Roland SH-2000

This synth came out in 1974, Roland's third synthesiser, after the SH-1000 and the SH-3. An analogue monosynth with minimal real time programmability, it features 30 preset voices selectable via flip switches that run along the front panel below the keys. Selecting a voice will override any selection to the left of it. Each preset flip switch selects, via a complex matrix of diodes, an oscillator range (footage), a waveform, vibrato, filter modulation parameters, and an amplitude envelope for each voice. What brings these voices to life is the “Touch Effect” i.e. aftertouch, which can be switched to bring in all or any of the following: Volume, “Wow” (filter sweep), “Growl” (filter fast-LFO mod), Vibrato, and Pitch Bend up or down. There also sliders for filter cutoff (which will affect the preset voice) and resonance (which won’t, except for one setting), and a rate control for the vibrato LFO. Portamento can be switched to a “long” preset time or a programmable time via a slider. There is also a wonderfully wacky Random Pitch effect, where the pitch CV is detached from the keyboard, and determined randomly via the noise generator, at a rate determined by the vibrato LFO - Lost In Space-esque!

So on initial impression, this machine looks like a curio, a bit goofy and definitely dated. But the sound… mmm, the sound…

If you find one of these, the first thing to do is flip ALL the paddle switches up (off), and play the keys. There should be NO sound. If there is, there’s a fault somewhere. When I first got this one, that was the case, and I mention it because I recall not being that impressed with sound of this synth, and that turned out to be the reason why. If there is a sound with all paddles off, that sound will be there with any of the paddles on, and will “pollute” that preset. On YT you can find people demonstrating the predecessor, the SH-3, and on that synth you have manual control over the footages and waveforms via sliders. Here you get a great example of the principle of “less is more”:- notice on these videos how as more waveforms and footages are added, the sound becomes bland and home-organ-like. The presets in the SH-2000 for the most part sound fabulous, strong and musical, with excellently chosen parameters especially for the filter and envelopes. Adding these presets together more often than not detracts from the sound, rather than enhancing it.

So what makes this synth sound so special? The interwebs will tell you it is down to the Moog transistor ladder filter that Roland “borrowed”, but of course it ain’t that simple.

For a start, what kind of VCO is that?





I had a poke around with the scope to see what was happening.

Scope shots below: note upper/yellow trace is always VCO output at connector 1 on the VCO PCB.

Frequency about 1.5kHz, low F - Pin 3 of the 555

Frequency about 11kHz, high F - Pin 3 of the 555

Low F - pin 1 of IC 101

High F - pin 1 of IC 101

Low F - capacitor C102

High F - capacitor C 102

My first impression was that it was based around the 555 timer chip. These chips can make VCOs, but they’re not very good for musical purposes. Advice from the Synth-DIY mailing list suggested the VCO is actually based around the thyristor, the SCR (silicon controlled rectifier) in the top right corner, and that the 555 is there to help linearise or scale the frequency response. It appears that this sort of VCO, as opposed to the regular saw-core reset integrator type as used by Moog and other American companies, were used in a few of Japan’s very earliest synthesisers. Roland’s aforementioned models, along with Korg’s 700, 800 and MS-20. By about 1977, it seems Roland had dropped this idea and changed to using the more conventional type of VCO design, as evidenced by the SH-5 and SH-7. However it was to show up in one more product that I’m aware of - their most famous creation, the TB-303!

The criticisms you will read about these “linear” type of VCOs are usually that of 1) range and 2) waveform purity. If you’re designing a commercial synth that may be required to emulate keyboard instruments, or provide “solo lead” type sounds, these are probably important considerations. If however you are looking for interesting or unique timbres to go with a piece of music you’re working on, they’re much less so. Regarding “range”, often you find that a particular instrumental part really only works musically over about an octave or two anyway. This is why there are orchestras! ;-). Regarding waveforms, this machine surely confounds the premise that you need pure or carefully constructed waveforms to create great sounds. The square wave output from the VCO goes to multiple flip flop dividers (via a LM3216 chip), then the different divisions are simply summed via a matrix of diodes and resistors. This provides a selection of rather coarse stair-stepped sawtooth waves, and pulse waves (see the videos below). Presumably they are rich in harmonics, giving that transistor ladder something to get it’s teeth into.

