That’s a very good point! Let’s examine the evidence.
I suspect the IC because:
It looks different than the one I got from the shop even though it’s supposed to be of the same company.
The price was a little too good to be true.
The particular seller had like a 99.8% positive rating, but the 0.2% negative reviews (a few dozen of them) were almost exclusively about fake ICs.
Not smoking gun evidence by any means but…
Could it be a fault in the build? Possibly! I’ve done many stupid things in the past, but in this case:
The soldering is very clean and I cannot see any bridges under the magnifying glass.
I checked the voltages at the IC pins and they were correct.
Checked all the components with the multimeter one by one before placing them, as well as the 6.35mm sockets (I once found a bad one and now check them routinely).
I cannot imagine the PCB being faulty in any case, it’s also a simple and tried-tested design by David Haillant that I cannot imagine it being wrong.
Yes, this is a PCB bought by Haillant himself. Per the multimeter check, the output at pin 5 is only connected to pin 7, and the output at pin 12 to pin 1, as per the Haillant schematic. Neither is shorted to ground or the rails.
Is there much to be said about my signal flow?
Vco,vco,expander - grr with adsr - vca - delay
Or should the vca be before the grr? Part of me is saying it should be before
Never used the Grr but as I understand it, it has a VCA built into it (after the filter), and it sounds like you’re using that VCA with the ADSR. So what’s the downstream dedicated VCA being used for?
You can put a VCA before or after a filter. To the extent that a VCA operates in amplitude space and a VCF operates in frequency space, doing them in either order wouldn’t really matter, I think. But in fact VCFs often are amplitude sensitive, and especially if (as, again, I understand is the case with the Grr) it has clipping designed in: Clipping a signal that goes between low and high amplitude due to an upstream VCA versus clipping a signal with constant amplitude and then varying that amplitude with a downstream VCA would give different results. But either might be the better option depending on what you’re going for.
You’re not wrong, grr does have an inbuilt vca. I’ll be using the quad for my second voice and hats.
I should possibly just make a dual vca to chuck in and throw in some more distortion/OBA stuff
I’d strongly recommend getting a non conductive cover over these wall voltage terminals. You want to be able to work on stuff inside the case without the risk of electrocution.
One thing puzzles me about that circuit, and that is the “Level” pot. It attenuates the signal before it gets split between the feedback and the output, so it reduces both the feedback voltage and the output level. It seems to me you’d want to do those separately (if in fact you do want to do both; I’m not particularly a fan of output attenuators on synth modules — unless this is intended as an output module to a sound system). But indeed there is a separate pot labeled “Feedback” which also reduces the feedback voltage. I’d think it’d make more sense to take the IC1/C output through a 10 µF back to the Feedback pot and just feed the output jack from IC1/D. As it is, lowering the output level will also modify the sound by reducing the feedback. I wondered if IC1/D was being driven to clipping in which case using its output for feedback would be different from using IC1/C, but no, per the simulation IC1/D input/output is down around ±2 V. Am I missing something?
Also, the 10k input impedance is rather low by usual synth standards. I’d think the 10k fixed resistors (not the pot) on the left should be 100k, and the 6.8k feedback resistor on IC1/A would become 68k.
Yes totally agree. For using this module a lot, it would be much better to have different input levels knobs and the feedback knob. I would still keep some sort of attenuator on the output (not in the loop) as the module does clip and gets really loud
Dont have a better picture. Finally got some. Polyphony going! Midimuso cv-12 doesnt have a panel yet. But I have 6 oscillators build. Finished my 4th dual vca today…
However… What a pain to tune all those vco’s! Matching all the volumes… I understand that polyphony might not be the best idea within modular. At least not like this. Its cool to try maybe a couple of times. But I don’t see myself doing this regularly.
Someone asked about the power supply connectors the other day. I got a new batch in today and yes Sir, they have a triangle marking in a different location than the ones I already had. I’ve experienced this before, so no surprises here. But I thought it would be good to show a picture of the 2 varieties here. This proves that the marking is not always trustworthy on this type of connector.
