AM1026 Preset Voltages


ARP 1026 Picture

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 1026 module was announced in  the Tonus August 1970 catalog but only a handful of production modules were produced, so it is very rare.

It provides two channels of 8x control voltages, the levels are set by the front panel potentiometers and either manually gated on/off by the front panel momentary push button or by  external control.

There are indicators for each of the eight stages and it looks like ARP used LED’s rather than bulbs (finally). 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 1026 was used as an expander module where it proves very useful in increasing the sequencer functionality of the ARP 2500.

ARP 1026 Modules

5U AM1026 Module Initially I attempted the 1026 as a 5U module in November 2019, but work was paused by my collaboration with Behringer on their 2500 modules. I had purchased a large lot of 100k PRV6 potentiometers and had enough spare to use in the 1026. To reduce the amount of hand wiring I designed a front panel PCB that could hold the pots and 5mm green LED’s.  A second Logic PCB is attached to the rear with the CMOS logic, manual wiring to the large Switchcraft momentary switches, and the analog voltage output mixers. However the design was never completed.

Eurorack AM1026 Module I revisited the 1026 module in 2024 as part of the “lost ARP 2500 modules” project. There are no ARP schematics for the 1026 but the module uses a similar design approach to the 1027 and 1050.

The 20HP wide AM1026 was re-designed to use the XOR logic of the 1050 modules. This ensures only one step voltage can be manually selected at a time, and there is a clear button to reset all steps to being off.

                           AM1026 Eurorack

The 8 steps can be selected manually or by the position gates or driven sequentially by a B1027 module (when the sequencer input is ENABLED using a push button). Momentary buttons have  green LED’s. The two CV outputs can be set at 2V range (for use with VCO’s) or 10V range for use with filters and VCA’s.

The module has the following front panel controls:

  • 8x Channel 1 CV levels
  • 8x Channel 2 CV levels
  • 8x Momentary Switches

There are 10x 3.5mm jack sockets mounted on the front panel:

  • 8x Position Gate Inputs on the right
  • 2x Control Voltage Outputs at the base

There is a 12-pin IDC socket on the rear of the PCB to connect to a 1027.

 

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