It would help if you published your proposed circuit.
Depending on your exact VCO config with the LM13700, I would expect you are feeding a control current via the control bias inputs (pins 1 & 16). If this is the case, then you shouldn't hammer 10mA through there!
What it sounds like you are building (8+ step sequenced synth) is usually done with a V>C converter between the sequencer and the VCO.
So a typical implementation would be:
8x potentiometers wired across 0v & 5v, pot wipers feeding the inputs of a 4051, output of 4051 feeding (possibly by buffer opamp) a V>C converter (this can be as simple as a resistor!) - I use current mirrors though as this makes a nice transition between the 0-5V world of the controls and the +/-Vcc world of the 13700.
You explained exactly what I'm trying to do. I'm guessing you've built synth modules before.
It's an 8 step up/down sequencer that puts out + and - voltages built out of just parts I happen to have.
The oscillator I'm using at the moment isn't the most important thing. I hope to be able to use the sequencer for modulating the pitch of different oscillators or the cutoff of any VCF or the volume of any VCA etc... A sequencer that's built to only control one VCO wouldn't be terribly useful.
Anyway.
- The 74c14 controls the clock speed (tempo of the sequencer) and I've already got that working.
- The 4029B counts up and down just fine because at the moment I already have it set up and connected to a 4511 BCD to 7 segment driver and it all works
- The LM13700 oscillator seems to work just fine and gives me nice square and triangle waves over a huge range of frequencies running off of +/- 9V
- The 4051 is the only part I wasn't sure about.
Here's what I came up with for images of this thing.