AM4000 Series Analog Synthesizer Modules
Inspired by the ARP 2500, 2600 and Odyssey Synthesizers

Overview The AM4000 Series Modules are replicas of some of the cicruits within the ARP 2500, 2600 and Odyssey analog synthesziers that was manufactured in the USA by ARP from 1970 - 1979. The ARP 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 and cheaper designs have their origins in the ARP 2500.

The Electronics Cloning a set of 30 year old analog circuits is NOT easy, but in the case of ARP 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. The digital TTL chips in the 1027/1050 sequencer and analog switch modules are more difficult and have been replicated using microcontroller technology.

The 1970 designs have been upgraded with modern components. So the the Op Amps have been replaced with ultra stable versions for CV circuits, and fast and clear Op Amps for the audio circuits. Resistors are metal film 1% versions, and capacitors have  been replaced with modern WIMA components and 1% polystyrene filter capacitors are used throughout. Overall these upgrades make an auible improvement on the sound of the syntheszier modules.

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 6" high and 3", 6 or 12" wide. I will be using a height of 4U and a width of 90mm. This provides more space for the panel layout and enables the modules to be rack mounted.
• The front panels are made out of blank PCB's, spray painted with car aryclics and lettering is laser printed onto Safmat. They aren't replacas of the originals.
• The cabinet is built in MDF and painted light blue. Each cabinet holds 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 module using high quality 3.5mm jack sockets and some firmware wiring internally.
• The PCB's are mounted to the front panel using pot brackets, the original edge connectors have been dispensed with.
• An Oakley MIDI interface has been added, so the beast can be controlled.
• Pots - they 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 black plastic slide switches.
• Lights - 3mm LED's mounted in chrome LED holders.
• The Power Supply is 1.5A +/-15V.
• The power bus structure is based around one Oakley Dizzy PCB's in each cabinet. These distribute +/-15V, ground and screen ground as well as two separate CV/gate buses.

The following AM modules are available as PCB kits:

• AM4016 - Noise source
• AM4023 - 12db LPFModulator
• AM4075 - 24dB LPF

R&D

The AM 4000 series may be expanded in the future to include:

• AM4003 - VCO (
• AM4005 - Dual ADSR
• AM4006 - 24db LPF
• AM4012 - 24dB LPF
• AM4035 - Moog LPF
• AM4036 - S&H