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AM4000 Synthesizer (Replica ARP 2500, 2600, 2800 Synthesizer)
 Project Status
Many of the module schematics have been transfered into Eagle CAD, and the Dual Noise Source has been successfulyy tested, along with the 4023 and 4075 filters.
Overview
The AM4000 Modular Synthesizer is a replica of the original ARP 2500 analog modular syntheszier that was manufactured in the USA by ARP from 1970 - 1975. more »
The 2500 modules were technically advanced for 1970, and the VCO's in
particular were more stable than their Moog counterparts. ARP went on to make the 2600 and Odyssey and these simpler designs have their origins in the ARP 2500. I have replicated some of the newer ARP filters for the AM4000.
 Why Build a Clone? The idea of building an ARP 2500 Modular clone became possible in
the spring of 2004 when MusicParts in the USA made the original schematics available, complete with the original construction and part listings. Whilst the schematics were only
copies, they did enable the original circuits to be recreated (with a bit of effort!). The ARP 2500 does have some weaknesses, some of which will be addressed (e.g. VCA performance).
The Electronics
Cloning a set of 30 year old analog circuits is NOT easy, but in the case of the 2500 many of the parts are still easily available, because the circuits are based on common transistors and
the basic LM301 Op Amp. The ARP uses sub modules for exponential converters and VCA's, fortunately the schematics for these are available and the 100 and 200 ohm tempco resistors within them can be
remanufactured. The digital TTL chips in the 1027/1050 sequencer and analog switch modules are moe difficult, but the analog designs can be built off the shelf.
The schematics have been transfered into Eagle CAD and the boards manufactured by Olimex in Bulgaria (www.olimex.com) from the CAD files. The PCB's are of a good quality and I certainly haven't experienced any problems with them.
Designing the AM4000
Confident that I could at find the necessary electronic components and design and manufacture the PCB's, I could now plan the physical format. The original physical design
stands out through its use of contrasting lights, switches and knobs - and of course the awesome matrix switches, which I am afraid I cannot hope to replicate.
- The original modules were 200mm high and usually 75mm wide. I will be using a height of 4U
(180mm) and a width of 90mm. This provides less space for the panel layout as the jacks needed to be accomodated as well.
- The aluminium front panel designs are similar to the original, but I have ommitted the boxes and
lines, and gone for the Eu Systems minimal appearance to keep costs down. Black lettering is etched into the 3mm thick panels.
- Four cabinets are planned, built in MDF and painted light blue. Each cabinet can hold up to 10 modules within a 19" racking system.
- The matrix patching system is too expensive to clone, and it gave cross talk problems anyway.
The AM4000 is a traditionally patched modular synthesizer using high quality 3.5mm jack sockets and some firmware wiring internally.
- The PCB's are mounted to the front panel using ECO pot brackets, the original edge connectors have been dispensed with.
- An Oakley MIDI interface has been added, so the beast can be controlled.
- The modules use three types of knobs;
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29mm diameter skirted knob for VCO and VCF frequency coarse adjustment
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19mm diameter skirted knob for fine adjustments and where there is more
panel space
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13mm diameter knob for general use and where panel space is limited
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ARP used a larger variety of knobs, and you can still get the original coloured small knobs, but they are expensive.
- Pots - they are Spectrol 248 series with 3.18mm shafts to fit the control knobs.
- Switches are either minature "round" toggle switches, the same large push buttons or small black plastic slide switches.
- Lights - 5mm LED's mounted in round plastic LED holders (Clip Lites).
- The Power Supply is +/-15V.
- 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.
Planned Modules The AM 4000 has the following ARP 2500 module clones:
- AM4003 - Single VCO (audio and LFO ranges)
- AM4004 - Dual ADSR
- AM4005 - Ring Modulator and VCA
- AM4006 - "Moog" 24dB transistor ladder LPF
- AM4012 - ARP 2600 "Moog" 24dB transistor ladder filter
- AM4016 - Dual analog noise source
- AM4023 - ARP Odyssey Mark 1 12dB filter
- AM4033 - Dual DADSR
- AM4035 - ARP Odyssey Mark 2 "Moog" 24dB transistor ladder filter
- AM4036 - Single Sample and Hold
- AM4075 - ARP Odyssey Mark 3 - 24dB filter
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Site Options
ARP Resources
* 1036 Module (154KB)
