Power Supply digital whine

I’m connecting the Mod Duo X via the FX loop of another device and experiencing a high pitch digital whine even on the default preset.

I carried out various testing and the issue resolved via using an isolated PSU (OneSpot CS12 Pro from Truetone) for the Mod Duo X. The device I’m connecting to is the Quad Cortex from Neural DSP and they have internal ground lift options for the fx loop which didn’t make a difference. Both PSU’s are connected to the same power strip/socket. Using the CS12 (which is located on my pedalboard) means I can’t have the DUO X on my desktop as the cable isn’t long enough from my pedalboard.

I tested other digital devices in the fx loop of the Quad Cortex with no issues; only the Duo X when using it’s native PSU has this issue. Can anyone advise as to what sort of isolation issue is/not present in the Mod Duo X power supply?


Do the other devices with which you have tested have 2-prong or 3-prong PSUs? Some of the problems with MOD units stem from its fully grounded PSU, as opposed to most Boss/Roland devices. Even the Quad doesn’t have the earth connection.

(I never looked inside Mod’s PSU, but given its size I would suspect it doesn’t have an isolator transformer inside. Also because isolated PSUs heat a lot more than non-isolated. But that is my guess, MOD staff may please weigh on this one.)

One quick question: did you combine multiple 12V outs to feed the Mod? Looking at the output ratings, you’d need all of them combined to produce the 2A (=2000 mA) you’d need to feed a Mod X – though it probably uses less than that in average.

If you just plug the MOD to one of them, the risk is overheating your PSU.

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Thanks for your reply. I’m in the UK so everything is 3 prong.

No need to use multiple outlets on the CS12. The specified per outlet mA is only recommended distribution across the device. They explain that, ultimately, it is total current consumption that counts and it has a 3A supply. I selected the appropriate 12v dip switch, applied the polarity reverse adapter and tested with multimeter to ensure centre positive voltage before connecting to Mod Duo X. As an extra precaution, I also checked at various intervals for any overheating but there’s no sign of it breaking a sweat at all.

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Ok, that clarifies a number of things.

Yes, but in the UK you have the plastic (usually black), non-connected central prong, which only serves to physically open the gate for the other two. Did they have an actual metal, earth-connected central contact?

The whine may have many causes, but to confront them with other equipment and their PSUs, this is a key piece of information.

If a grounded power supply (like the one you’ve used) produces no noise with the Mod, then you might have a faulty PSU that’s not properly filtering interference from other sources. But it’s hard to say without testing it.

Makes sense, or else it would not have powered the Mod X at all. And it’s wise of you to check polarity.

However, in that case the PSU is not “fully” isolated. You get the isolation from the AC stage to the DC one, but the various outlets run in the same circuit. (This is a thorny topic and some engineers disagree with that assertion. My learning of it was that, to fully de-couple the circuit, you need one isolation transformer per outlet.)

I had this issue when I first got the Dwarf. Moving the power brick well away from the Dwarf resolves the issue.