The audio path is then completed, the signal from the filter, via some level-selecting transistors, going on to the VCA, that itself is controlled by the CV from the preset envelope board. There is no user control over the envelopes, but the aftertouch can be switched to send a voltage to control the VCA directly (this turns out to be of great use when modding for external control).

So selecting a voice preset brings into play various parameters such as footages, waveshape, vibrato, filter modulation and level, VCA envelope and level etc etc.. These parameters are selected by transistor switches, controlled from the matrix (think of the matrix as a hard-wired, read-only memory). About 30 of these switches are based on FETs, and the other 14 or so use BJTs. The FET switches need a gate voltage more negative than about -4 volts to stay fully off. Higher than this, and there is a variable amount of leakage possible. So a switch might fail due to the FET failing, but it could also appear to fail if the gate voltage wasn’t negative enough. If the switch that fails controls, say, the 16’ sawtooth wave, then that is what you will hear with all paddles in the off position. If it controls one of the three “transpose” positions, this footage will be added to the voice. If the FET switch controls an envelope parameter, then the voice might just sound a bit too muffled, or staccato… you get the idea.

FET switch detail

In the case of this particular machine, I was scratching my head at the voltage measurements I was getting at the gates of various FETS - of course, the common link turned out to be the power supply. Although, when I checked it initially as a matter of course, the electros looked fine and the loaded supply voltages seemed rock solid, when I finally replaced the electros and reflowed all the joints many of the faults just disappeared, and the gate voltages were much more consistent. Immediately the sound of the presets improved dramatically. There was still a tone present with all presets off, which I later tracked to a faulty FET switch governing the “Chorus” sound (which is added to the audio bus, along with the “Noise”output, AFTER the point where the wave/divider board output is added).

Having got the thing fully functional, and then being completely gobsmacked at how good it sounded, I then simply had to find a way to control it externally from my sequencers.
After breadboarding up a circuit based on 3/4s of a quad op-amp, and fiddling with some resistor values, I had a Hz/volt pitch CV and 10 volt gate control for notes, and an input tapping in to the Touch Effect, along with a separate control over voice volume.
The incoming Hz/volt CV had to be inverted and scaled. This was applied to pin 8 of the VCO board. A 10 volt gate applied to pin 9 seemed to be the easiest way to implement note on/off, given that it was important to not just trigger the envelopes, but also the envelope CV for the PWM ("Chorus"), see below. This little circuit gives the "Fuzz Guitar" presets their buzzy twang at the start of a note. (There is also a dedicated fixed LFO just below this, for the more conventional PWM effect as used in the Planet and Singing Voice presets. Check the scope video for a demonstration).

Accessing the voltage buss for the "Touch Effect" gives you control over voice volume, as well as the modulation parameters "Wow" (filter sweep), "Growl" (a fixed fast LFO mod of filter), Vibrato, and Pitch Bend up or down. I applied the CV to a wire attached to the wiper of the sensitivity pot, see below

If you do it that way, you can use the pot to drop some of the voltage to ground to help fine tune the effect but if the pot is turned all the way down, there goes your external voltage. The CV, Gate, and Touch controls are buffered by op-amps, which need to be switched out if you want to use the synth from it's own keys and controls. Roland have very conveniently provided a 3 pole, 3 position switch on the back panel (originally for output level adjustment) that can be used for this purpose.

Above: space enough on the back for a small proto board.

Above: re-purposing the back panel switch.

Since there is no dead simple way of getting user control of the envelopes, I also elected to add separate external control over the VCA, via the Volume Touch switch connection. I put this on a switched jack, so that with nothing plugged in, the aftertouch control of Volume behaves originally. Having the minimum voltage here go a little below ground (say about - 0.5 volts) means the voice cuts off to complete silence.
This four-way external control makes it a good fit for a Kenton Pro Solo (remember it needs Hz/volt scale), but it's a lot of fun with one of those Korg SQ-1 step sequencers as well.

Above: there's enough room on the back panel for the 4 mini-jacks.

Videos below: Top trace = audio out

Bottom trace = divider output

Presets: Planet, Singing Voice, Fuzz Guitar 2 and 1

Presets: Clarinet, Flute, Oboe and Bassoon