Hello! This is my second schematic to stripboard layout attempt. After my first attempt (sub oscillator) actually worked, I felt it was time to try something just a bit more complex (though still very simple).
My questions are as follows…
1-I don’t fully understand what the pots are doing and how to wire them… does one pin of each pot go to ground?? In the video it seems like they are pitch modulators.
2-I’ve had good luck with adding vactrol based CV control. Would these pots be a candidate for such a modification?
3-Does the stripboard layout look ok? Just want some other eyes to look at it.
I will build it once I get the chips and test it out so I can either verify it or throw it in the trash! It sounds really cool!
You probably could get vactrols to do… something. Put one in parallel with the variable resistor and the resistance you end up with would be something lower than either of the two separately, which means the vactrol would be largely ineffective if the pot is near one end (low resistance) but a lot if the pot is near the other end (high resistance). If it were in series it would add resistance, so would have a lot of effect if the pot is at low resistance but very little if the pot were at high resistance.
Another option would be to use the vactrol in place of the pot, and then use a pot to attenuate the vactrol CV. You could normal the CV input to something like +10 V and then with no CV plugged in, changing the pot would manually change the frequency (while with something plugged in, it would reduce the maximum effect of the CV). But you’d probably need it to be something like a 500Ω pot at most.
You’d need six vactrols if you wanted to control all six oscillators, of course. Maybe just controlling two oscillators would be good enough? And whether sweeping the oscillator frequencies with CVs is actually a useful thing to do with this circuit is I think not obvious (at least if you’re using it for percussion. Since there’s no envelope generator built in you could also use it for a noisy drone, in which case voltage control would make more sense.) Nor is it obvious which if any of the above three approaches would give you a useful setup with a useful range. Breadboarding before building would be a good idea.
The pots are wired as variable resistors (rheostats). Looking at R1 in the schematic, connect Pin 1 and 2 of the pot to Pin 1 of the 40106, and Pin 3 of the pot to Pin 2 of the 40106. Do the same thing with the other pots and their corresponding IC pins.
This circuit is a great candidate for using vactrols for CV, because it doesn’t matter at all if you’re not tracking at 1V/Oct!
I’ll let someone else comment on the stripboard layout – not my forte.
One thing I would add are DC blocking capacitors between the outputs of the 4070 and the 10K resistors going to the (–) terminal of the opamp. This should result in no dc bias on the output, this isnt essential but avoids dc getting mixed in with the signal which could cause issues in subsequent modules.
The caps should be around 10uF with the +ve end going to the 4070 and --ve end to the 10
Also add a 1K resistor between the output of the opamp and the output jack, this will limit the output current if you accidentally connect the output of this module to the output of another module (easily done!)
As another matter of taste, it looks like you have only one thing that needs to connect to -12 V — and it does so via a very long jumper from the top of the board to the bottom. You could just connect the -12 V from off the board to that strip directly.
Likewise, since all the chips have to connect to +12 V and ground, if you had each of those entering the board near the middle, connecting +12 V to strip M on the right and ground to strip S on the left, you could reduce both the lengths and the number of jumpers. (You’d have to figure out a way to get the 10 µF cap between +12 V and ground, but I think you could still end up saving jumpers, or at least jumper lengths.)
But those are just matters of style and if you feel better about having all power enter at the upper left, that’s fine.
Things that are more matters of good practice rather than just style:
It’s best to have a (100 nF disk) bypass capacitor near each chip power pin connecting to ground. It matters more for high speed logic circuits and you might never really require them in an analog synth circuit but better to have and not need than to need and not have. This would probably require adding ground strips between and close above/below the chips.
Since you’re not using the second op amp in the TL072, you should not leave it floating; that can cause strange behavior on the op amp you are using. Pin 7 should connect to pin 6 and pin 5 should connect to ground. Alternatively you could switch to using a TL071.
Thanks for all your guidance ! I built it and it works! It is pretty gnarly if used as a drone. When used with a low pass gate it can sound like anything from a distorted kick, snare, up to hi hats, gongs and bleeps and bloops. Increasing pot values increases range of pitch available. I used 2 25k, 2 250k and 2 500k pots just to experiment. I will make an updated layout implementing some of your ideas and share it on verified strip boards.