AM1028 Sequential Volts

AM1028 Module

Overview I revisited the ARP 2500 in the Spring of 2024 and designed a set of ten “lost modules” that ARP mentioned in 1970 but never manufactured. These Eurorack modules are commercially available from the AMSynths webstore here. The ARP 1028 “Slave” module was announced in  the Tonus August 1970 catalog but never made it into production.

The original ARP design provided three channels of 10x control voltages, the levels being set by the front panel potentiometers or controlled by a 1027 sequencer. The module was probably intended as double width and there were preset cards with trimmers that could be used.

There were probably indicators for each of the eight stages and it looks like ARP used LED’s rather than bulbs in 1971. The 8x steps can be sequenced by the 1027 gate positions via an external RS232 cable at the rear of the modules, and this is typically how the 1028 was used as an expander module where it proves very useful in increasing the sequencer functionality of the ARP 2500.

Eurorack AM1028 Module I revisited the 1028 module in 2024 as part of the “lost ARP 2500 modules” project. There are no ARP schematics for the 1028 but the module uses a similar design approach to the 1027.

The 8HP wide AM1028  has just one column of 8 steps, and control voltage outputs for both 2V and 10V ranges. There are green LED’s mounted in the front panel to indicate step position and the module is connected internally to the Behringer 1027 using a 12-way IDC ribbon cable. There are eight rotary potentiometers for setting the voltages. Multiple AM1028’s can be chained together.

Outcomes Prototypes of the AM1028 were demonstrated at SynthEast 2024 and production versions were release in the summer. The delay enabled real ARP 2500 coloured control knobs to be used, and the design was updated with LED light pipes, ,which give a better colour rendition (and replicate the look of the Behringer 1027).


Copyright AMSynths 2024