ARP-2600 - Trigger and gate inputs

The vast majority of synths made today have two primary types of control voltages : 

CVs and gates. 

The CV is for pitch & gates are used to fire envelopes.

Most Eurorack modules output a 1V/oct pitch voltage, and a +5V gate. 

Korg and old Yamahas use Hz but that's another story.

When I first bought my 2600 , I exclusively used the S/H gate

jack as my gate input.

This mostly worked as long as I had a +10V gate.

And if you had installed a gate booster you could boost those

pesky Eurorack +5v voltages to keep the ARP happy.

For about 10 years I mostly ignored those two jacks next

to the S/H Gate thinking they were just outputs from the keyboard

since the arrows pointed out.

Actually, they are inputs !!

After a bit of research I learnt that the old ARP 2600 (& ARP2500)  use an almost 

forgotten system of triggering envelopes.

They use both triggers & gates.

How does this work?

The ADSR is as you'd expect.

The "trigger" is the envelope's cue to start the ball rolling but it wont do anything

unless it also sees a gate.

Here is a common Envelope Shape and how triggers & gates determine the final shape 

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 inputed. In this case the envelope will then restart the attack phase.

This system of gates & triggers makes very complex envelopes possible 

If you don't have a sequencer with both triggers and gates

you can "trick" the 2600 by plugging into both the trigger & gate jacks the same gate signal.

I've tried this with a Arturia keystep and it works fine.

Another option is to set two VCOs into LFO mode.

I like to use a pulse for the gate, and a saw for the trigger.

It works too !

Links:

+ Arp 2500 - 1003, 1033, 1046 envelope generators

+ ARP 2600 - Envelope Generators

+ ARP 2600 - Sample and hold (& electronic switch)

+ ARP 2600 - Ring Modulator

+ Arp 2600 - Envelope Follower & pre-amp

+ ARP 2600 - Voltage processor

+ ARP 2600 - Filter