JH-720 Solo Synthesizer
New location for my  
Available Now: 
Hear the JH-720 on several tracks of 
my new CD "Dark November"

A Performance Synthesizer ...
You've probably heard me talking a lot about ergonomic synthesizer user interfaces on the synth-diy or analogue heaven mailing list. Sometimes you want a Modular System to try everything possible - and sometimes you want a Performance instrument that can be played straight forward like a guitar. The JH-720 is my attempt to build an easily usable Solo instrument.

A collection of features from various instruments ...
The instrument is called "720" because the main inspiration came from two Korg instruments, the Korg 700 (Mini Korg) and the MS-20. I'm giving a list of my sources, but some of the circuits are actually my own inventions. For instance, the HADSR structure of the main ENV generator is clearly inspired by the MS-20, but the implementation is completely different, using a fully voltage controlled envelope circuit (see schematics below).

The Woodwork
The wooden frame around the synth was made by my brother, Thomas Haible. As the following pictures document, it turns a piece of electronic junk into a usable instrument. Danke, Thomas !
Some JH-720 pictures - click on the thumbnails

Important note: This is not a complete description to build a copy of my JH-720 Synthesizer. It should give a good impression of the circuit design and it's oddities nevertheless, and hopefully the synth-diy community will find some if it inspiring. I've taken the scans directly from the folder where I keep the JH-720 documents, so the drawings should be close to what I've actually built, but there is no guarantee that it will work exactly as presented. 
Many of these circuits are based on various Korg circuits, but the blend of different circuit parts, and some additions and optimizing, are my own. The circuits (speaking of my part, and not for Korg) are free for private, non-comercial use. (In particular, I don't want to find them in modules starting with "A-" of a German manufacturer starting with "D".)
JH-720 VCO Core One of two identical circuits. 
Linear Keyboard CV, exponential Modulation CV, Saw Wave Frequency Divider. 
Based on Korg MS-20 and Korg 700 circuits 
JH-720 VCO Waveform Converters Both VCOs shown. 
Based on Korg 800DV and Korg MS-20 circuits
JH-720 VCO Scanner Very simple version of the waveshaper part of the Interpolating Scanner: Evenly spaced rectangle functions instead of variable triangle functions, and no multiplying. 
JH-720 VCF One of two circuits. JH-720 has one HPF and one LPF. Both options shown in one drawing. 
JH-720 Keyboard An old Roland SH-2000 keyboard konverted to V/Hz, the defective Hall element replaced with a different one + discrete amplifier 
JH-720 VCA Based on Korg 700 VCA. Select diodes for identical drop voltage (+/-1mV)
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