George Mattson’s description:
The Quad AD/ASR Envelope Generator consists of 4 identical channels. This is designed as a utility module for basic Envelope utilization. Each channel has an Attack and Decay user control. There is a 4x dip switch on board for user selection of independent channel EG function. (AD or ASR mode) AD Mode: When a gate is present at the channel input, the Attack stage is initiated, self completes, transfers to the Decay stage and drops at the Decay rate to 0 output level. The cycle won’t repeat until the gate is dropped and re-applied. ASR mode: When a gate is present at the channel input, The Attack stage is initiated, self completes and the output sustains at full output until the gate is dropped. When the gate is dropped, The Decay (as a Release) stage is initiated and the output drops to 0 at the decay rate. Gate Input: The Gate inputs are for a 5-15V gate input to initiate the envelope sequence. The gate inputs are cascaded. A gate input applied to channel 1 will initiate the Attack stage of all four envelope generators. A gate input patched into a different channel will interrupt the cascade and apply the new gate voltage on the selected and all subsequent channels. Attack: Adjusts the Attack time from minimum to maximum time. (Specs TBD) Decay: Adjusts the Decay (or Release in ASR mode)time from minimum to maximum time. (Specs TBD) Output: Envelope CV output. 0-5V Requires wire kit WK-16A if desired.
Download the Front Panel Express Panel for Mattson Quad EG
This is another small-knob MOTM style panel, using the jack-grid spacing. For this module I located the pots at the top and jacks at the bottom. An alternative would have been to put the pots down the left side with jacks to the right, clustering the knobs for each generator next to the corresponding jacks. Either approach has its benefits. Locating all the jacks at the bottom separates patch cords from knobs. But then the side-by-side knobs are darned close together for fingers.
The description above applies to an earlier version of the board. George later modified the circuit to trigger at about 2.5V and this is the version I have. It works nicely with many gate sources. There remains one oddity that a negative voltage, below about -1.5V also triggers the envelope.
As noted in George’s description, the PC board has four DIP switches to allow selection of Attack-Decay vs. Attack-Sustain-Release function. The DIP switch was in a socket. I removed the switch and plugged in an 8-pin header with wires going to switches on the backs of the Decay pots. (The Alpha pots with pull switches came from Small Bear electronics.) Here’s a photo of the assembly. The DIP header is in the middle to the right.
The pull switch on the pot is wired so that with the knob IN the AD mode is selected, and when OUT the ASR mode is selected. This photo shows two knobs pulled out. In practice this feels nice and works well.