[sdiy] patch matrix

Tony Allgood oakley at techrepairs.freeserve.co.uk
Thu Jun 20 18:22:03 CEST 2002


Hi Ian and all,

>I am about to start out on my first DIY project - building myself a
Maplin 5600S (also known as the ETI 4600)

Before you start, I would recommend that you try to listen to a working
one. This is a very old design, which isn't always a bad thing of
course. But the designer used the then state of the art op-amps and
other older technology bits to do the work. This unfortunately has not
stood the test of time. Unlike the fully discrete designs of that time.

I find the VCOs horrendously hard to tune, and they don't track very
well. Although the VCOs are linear, as opposed to expo driven, the
op-amps and design chosen do not lend themselves very well to stability.
There is room for improvement here, and I guess with time you could get
them to be very stable. The sync function is horrible and is pretty much
unusable to my ears.

The VCFs are very odd, interesting switch capacitor units. But they have
very very small operating range. Build one, but don't make them the only
filter in your system. An op-amp based state variable such as on the
later Transcendent 2000 sounds miles better.

The general design of the boards is poor too compared to other later
designs. The interboard wiring is close to a nightmare.

I did like the phaser, but the way it connects to the output mixer is
odd. Internal reverb is nice too, if a little noisy.

The patchboard is interesting too. But it does not support mixing
capabilities. In other words outputs cannot be mixed on the patch bay
itself. They must be first mixed in the many mixer sections and then fed
to the matrix. This is not like the more useful system from the EMS
series of synths. I found this to be the most confusing part of using
the 5600. The EMS patch bay could be smaller due to its inherent mixing
capabilities, ie. patch pins could route several outputs to one input.
You cannot do that on the ETI, only one output can go to any one input.
It was quite unforgiving if you placed more than one pin in that input
line.

Crosstalk between the sections of the synth is poor. This is more down
to the appalling wiring between modules. Screened cable is to be
recommended.

The EG/transient generators are very nice. Although the implementation
is a little tempermental.

The keyboard scanning circuitry was improved in later versions of the
synth. But you are best avoiding this and using a standard linear output
midi-cv convertor. The onboard expo in the interface section is not temp
stabilised so don't use that. I found the setting up procedure of the
key scanning multiplier one of the most unpleasant experiences I have
had with a synth.

There are some lovely pictures of one built in Australia, it was an
Australian design. I think its on Ken Stone's site.

If you want to build a synth from a 1970s magazine, then the superior
Elektor Formant is the way to go. Although there are more options
nowadays... :-)

Regards,

Tony Allgood                       Penrith, Cumbria, England

Oakley Sound Systems                     www.oakleysound.com
Modular projects            www.oakleysound.com/projects.htm






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