JH Schematics

One-OTA Ring Modulator (from JH-1)

Analog shift register (from JH-3)

Quadrature VCO (from JH-3)
Based on a circuit in Tietze/Schenk's "Halbleiterschaltungstechnik". This is *not* a state variable design (as it might look like at first glance), but a schmitt trigger / integrator *triangle* VCO, with an extra comparator and integrator to produce a 90 degree phase shifted second triangle wave. Triangle waves are then converted to sine/cosine waves by overdriving two OTAs. This module is nice as modulation source, but it's not exactly a high precision circuit. For a more advanced Quadratature VCO, see the Frequency Shifter Schematics.

VariLogic (from JH-3)
AND, NAND, OR, NOR, XOR, XNOR selectable with two switches.
Also works as Inverter and Switch Trigger input.

Voltage Controlled Divide by N (from JH-3)
I prefer this way of clock division to the "digital" FlipFlop / Counter method. The circuit works nicely for both clock division and at audio frequency (subharmonic generator). You can find another interesting implementation of the core of this circuit, using a Norton OpAmp, in the LM3900 data sheet.

Voltage Controlled envelope generator (from JH-4)
This is part of the JH-4 Polysynth. First I wanted to use SSM2056 or CEM3310 chips, but the discrete version is much cheaper and uses only standard components.
This is only an ADS type envelope, but it would be easy to make a full ADRS by just switching two CVs (D and R) with the Gate voltage.
The circuit uses rather cheap OTA's (LM13700), so don't expect low offset voltage.

VCA / Inverter/ Overdrive (from JH-3)
One input is routed to the output via two separate paths: One VCA with zero to positive unity gain (approx.), and one manually adjustable path with zero to rather high negative gain. The output voltage is clipped by a set of zener diodes, so the module can also act as Overdrive / Distortion device.

Frequency Shifter Schematics (from JH FS-1)
My frequency shifter doesn't use the BFO method for generating the Sine and Cosine modulation waveforms. I have built a Quadrature VCO with thru-zero FM capabillity instead. A pair of LM1494's is used for triangle-to-sine waveshaping and 4-quadrant multiplication. A compander system (borrowed and slightly adapted from the Roland Vocoder Plus) is used to get rid of both noise and carrier bleedthru.
The Hilbert transformation of the audio signal is performed by a set of all pass filters from Electronotes.

SSM2040 Style 4 pole Filter
In my opinion, the SSM2040 was the best filter chip ever produced. Here's a discrete version of this famous filter, that reproduces the original sound. A lot of component selection is needed (matching transistor pairs). The circuit is *not* a pin for pin replacement (though it's easy to adapt it to be one), and it has a voltage controlled Resonance path added.
There is a small error in the schematics, but it's quite obvious, so I won't redraw it: All the pnp transistors in the current mirrurs are shown upside down, i.e. C and E are mixed up.

Sanple & Hold / Glide (from JH SYNTHI CLONE)

Interpolating Scanner (from JH-3)

Filter Scanner (from JH-4)
Smaller  version of the Interpolating Scanner, as used for Filter Mode Control in JH-4. Triangle functions are not equally spaced here, but optimized for the multimode filter.

Dual VCO (from JH-3)
Based on the (now long obsolete) CEM3340, so I don't really recommend to build this circuit (Save those 3340's as replacement parts for the polysynths which need them ! ) - but you might find the linear thru-zero FM feature interesting for other triangle-based VCOs.

JH Wasp Filter Clone
The EDP Wasp has a very special implementation of the classic state variable filter: opamps are replaced by unbuffered CMOS inverters. My clone has a Notch Filter mode added, plus a distortion and speaker simulator section.

A very simple ADSR / LFO circuit
Designed for the wasp Filter Clone, powered by a single 5V supply.

A low noise Opto Electronic Compressor
Built around an SSM2017 preamp chip and a Vactrol VTL5C4

A (slightly modified) ARP Quadra Phase Shifter as a standalone unit. It's a 14 Stage phaser built around a transistor ladder, and it sounds quite different than any other phaser I've heard.Construction is very compact - everything is on a 16cm x 10cm Euro card - you will need small components if you are going to use my pcb design.
Schematics 1  Schematics 2  PCB layout  Component Overlay

Voltage Controlled HADSR envelope generator
This one doesn't show the offset problems of OTA-based VC envelopes.

Linear KOV / Expo Modulation VCO
From JH-720 synth.
This is a mix of Minikorg and Korg MS-20 circuits, and a few useful additions from myself. Octave switching is done by frequency dividing (for saw waves - no stupid staircase stuff !) which has big advantages for stability. Nevertheless, this is a true VCO, and it resembles the sound of early Korg synths like 700S or 800DV.
Linear (V/Hz) VCOs have the big advantage of better stability, i.e. no scaling error with temperature changes. Frequency Modulation is more convenient on exponential (V/Oct) VCOs. Therefore the FM is done with an exponential input. No tempco resistor is required, as it's only the modulation depth that will slightly change with temperature, but not the keyboard scaling.

MS-20-Style VCF
From JH-720 synth.
I do not claim that this is an exact clone of the old-style MS-20 filter chip (Korg-35).
But from all I've seen and heard, it should be close at least. The sound is very similar, and it also shows some of the original's unpleasant side effects, like almost no CV feedthru suppression. If you are after a "better" MS-20 style filter (as built into later MS-20 models), I advice you to get a the MOTM-420 module from Synthtech, which is a very close emulation of the later version MS-20 filter. (Less noise than the earlier version, and no more "thumping" at fast envelopes.)
The old-style version shown here (or my attempt to reproduce it) has its interesting features, nevertheless. Even a bit more on the weird side, maybe ...