The core of the VCO is borrowed from famous Russian synth Polivoks VCO and in exponential converter we use the original matched transistor IC that was used in Polivoks. But there are significant updated schematics to have the most out of your modular setup.
Erica Synths DIY Modulator is 35mm deep, skiff friendly, has solid mechanical construction and doesn’t require wiring.
The Modulator essentially is LFO with simultaneous triangle and square wave outputs, clockable S&H with external CV input and noise source. A kit comes with two versions of noise generator – simple, transistor-based and more complex Zener diode-based one. Latest provides perfect, full spectrum white noise.
LFO with triangle and pulse wave outputs
Choice of transistor-based or Zener diode-based noise generator for massive, full spectrum white noise