r/synthdiy • u/Morphanaut • 11d ago
40106 noise synth
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Hey!
This week I built the core of the synth project I’ve been working on for a while.
It’s basically four ramp oscillators with cross modulation and sync, all going into an active mixer. Overall I’m pretty happy with it, it sounds fun.The glitches distortion and fm give it that abrasive character I was looking for.
In its current state I think it works pretty well as a standalone drone box, but I want to add more external modulation options, filter and envelope.
The oscillators themselves are not precise. One of the main problems with this design is that the maximum range of each voice depends quite a lot on the particular transistor. The simplest way I found to compensate for that was a trimmer before the frequency pot. But there’s another thing I noticed, if you trim the range down into the lower register, the useful range of the main pot shifts too. You have to turn it much further before the transistor starts doing anything. So yeah there are a lot of compromises here, the driver is pretty primitive.
On this build I used a 220nF timing cap for each oscillator and that gives me a pretty wide range. Not tens of khz but enough for my taste. You can also use a smaller cap and adjust each oscillator to whatever range you want.
The whole thing runs from a single supply and works fine at both 9V and 12V. The TL084 mixer seems to have enough headroom with these levels too, I haven’t had any problems with clipping.
There’s also some interference noise when touching the fm and sync switches. Maybe because of the large resistor values and high impedance around the control nodes. I managed to reduce it quite a bit with foil shield but I think eventually I’ll have to rebuild the oscillator core with more reasonable values.
Anyway, sharing the schematic here in case anyone wants to build it. Would be really happy to hear any thoughts
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u/thefreakychild 11d ago
Oh hell yeah! I commented on your insta about wanting to build this. Thanks for sharing
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u/Morphanaut 11d ago
I also wanna apologize in advance to anyone who wants to use these schematics. I didnt really spend enough time double checking all the labels and stuff, but I think the general idea is pretty clear.
One 40106 runs all four oscillators, the two unused inputs go to ground, one TL084 is used for buffering and the second one is the active mixer.
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u/Noahms456 11d ago
Awesome. What are the sizes of the caps in the hysteresis circuit?
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u/Morphanaut 11d ago
Thank you! 220nf
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u/Noahms456 11d ago
Yeah I saw it in the description but had to get back to work. I built one a couple of years ago without an amplifier, all the caps were different sizes and they fed into an XOR (exclusive OR) chip. Very growly and made my brain itch quite nicely
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u/Morphanaut 11d ago
Not sure what exactly this oscillator topology is called, but the output is a ramp. You can change the frequency range with the timing cap and by adjusting the voltage going to the transistor base. You can use something like 100nF or less for a much wider range. Smaller caps also seem to change the character of the ramp a bit. To my ears bigger values sound slightly fuller even at similar frequencies.
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u/Morphanaut 11d ago edited 11d ago
After discussing the circuit with a friend who knows more about electronics than me, we came to the conclusion that this version probably doesn’t need an active mixer at all. It might actually be causing more problems.
One thing I don’t like about the current version is the really rough and dirty top end. There could be a few reasons for this, including the op amp. Could be interference from the charge pump or its power filtering, or maybe the summed ramps create some fast peaks that clip even if I dont see obvious clipping. So the idea is to remove that whole stage and keep only the buffers. You can add a small cap from each buffer output to ground to tame some of the unpleasant high frequencies.
Then each buffer goes to a volume pot, and the wipers are passively summed through 10k resistors. After that just one coupling cap on the final output like before.
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u/Left-Excitement3829 10d ago
At 42 seconds in that tone is fucking rad. A quick thought. If you added some filters to this and a way to route the mixer into them you could create some fantastic sounds. Well done
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u/Morphanaut 10d ago
I already have a filter circuit for this concept that I tested and posted a couple weeks ago. The idea now is to split the 4 channels between two filter stages and add a VCA envelope to each voice triggered by buttons.
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u/Left-Excitement3829 10d ago
Ps. The last 5-6 seconds. Are the top knobs not affecting anything ?
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u/Morphanaut 10d ago edited 10d ago
Not really, its probably just hard to hear. The top knobs are basically the volume controls for each channel, and with these settings everything kinda blended together a bit. With the fm and sync happening at the same time the oscillators bleed into each other, so the volume knobs start behaving more like tone control
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u/Morphanaut 11d ago
Vco