I’m using a lm13700 electric druid vca and the attack/release from a Sam’s Kosmo page. I can’t get rid of pulse clicking unless I reduce the attack substantially. Is there a waveshaper or something I need at the input of my envelope?
Have you made any more progress with this?
Assuming you are using the circuit below you could try increasing the value of C1, though not by too much otherwise the vca will get sluggish.
It is the same circuit. How much is too much, you think? Should I try a 10n or 4.7n?
Try 4n7 first, to be honest I’m not sure what would be too much, its a very subjective thing. You could try higher values, but at some point the delay will become noticeable so its a tradeoff between silencing the click and slowing down the VCA.
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Understood. I can tolerate some experimenting with a few caps. Thank you!
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Have you tried adding a pot across +/-12v and the center to a 1m - 2.2m resistor to the input of the LM13700 to adjust the bias.
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Definitely worth a try, I hadn’t considered offset related problems.
I know I have not tried this, but I also don’t understand how to do it…
Can you possibly illustrate this idea for me? A schematic or just restate what you’ve said. I’m just unclear on your instructions, but I definitely want to try what you suggest.
I think I understand what you mean now. Pot (10k?) leg one to -12, leg 3 to +12, and leg 2 to the inverting input (pin 4/ 13) of the lm13700?..
Well I just read what the blog states in the electric druid website regarding the VCA design. Have a read of it, lots of good tips on improving the VCA design.
They suggest a pot between 0v and -12v, but maybe having +/-12v might be a better option. It will allow you to trim the VCA to ground.
So a 100k pot across the supplies, center pin to a 1m or bigger that feeds the input pin of the VCA
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At https://electricdruid.net/design-a-eurorack-vintage-vca-with-the-lm13700/:
The principle of connecting a little bit of negative voltage into that mixer is good, so your -12V via 3M is working, but it sounds like it’s still a bit too much if it’s cutting off the end of the envelope. How about trying a trimmer pot between ground and -12V and then take the wiper output via 1M/2M2 to the mixer or something?
Is that what you’re referring to? For clarity, they’re talking about adding this to the CV input, not the signal input. So not pin 4/13.
Maybe there’s somewhere else they talk about adding an offset to the signal input, I dunno.
Yeah, sorry, the CV input to bias it, might stop the popping
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Right on! So a 50k should work right? I said 10k first but I don’t have any… I will try a 20k I have some of those too.
Should be fine, they’ll use a little more current than a 100k but otherwise no difference.
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I just remembered something… Im not using the cv attenuator in this circuit. I only had room on the panel for one pot for each vca (it’s a dual vca panel, using the whole lm13700 obviously), and didn’t think I needed it since I only really use it with an envelope or an LFO with an output attenuator. Should I be using that part of this circuit before I try the bias solution? I’ll need a bigger panel either way. So what do you think, with or without cv level?
Do you know what the peak voltage of your envelope is? The VCA is designed for a max input of +5V, so it may be possible that the clicking is due to a higher voltage than expected and thus an attenuator might help. I can’t guarantee it will fix the issue, but it would be simpler to troubleshoot than the bias circuit!
Out of curiosity, do you have this issue with other envelope generators on this VCA?
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Surely not if you use a trim pot for the bias adjustment. This shouldn’t be something you’d need to change often.
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I only have the one panel with two egs. They both react the same with the vca. I plan to build some in line attenuators tomorrow so I will test the theory for sure.
I can definitely fit a couple trimpots on the strip board. That with the in line attenuators I plan to build should cover all these mods I need to make/test.