behringer/abacus
Abacus
Analog Music Computer for Eurorack — dual function generator with four channels (Ch1 and Ch4 as full Rise/Fall function generators; Ch2 and Ch3 as attenuverters), voltage processing, logic outputs (OR, SUM, INV), and unity/EOR/EOC outputs.766
Capabilities 3
- Attenuverterattenuverter
- All four channels have attenuverter knobs. Channels 2 and 3 attenuvert externally patched or internally generated voltages. Channels 1 and 4 attenuvert the Rise/Fall processed output.766
- Function Generatorfunction-generator
- Channels 1 and 4 are full Rise/Fall function generators with CV-controllable Rise, Fall, and Both time inputs, Response curve control, Cycle button, and unity/EOR/EOC outputs.766
- Voltage Summervoltage-summer
- SUM and INVERTED SUM outputs provide a mixed and inverted-mixed voltage from all four attenuverter-processed channels. An analog OR output is also provided.766
Jacks 25 — 14 in / 11 out
| Name | Signal | Voltage | Description |
|---|---|---|---|
| Inputs (14) | |||
| CH1 BOTH CV INPUT | cv | -8V to 8V | Exponentially scales total Rise/Fall time for Channel 1. Positive voltages decrease time; negative voltages increase it.766 |
| CH1 CV INPUT | cv | -10V to 10V | Accepts variable voltages in the range +/-10 V for processing by Channel 1. If no voltage is present, uses a self-generated voltage of approximately +10 V.766 |
| CH1 CYCLE TRIGGER | trigger | ≥2.5V | Allows an external positive-going gate or trigger of +2.5 V or more to trigger Channel 1's Cycle function.766 |
| CH1 FALL CV INPUT | cv | -8V to 8V | CV control of Fall time for Channel 1. Positive voltages increase Fall time; negative voltages decrease it.766 |
| CH1 RISE CV INPUT | cv | -8V to 8V | CV control of Rise time for Channel 1. Positive voltages increase Rise time; negative voltages decrease it.766 |
| CH1 TRIGGER INPUT | gate | ≥2.5V | Accepts any positive-going gate or trigger above +2.5 V. Causes the Rise/Fall function to be activated.766 |
| CH2 CV INPUT | cv | -10V to 10V | Accepts voltages in the range +/-10 V for attenuating by the Channel 2 attenuverter knob.766 |
| CH3 CV INPUT | cv | -10V to 10V | Accepts voltages in the range +/-10 V for attenuating by the Channel 3 attenuverter knob.766 |
| CH4 BOTH CV INPUT | cv | -8V to 8V | Exponentially scales total Rise/Fall time for Channel 4. Positive voltages decrease time; negative voltages increase it.766 |
| CH4 CV INPUT | cv | -10V to 10V | Accepts variable voltages in the range +/-10 V for processing by Channel 4. If no voltage is present, uses a self-generated voltage of approximately +10 V.766 |
| CH4 CYCLE TRIGGER | trigger | ≥2.5V | Allows an external positive-going gate or trigger of +2.5 V or more to trigger Channel 4's Cycle function.766 |
| CH4 FALL CV INPUT | cv | -8V to 8V | CV control of Fall time for Channel 4. Positive voltages increase Fall time; negative voltages decrease it.766 |
| CH4 RISE CV INPUT | cv | -8V to 8V | CV control of Rise time for Channel 4. Positive voltages increase Rise time; negative voltages decrease it.766 |
| CH4 TRIGGER INPUT | gate | ≥2.5V | Accepts any positive-going gate or trigger above +2.5 V. Causes the Rise/Fall function to be activated.766 |
| Outputs (11) | |||
| CH1 END OF RISE OUTPUT | gate | ≤9V | Outputs +9 V at the top of the Rise function; remains active until end of Fall cycle.766 |
| CH1 OUTPUT | cv | — | 766 |
| CH1 UNITY OUTPUT | cv | 0V to 10V | Outputs 0–+10 V following Rise/Fall when cycling; otherwise passes channel input unaffected by the attenuverter.766 |
| CH2 OUTPUT | cv | — | 766 |
| CH3 OUTPUT | cv | — | 766 |
| CH4 END OF CYCLE OUTPUT | gate | ≤9V | Outputs +9 V at the end of the Rise/Fall cycle.766 |
| CH4 OUTPUT | cv | — | 766 |
| CH4 UNITY OUTPUT | cv | 0V to 10V | Outputs 0–+10 V following Rise/Fall when cycling; otherwise passes channel input unaffected by the attenuverter.766 |
| INVERTED SUM OUTPUT | cv | — | Outputs the inversion of the SUM output.766 |
| OR OUTPUT | cv | — | Analog OR of the attenuverter-processed voltages from all four channels. Channels 1 and 4 require an external voltage to be included.766 |
| SUM OUTPUT | cv | -10V to 10V | Summed voltage of all four attenuverter-processed channels in the range +/-10 V. Channels 1 and 4 require an external voltage.766 |
Parameters 12
| Name | Type | Range | Behavior |
|---|---|---|---|
| CH1 ATTENUVERTER | knob | — | Attenuates (CW) or inverts (CCW) the output of Channel 1 after Rise/Fall processing. Does not pass internal voltage unless processing is taking place.766 |
| CH1 CYCLE | button | — | Initiates or stops cycling of Channel 1 Rise/Fall. Lit when cycling. Flashes when externally triggered. Internal cycle takes priority over external trigger.766 |
| CH1 FALL TIME | knob | — | Sets the Fall time for Channel 1. Can be modulated by CH1 FALL CV INPUT. Maximum fall time varies by response setting: Log = 25m15s, Lin = 50s, Exp = 5s.766 |
| CH1 RESPONSE | knob | — | 766 |
| CH1 RISE TIME | knob | — | Sets the Rise time for Channel 1. Can be modulated by CH1 RISE CV INPUT. Maximum rise time varies by response setting: Log = 9m0s, Lin = 55s, Exp = 7s.766 |
| CH2 ATTENUVERTER | knob | -10V – 10V | Attenuates (CW) or inverts (CCW) voltages on Channel 2 input or internally generated voltage. Output range -10 V to +10 V.766 |
| CH3 ATTENUVERTER | knob | -5V – 6V | Attenuates (CW) or inverts (CCW) voltages on Channel 3 input or internally generated voltage. Output range -5 V to +6 V.766 |
| CH4 ATTENUVERTER | knob | — | Attenuates (CW) or inverts (CCW) the output of Channel 4 after Rise/Fall processing. Does not pass internal voltage unless processing is taking place.766 |
| CH4 CYCLE | button | — | Initiates or stops cycling of Channel 4 Rise/Fall. Lit when cycling. Flashes when externally triggered. Internal cycle takes priority over external trigger.766 |
| CH4 FALL TIME | knob | — | Sets the Fall time for Channel 4. Can be modulated by CH4 FALL CV INPUT. Maximum fall time varies by response setting: Log = 25m15s, Lin = 50s, Exp = 5s.766 |
| CH4 RESPONSE | knob | — | 766 |
| CH4 RISE TIME | knob | — | Sets the Rise time for Channel 4. Can be modulated by CH4 RISE CV INPUT. Maximum rise time varies by response setting: Log = 9m0s, Lin = 55s, Exp = 7s.766 |
Firmware history 0 versions
No firmware history recorded.
References 1
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[766]
Behringer Abacus Quick Start Guide (official QSG PDF, model 0720-ACO, via mirror)manual● verified 2026-05-22