Troubleshooting Noise Within a Eurorack System

Hi All. Hoping someone might be able to help me diagnose some noise trouble. I just put in Doepfer’s VC performance mixer, and I’m getting a high freq spike out of the output module. I’m well within my power limits for the two 4ms row power 40s I have, and I’m using a furman pl-8c power conditioner between my rack and mains.

The first thing to do is always: remove all modules, put them into the case one by one starting with the Mixer (since that made you notice the problem) and see which one triggers the problem. Maybe it’s not the VC mixer, but that combined with another module, i.e. it could be a crosstalk problem.

@papernoise So it is definitely the mixer. When both the mixer and normalled output module are powered I can hear the noise. Just the output module on its own won’t reproduce it.

So it either doesn’t like my power supply or is just defective? :frowning_face:

But do you get the noise when just the mixer and output module (and no other modules) are in the case?

You mean unscrewed from the rails and taken out? Isn’t just unplugging all the other modules from power connections enough?

I meant just unplugging the power.

I’ve been having a lot of trouble finding the cause of some irritating noises within my eurorack system. This definitely crosses over into a few other thread topics so I apologize if this is redundant.

I was sure that the route of my problems was power related. I was using all uZues power modules and was told that they are an old design and not that high in quality. I bought a 4ms Row 40 with their power supply today but nothing has changed.

One of the problems I have is with the standard hiss you find in all audio equipment. I’m generally fine with this although it could be a lot lower. The bigger problem I’m having is with a ringing/whining sound. This sound is coming directly out from behind two of my modules face plates and it’s in the audio signal path too. The two modules are the Morphagene and the Just Friends. The sound is also in the audio path of random modules both on and off of the same power supply as the Morphagene and Just Friends.

So far I have switched out my power module, unplugged all other equipment while listening for the sound to disappear, bypassed my USB hub, disconnected and rearranged modules, and tried different ins and outs.

I guess my question is, how can I definitively find out that this is still a problem caused by power so I don’t waste my money on really expensive (and confusing) PSU’s/noise filtering bus boards only to find out the noise persists?

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Have you tried using a different outlet or power strip? Those are often sources of annoying noise.

I recently solved an issue like this by running my modular into a passive behringer direct box with a ground lift. It got rid of the whining I was experiencing entirely. It was really a combination of using the balanced xlr cables and the ground lift.

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Oh yeah I forgot to mention I have everything plugged into a Furman Power conditioner. I tried plugging that Furman into a regular outlet in my bedroom and an air conditioner outlet. Getting noise in both. It’s a little more difficult for me to try another room but I might have to at some point.

I have a direct box and it helped a lot with my pedal noise. Unfortunately this problem is happening throughout my entire modular system. I’m wondering now if I should try a ground lift adapter before going into the Furman.

I’m not sure, I don’t have any experience with a ground lift like that. This is just one right in the side box.

https://www.sweetwater.com/store/detail/DI400P

I used to have pretty bad noise problems… first I switched to busboards (Intellijel FWIW) from a uZeus which helped lower the noise floor and some of the general errata but not nearly enough, then I got a nice~ish transformer-based DI with a ground lift which helped a lot (this), then eventually I ditched the switching Meanwell I was using and threw in a linear PSU which seemed to eliminate the same noise I was nuking with the DI after A/Bing with the ground lift (what that’s about I have no idea). I’m not an EE ha.

4ms is a great company but I will say that the 4ms busboard doesn’t look like much more than the equivalent of a glorified flying busboard in PCB form. I might suggest saving and get a linear PSU, better busboards and crossing your fingers…

I haven’t had any of the whining issues some people have with the Morphagene and JF, dunno.

edit: oh yeah if all you did was switch the inlet module and to another switching PSU… probably not going to help much unfortunately.

Thanks this is really helpful!

Where in your setup is the USB hub that you mentioned? I get an irritating high pitched noise when using my Qunexus keyboard as a CV source if the Qunexus is running on bus power.

You mentioned disconnecting and rearranging modules but have you disconnected and reconnected (and listened to) the modules one at a time?

I don’t know about Just Friends, but the Morphagene does make an “acoustic noise” as Make Noise worded it, which isn’t in the audio path, but IIRC is basically something in the circuit which vibrates and produces that noise.
Now you know why they are called Make Noise :smiley: but jokes apart, that should be just a thing you hear when you are in front of the modular and not something you get in the audio.

