SH02 Modular Synth

Overview The AMSynths SH02 Project is a set of four Euro Rack modules that form a complete replica of the Roland SH-2 monophonic synthesizer, which was introduced in 1979 and proved very popular with over 7,300 sold. This is one of Roland’s most iconic mono synths, with stable oscillators, a fantastic sounding 24dB low pass filter, a snappy ADSR envelope and a simple but useful LFO.

There are four SH02 modules each 10HP and skiff friendly, which when set up as a dual VCO synth occupy 50HP of Eurorack space.

The SH02 Project adds the flexibility of a modular synthesizer to a traditional design, with 3.5mm cable patching to either recreate the original signal flow or to create new internal and external connectivity. AMSynths have retained the original sound of the SH-2 with minor modifications to improve oscillator stability and to use modern components.

Design History In the late 1970’s Roland launched a new range of mono synths starting with the single VCO SH-1 in 1978. Smaller and lighter then the SH-5 and SH-7 but with a streamlined feature set to reduce the price. The 100M modular system was introduced at the same time to cater for more complex sound design. In 1979 Roland launched the SH-2 with dual VCO’s which were an improved design, taking advantage of the TL082 JFET Op Amp, replacing the CA3130 and and its need for separate voltage rails. The new VCO design would go on to feature in the SH-09, 100M and Jupiter-8.

The rest of the circuits are improvements over the designs in the SH-1, with the same 24dB low pass filter but built from the then new BA662 OTA chips. Carefully hand matching ensured that the VCF would oscillate down to 50Hz and below and the SH-2 became famous as a bass synth. The sub oscillator helped with this!

The ADSR is a discrete transistor design famous for its snappy timing with the Attack going down to 1ms minimum. The envelope can be used by both the VCF and VCA, with the VCA having both Hold and Gate options. The BA662 OTA chip is at the heart of the VCA.

The LFO is a traditional Op Amp based circuit which generates triangle and square waves from 0.2Hz to 20Hz. There is a sine waveform generated from the triangle waveform, using a complex circuit to provide an accurate sine wave. We have retained this circuit as well as the sample sample & hold circuit. The noise source generates white noise from the 2SC828R transistor, the same one used in the TR-808. Care has been taken to ensure the LFO does not bleed into the power rails, as the oscillator swings between the + and – power rails pulling current from the Doepfer power supply.

The SH-2 uses the Roland 1970’s keyboard design with brass fingers and a metal bus bar, which is a bit clunky and only supports note on/off. It was featured on all Roland products until it was replaced by a modern design in 1981 (starting with the RS09 Mark 2 and 184). This keybed used lighter keys, rubber contacts and by 1985 was set up with velocity and aftertouch, the perfect MIDI companion.

Normalisation The AMSynths SH02 modules have been normalised to a common modulation CV range of 0V to +10V, which means all the CV generators create signals in this range and all the modulation and envelope inputs of the VCO’s, VCF and VCA are at maximum depth at +10V. The gate and trigger inputs are all set to the standard Eurorack convention of 0 to +5V operation.


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