ETI 4600 Owner Richard Hallum's Page
Current 4600 & 3600 Owner
Richard's ETI 3600 Page
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In 1969 I was in my
first year in secondary school, and took music as my optional class.
This turned out to be rather boring, but occasionally students were
allowed to bring a favourite record along and play it to the class.
One day a boy named Tim Snow brought along a record that was simply
the highlight of all my music classes at high school. That album was
Switched on Bach.
So began my interest in
synthesizer sounds. I started collected albums over the next few
years as they became available. There were quite a few in the
footsteps of SOB. As a youth I was more interested in rock than
classical music (of course), and was quite impressed with Keith
Emerson’s use of the Moog. ELP’s Lucky Man certainly gave a
different dimension of what a synthesiser could do. Time moved on (I
got a job as a telecommunications technician, got married, did the
big OE…). It was when I got back to New Zealand in 1979 I decided to
build a synthesiser. By this time I had developed an interest in
electronics and had built several other projects such as audio
The 3600 was very much a build it from scratch project (not a kitset). The front panel was a sheet of aluminium I drilled and designated with Letraset. Several of the circuit boards were my own layout and/or construction. Etching, drilling … looking back it is a wonder I didn’t try to make the potentiometers too! I mounted the front panel on hinges, which was just as well given the amount of calibration and modification involved.
Fast forward to the mid 1980s when I purchased the 4600 from someone who had made a start but lost interest. This was much easier to construct than my 3600. All the circuit boards and mounting brackets were present, as were most of the electronic components. As well as that, I had the experience from the 3600 to draw on.
The previous owner had made a case according to the ETI pattern, but didn’t have the keyboard. This was not a problem as by then I owned a commercial studio and MIDI was available, and I had a Yamaha KX88 master keyboard, which drove several MIDI rack units. For this reason I re-housed the synthesiser in a shallow case so it would sit against the wall, and provided it with MIDI input. The MIDI-CV converter uses a 6402 UART and ZN559 D-A converter. The MIDI channel is set using the DIP switches below the MIDI in socket. I used a Korg MS-02 interface to convert from V/oct to V/Hz.
The box of bits I got did include the silver front panel, which saved a lot of time over my DIY 3600 one. There was no patchboard included so I instead used a larger one out of an obsolete computer (a PDP mainframe). This is a 50 x 50 matrix that is more than big enough to provide all the ins and outs for both the 4600 and the 3600 modules. The only downside is that without proper designations I had to refer to a chart and this sometimes made setups a bit prolonged if I hadn’t used it for a while. Other than that I did add a couple of modifications to the 4600 – 2 inverter circuits, 2 exponential converter circuits, and the ability to sync the oscillators together.
The filters in my 4600 are the 3600 type. Originally the 4600 had a different filter with a LP-BP-HP switch but no resonance. As with the 3600, I hinged the front panel to allow for easy servicing. Unlike my 3600, the 4600 was only used in the studio. It got included on a few recordings, but was a bit slow to set up for most occasions so it was more of a pet really. Some time after completing the 4600 I came up with the idea of combining the two ETI synthesisers into one uber-modular. This provided one larger modular synthesiser with 6 oscillators (or 5 + 2 LFOs), 2 noise sources, sub-octave, 5 mixers, 5 EGs, 3 VCFs, and 3 VCAs. You can see in the photos of inside the 3600 that there is no longer any wiring to input / output selector switches, as all the audio, CVs, and triggers go through the 4600 matrix. Three multicore cables go between the two synthesisers to make the connections. Probably about the same time I removed the phaser and the sequencer – I can’t remember why.
After a few years
I lost interest in the ETI synths, as things went from 2 to 4 to 8
to 16 note polyphony. I bought synths by Roland, Yamaha, Korg, Arp,
Moog. Who would have thought that analogue synthesisers would become
popular again (not me – I sold mine for a pittance). Maybe one day
I’ll restore the 3600 to its former state and take it gigging for
old times sake.