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VCA distortion
MUFF WIGGLER Forum Index -> 5U Format Modules Goto page 1, 2  Next [all]
Author VCA distortion
eolianmollisol
I've checked all my ins and outs and I most definitely have noise coming from four of my dotcom VCAs. At first I thought it was my mixer, then interface, maybe computer noise, isolated filter bank on a separate power bar did nothing, no interference from speakers. Unplugged everything but my 5U, only powered one cab of the two and rerouted back to these 4 VCAs. Tried multiple cords, etc.[/s] I didn't go as far as to unplug every module from power in this cab but I'm scratching my head why they are so noisy. Here's an audio clip, whats bizarre to me is that it sounds like a CPU from a computer, that bad headphone out sound.

I'm finally back home after leaving last April and get to recording and...

Any suggestions?

[s]https://soundcloud.com/eolianmollisol/vca-at-full-gain/s-ifk2n[/s]
Flareless
Question: Do you have a Q174/Q175 MIDI interface and is it plugged in to a MIDI connector?

sometime get VCA noise when my Q175 has my Yamaha UX16 MIDI interface plugged into it even if nothing is patched.
eolianmollisol
I have both yes...I actually just removed all of the modules out of the bottom cabinet and disconnected the second and its still making the noise. I tried another PSU but same noise...I've tried putting the VCAs as far away from the PSU as possible and no change, it is intermittent and its intensity fluctuates dependent on where I move it around, but there isn't any rhyme or reason to it, kind of like a radio going in and out randomly. I checked all my PSU connections and everything looks good there. Very confused.
Flareless
If it's all Dotcom gear you might want to ask Roger about it. He provides excellent support!
eolianmollisol
I haven't had luck with Roger in the past...he's always suggested to just ship the module in.
Flareless
Is it possible that you have something plugged into the same circuit breaker that your modular is on that's causing the noise? Something with lots of current draw? A motor perhaps or dimming lights?

I'm having my studio rewired with isolated grounds because of the crazy noise problems I get.
eolianmollisol
It's possible...but not likely. I've plugged other stuff into the same outlet, i.e, my eurorack stuff and no problems there. I have it plugged into an isobar, and tried without and no difference.
Squattamolie
Do you have any modules that could be letting digital clock noise into the system? I have had that in the past.

Is the noise exactly the same with all 4 units? I have 3 of those myself, and they are quiet (no problems). Do you have any other VCAs? If so, do they have the problem?

I realize it is a pain, but to really track it down, try unplugging every module in the system except the VCA, then add them back in one-at-a-time and keep notes about what happens and when. That at least would tell you if it is from (or mainly from) a specific module.
Flareless
eolianmollisol wrote:
It's possible...but not likely. I've plugged other stuff into the same outlet, i.e, my eurorack stuff and no problems there. I have it plugged into an isobar, and tried without and no difference.


Not necessarily the same outlet but the same circuit on your electrical panel. Each power supply is different and may react differently to noise on the power line or a floating ground.
eolianmollisol
squattamolie...I did end up unplugging everything last night and it seems all the VCAs have the same issue, one is particularly more noisy than the others. The noise is intermittent and does go away, but there's no rhyme or reason, seemingly. This happens if I just have one VCA plugged in and I move it around the cab, turn it over, that sort of thing. It behaves like there's a loose connection but I can't seem to find one, since all of them are doing it, it would suggest a problem with the power supply? But I have two clean PSUs that I've tried and the same result.

Flareless...I tried it on six different outlets, different circuits and the noise persisted. But, I'm going to try shutting off breakers next.
josaka
sounds like electrical noise.. those sound like radio waves..
very very unlikely to be 4 vca's.. power supply grounding..
also keep phones/speakers away smile
eolianmollisol
Josaka...that's kinda where I've led here, with the PSU itself or the outlets? Radio waves is exactly the vibe. I'll mess around with that tonight.
eolianmollisol
Is there some additional way to shield the cab from this type of noise?
josaka
smile read the top and paraphrased to the bottom smile

https://www.youtube.com/watch?v=duzNMgbI2G4

https://www.youtube.com/watch?v=l4famaQmWnA
eolianmollisol
I'm still skeptical that a ground loop is the issue because other modules don't do this and my eurorack isn't having this issue, and there's no hum on the mixer or interface. Monitors and everything are isolated. But, I'll look at the videos when I can and see if I'm missing something. I'm guessing since nothing else is making noise it could be a grounding issue with the PSU itself, but why the VCAs and not other modules? I guess the why doesn't really matter. Just need to know how!
josaka
vca is the output and boosts levels.. clue is in the A.. 5u runs hotter than all that other stuff(big part of why we love it and spend the extra wedge..) pretty much 100% convinced its not a fault with the VCA(4 going wrong?) ..modules can develop faults of course.. but that sound is radio wave sounding..
snevlida14
I know it's not convenient, but if you sent them in you could rest easy as they were tested correctly. Not like I know him personally or anything but Roger seems like the kinda guy that just wants to check out the functionality in person. There is no other way to be sure. When someone asked me about a sound or issue they are having with the bicycle they purchased from us, I just tell them to bring it in the shop and I'll look at it.(we're talking bikes that cost thousands here also) It's not that I don't care or am ignoring there complaint, it is just the path of least resistance when fixing something professionally. I'm not trying to be a diehard dotcom fan boy, I have a mixed system myself I can just see it from the other side.
eolianmollisol
I agree, Rogers time is valuable and better spent not holding someone's hand through a troubleshoot. I'll mess around with grounding and report back. If I exhaust all of those possibilities I'll be shipping them in. My MIDI interface aid needs to be sent in cause the MIDI connectors came loose, less someone wants to take the time to snap a clear foto of the back of theirs!

