Implementing full digital control on an analog pedal

[mzy12]

How about something like the H11F? Opto fet that can apparently act as a vr, according to datasheet: https://www.farnell.com/datasheets/2298731.pdf

One thing I'd be concerned about is the voltage noise in the low frequencies that MOSFETs introduce.

[PRR]

How about something like the H11F?

Usual audio trouble for FET as resistors is narrow range of linear resistance, like 50mV peak. The potentially high hiss does not help either.

[mzy12]

Looks like vactrols are still the best option haha!

EDIT: Would BJTs inject more noise into the signal than LDRs? Looking at BJT octo's rn.

[Matthew Sanford]

On the BJTs I'd say yes as base current is added in to the signal, no true isolation. On Vactrols you can diy them slightly smaller (or bigger) than commercial products, and have the option to have multiple LDRs ran from one LED if you want them to control multiple things with one CV.

On my Filter FX I just stuck the LDRs into the pot solder pads with the LEDs hanging off, bad idea. For things where the main PCB doesn't mount via pots I'm thinking to create small PCBs to mount the vactrols to the pot, moreover was thinking a DPDT to receive the CV & complement to feed the vactrols in two ways (between pot pin 1&2, 2&3, choosing which side + & - go to, or off), then through a dual pot to set the level for the vactrols. I'm thinking best for a board for all 5 (2 pots, 2 vactrols, 1 DPDT) to keep them off the main board and sort of minimize wiring. Kinda riddling myself to figure a lower part/same options way, as the level pot is an off switch, and inversion might be done more simply...but I dunno.

For all that madness, I set up a PCB (my first one!) to have an LM358 make a triangle wave to a TS jack w/extra so unplugged it goes on or replaced w/incoming CV. From there to a 4007 to buff/invert, feeding 4 BJTs to drive the LEDs/vactrols. Just got the jlcpcb order (10 for $7 slow shipping!) so I'll let you know on that method, but on BB works nicely.

Druids right though, gotta dive in to VCAs too...

[mzy12]

I'm trying to think about how to implement VCAs, would they not be only good for volume control? Or am I missing something.

[ElectricDruid]

I'm trying to think about how to implement VCAs, would they not be only good for volume control? Or am I missing something.

You're not missing something, you're missing *lots*! And that's a *good* thing, because it means there's a whole load of interesting and exciting ciruits to discover!

For VCA applications, have a look through the full version of the LM13700 datasheet for a ton of ideas of what exactly you can do with these things:

https://www.ti.com/lit/ds/symlink/lm13700.pdf

And also have a look at the SSI application note "Designing Voltage Controlled Filters for Synthesizers with the SSI2164":

https://www.soundsemiconductor.com/downloads/AN701.pdf

Both of these should be gospel texts for anyone interested in analog audio electronics. The 13700 one is an original classic. The 2164 one is a fantastic summary of information from a huge number of previous sources (Electronotes, the SDIY list, all over) and covers the absolute state of the art for analog filters at this point.

[PRR]

VCAs, would they not be only good for volume control?

Nearly all "tone controls" are filters and variable-gain stages. The common "treble" control leaves the bass at constant gain but passes the highs more or less at user choice.