Quad Cortex power — no ground, weird current and noise… anyone else?

[Jeff]

Hey all,

Kinda curious if anyone’s run into this.

So, the Quad Cortex power supply doesn’t have a ground pin — just live and neutral.

Because of that, when it’s plugged in, I can feel a tiny bit of current on the chassis. Not dangerous or anything, but definitely there.

It gets more annoying when I plug in my guitar. There’s noticeable hum/noise, and it’s not single coil hum — noise gate doesn’t help at all.

I’m thinking about trying a grounded power supply, but here’s the problem:

Quad Cortex uses that weird center negative thing (outside positive, inside negative).

Honestly, I’ve never seen anything else use that. Super strange.

My plan is to grab a normal grounded power adapter and rewire it to match QC’s spec, just to see if grounding fixes the noise.

But yeah… would be nice if Neural DSP actually addressed this properly. Seems like a pretty basic issue to have on a pro unit.

Anyone else noticed this or tried something similar?

Appreciate any tips or thoughts!

[NigelGBR]

This is a very well known issue. It’s hard to believe that you were not aware of it. A “grounded” power supply, even if there is such a thing, will not ground the Quad Cortex.
It is designed to be grounded via XLR to a grounded power amplifier, and that is the only way it can be grounded.

[PickinPete]

I don’t mean to be argumentative but, I doubt that anyone is able to feel 12 volts DC at such limited amperage capability. If so, never touch your car door! Is there a possibility that somthing the QC is connected to is leaking current?

[Frozenguy1]

The QC is not grounded on purpose. You have to hook it up to something to ground it. It is this way to prevent ground loops during performances. Pluggin into your pc via the USB, plugging the XLR’s into a grounded device or plugging into an amp (can be off) via the jacks will ground the device.

I’ve been thinking of making a cable with a 6.3mm plug on one end and a wall plug with ground on the other. Simply connect the grounds together and leave the rest untouched. Havent tried it yet though.

Anyway, using a grounded supply isnt gonna fix your issue because the qc itself just doesnt have a path to ground via the 12v input.

Also fyi, center negative barrel adapters are the standard in guitar industry. No idea why though.

[DavidRSTV]

You can in a lot of cases feel the build up voltage (it’s common-mode interference to be exact) if the devices case is made of metal and not grounded to mains ground. Almost all MacBooks have this ‘problem’ if used with an ungrounded power supply. It’s not that they shock you but you can feel a weird ‘resistance’ when moving your fingers across the metal surface. (Newer MacBook Air MagSafe Power Supplies deliver around 14v at 3 amp max for comparison)

[PickinPete]

Interesting. I’ve never heard of this issue. I assume that all MacBooks come with a grounded supply. I stand corrected.

[DavidRSTV]

Nope. At least not the newer ones. Some time ago (before the introduction of the m-chips I guess) apple shipped the power supply with two adapters: One with a meter or two of additional cable and one without (wall-wart style). The long version is/was grounded (three prong plug) but the short version isn’t (two prong). Today at least the smaller supplies are only shipped with the wall-wart style insert.

[Jeff]

That’s true , now the new Mac doesn’t have that option.

[Heretolisten]

I’ve only seen negative center positive on the outside. One time out of many pedals an older Digitech pedal had the opposite adapter. Negative inside is the norm.