Thanks for the suggestions all
eolianmollisol
Approached this from an audio ground loop perspective and got a few things coming in the mail. Should be able to report back here by the end of the week next week.

Roger has been helpful, if I still get noise after my initial fix I got a couple options!
eolianmollisol
I balanced all of the ins and outs of my system and nothing changed Dead Banana
BudgetInfinity
If you are monitoring through your sound card / audio interface that USB connection isn't balanced and can introduce noise from the computer. I used to be able to hear radio stations through mine.

Make sure your cell phone is far away.
ranix
can you post some details of exactly how you have patched and what you are recording with exactly?

This type of noise is common to get with a large 5u system. Any long unbalanced cable will pick up noise.

Most likely culprit: are you using an insert cable or the q120 connector interface with both the +/- outputs of the q108 to create a balanced output from the modular to the PC? If not, do so and report back. We also need more information about the device you're recording with.
eolianmollisol
q108 + out to a Hosa PHB 265 Patch Bay with balanced output going into the balanced inputs on a mackie vlz 1402 14 channel mixer (patch bay makes no difference in fidelity). The mixer goes directly into the two inputs of a Focusrite scarlett 2i4 which is routed to a KRK10s subwoofer and two JBL SLR308s. All of the cabling here is balanced.

I get the noise from these VCAs even when I just have headphones plugged in.

Roger sent me this e-mail this morning when I replied to him and said balancing my system did nothing:

A regular signal coming out of a VCA should be about 10v
and the noise should be less than .01v which is a 60dB signal-to-noise ratio
and as low as .001v which is 80dB.

You can amplify that small noise signal and hear the noise.
But then the amplitude of the signal would be too big.

Can you send me a recording of a patch
where you turn on and off a simple wave from the oscillator
and I will see if I can measure the noise level relative to that?

For this, use 3 modules:

Q106 oscillator
Range at 4'.
No other inputs.

Q108 amplifier
Linear mode.
Gain knob at 0.
Control knob at 10.

Q109 Envelope
Attack, Decay, Release at 0.
Sustain at 10.
No input.

Patch the saw wave of a Q106 oscillator into the Signal Input #1 of the Q108 amplifier.
Patch the envelope output of the Q109 into the the Control Input #1 of the Q108 amp.
Record the +OUTPUT from the Q108.

When pressing the manual envelope button, you should hear a tone.
This tone should be 10v.
When there is no tone, you will hear the residual noise.
We can compare those 2 signals.

Warning, this output may overdrive speakers/headphones, so attenuate it
on whatever equipment you're using.
We're only looking for the relative volume of the tone vs noise.
I can look at the waveform visually using Audacity.

So I'm going to do that tonight and see what he says.
slow_riot
Troubleshooting problems like this is really best done pre-emtively by the manufacturer, rather than tearing things apart to find the individual aspect of poor engineering that is causing the problem.

Instinctively, this sounds like noise on the safety earth which is being drawn into the 0V line (which always forms part of the signal path) through common impedance coupling.

How have you balanced the connection from the Q108? Balancing seems to fool even experienced engineers so it is worth checking how you have done it. Balancing is enacted through matched signal impedances and the physical proximity of the 2 hot and cold lines to each other. Ideally the shield should be connected to chassis and not to 0V.

If you have employed a proper balancing scheme there are several things to try, to reduce or defeat the mechanism which I believe will be causing your problem.

One is to reduce the resistance between the 2 devices on the mains wiring, and in particular the safety earth. Instead of using different sockets and daisy chained randomly interconnected mains extensions for your system (apologies if this is not the case). It is better to use a single mains socket for your whole system, starting out with an industrial grade distribution device, then fanning out from that into normal consumer plastic 4-way extensions.

I like the Canford series in the UK:

http://www.canford.co.uk/EMO-C-SERIES-POWER-DISTRIBUTION-SYSTEM

I'm sure there will be similar devices in your country. Maybe Olsen brand are also available?

Another option is to defeat the mechanism altogether. In this case it would be disconnect pin 1 at one end. It's not ideal as you can end up with a specialised cable that needs marking, and it also helps to defeat the reason for using the pin screen which is for shielding which ideally forms a continuous RF reference for screening against EM signals.
Thalassa
Hello , i just see the photo of your studio on the 5U pictures thread. you have a beatstep pro an it's really noisy if you power it using directly with a USB and not a PSU. Be sure that it's not connected while you are making the tests because maybe it's the source of your problem.

Here you have an explanation from Arturia

https://drive.google.com/file/d/0B-1e9zXr5JIlck5PUHVkQVpodFE/view

and here you can see a video showing the problem

https://www.youtube.com/watch?v=OyPutuuEYFQ
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