1181 dual vca module

This thread is for the building and use of the 1181 Dual VCA. Info Here :slight_smile:


I’m really liking the artwork on this one!

haha thanks! this one took a rather long while to doodle out!!!

also I have just realised, the front panel is symmetrical so It can be put on either way!


welp, looks like I am using this Panel backwards. lol :smiley:


Here is a BOM for the 1181 Dual VCA. :slight_smile:

When I tested my Dual and Quad VCA, I seemed to get very little range. I was using this out of my sequencer so don’t know how many volts it’s putting out but it was the same on both my outputs which worked with the VCO…

I need to find time to get back to testing, but is there any known issues?


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rather try to use a signal from an Envelope to trigger a VCA

Edit :

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Well I dug this out again, thinking it was fixed. But it was behaving even worse.

I noticed the LED’s never worked. And whilst watching the builders stream was looking for any glimmer of information… Before he even got to it I spotted I had left of the 2n3904’s Looking at the schematic i’ts obvious why the LED were not working. But still I was getting eratic behaviour or silence.

Re-hit all the solder joints on the IC sockets and hey presto it’s at least working manualy… :slight_smile:



I’m looking at the schematic for this and… uh?

[Incorrect circuit analysis deleted to avoid anyone else getting as confused as I was]

Another minor matter: the input CV is divided down by a factor of 4 by the voltage divider on the CV pin. But per the Kosmo spec a CV range -10V to +10V is okay, and potentially the voltage on the CV input could be -12V to +12V. If that happens the maximum range for the CV input to the 3360, -2V to +2.5V, is exceeded.

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II2 is a current summing input, there shouldn’t be any significant voltage there to truncate.


Right, I was more confused than usual. Thanks.

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Maybe that’s where the zener diode was meant to be?


Should I always attenuate a signal as it is done with the cv input in this schematic? I’ve been running the signal in through the pot then into the circuit with my own experiments. I haven’t noticed that I have used this setup in other schematics. I just hadn’t paid attention to this detail previously, although I may have been doing it correctly. I’m trying to understand this method.

I’m putting together the material to build this module. While going through the alternate BOM and generating some carts, I noticed this at Tayda:

Tayda’s details are thinner than Mouser’s, but I’m wondering if they’d work.

You can probably just leave the Zener diodes out. At least in the first run they were connected to the wrong place (signal instead of CV), and they don’t really do much of anything in the right place. This is from the discussion of the 1184 but it’s the same issue:

The BOM calls for a BZX55C2V0 which is a 2.0 V Zener, the Tayda one you show is a 2.4 V so isn’t equivalent.

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