1184 quad mixer vca (AKA 1183)


I use a pair of flat jaw hemostats .

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my luck is i would buy this thing and bend the fucker putting it in there.

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I usually just unevenly squeeze them together between finger and thumb and then shimmy/jam them right in :rofl:

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Talking of bending pins, did any of you have a hard time fitting in the single pole switches?
The holes in the PCB footprint are spaced out a little more than the ones for the double pole switches, so if you get all your switches from the same family, either the double pole or the single pole ones don’t fit quite right.
I had to slightly bend out the pins of the SPDT switches to make them fit (and hear some epoxy glue cracking while doing it).

Yeah, the 2V Zener doesn’t seem to serve any purpose where it is.
@lookmumnocomputer is it possible you meant to put it on the linear control voltage input instead of the signal input?

Indeed.

The datasheet that I have says “Current Outputs Capable of Swinging to Within 1,5V of Each Supply” so that first 100k resistor would limit the maximum output current to ±10.5V/100k = ±105µA so input signals above ±105µAx47k=±4.9V will get truncated at higher VCA gain settings. So as you say @fredrik the first resistor would better be replaced by a 0 ohm link (anything below 1k would probably have very little detrimental effect).

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yeah the zener diode I have updated this on new ones I need to update the documentation I did it last week. its completely pointless.

initially I had it on the cv input, it took this long for me and a friend to realise it wasn’t on the cv input and on the signal input. proper nelson Mandela effect. and since its not needed on the cv input as it stands. been working perfectly fine you can ditch it. however it may explain my wonky signal which im not gunna complain about a bit of character, that stuff only adds to things. but yes the newest versions don t have these diodes and ill put an update on it right now as they can be a ball ache to find for something that serves no purpose!

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I have tried numerous brands of mini toggle switches and haven’t come accfross one that needs to be bent to fit, what one is it?? do you have a link?

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so Antoine are you saying the 100k effects it detrimentally? this to be honest would explain the squaring off at very high signal. which I think is a good aspect to this vca.

Yeah, assuming ideal circuits it doesn’t do anything (the amplifier tries to output a current, not a voltage), but @antoine.pasde2 points out that with 100k you hit the voltage drive capacity limits before any other limit.

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in an ideal world Antoine and Fredrik what would you like to see on this? I have a version im sitting in front of which is a 4x4 cv matrix, and a larger 10x4 cv matrix. is there anything you would suggest id adjusted in the circuit? the zener diodes went a while back. I have since updated them, and said on the site not to plop them in.

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im gunna have a look again on breadboard, back to the data sheet and see if it saturates, maybe the 100k is the good stuff. I dont understand why it would be useful to have hotter signals its very useful for things like distortions that don’t have clipping circuits not blowing your head off. but like I say in the above comment I’ll re visit it before I put these vca matrix’s up. Just out of interest.

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The problem (*) with synth stuff is that you cannot treat it as audio gear, so that “surely this is wrong” reflex isn’t always helping :smiley: I’d say if you like what you’re hearing with 100k, keep it, but with a note that builders can use a lower value or a link instead. Or the other way around; design with a link (or small resistor), but mention the option to use a 100k to get a tiny bit of sweet clipping.

*) not a problem, really :smiley:

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would be useful to have hotter signals

Which reminds me – is there a Kosmo definition of “hot”? :smiley: @antoine.pasde2 wrote “-10V to +10V typical” (20 Vpp) in the draft here:

but seems you may be designing for closer to 10 Vpp in practice, maybe? (also see the many discussions about the 3340 output levels).

(I guess we should all be responsible audio adults and talk dBs instead, but I find that a bit confusing tbh and not at all helpful when looking at circuits…)

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ok fredrik cool! its great that your challenging these things, thankyou. the thing is im going into this treating it as audio gear, the main focus point is the end product coming out of the speakers. Which yes to get to that point many philosophies and approaches can be taken… The thing that attracted me to synthesisers is there is no right way. even the most absolute wrong way can exhibit interesting outcomes. and yes when designing these things I tend to go from what it should be and take away or add till it seems right to me. Which im sure to some people may not seem correct, like this character. This module is meant for one of the last in the line, the closest to the speaker.

but yeah the 100k ill play with later on and then do a note to it! im going to do a vid on the more serious channel about all these things regarding this synth! so ill talk about it ill adjust this and see what changes it represents practically in the vid. as im doing the vid to show the mod of bypassing the normalising of the jacks.

thanks. please keep criticising and analysing these circuits.

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well this is all very up in the air. Antoine will be please to know I listened about his comments on the oscillators. all future oscillators will have an adjustable offset for unipolar and bipolar moving forwards! however yeah its seeming 10vpp is the aim. 20vpp is quite high is it? the 10vpp leaves space for things like feedback dynamics, and distortion to take it the rest of the way. and go into clipping territory nice and early on. which in the end of the day gives an analog synth its goodness.

however 20vpp would make just as much sense, as the 1222’s are unipolar, you put a bipolar oscillator in with a unipolar oscillator, it would end up being 15vpp, the great thing about this is if you clip the merge of these 2 oscillators after you get very uneven clipping which sounds rather gnarly in a good way!. so yes I think the standard may be subject to evolve. I have found distorting oscillators can be quite difficult to get a nice character, and if they are offset and unsymmetrical with each other its much easier to get that frazzle like in a guitar. I have a digital vco coming that has an offset so the waveform can be bipolar or anything inbetween, and after that a dual vco that is doing what the fart box does

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Oh, it’s definitely “audio gear” in that sense – I was more thinking of the Hi-Fi “there can be no distortion anywhere” ideal (which is usually just “I like this distortion better than that distortion” anyway, no different from here). If it sounds right, it’s probably ok :smiley:

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thats funny about hifi. “I like this distortion more than that distortion”. I always questioned “hifi” im glad you said that. glad thats out in the open!!!

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I haven’t done it yet, but would bypassing the first 100k require the removal of the 100k feedback resistor? does this not mess with the gain of the circuit? not had a chance to mess with it as of yet.

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No, that one controls the output level. The configuration here is a current to voltage converter (basically, the VCA outputs a current, the current cannot go anywhere other than through the 100k, which results in a voltage across the resistor, the opamp attempts to keep the −input at 0 V since that’s where the + input is, so it pulls the output low, and you end up with Vout = −Iin×100k)

(what Antoine pointed out that I missed in my initial analysis is that with enough resistance on the way to the converter the VCA cannot produce the output current it’d like to; the output resistor gets in the way.)

The alternative is to shunt the voltage to ground through a resistor and get a voltage that way, as it’s done in the datasheet, and add a voltage follower after that, but I’d say this is more elegant :smiley:

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ok that explains the dynamic clipping! which is fine good for this module but yes I will for the matrix mixer which is equally for voltages… Quite excited about the matrix module, as I have made it in such a way thats its modular within itself, each row is a separate board, so you can make a matrix module as big or as small as required, then I have 2 different panels 1 that houses 4 columns or one that houses 10 columns. but because its in a setup that suits the mixing of control voltages too. I will revisit the above.

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