Hey guys,
so the super simple oscillator is finally working, and I’ve been wondering on how to evelove it into something more complete. First of all I added a low-pass filter and I would like to integrate a CV inlet to send in LFO’s, envelope generators or a keyboard/sequencer. The idea is to make a normalized/semi-modular synthesizer out of 2 of these circuits with different capacitor values, in order to have one playing in the low/mid range and one in the high.
Now, I have a bunch of questions for you:
Is the CV socket the same as the audio socket or it is of a different type?
Is the CV input enough to patch an LFO or an envelope generator or a keboard/sequencer? Does it make sense to have 1x CV input per oscillator, 1x filter and 1x for keyboard/sequencer (total of 5)?
Since the envelope generator is gonna be patch into a VCA, do you suggest to add an amplifier as well?
Can I power the two circuits with the same 18V source? How does it work?
Most synthesizer formats use the same connector for CV and audio signals. Not all. Kosmo uses 1/4" TS audio jacks for both. Eurorack uses 3.5mm TS audio jacks for both.
1x CV input will let you use one CV source at a time (unless you have an external CV mixer). If you want to control an oscillator with an LFO and an envelope generator and a keyboard all at once, you need three CV inputs. Typical oscillators, filters, and VCAs will have a couple of CV inputs each.
To make signals to send to a sound system you don’t need an amplifier in addition to the VCA.
Most modular synth circuits use ±12V or ±15V power supplies. Kosmo and Eurorack use ±12V. I don’t know of any common synth format that uses 18V.
One thing I’m not sure whether you realize is that the SSO cannot be used very well for playing conventional melodic music. For that you need an oscillator that responds accurately to voltage control, typically exponential 1V per octave. To be useful it needs to be temperature stabilized, otherwise it goes out of tune very rapidly. Sam’s used it in his MegaDrone projects but those are simple drone synths, not intended to respond to a keyboard etc.
Thanks for clarifying that CV and audio signal connectors are the same! I still need to decide which size I want the connectors; aesthetically I like 3.5 mm more, but since I’m probably gonna do some other projects based on Sam’s schematics, (1V/o oscillator, low-pass filter, LFO…) it would be wise to use 6.3mm connectors for compatibility. What do you think?
Then maybe I’ll have 2x CV inputs for each oscillator and for each filter (I have a total of 2 oscillators and 2 filters). Does it make sense?
If I plug an envelope generator into the oscillator pitch the envelope is gonna cause pitch shift right? To affect the ‘volume’ the EG should be patched into a VCA correct? Would you suggest to add a VCA to the synthesizer for this purpose?
The synth is gonna be a standalone unit, which can still interact with other modules through CV. Thus, I can power it with a 18V power supply!
I’m ging to use the synth for drones and stuff, I know that it’s not going to be tuned so my itention wasn’t to use it to play melodies on the keyboard. However, I thougt that it’s nice to have the option of connecting a sequencer to it and play some weird out of tune sequences
Whatever! Kosmo uses 1/4" normally but you can always build those modules with 3.5 mm if you want.
Sure.
Yes, if you want EG control of volume you need a VCA.
And the VCA and EG circuits you’re likely to find will probably be powered with ±12V or ±15. But if they’re in a separate box with their own supply that’s okay. Or even the same box with their own supply. Still, if you can get the SSOs working on 12V with SS9018 transistors, or on ±12V using 2n3904 between the two rails, it’ll simplify things.
Dope! I think that I’ ll keep this as a standalone unit, also because I’m not ready to buy a modular case and the power bus eheh. Could u suggest me a fairly simple project to build a VCA please? That would help!
Also, would it be possible to add a volume control knob on each oscillator? How does it work? I suppose that it’s just a matter of reducing the voltage to 0 at the beginning of the circuit, is that right?
you can see the thing I did (it was for me a project apart from the modular), 5 SSO in 1 with a passive mixer and i was using with an MS20 filter clone in another box (because 9V),
maybe it can give you some ideas
Control the individual volumes at the input to the VCA — if it’s not in the circuit you use it’s just a matter of adding a potentiometer from the oscillator signal to ground with the wiper going into the VCA input.
Hey @Dud thanks! I checked out the link to your webpage and I undestand everything apart from 2 things:
How is the passiv mixer working? I see audio in/out sockets, did u just plug small audio cables inside the machine? I don’ t see any of them out on the front panel.
Should the pot for the master pitch go to the 1st resistor in the VCO circuit?
Great! I connected a 100k pot between the 100k resistor and the audio output and it works as a VCA! Though, the volume goes up but the audio doesn’t shut down completely. Is it just a matter of placing there a bigger pot? (100k is the max I have now but I can buy a bigger one)
I noticed that with a 0.1 uF cap (which is more than it should be) the filter becomes effective at quite a low frequency. Is it because of the capacitor size?
A filter’s frequency response depends on the resistance and capacitance (*) that make up the filter core, where higher R or C values move the filter’s “cut-off frequency” downwards. So larger capacitor = lower cut off, which for a low-pass filter means that it kicks in at lower frequencies.
*) you can build filters with other components, but R and C is the most common variant.
Right, I see! The resistor that u’re talking about would be the 100k right? Cause that’s were the signal is coming into the filter. I tried to rreplace the resistor with a much bigger one but the only thing I noticed was a drop in volume, which also makes sense
Yeah, the “R” here is a combination of the 100k and the potentiometer, with the “C” being the 47 nF capacitor. Usually filters take their output from between the resistor and the capacitor, but that only affects the levels afaict.
(The cutoff frequency is ~0.16/(R×C) Hz, which is the point in the filter curve where the output power has dropped 3 dB from peak (50% of max power, 71% of max voltage) but your hearing isn’t exactly linear wrt power and frequency, so those values are a bit abstract. The equation gives you an idea of how things move around when you change the component values, though.)
Hey guys I got some questions about the filter and CV.
I replaced the filter capacitor with a 47nF and tryied out different pot values up to 500K, but the cutoff frequency doesn’t seem to change. Do you know why?
Click HERE to listen to the different filters on soundcloud, might help! I also added some more infos there.
Where should I insert the CV in the circuit? I watched this image here
, the problem is that I don’t have anything to test wether the CV works or not. I was thinking to build a small vactrol LFO, since I have LEDs and LDRs. What can be another solution?
Also, I want to add 2 CV per tune frequency, 2 per filter and 1 per passive mixer. How do I do that?
I’d like to add a CV/Gate input that allows me to connect a sequencer to the synth. Where sould I insert it?
Thanks for your time!
