I edit my answers cause as a new fellow, I only have 3 comments allowed here.
The starting point of this project was to beef up my Behringer Crave basses. As you know the Crave as only 1 VCO. It can output SAW & âSQRâ at 10 Vpp (it outputs Square, Pulse & PWM in fact). A basic circuit like the one published by âAnalogoutputâ will probably work but it can only track a square or pulse wave. Adios PWM with a sub osc !!! Because as mine this circuit cannot track a PWM square without a pitch shifting effect on the sub osc. Can be usefull in some case but not for every purpose.
I wanted to track a stable signal and decided to track the SAW output from the Crave. Simple : put an input stage that convert the saw to a sqr (BJT distortion) and feed the 4013. But it didân worked at all⊠I decided to study more the 4013 and understood that the edges and the ground of input sqr are very important. I had to remove some harmonics and be sure to ground it. I ended with the 10nF cap, diode and pull down resistor. And it worked⊠till I decided to test it over the keyboard range and it was working on 2-3 octaves only. I studied more the 4013âŠand after days of changing resistor values I ended with this circuit. It can track an input signal from 0.2Hz till 24kHz with at least 2 Vpp amplitude. This is tested with the input cap. You can probably achieve better results without it.
The input cap is here to allow a wide range of signals input but in most cases itâs not needed (euroracks for example).
After many tests, It can track a Sin, Saw, Tri, Sqr & Pls input. But I suggest you to track a non modulated signal cause it can track at least a 2 Vpp amplitude signal.
Jos, I can see on your oscilloscope trace when the signal of Sawtooth in small (at the end of the trace) it stops to track it. You can see a little gape on the sub osc trace beffore the Sawtooth goes high again. So for tracking accuracy, itâs really important to feed a non modulated signal !
I had the choice to make separates outputs but I decided to mix them. If you put the mix pot at 50% youâll get the famous SH-101 PULSE SUB OSC.
I had some feedbacks asking me if this circuit can act as a clock divider. Itâs not ment for that but with a simple mod I added 2 ouputs that can generates a Eurorack compatible clock signal (limited at +5V).
Look at the V2 update posted on this forum for this simple mod and avoid the input cap if you built it for Euroracks.
Great work Jos ! Happy tha circuit could inpire you !
This circuit was ment to be used with a 9V battery as a pedal expansion for the Crave or for schmitt trigger projects and also as a module for Eurorack with minimalistic elements.
About the output level. Eurorack can handle 12V input but youâre right, this not standard. For people that has no oscilloscope and want to power it with 12V you can simply replace the 1K output resistor with a 22k. The line input of the Crave and most of Eurorack mixers have a 100k pull down resistor that will do the division. Youâll get a 9.88 Vpp signal. Another solution is to use 2 Zener diodes (check my last revision) to limit the output signal.
I made another schematic that I published only on my instagram @analog_lab.swiss that is 100% Eurorack normalized.
About transistors, If you replace the 2n3904 by a BC548 or BC337 it will work exactly the same from 0.2Hz to 24kHz. With 2n2222 it will not track the input signal correctly on a wide range. I did not tested the BC547. Do you have tested the range of accurate tracking with it ? I did not tested my circuit with JK flip flops but this is a good idea !
The 56k resistor is a bit of a mystery to me, I must confess. Using a direct connection resulted in a not working circuit on my bread board. It may be because apart from making a DC-level connection it introduces some sort of a delay, but I am just guessing here. B.t.w. the added LED is of good value, because it gives some feedback about the input signal.
I guess itâs part of the âdays of changing resistor valuesâ @Analog-lab.swiss mentions? Buffered CD4000-series inputs can have up to (checks spec) 7.5 pF input capacitance, so 56k gives you a time constant of around 0.4 ms (probably a bit lower in practice), so the delay theory seems likely.
I took one look a that super dense stripboard layout and decided to make one with a bit more space for my clumsy fingers, so I made my own, with space for a mounting hole (m3) and room for a standard shrouded Eurorack power connector. I confirm that it works:
What a superb build. Thanks for the big finger layout too. This is going on my project list now. I love the SH101, itâs the Swiss army knife of synths.
It really is a nice sounding circuit, let us know how it works out for you. I found it can track with nearly any kind of wave I throw into it, and the signal output level is decently high. I canât wait to make a second one and get them beating on each other with a slight detune. The only thing I could possibly wish for would be a way to adjust the output pulse width, but Iâm not gonna complain on such a cheap and easy build.
Edit: Built that second one - sounds real fat! I find itâs easy to saturate my filters when the two signals heterodyne though, gotta be careful about gain staging. I just got my to LMNC tuner VCOs in the mail - I think Iâm gonna build the sub oscillators right in!
I drew up a PCB for this and a Kosmo 5 cm front panel for a dual sub oscillator module using two copies of the PCB. Got an order for 5 panels and 10 PCBs in at JLCPCB. Once Iâve built and tested one Iâll make the others available.
Interesting what youâve done with the output. Why have you decided to put D5 and D6 in series and not parallel to GND? Now they trigger at 5.1 V + 0.7 V (Forward voltage of the other diode) = 5.8 V. The capacitor C4 will block DC from the potentiometer, so this must be to ward off DC from the device you connect the SubOsc to?
Hmm, I donât think Azarello took the forward voltage into account and I didnât think about it. The intent was to limit to ±5.1V but the forward voltage is 1.2V. So maybe a different part is called for here. Or nothing, Azarello did call it optional. Redirecting...
Nota : If you look at the schematic (3d picture) there is 2x 5.1V Zener diodes to help the output mix signal to shrink to +5V/-5V amplitude. But the output is already about 11Vpp without that. So this mod is really optional & I decided not to use it on my stripboard but some of you want maybe to add it.
I left them in for the PCB but of course you can just omit them.
I donât know if this is helpful at all or not and I donât know if he posted this elsewhere (I assume he did) but this is the schematic that Carmello sent me at the end of April. He followed up with a message that said:
âI see that I forgot to put a second BJT on the schem to make the phase right for clocks.â He said he would send a corrected version the next day but then I never heard from him again.
Note: pin 8 of the 4013 (i.e. Set) should be grounded. This is not drawn in the schematic (the same goes for my hand drawn version of the schematic in later posts), however in the drawing of the strip board it is. If it is not, the circuit will likely work but may show odd behaviour if the set input picks up some signals ( e.g. if you touch it or come near it ).
Happy tha circuit could inpire you !
