Loud hum when connecting QC input to patchbay

Quad Cortex
1

Hi! I’m just starting to use my brand-new Quad Cortex. Amazing piece of hardware/software BTW! I also bought a Rockboard TRES 3.0 pedalboard to attach the QC there and a Shure wireless receiver. With the idea of reducing the wear and tear of the QC unit to a minimum, I installed a Rockboard MOD patchbay:

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All connections in the patchbay, including the AC, are just pass-thru.
I connected:

  • Input 1 to the Shure wireless receiver.
  • Input 2 to the TRS patch A, with a TS cable.
  • Outputs 1 and 2 to patchbay’s XLR 1 and XLR 2.
  • Outputs 3 and 4 to TRS patchbay’s B and C, using TS cables.

Everything is working fine; except I’m getting a very loud hum in input 2 when nothing is plugged into the patch A:

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Input 2 in configured with a 10MΩ impedance since I usually connect my NS Design EUB there, which have a noticeably quiet piezo. If I connect the EUB to patch A, the noise almost disappears, but it’s still present. I’m not having this problem with the patches B and C, only with the patch A. Of course, if I connect the EUB directly to QC’s input 2 there is no appreciable noise. The QC is powered using its factory power source, which is located inside the pedalboard and connected to the patchbay’s AC outlet.

I’ve already tried the ground lift option, with no results at all. Do you think this problem could be solved by using an ISO power source like CIOKS or similar? Or could this be another problem? Should I use TRS cables to connect the A patch to QC’s input 2 (both are TRS)?

Thanks in advance!

2

Why are you boosting Input 2 level by 30 db??!! Maybe that is contributing to the noise?

2 Likes
3

Surely, this is why the noise is so loud. The previous owner of my EUB made some enhancements to its electronics. The sound is good (quite good, actually), but the output volume is really low. I have no noise issues when plugging the EUB directly to the QC, only if I do it through the Rockboard patchbay.

4

I am having the same problem with the same setup. I have a TS patch cable from input1 to a Relay G50 which is completely quiet. However the TS patch cable from input2 to the Rockboard bay “A” is unusable when it is not plugged in, and also not completely quiet when connecting my guitar.

I did have improvement by using a TRS cable to the patchbay but I feel like it could be quieter. Did you resolve the issue?

5

I had a similar issue with a rockboard + patchbay a few years back (so, no QC envolved at the time). The problem to me seemed to be that the patchbay grounding is shared between all the connectors (no isolation?), so doing ground lifting on any of the connected devices had no influence in the ground loop. I even tried with my palmer PLI-05 but nothing solved it. It still had an unusable level of hum noise.
I ended up returning the patchbay.

3 Likes
6

I gave up using the patchbay for connecting my EUB. I’m using the patchbays’s TRS for the headphones and QC outputs. No issue with that.

7

Hi. I had the same problem. After a lot of experiments i ended up that this A input , because of the proximity to the mains plug introduce 50 hz hum to where you connect to. I just don’t use A any more and everything is fine…

1 Like
8

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I moved my guitar input to C. No hum at all.

9

Seems like there is no shielding of the individual connections inside the patchbay. Probably a very (!) bad design choice made by Warwick / Rockboard.

2 Likes
10

Exactly what i thought. Since all other connections are very low voltage there is no interference between them. But putting 220 v plug so close to a possibly instrument input or line out signal plug without proper shielding is for sure a very bad design choice…

1 Like