I couldn’t get this original schematic to work the way i wanted it to. I couldn’t get the volume to zero out all the way and i had a lot of noise…soooo, i modified it to my liking. The original does work, and plenty of YouTube video to verify without building, but i modified the schematic to work on +12 and -12 and i changed the layout of the level pots (just to make more sense to me and i think they work better this way ). I intend to add mute switches and a main output level pot. Here is the modified schematic so far:
If the top schematic is the original, this makes perfect sense. Whatever position you set the 100k pots to there will always be a signal from the 100k resistor connected to the pot that will find its way to the summing (inverting) opamp. If the pots are connected to GND, as show in the 2nd schematic and you turn them to the lowest value (i.e. to GND), then no signal from the respective section will be added to the sum.
Volume pots in a lot of use cases are implemented as voltage dividers. When attenuating they select a proportion of the original signal varying from 0 to 100%. If you ever encounter a schematic where the volume control is merely a series resistance, then double check the design e.g. by running it in a simulator. Unfortunately there are a lot of designs out there search engines come up with that contain errors.
What changes did you make to make the design suitable to -12V to 12V?
Oh, and please be so kind to add the ‘verified’ text to the picture, so that it is still there when the picture is found presented in isolation (without a textual context) by a search engine.
All i did was ground all the vref and connect pin 4 from all lm358 to -12v. I’m sure there are probably some resistors that could be changed but it does work. There is still some sound bleeding through when all pot are down but running it through an active attenuator (cv/audio mixer) stage helps. It’s barely audible and only on the highest tones. I will change the text on both schematics tho as i have verified both on breadboard. Thanks!
I couldn’t say. I don’t know anything about crosstalk, but i have other circuits that behave similarly. Like any Atari punk circuit in my modular case. I run them on 12v as well, so my only deduction from that is that it is possibly related to this as all the schematics in question originally called for 5v or 9v, respectively. I believe there are some resistor values that could be adjusted for the voltage increases, but they work and i have plenty of mixers (attenuators) so i just use them.
Good to know how you converted it to 12v
I wanted to put mine in my rack too, i feel it’s a great circuit Paul in the lab shared(beaucoup respect for Paul)
It reminds me of being back home in Scotland and the 3 oscillators hum like bagpipers up in ma brain!
lol have you added a trigger circuit to the oscillators?
Yeah i love this circuit. I built Paul’s circuit on breadboard almost 2 years ago. It was one of the first circuits i was able to build successfully. I forgot about it though until recently after messing with trying to get a good reverse avalanche drone to work right. I just got tired of messing with the unreliable reverse avalanches and i remembered. No trigger circuit, though. Just the drones.
). I intend to add mute switches and a main output level pot. Here is the modified schematic so far:
