Crackling on Pots

Hello,

I guess I’ve always noticed this to some extent, but now that I’m taking the time to look at it more carefully, all the pots on my two Mixup modules and my Outs module are noisy. When they are not passing audio, they are pretty much quiet when I turn them. But when they are passing audio, they are noisy. For the Mixups, the noise is especially apparent from around 2:00 to fully CW, and for my headphones out on the Outs module, it’s more apparent closer to fully CCW and fully CW. I tried using two pairs of headphones (monitoring both the headphone out and the main out). I’m also taking care to make sure I’m not clipping. It’s not really a loud crackling, more of a soft whooshing at times, other times more crackly, but never really horrible–which is probably why I kind of ignored it for so long.

So why is this the case? Can anything be done to fix it?

Note: On my Quad VCA, none of the attenuator pots have this problem.

Happy to send audio samples if needed.

PS: It’s only really audible with lower frequency signals like sine or triangle waves or filtered stuff.

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What you are experiencing is the effects of listening to DC or signals with DC offset through potentiometers. The OUTs and Mixup modules have AC coupled inputs that help block DC but if you have low frequency, pure waveforms like Sine and Triangle (which are closer to being DC), it is very difficult to mask the effects of this. The reason this problem is more pronounced on Mixup and Outs vs. Quad VCA is that on Mixups and Outs the audio is going through a potentiometer, specifically audio is going through the wiper of potentiometer and this is always much more sensitive to DC. In contrast, the audio path on a Quad VCA is entirely through the VCA cells (and opamps) and the potentiometers only act as voltage controls of the vcas. This is a much better way to dynamically alter a signal without creating these sharper discontinuities.

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Thank you very much for that detailed answer!

Hello Intellijel, I thought I’d be bold and re-open this can of worms. :innocent: I have continued using my Mixup modules, but for a song I made recently with a very “warm” (low-frequency) stereo signal, I was hearing the crackling a little bit when I was adjusting the volume with the Mixup live. As for your comment about using a VCA (which have opamps apparently) instead for live attenuation, the problem is that these are stereo audio signals I am mixing.

So I wanted to ask you all: If you don’t have a mixing module that will mix stereo signals with one control (knob) for each stereo signal that also won’t make this crackling noise, can you please make a suggestion, at the very least maybe offer a spec I should look for in an alternative? I don’t know what an opamp is lol but should I be looking for something like the Mixup that uses opamps instead of pots, if that even makes any sense? :upside_down_face:

Thank you!

It is super easy to make a stereo VCA. For example, on the Quad VCA, the CV inputs are normalled in a cascade.

So put your left signal in Ch1, right signal in Ch2, patch a single CV source to the first CV input and then make sure the CV attenuator is open the same amount for ch 1 and 2. Now one CV source is controlling both channels equally.

Ok but what if I simply want to control the volume of the stereo signal manually by turning a single knob? Pair it with a Triplatt or similar attenuator module with at least two channels?

you only need one channel from a triplatt/quadratt/duatt if it is controlling a VCA pair.

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Got it! I guess I was asking assuming you wanted to use the entire Quad VCA for two stereo channels.