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 Gates and Triggers, Mystery Solved
 
The goal of this page is to squash the confusion over Gates and Triggers. Let the squashing begin!

In the Beginning,
Dr. Bob Moog's modular systems used a signal called "Trigger" to identify when a key on the keyboard was pressed and released. Of course, this signal could also be generated by other sources such as sequencers, foot pedals, drum controllers, etc. Triggers are used to start envelope generators, sequencers, etc, and are a critical function in any synthesizer system. Moog systems use 2 types of Triggers: Voltage Triggers (AKA V-Trig) and Switch Triggers (AKA S-Trig, sometimes called Shorting Trigger).

Voltage Triggers
V-Trig signals are patched using normal 1/4" plugs and jacks, and are approximately 3 volts when ON and 0 volts (Ground) when off. V-Trigs in a Moog modular are created by the 960 Sequential Controller (90% duty cycle) and by the 961 interface that can convert S-Trigs to V-Trigs. V-Trigs are the same as what we call a 'Gate' today. Gate signals allows for easier, more intutive patching and eliminate conversion.
 
Switch Triggers
S-Trig signals use a special 2-pin blade-type connector made by Cinch/Jones. Basically, an S-Trig is simply the signal being shorted to ground. This can be accomplished by a circuit, or by a passive (no power required) device such as a mechanical foot switch or push button. Moog keyboards produce S-Trigs and Moog 911 Envelope Generators use them to control their cycle. The one advantage to S-Trigs is that many source signals can be connected in parallel to create a logical OR (any signal makes it through). The disadvantage is that the S-Trig must go through a conversion module to interface to modules requiring a V-Trig (Gate).

Today,
Virtually all synthesizers use 'Gates' which are essentially V-Trigs. Usually Gate voltages are +5 volts or more. Usually they have a positive polarity, but not always, and some synthesizers have a switch to select polarity.

Yet Another Type of Trigger
To confuse matters worse, some systems have a signal called 'Trigger' that is neither a Gate (V-Trig) or a S-Trig, but instead is a short pulse that happens only at the initiation of a keypress. Some envelope generators can accept this type of trigger to RE-Trigger it before the envelope cycle completes.

Converting to Switch Triggers
You won't need to convert between S-Trig and V-Trig (Gates) unless you're using older Moog-style systems, because most modern equipment uses Gates. If you need to, here's how.

This special cable converts Gate signals from a Synthesizers.com system to Switch Trigger signals needed to activate Moog envelope generators. It has a male 1/4" plug on one end and a 2-pin Cinch/Jones plug on the other. Here's the circuit if you want to make your own.

To convert from a Moog Switch Trigger to a voltage gate needed by Synthesizers.com modules, you'll need to run the Moog Switch Trigger signal through the Moog 961 module to create a voltage. You can also use the Q142 Pedal Interface which will convert any mechanical switch to a voltage level. You'll have to construct a special cable. You can build a simple circuit to do this also. The reason that a simple cable is not available to make this conversion is because a voltage source is needed.

Summary - Gates and Triggers in a nutshell
Here are the main things to know.

  • Gates are on/off signals, usually from a keyboard controller to indicate a keypress.
  • Voltage-Triggers are the same as V-Trigs are the same as Gates, and are normally a positive voltage around 3-5 volts.
  • Almost all modern synthesizers use positive Gates.
  • Switch-Triggers are the same as S-Trigs, and are switch-to-ground signals - not used much any more.



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