Hi Dieter and Florian --

Thanks for your replies.

Florian: you were right in your diagnosis -- it was my USB-powered audio interface. The synth was totally quiet until I plugged it into the interface.

So, that's sorted but it's a bit of a pain! Now I need to get a new audio interface !

Thanks for your help -- glad to know that my PSU is not stuffed.

Kind regards,
Jon

--- In Doepfer_a100@yahoogroups.com , Florian Anwander <fanwander@...> wrote:
>
> Hello
>
> to both Nathan and Jon: is this a mechanical sound or does it come from
> the speakers
>
> If it comes from the speakers, disconnect the audio out from the A100
> system, and connect a headphone with a mini jack connector to the output
> of the last module in the audio chain (example: VCA or mixer) and turn
> it up. Do you still hear the noise
>
> If yes, then the problem is in the A100
>
> If no, then the problem is in the combination of the A100 with the rest
> of your system
>
>
> To Jon:
> Do you use an computer with and USB Audio interface
> If yes: Is the interface USB-powered
> If yes: use an interface with an separate power supply.
>
> USB-power on Audiointerfaces in a studio like environment introduces HF
> from the digital signals of the computer in the audio ground. Those are
> useful only for standalone usage.
>
>
> Florian
>