JH-720 Solo Synthesizer
A Performance Synthesizer ...
|New location for my
Hear the JH-720 on several tracks of
my new CD "Dark November"
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).
VCOs, Diode Ring VCA, Glide circuit - Korg 700 and 800DV
VCF, HADSR + HAR envelopes - Korg MS-20
LFO - EMS VCS-3
Delayed Vibrato - Roland VP-330
Keyboard with magnetic Aftertouch - Roland SH-2000
Front panel layout - Steiner/Parker Synthacon and Korg MS-20
Scanner - my own JH-3 Modular
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
back to my homepage
|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
|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.
|One of two circuits. JH-720 has one HPF and one LPF. Both options shown
in one drawing.
|An old Roland SH-2000 keyboard konverted to V/Hz, the defective Hall
element replaced with a different one + discrete amplifier
|Based on Korg 700 VCA. Select diodes for identical drop voltage (+/-1mV)