5V (?) trouble, heavy buzzing

dear all,
i’ve been struggling with this for quite a while and it appears to be back! heavy buzzing and humming on the ER-301 and my monome teletype.

i thought i had it solved for the grid by powering it externally – but i must have mistaken. the preamps are quite cranked up in the video, but even without there’s audible noise.

i’m pretty clueless when it comes to power-issues. running my rack off a trogotronic m15. any idea what i could do to pin the problem down? it’s obviously only the mentioned modules and it definitely relates to how many LEDs / display activity is going on.

thanks! :frowning:

ps: posting this in a thread on lines, too…

Does it only appear when getting audio from the 301?

Does the 301 make the hum when the TT is unplugged from power?

Does any other audio line give you hum, with all modules on, and the monome plugged into the TT?


thanks @2disbetter!

buzzing appears only on the output of the er-301… other channels in my rack going to the mixer don’t buzz (no matter whether monome is connected or not).

i should mention: the teletype and the er-301 are connected via i2c.

just checked: unplugging teletype doesn’t solve the problem… |:

What if you unplug the TT from the power rail, so that when the system powers on, the TT does not. If you do this, is there hum?


that’s what i tried… yeah, there’s still humming ):

You sir, have a ground loop. Prepare yourself for a long journey of plugging and unplugging things.

Basically, your mixer is providing a more attractive return path for some of the current running through at least part of the modular which includes the ER-301. Even this just a guess based on my limited knowledge of your setup. First get all of your gear on the same power strip, if it isn’t already. Make sure the ground impedance inside your modular is as low as it can be, a multimeter is your friend here. DI boxes and even trying different cable lengths for the connection to your mixer could make a difference. Study your mixer’s manual to see if it has suggestions on how to debug ground loops.

In a perfect world all grounds would be isolated but unfortunately this is not really practical in eurorack.

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thanks for helping out, @odevices – really appreciate it!
having pinned down that the problem most probably doesn’t lie within the ER-301, i’d be gracious if you could still lend me a hand. i’m reaaaally lost with this stuff!

i’ve attached a sketch of my current configuration. the problem at the place i live is that it’s not possible to connect loads of gear to one outlet – my fuse is constantly chopped (pardon my english … you know what i mean? … have to go to the fuse box and “click” it back up :nerd_face:).
even when i turn the modular on the way it’s connected now, this frequently happens.

so everything red is connected to one fuse and everything green is connected to another.

i have a voltmeter here, and several DI boxes. before randomly disassembling my room, maybe you have some other concrete thoughts judging by the sketch? thanks :rose:

Make sure the ground impedance inside your modular is as low as it can be, a multimeter is your friend here.

can you hint me as for how to do that? sorryyy i’m such a novice with this stuff! here’s my voltmeter

It’s a time consuming task with a LOT of test cases to go through. So unfortunately it is not really practical to go through all of the possible permutations remotely like this. However, this is where I would start:

  • Isolate your system to just the mixer and the modular, plug headphones into the mixer if you need to. Absolutely no cables to anything else!
  • Next analyze the cables that you are using to connect your modular to your mixer. Here is a chart:

Reference: http://www.rane.com/note110.html (This is very good reading by the way.)

Don’t just assume based on plug visual, check the connections using your multimeter in connectivity (200ohm) mode (like you have it set in the picture).

Optimally you want a cable like #14 but probably you have something more like #15. This #15 cable is sub-optimal because it connects your modular’s (poor) ground to your mixer’s (supposedly better) chassis ground AND it most likely shorts them all together with the signal reference (not good). So first try to get or make a #15 type cable.

  • If that is not practical or easy at the moment try putting a DI box between your modular and the mixer.

  • Try putting another module in the path between the ER-301 and your mixer. Choose a module with low current consumption. This might break the ground loop.


thanks thanks thanks for your help! this is great!
(– and that link is incredible! have been looking for something like that for ages)

Don’t just assume based on plug visual, check the connections using your multimeter in connectivity (200ohm) mode (like you have it set in the picture).

on last question for now: can you guide me through this measuring a bit more? especially as for:

Make sure the ground impedance inside your modular is as low as it can be, a multimeter is your friend here.

what would i need to measure / where would i have to place my multimeter and what’s a value that i would like to see?


As someone still pinning down my own ground loop, I sympathize with you. When I see companies popping up with new power products that try to address some of this stuff it makes me happy. The real problems is that while some modules might be designed with good power filtering most do not. This means that those modules that do try to minimize noise, etc. are almost always defeated by the sea of unregulated modules out there.

Modular synthesis is the king of synthesis, but it is certainly not without its drawbacks.

A ground lift might be a quick fix for you, if you can confirm that you in fact have a ground loop on your audio signal.

I thought I did, so I got an ebtech hum elimnator, and get this, it actually made my hum a buzz!

I run my modular through an octatrack, and because of this, I tried to just record the modular anyway to test if the buzz was present in the actual audio signal. Turns out, that when I turn the modular off and just play back what the octatrack recorded from the modular, there is no buzz or hum.

SO I just have no idea. Got an electrician coming over again, but I’m doubtful he’ll find anything.

All this to say best of luck to you!


There are a few modules out there known for creating hum; in some systems Radio Music creates a hum, the hum disappears when you patch any cable into one of the inputs - so far no one has worked out why it does this:

Hmm…this assuming a lot (about your multimeter) but let’s try this:

Turn your modular off and unplug it from mains. Wait about 5 minutes. KEEP it unplugged from mains for the duration of this exercise. Unscrew your ER-301 but leave it plugged into your case. Find the test point labeled DGND:


Place one of the test leads there. Then place the other test lead in the following locations:

  • Any ground pin on the same bus board as the ER-301.
  • The barrel of the DC power connector for modular case.
  • The ground prong of your power brick’s AC plug (with DC barrel connector plugged into your modular).

The measurements should all be less than 1ohm, hopefully around 0.2ohm which is what I get in my cases on all of those locations.

I find USB is often a culprit, especially when you have devices like your mixer and iMac that are connected to both USB and audio cabling. Try disconnecting the USB from Mac to mixer and see if that changes anything. Or disconnect the audio cabling from your Mac (what’s it for? Are you out of mixer channels?)

If one of those helps, there are some optoisolated USB hubs out there that can help break the loops.

I second this!