AM1026 Preset Voltages

ARP 1026 Picture

Overview 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 indicator maps 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 or 1050 clocks 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

AM1026 Module There are no ARP schematics for the 1026 but the module uses a similar design approach to the 1027 and 1050. The momentary push buttons latch a flip flop which then activates the step position and drives the control potentiometers via transistor buffers. I have used HEF4013 chips which although obsolete in THD have internal Schmitt triggers, which make for perfect switch debouncing.

The 0 – 10V external sequence inputs from the AM1027 are buffered by two 4050 non inverting buffers, which then upscale the 10V to 15V pulses and drive the step position transistors via a digital OR circuit with the panel switch latches, and the external Position Gate input jacks. The gate positions act as triggers to the HEF4013 chips, and a trigger will hold the step value until a second pulse is received. The lamps are green 5mm LED’s in lens, driven directly by the CMOS logic, to reduce the power consumption of using bulbs.

ARP 1026 Brochure

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 at the base of the front panel:

  • 8x Position Gate Inputs
  • 2x Control Voltage Outputs

There is a 10 pin DIL socket on the rear PCB to connect to a 1027 or 1050 module. The analog circuits use 15V power, whilst the digital uses 10V power.

Build Outcomes I played around with the 1026 idea in Spring 2017 and laid out the PCB’s in the Spring and Autumn of 2019. 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.

The PCB’s were ordered on 5 November 2019 and the panel arrived at the same time.

2024 Update A range of Eurorack 2500 modules were developed by AMSynths in the Spring of 2024 using SMD components. The AM1026 has not been included yet. The AM1028 Sequential Volts adds a single row of 8 stepped CV’s, and the AM1029 Ratchet adds precise timing CV’s to enable ratching on the B1027. More details are here.


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