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 AM2000 Synthesizer (Replica Eľ Modular Synthesizer)
Project Status
Nearing completion! All the modules and front panels have been manufactured and all the PCB's populated and tested. 3x 2350's still being built and the 2140 needs re-testing. The two cabinets are in the final stage of assembly.
Overview The AM 2000 Modular Synthesizer is a replica of the original E-mu Systems Modular synthesizer that was manufactured in California by E-mu Systems from 1972 to 1980. Over 125
were built, and the last model was given to Scott Wedge when he left E-mu Systems in 1993 - he still has it.
The modules were updated with new circuit ideas during their life time, and Dave Rossum
exploited SSM chips in many of the later module revisions from 1976 onwards. Some of the circuits are unique designs, not available from any other manufacturer. For example the
Resonant Filter and the Universal Active Filter (an improvement over the ARP 1047 filter show cased in the ARP2500 Modular).
 Why Build a Clone? The idea of attempting to build a E-mu Systems Modular clone really took hold when I was in a motel in Scotts Valley in February 2002. I had just visited Scott Wedge and
fired up his mint Modular. I was very impressed with the build quality and magic sound, and whilst buying one was not an option in terms of availability and cost, building one was a vague possibility.
A few days later I met up with Riley and Ed at E-mu Systems and realised that they might have some schematics, as they were both into Eu Modulars. I didn't manage to get any details whilst in
the USA, but a few months later when back in the UK both Riley and Ed have manged to share some schematics with me over the Internet. In October 2003 I bought a set of additional Modular schematics from Martin
Newcombe (remember the UK Sythesizer Musuem?).
The Challenge Cloning a set of 25 year old analog circuits is NOT easy, even if they were designed by a genius like Dave
Rossum. The first stage was to get the schematics onto paper and touch them up so they could be read. The next step was to
see what kinds of transistors and IC's were used, and try and locate them. Whilst there are some easy 2N5828's and 2N4250's,
there are also rare SSM chips and ultra rare dual matched transistors. Most of the Op Amps are still around, like the trusty 741
used in control paths, whilst the obsolete 556 can be substituted for. It was soon clear that I would need to replicate the circuits
exactly and only once a module was working could I move onto substitution with modern parts. That meant a six month trawl of
the Internet looking for rare components...and piece by piece I have managed to acquire nearly every rare part in sufficient numbers to build a large modular!
Designing the AM2000
Confident that I could at least find the necessary electronics, I could now plan the physical format. The original physical design was based on high quality electronics and mechanics, and I hope to get reasonably close to the same
objectives albeit with some compromises and changes:
- The original modules were 6" high and 3", 6 or 12" wide. I will be using a height of 4U and a width of 90 and 135mm. This
provides more space for the panel layout and enables the modules to be rack mounted.
- The aluminium front panel designs stick closely to the original, but with some tidying up of layout and the omission of the
blue painted surround. Black lettering is etched into the 3mm thick panels (the originals were 1/8").
- Two cabinets are planned, built in MDF and painted blue. Each cabinet can hold up to 20 modules within a 19" racking system.
- The separate sub-module and module concept of the original has been ditched in favour of one circuit board - I don't plan improvements to each module!
- More modules are being added from other manufacturers (like ARP and Oberheim) to enable a wide range of timbres.
- An Oakley MIDI interface has been added, so the beast can be controlled.
- Modules use original E-mu control knobs - see below for information
- Pots - they need to be 6.35mm shafts to fit the control knobs. So I have used a mixture of Bourns 91A and Spectrol 248.
- Minature "flat" toggle switches - as per the original.
- Lights - 5mm LED's mounted in round plastic LED holders (Clip Lites).
- The power supply is 1.5A +/-15V.
- +5V is used on many E-mu modules but is generated on each PCB that needs it.
- The power bus structure is based around two Oakley Dizzy PCB's in each cabinet. These distribute +/-15V, ground and screen ground as well as two separate CV/gate buses.
- The CV/gate busses are selectable from some of the module front panels (just like the original) and the busses are configured as MIDI and SEQR.
- The MIDI bus is driven from the MIDI interface and has an external MIDI IN.
- The SEQR bus is driven from an external CV/gate
Knobs
The E-mu Modular (and Audity) have distinctive solid aluminium knobs with a black body and a clear top (nice..). These
knobs are still manufactured by Tyco but they are $5 a piece with a minimum order of 250. This is too expensive, so I had a Taiwanese knob manufacturer make me 500 knobs at less than $2 each.
E-mu Modules
The AM Modular has the following E-mu Systems module clones:
- AM2010 - Dual VCA (using the SSM2020)
- AM2100 - Low Pass 24dB Filter (using discrete transistors)
- AM2140 - Resonant Filter, with HP, BP, LP modes
- 4x AM2350 - Transient Generators (using the SSM2050)
- AM2400 - Digital Noise, with additional Audity pink noise source
- AM2430 - Ring Modulator, with additional LFO
- AM2470 - Dual LFO
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