The monotrons are sweet little analog toys to fiddle around with. And if you own one you have at least once thought about hacking it, right? Well, so did I and aimed at the monotron Delay. For the standard monotron a couple of resources for modders are available, and especially dinSync´s mod seems to work well for it. But the Delay version appears to handle things a little different…
The main issue is that the gate affects pitch and vice versae.
But only if you look at it from the input side, where you apply external signals to the respective testpoints. From an internal point of view the gate signal is simply derived from the same source as the pitch. So if you apply a +5V gate you are already exceeding the maximum frequency of the oscillator. This results in only a short click.
My idea now was to emulate the ribbon in some way.
The external gate signal would basically just switch the CV signal on and off. This is what the transistors do.
The first one is a gate signal switch. As it inverts the signal, a second switching transistor is required. This one is fed by the CV voltage source.
The device is gated at a voltage leve of ~1.4 Volts (if I remeber correctly). So the lowest note signal must hit that threshold.
It appears that the gate pin carries a constant voltage of ~0.8V. I am using this as the collector voltage for the gate transistor and at the same time to generate a ground offset for both transistors.
The trimpot lets me adjust that offset so that I can shift the CV signal to the gate threshold level. The diode prevents the emitter current to flow into the gate circuitry.
As a matter of fact this works, and the CV tracking seems to work quite well as you can see in this video:
