How to add Sample and Hold to MFOS Subcommander

[Atodovax]

Hello everyone. Does anyone know how to add a simple Sample and hold circuit to control one of the LFO`s on the Subcommander? I know a lot of circuit that would output sandom voltages out of a transistor noise to use as a source of random voltage, but i do not fully understand where to feed those random voltages into the lfo design of the Subcommander.
Ideally i want to run two separate noise sources (random voltages) to inividually feed each one of the two lfos in the circuit.
Thanks

[ElectricDruid]

Here's the schematics:

Guitar SubCommander

Looking at page 6, we have the LFOs:

http://musicfromouterspace.com/analogsynth_new/GUITARSYNTHAUG2007/subcommanderschempg6_schem.pdf

The resistor ratio R110/R112 and R120/R120 sets the trip point for the comparator. So we have 39K / (39K+100K) = 0.2806.
0.2806 x 12V = 3.37V close enough. So the LFO will generate a triangle wave of +/-3.37V amplitude, about 6.7Vpp.

I'm working out a schematic to replace this page with two StompLFOs. That'd give a useful upgrade in terms of features without getting too much more complex. You'd get eight waveforms for each LFO, including S+H/random levels and random slopes. The only thing is that the two LFOs will be the same - the original has a much faster rate for the VCA LFO (not sure why exactly - to get AM effects?). You could get around this by using a different one of my chips like the VCLFO10 (which has several different frequency ranges) but that's a bit bigger and a bit more complicated and I was desperately trying to keep the number of knobs under control!!

More soon!

[ElectricDruid]

Ok, here you go! Here's one way to do it! (I might have got slightly carried away with this!  Still, it makes a decent improvement to the SubCommander!)



This circuit replaces the original Page 6, and provides the same LFO1 and LFO2 outputs as the original schematic.

I've tested this on the breadboard and it's fine. As noted on the schematic, the LFO output is only 5Vpp, not 6.67Vpp, so you can adjust a couple of mixer resistors to compensate for the loss of LFO depth. I don't know how extreme the LFO depth is on the original, so you might want to adjust those resistors anyway, to either get more depth at maximum or less if you find you never use the control much past half way, say.

I've also included an optional "Tap tempo/Sync" part in the grey box top-left, which could be added to either/both/neither LFO. This would allow you to set the rate of each LFO by tapping, or by feeding in an external pulse signal from somewhere else. If you don't want/need that feature, just leave it out. Pin 4 on the StompLFO has an internal pull-up, so is happy to be left unconnected (this is not always the case with uP pins).

I hope you like it, and good luck if you try it!

<edit>The schematic now includes the two depth pots, which are on the original Page 6, but which I hadn't included. The new version is a more exact replacement for the original page of the schematic, which makes things a bit clearer I hope!
PS: If you're not seeing the new images, try clearing the browser's cache. Honestly, I've changed it!

[Atodovax]

Ok, here you go! Here's one way to do it! (I might have got slightly carried away with this!  Still, it makes a decent improvement to the SubCommander!)



This circuit replaces the original Page 6, and provides the same LFO1 and LFO2 outputs as the original schematic.

I've tested this on the breadboard and it's fine. As noted on the schematic, the LFO output is only 5Vpp, not 6.67Vpp, so you can adjust a couple of mixer resistors to compensate for the loss of LFO depth. I don't know how extreme the LFO depth is on the original, so you might want to adjust those resistors anyway, to either get more depth at maximum or less if you find you never use the control much past half way, say.

I've also included an optional "Tap tempo/Sync" part in the grey box top-left, which could be added to either/both/neither LFO. This would allow you to set the rate of each LFO by tapping, or by feeding in an external pulse signal from somewhere else. If you don't want/need that feature, just leave it out. Pin 4 on the StompLFO has an internal pull-up, so is happy to be left unconnected (this is not always the case with uP pins).

I hope you like it, and good luck if you try it!

<edit>The schematic now includes the two depth pots, which are on the original Page 6, but which I hadn't included. The new version is a more exact replacement for the original page of the schematic, which makes things a bit clearer I hope!
PS: If you're not seeing the new images, try clearing the browser's cache. Honestly, I've changed it!

Wow Tom, this is so embarrasing. I just saw your email and came to see this. I never saw these two awnsers. All this informatiuon is just priceless.. Thanks so so miuch! I will order some of those chips not just for this project but for a new pedal that im trying to develop. I actually ended leaving the subcommander for the future , since it was giving me some trouble and didnt have much more time for it.. THanks so so much again and please forgive me for the late reply!