Not an EE either, but I’ve gotten a bit into “noise paranoia” recently and have started to check all my modules and the PSU for noise… just to find out that yes my PSU (TipTop Zeus) does produce a bit of noise, but it’s so low I can totally ignore it. Still I had some big problems in the past and I wish I had known some things I now know back then. So here’s a quick list that might help you:

  • usually the noise comes from the PSU (except if it’s EM-related) and propagates on the 0V bus (confusingly often called “ground”).
  • if you have noise problems 99% of the time it’s due to having a switching PSU, so if you can, get a linear one, or at least a good hybrid one.
  • if your PSU does not connect to protective earth (the third pin of your wall wart) it might also worsen things in certain situations.
  • ground lifts sometimes work, sometimes not. If you’re just using the modular at home/in the studio that might be doing the trick, but if you need to use the modular in different places, better solve the problem from the ground up.
  • first of all there’s modules that inject noise into the system, and there’s modules that are prone to receiving noise. So I would also ask: did you try to put the modules into the case one by one to see which ones were causing the problems? Sometimes this is a matter of having a wrong circuit design, sometimes it’s an inherent thing to the circuit. For example: overdrives, waveshapers, preamps and VCA that go beyond unity gain will apmplify the noise in the circuit. So if these produce the noise, you need to find out where it comes from, because it’s not a problem of the module’s circuit being done wrong.

Also, about “noise filtering busboards”: I’ve done some research into the matter and to me it seems there is no conclusive proof that these actuallty do much more than cost money. What seems to work is to have a busboard system with a very low-resistance 0V bus. I.e. things like Hinton’s busbars or busboards with thicker copper layers, but that will be expensive.
Before trying any of that I would first try to find out what is making the noise, isolate that from the system, and see if you still have problems. If not… well I guess you need to replace those modules with some that are better designed.

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Man this is so helpful thank you. Are there any linear PSU’s you could recommend?

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Oh and another thing I just realized is that the power brick that came with my 4MS Row 40 is ringing and buzzing like crazy! I think it actually introduced more noise. I’m going to test each individual module for sure but I think I also need to return this Row 40 and get a nice linear PSU and good quality bus board. It’s not a good sign that the power supply itself is emitting a very loud noise. I also considered going to go with the Intellijel Triple Power Supply until I noticed it was switching. It does claim to be low impedance and low noise though.

It might at this point help to understand how a switching PSU works (hoping I’m not telling you things you already know, but from what you write it seems that you do not have a full understanding of these things).
Here’s my layman explanation, that does help me to imagine how these things work internally:
Switching PSUs lower the voltage by quickly switching the power on and off and then modulating the duty cycle of the on period. That’s why they are sometimes also called “digital”, since they work by using 1 (current flows) and 0 (no current is flowing) states. To me this is misleading and somehow silly, so I stick to “switching”. Anyway, the noise you get from these PSUs can be both in the audio signal and can be an acoustic noise from the brick vibrating. Both are common and both can be very annoying. Nearly 99% of all bricks that you get with electronic devices are switching, and I have a bunch of them here that do white and buzz in all sorts of ways. What brand of brick did they give you with the PSU, and does it have a “protective earth” connection?
Anyway, if it does make noises it might be normal, or it might be that the one you have is malfunctioning a bit, so better ask. I have both the Cincon brick that is used with the TipTop Zeus boards, and the very common Meanwell brick that many hybrid PSUs use, and neither of those does make any noticeable noise.

The Intellijel is – as far as I know – a hybrid design. This means that it uses a switching brick (in their case the Meanwell one) that does the heavy lifting to take the voltage from 220VAC (or 110VAC) down to 15VDC, and then they have a linear stage that produces all the voltages your modular needs from there.
The busboard is arranged using a “star” design, which IIRC means that all the connectors go directly to a central point and are not connected in series as in most Doepfer-style busboards, which lowers the resistance and makes the system less prone to noise.
Of course every PSU is being marketed as being low noise and all that. Only very few will give you actual specs. Intellijel does better than most in that they at least state the stability (which is rated +/-1%). I don’t know how to actually read these numbers, but I’d say it might mean that the voltages can oscillate for example between 1,88V and 12,12V, but that spec might be a “worst case scenario” as well as just the “typical” value.
1% is worse than a some good quality linear PSUs but seems good to me for a hybrid one. You can do some some comparing here if you want: https://docs.google.com/spreadsheets/d/17qu-PkyJnjZf9YzhNYy7X7-d-lmZqhahyUW0YM1b2N0/edit#gid=0

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