I combined the Mattson Envelope Generator and VCA modules into one panel. Here is George Mattson’s description of the Envelope Generator:
ADSR transient generator with independent control of the Attack, Decay, Sustain and Release stages of the envelope.
Output is a varying control voltage from 0-5V.
Repeat switch. Allows for automatic repeat of the envelope sequence.
Repeat Level. Allows for selection of the envelope output level where the repeat function will re-trigger.
Man gate pushbutton allows for manually triggering the envelope.
And his description of the Voltage Controlled Amplifier:
Audio In jack for injecting audio signals into the amplifier.
Manual level allows for setting the master gain cell level manually. This allows any audio signal present to “bleed” through the amplifier output. This control comes in handy for checking the audio signal or using for continuous “drones”.
Master CV In Jack for inputting the main gain control voltage signal. Primarily, an Envelope Generator is patched into this jack, but other CVs can be used here for variable gain control of the VCA output. This input responds to a 0-5VDC control voltage which controls the master gain. No output will be present at 0V unless the manual level adjustment has been set above minimum.
Mod in jack allows for modulation sources to be input into the VCA.
Mod amt control allows for variable control of the amount the CV effects the VCA. As the control is rotated clockwise, the modulation goes from amplitude modulation through ring modulation then, back through amplitude modulation. This modulation affects the audio input signal, not the master gain.
Output level control allows for overall output level adjustment.
Main output jack provided for sending the VCA output to another module, an amplifier or headphones. The jack is a TRS jack and will source both sides of a set of headphones in dual mono.
I made the following minor modifications:
- Instead of an output level control, I have a CV input attenuator pot. This is nothing more than putting a pot in front of the master CV input jack.
- Soldered a resistor on the back of the VCA board, acting like the output level pot turned all the way up.
- The VCA output is a normal jack, not a stereo jack.
- The output of the EG is patched to the switch lug of the VCA CV input jack as the normal path.
The Front Panel Express Panel uses the MOTM-jack grid design I’ve standardized on for my own miniature MOTM format.
Download custom FPE panel
As with my other Mattson conversion projects, I used a Bridechamber 3-jack bracket, combined with an adapter that I fabricated out of thin aluminum stock. The adapter is needed because the Mattson PC board mounting holes are a bit too widely spaced to mount on the Bridechamber bracket. In this case I also needed a bit more depth to get clearance for the jacks in front.
I used the convenient wire kits from Mattson. Notice the power cable between the two boards. George made them shorter than usual, just for this application. The MOTM 4-pin MTA power connector on the rear supplies power to the whole module.
Both the EG and the VCA sport special features. The repeat function on the EG is controlled by the Repeat switch, which disables the external Gate and manual push-button inputs and re-triggers the envelope at a point adjustable by the repeat level pot. A quick trial run shows that audio rate re-triggering is possible by setting a short release and increasing the repeat level. The EG can be an oscillator! With repeat off, the Gate input and manual button both function, with a logical OR relationship.
The VCA is a high-quality AC-coupled, linear design with initial offset and CV attenuation (with my panel change). The cool, unusual feature is the “modulation” input for audio-rate ring modulation effects.
The EG and VCA are completely separate and independent modules, other than the connection of the EG out to the CV in to save a patch cord for the most-common usage scenario. This fits my goal of putting more functionality in a small panel space perfectly! Yes, I built TWO of these.