This is crazy! Is this for a module or a stand-alone device? Why 5 VCAs?
Iām planning to make it a module, probably quite a beefy one, 20cm at the least. The SS2130 has a 5-channel current-controlled mixer on board, basically 5 VCAs with their outputs summed. Iām additionally putting attenuverters on their control inputs to enable cross-fading between waveforms etc.
5 Likes
Looking good, this is going to be one beefy module, I was trying to look at your schematic earlier, but was hindered by the resolution. I am hoping you have a spare board when you are done. 
I have to admit that was done entirely on purposeā¦ the full version will be up once everything is tried and tested! 
1 Like
What does the FET do?
3 Likes
It switches the oscillator direction to allow for through-zero FM
3 Likes
Got some PWM working on this Blackpill:
Getting decent audio out of it might be a challenge thoughā¦
5 Likes
the Mutable Instruments Shruthi uses PWM for both for 8 bit audio and for control voltage!
Yeah - I have a Tubeohm version - Iāll have a dig through the code / schematic to try and figure out whatās going on there. I started out with12 bit first, but I think the RC filter needed to get rid of the ripple makes the whole thing very slow. There are some tricks for summing multiple fewer bit PWM channels though - to be investigatedā¦
1 Like
i never tried summing but Iāve seen people passionately arguing over its efficacy which always makes it worth a shot haha.
been wanting to try it on Teensy 4.1, which can do 12 bit resolution at ~40kHz.
1 Like
Dave Brownās adaptation of Marc Bareilleās version of Vladimir Kuzminās Polivoks VCF.
so far minus the costly Spectrol 149 pots wow. and tuning, havenāt given it a proper tune yet.
This thing sounds nasty. absolutely vile. Putrescence the likes of which Baron Harkonnen would applaud. Iām in love.
i intend to add CV resonance, using the OTA portion of the following design. No worries with the extra half of the LM13700, i like doing things in pairs.
however i have heard tell that this configuration would affect the audio in the resonance path. anyone have experience with this? Alternately i was thinking an opto isolator, transistor based if that works any better.
7 Likes
I used something like that in my diode ladder filter:
It works okay - the resonance is pretty harsh and whistley - but I guess that just adds character.
Cheers
3 Likes
Thanks for the tip! Will look into this. Gotta give it a try and see if it passes the taste test.
1 Like
Cant you/we (i am looking jnto this as well) use a normal VCA type circuit ? Something that would define how much is going into the resonance loop ā¦ often that is what the resonnance pot is doing.
1 Like
when will the module documentation be available on github/wordpress?
1 Like
I built my VCA using LM13700ās - itās more or less what this bit of circuitry is doing.
2 Likes
In the right hand picture in Method 2, the capacitor attached to the A and B resistors is something I would not expect. Including that in the circuit would only allow changes in CV to do something. But what about constant values?
Have you tried this particular or any of the other methods?
2 Likes
It is there, link is in this post
3 Likes
i havenāt tried that method, no. Iāve made a crude vactrol circuit a few times but the result was unsatisfactory.
i may try it out and will let you know if i do! supposing i remove the cap to allow constant voltage, would it break functionality elsewhere in the circuit? (sorry Iām still very amateurish)
