Roland SH-3 synthesizer

This is a early Roland SH-3 synth probably from around 1974.

 

According to Wikipedia the SH-3 used a diode filter like the EMS VCS 3.

 

The later SH-3a  uses a transistor ladder-filter and as a result can generate Moog-like sounds." The Roland SH-2000 used a similar Transistor Ladder circuit.

ARP used Moog style filters in their 2600s and Odysseys until threatened with legal action in 1976.

 

Looks like the VCO & VCF respond to voltage control.

 This is a comparison of the SH-3 vs the SH-3a

They are identical

Both these synths can do additive synthesis by mixing in up to five different waveforms.

The synths are both monophonic, having just one VCO & a noise module.

Interestingly there are two LFOs

LFO1 has a sawtooth waveform

LFO2 has a  sine & square wave with a delay slider.

The LFO's can be assigned to the VCF, VCA, or the VCO.

 

There is a Sample-and-Hold with level and sample time sliders. 

The filter is a resonant self-oscillating low-pass with frequency and resonance controls.

There were very few SH3s (estimates range from 40 up to a hundred). 

These were made before Roland changed the filter. The new version was called the SH3a. There is a lot of debate about the differences in filters between the SH3 and the SH3a

and why Roland changed the design. Some say it was due to a Moog lawsuit, though I don't think this is the case as the SH3 uses a diode lader

Maybe the engineers just didn't like the sound. 

I haven't heard a SH3a in the flesh, so can't really compare.

 

 

Interestingly, the diode filter was originally developed by EMS in order to work around a Moog patent. This diode filter is best known as the sound of the Roland TB-303.

 

Filters basically work by controlling current flow to a filter capacitor.

The diode or transistor, under the influence of a CV, controls the current flow to the capacitor.

 

The main difference between the two filters is that the Moog style, transistor filter 

design electrically isolates or buffers each pole of the filter.

The diode ladder filter however, doesn't behave this way. The poles interact electrically with each other.  This non-linear design contributes to the dirty, squelchy sound of the 303.

A excellent resource to compare filters is  Florian Anwander