Arp 2500 - 1003, 1033, 1046 envelope generators

The ARP 2500 has a variety of envelope generators.
The 1003, 1033 & 1046 share common features.

The 1003 is identical to the 1033 except that it contains no gate delay circuits.
The 1046 is equivalent in function to a 1003 plus a 1033

EG's are used to produce repeatable transient control signals.
They can be used to control volume (in the case of a VCA) or timbre (VCO or filter) with respect to time.

A unique feature of all these envelope generators is their use of both gates & triggers.

 These gate and trigger inputs are connected to the gate & trigger inputs of the keyboard
All ARP keyboards have 51 notes.

This is a 3001 - a one-voice 5 octave keyboard

It produces 3 types of Control Voltages:
1. Trigger - a short transient 10V pulse which occurs whenever a key is depressed.
2. Gate - a switched 10V signal indicating that a key is depressed.
3. Output - a control voltage whose amplitude is related to the lowest key being depressed.

The two voice keyboards have an additional output:
 4. Aux - an additional CV proportional to the interval between the lowest &
     highest key depressed if 2 or more keys are depressed simultaneously.

The trigger & gate voltages are typically used to control envelope generators.
The Output & Aux voltages are used to control oscillators , filters & amplifiers.

Envelope Shapes

Envelope shapes are very similar to a modern ADSR

ATTACK
When a gate signal is applied, the EG's output will rise exponentially to 10V
(the rate is determined by the "attack" setting).

DECAY
When 10V is reached, the attack phase is ended, and the voltage will decay exponentially to the Sustain level. (the rate is determined by the "initial decay time" setting). In modern synths, we just call this the "decay".

SUSTAIN
The sustain level is adjustable from zero to 10V
The output remains at the sustain level until the gate is removed.

RELEASE
When the gate is removed, the voltage drops to zero volts.
This is called the "Final Decay Time".
The rate of the drop is exponential and is determined by the "Final Decay Time" setting.

If the gate signal is suddenly removed, the envelope will immediately start to decay to zero unless
another gate is imputed. In this case the envelope will then restart the attack phase.


Trigger Modes

There are 2 trigger modes: Single vs Multiple.

When the Trigger modes switch is in the "single" position, only Gate voltages are needed.
When the Trigger modes switch is in the "multiple" position, both Gate & trigger inputs are required for the envelope to fire. The attack is initiated by a positive pulse at the trig input. But the envelope will only fire is there is a gate signal also present when the trigger occurs.
The presence of a gate signal or a trigger signal alone will not start the envelope.

Connections for a sustain pedal can be made via jacks at the back of the module.
This terminal, when connected to ground through a switch, acts like the sustain pedal on a piano.

1046 Quad EG (rear sustain pedal inputs)

Notice, there is also an inverted envelope output
This is zero to -10V
This output is only available at the lower matrix switch.

Electrical specs of the 1003 envelope generator:

Controls
Attack time: 0.001 secs to 2.0 secs
Initial Decay: 0.001 secs to 2.0 secs
Sustain: 0 to 10 Volts
Final Decay: 0.001 secs to 2.0 secs

Inputs:
Gate sensitivity: 1.8V in the lower matrix switch
                        9.6V in the upper matrix switch
Trigger sensitivity:  1.8 volts
All impedances are 100K

Outputs:
0 to +10V @ 1K
0 to -10V @ 1K

 Power requirements:
+/- 15 volts @ 50ma , regulated to +/-0.1%
The lamps require +12V to +15V # 40ma.