I had a go at the SubOsc on a bread board and liked it so much that I thought I’d turn it into a module. Since I use EuroRack I thought that one SubOsc would be a waste of space so why not make 2? Well, it happened that I could only find one 4013, so I had to look for alternatives. Luckily I found 2 dual JK flip flops (4027) so I decided to use those. This meant that I had to alter the schematic a bit, but I got it to work exactly in the same way. I’m including the schematic here which firstly shows the original schematic with the 4013 and the output calibration I posted about earlier and secondly shows the alternate version based on the 4027. The asterisk marks the point where you pick up the pulses from the synth which you can either feed into the 4013 or the 4027 circuit part. For the transistor I used a standard BC547, but any plain NPN transistor will do.
The output is a mix of two square waves coupled through a capacitor. As the capacitor does a differential on the square waves, couldn’t the output in theory be higher and lower than the power voltage, if the edges of the square waves are sharp enough?
@d42kn355 : Well, the circuit is very simple. You should be able to do that yourself. But I will do one more thing, which is show a few pictures of the signals the SubOsc produces:
This first picture shows in the bottom (blue) trace the output of the SubOsc before it is fed into the crave’s ext audio input. The top (yellow) trace on the oscilloscope the output signal of the crave, no SubOsc signal is mixed in here. So the crave outputs a sawtooth and nothing more. You can see here that the frequency of the SubOsc is half that of the saw tooth. The sawtooth is modulated by the amplitude envelope of the Crave.
In this second picture I show the output signal of the crave after mixing in the SubOsc signal at a low amplitude. You ca see the square waves are mixed with the saw tooth and both are amp modulated by the envelope of the Crave.
In the last picture you see what signal the SubOsc outputs when you set the 100kOhm potentiometer near its center position. Then the signal divided by 2 from the first flip flop and the signal divided by 4 at the output of the second flipflop are added together (depending on the potentiometers setting you can make a perfect staircase if you want) and the resulting signal is fed into the Crave. Neat isn’t it ?
Why do you connect both circuits to the same input? Wouldn’t it be more flexible/useful to have two independent inputs? Seems to me that with a single input, both outputs will be very similar with just a different mix of the -1 and -2 octaves.
No, sorry for the confusion. Those will be 2 identical implementations that I can use independent from one another (e.g. on different synths). I changed the diagram, to make this more clear.
On the theme of sub-octave generators and such, has anybody seen or tried to make one, based on a PLL circuit?
(Like the XR-2212 for example)
In theory you could then generate other frequencies than just sub-octaves, e.g. a fifth above, an octave above, a fifth below etc.
There might be a slight lag/glide, but that could potentially be an interesting transient in the sound.
lmao, i just realized I already have a stripboard layout… and I posted it at the beginning of this thread… sigh… COVID-19 scare got my mind in a flurry… bahahaha
The 4013 works from 3 to 18 Volts, so 12 Volts is no problem. It is interesting to see that in this schematic they put the diode in front of the transistor. Mind you the input capacitor is missing, so this works only as intended when a signal is supplied to the input that does not have a DC offset. Furthermore the switch makes one choose between the divide by 2 OR divide by 4 frequency. I like the other design published by Carmelo more because it allows one to choose either and / or mix those.
Please somebody make a stripboard layout for this! I’ve been looking for a subOsc for a long time. I don’t know how to read a schematic and translate it to a stripboard yet (I am still trying to figure that out.) However, I am amazing at paint by numbers and can follow a photo really well. If someone can help by posting a stripboard layout that would be amazing!!
I haven’t tried it but it looks to me like it would work for any square wave as long as the upper value is enough to turn on the transistor and the lower value isn’t, so as long as the DC offset isn’t much larger than the AC amplitude it should be good. Unless I’m wrong.
Yeah, but that’s an easy change to make, as would be providing separate outputs.
The only thing about Carmelo’s is that it is powered by a 9volt. I’m looking for a subOsc with a eurorack power connector and I’m not sure how to change his power source from 9volt to Eurorack. I like the idea of the one you made because 1) it is dual 2) I’m assuming yours has a Eurorack power connector since you said that you made it into a module. You’ve done the hard part already (in my eyes.) I was just hoping someone will build it and if so they would then post their stripboard layout.
I will attempt to create a stripboard layout from the schematic. (I really do want to learn how to do this.) If you or someone else could check my layout before I build it that would be helpful so I can make sure that I’ve laid it out correctly?
I just finished my implementation of the sub oscillator in eurorack format. Since the circuit is only small I decided to build 2 in one module. In a previous post I wrote that a JK-flip flop of type 4027 should be equally usable for this purpose (as I did only have one 4013), and this worked on my bread board, in the end my version showed some instabilities which I can not explain, other than maybe that I have no idea where I salvaged the ICs from and whether they were trustworthy to start with. So I decided to go with the 4013 and order a few more.
I added a little something to the design though. I thought it would be useful to be able to “see” that the cable connected to the module is indeed feeding a signal into it. So I added a PNP transistor and a LED to the circuit. The base of the transistor is connected to the collector of the NPN transistor in the input circuit. So the schematic looks like this now:
Because the input transistor’s collector is always high if there is not input signal, a negative pulse will indicate that there is an input signal, hence the choice of a PNP transistor (center of diagram) to control the LED. You can also use a BC558, BC559 or whatever small signal PNP transistor you have lying around.
Next I printed a panel, like the one in the following picture:
Apart from a few holes this panel (middle, left) contains 2 low structures ( for lack of a better word ) which can be used to hold a circuit board. Hot glue is your friend!
I’ve been looking for a subOsc for a long time. I don’t know how to read a schematic and translate it to a stripboard yet (I am still trying to figure that out.) However, I am amazing at paint by numbers and can follow a photo really well. If someone can help by posting a stripboard layout that would be amazing!!
