Input Jack Noise?

I bought a used PO-33, and it’s great fun. At first I was just sampling w/ the mic and didn’t have any problem. But when I plug a 3.5mm M-M interconnect into the input jack, the unit’s speaker or a headphone will start having a high frequency humm. It doesn’t matter if the other end of the cable is open ended, or plugged into another device like a Macbook Pro, or any piece of gear, the humm is there. As soon as I disconnect the cable from the input jack the humm will go away.

I’ve tried various things:

  • Putting a ground-loop isolator between the output device and the PO-33’s input. Didn’t help.
  • Try various 3.5mm cables

If I actually hit RECORD to sample the audio, at playback the sample will also have a noise, although it’s a lower frequency, I assume it’s due to the sampling resolution / frequency.

Has anyone experience this issue on any of the PO, particularly the PO-33? I know this is not meant to be a “serious” bit of kit, and that the design with its unenclosed PC board may not be the best shielded, but it does take a lot of the usefulness of sampling out of it. And once you hear it you can’t unhear it!

I really like the form factor of the PO and was planning to get more, namely the PO-32 and PO-35/137, but if noisy input stage is a general PO problem I may not add more. Chaining additional PO units will just multiply the problem!

it may be a ground hum from the jack.
If you have access to a soldering station I would suggest to wiggle the jack input a bit to see if it’s loose and solder it back in place.

did you try the 33 with different cables?