CEM3340 VCO (Voltage Controlled Oscillator) designs

Posted by & filed under Memorymoog, MKS-80, Moog, OB-Xa, Oberheim, Oscillators, Prophet 5, Prophet T8, Roland, Sequential, SH-101, Synth DIY, Vintage synths.

To celebrate the 2016 return of the CEM3340 chip, I thought I’d do another page in my series looking at how various synths implemented classic synth chips (the others being CEM3320 Filter designs and SSM2044 LP Filter designs). This is especially useful right now, since many people have bought a few CEM3340s for their own use and are looking around for circuits to use them in. If that’s your purpose, note that these are all synth voicecard circuits, so they’re used in… Read more »

SH-101 replacement processor – a feasibility study

Posted by & filed under Roland, SH-101, Synth DIY, Vintage synths.

The Roland SH-101 is a late-era analogue monosynth which uses a microprocessor to perform keyboard scanning and various related functions, much like the Sequential Pro-One. Since the original uP is a 40-pin DIP, it would be possible to replace it with a more modern 40-pin DIP uP, like the PIC 16F777, or with a modern surface-mount processor on a daughter board. This page is a look at the feasibility of this idea. Original Processor pins and functions The datasheet for the… Read more »

Roland Juno DCOs

Posted by & filed under Juno, Oscillators, Roland.

This page is a brief look at the technology of the Roland Juno series digitally controlled oscillators. These are an interesting hybrid design. Although digitally controlled and digitally stable, the oscillator produces a true analogue output, even for ramp waves, rather than the typical staircase waveform produced by feeding an incrementing count to a DAC or from a wavetable. Here we will look at how this is done. Contents General Scheme Master Clock Counters Waveshapers Sub-Oscillator Sawtooth PWM Frequency accuracy… Read more »