Hey guys, I’m finally back to DIY projects and, during this whole time, I thought about how to use the SSO in an interesting way without changing the circuit too much (I still don’t feel confident with what I’m doing).
So, since I bought the Behringer Crave (analog semimodular synth > CEM 3340), I thought it would have been nice to have an external oscillator that I can use as modulator for crossmodulation synthesis.
Therefore, I built the circuit again and put a 2.2 uF cap to make it oscillate very fast. Patching SSO audio output into VCO CV of the Crave I get what I want, BUT:
The frequency at which Crave plays gets a massive shift towards the higher range of the spectrum. Is that normal? Is it the audio output that I have to patch?
Crave’s VCO CV seems to be the only parameter that responds to SSO. I wanted to use it also as a LFO to modulate Filter Cutoff and stuff like that but, even with a huge capacitor (1000 uF), the only result I seem to get is that the filter is always open and it doesn’t respond to modulation. Do you know why?
Why the knob to set the amount of modulation doesn’t work? Is it because it is prepatched inside the circuit and only works with the internal LFO?
You’re feeding an audio signal into various Crave inputs. If you’re doing that with the VCO it’s essentially frequency modulation (somebody correct me if I’m mistaken.)
With the filter cutoff you ought to get something like what you expect if the output of the SSO is reasonably low in frequency, but have you checked the signal amplitude? The VCF inputs all expect 0-10V. For further reference on signal levels check the quick start guide which can be downloaded here:
PS: the VCO CV expects signals in the range -5V to +5V, so if you’re feeding it an audio signal in the positive range you would expect to get only high frequency oscillations.
As with any oscillator output, you can adjust the super simple oscillator’s amplitude range using fairly simple Op Amp circuitry, but as I don’t know what precise range your current circuit outputs I’m unable to suggest exactly how you would do it in this case.
I checked the output of the oscillator and it is fairly stable just above 10 V. I replaced the output resistor (100k) with a 10k because I thought that it would drop down the voltage by impeding it but apparently it doesn’t work like that how should I do that?
@Bitnik I don’t know if I made it clear but the filter input is also a CV, i want to modulate the cutoff with the Super Simple Oscillator (big capacitor to bring its oscillation frequency under the audio rate > LFO).
For crossmodulation I mean analog FM yes
Use a voltage divider to attenuate the output signal of your oscillator. A couple of 100K ohm resistors should do it, I think. Put them in series, feed the oscillator output into the top resistor, and tap the ground and the mid point junction between the resistors for a half strength signal.
Or just use a single 100K pot and tap the wiper and the ground for a variable attenuation.
I tried with two resistor in series but now the output rages between 00.2 and 00.4 mV if I tap the leg where the second resistor is connected to the first and ground
I added a 100k resistor after the other one and connected them in series as you drew up here. I measured the voltage tapping the output wire between the two resitors and ground and the VOLTAGE ACTUALLY DROPS DOWN TO HALF OF ITS PREVIOUS VALUE (5.2 V ca.) and the oscillator pitch doesn’t get shifted as high as before.
Then, I tried different resistor values and this is what I got as output voltage (I’ll call the last resistor R3):
R3 > 10k = 0.9 V ca
> 47k = 2.5 V ca
> 100k = 5.2 V ca (I use this)
> 470k = 8.58 V ca
> 1M = 9V ca
Surprisingly Crave’s pitch shifts much more up when I have a 470K or 1M resistor than when I have a 100K, as the measured voltage output also shows.
STILL NOTHING USABLE FOR THE FILTER. I tried to add the 100K resistor and put there a huge cap but it still doesn’t affect the filter, even though the output voltage dropped to 5-6 V.
Probably I’ll have to use an Op Amp there; is there a specific type that I have to buy?
how should I do that?
