate PSUs for each pedal, but it should improve things.

[Jahloon]

Thanks for the reply James.
The PSU is in a chain, so it goes from the PSU to the Wahoo and then on to the Voluum.
A quick thought.... presuming the +9v is on the outer shield side of the socket, is this +9v the natural ground?
So if I were to isolate the outer shield would that eliminate the loop as the common ground would run through the jack lead grounds.
Need to check if this would be OK and not damage the unit.

[james]

You don't want to isolate the power ground. You want to make sure the power ground is as good as possible. What you are trying to do is to make sure that all the currents from the power supply get back to the PSU as easily as possible. In my example of using 2 separate leads, this helps because the ground from each pedal goes back to the PSU and therefore finds it difficult to go between the pedals.

What you can try to do is to isolate the audio ground. A resistor (maybe around 1k ohm) between signal ground of the jack cable and the ground of the pedals may help. This will prevent ground loops flowing along the audio cables. You can't disconnect the ground entirely as this will affect the signal and probably give you much worse hum problems.

An optimal solution is to use an isolation transformer (designed for audio). This lets the signal pass but does not allow any ground currents to flow. This is more expensive though.

[Jahloon]

Thanks James, will try those solutions, a 1K in the audio ground sounds like the easiest option, did not realise how expensive audio isolation transformers had become!