Something of a novice here (I have experience building signal processors/guitar effects from scratch but little else) and I've been meddling with the circuit below.
It works, although I only have the one capacitor wired in between pins 1 and 2. What I would really like to do now is run use this with a CV/Gate sequencer – specifically, the Korg SQ-1 which I own.
Korg SQ-1: http://www.korg.com/us/products/dj/sq_1/
I'm not sure where to start with this. The sequencer has two cables coming out – one for CV and one for GATE (duty cycle). I'm guessing as this is generating the control voltage, I'll be disconnecting the circuit's +9v from the part of the circuit whcih determines the pitch, without powering the circuit down, but am unsure if I even need to do this, or if the control voltage from the korg is enough to power the circuit. I'm also totally stuck as where the gate input would go.
I'm guessing that I'll need to wire two sockets in somewhere but I just don't know where. Can anyone help? I'm not fussed about it playing the exact right pitch (you can change the scale of cv-to-pitch on the sequencer) as there is a pot you can adjust, and I can figure out which capacitor I need afterwards.
Thanks in advance!
Best Answer
If the Korg's control voltage is the old analog synth standard of 1 V/octave then it's not a suitable circuit as it is not voltage controlled.
To make a voltage controlled oscillator with enough linearity to be reasonably musical is an electronic design challenge. It can be done (but you'll need to progress past the 555) and there are published designs including some discussions on this site.
There is a design discussed in Help Needed with Voltage Controlled Synth Circuit. The component count is reasonably low and it looks as though it would actually work!
Note that the gate signal is not used in the oscillator - it is used in the envelope generator to control the ADSR - attack, decay, sustain and release. A separate circuit is required for that.