“The DOD Envelope Filter 440 is a band pass filter that can be swept across a portion of the audio range producing a wah-wah like effect without having to use your foot. The sensitivity control compensates for different instrument input levels and adjusts the level at which the filter begins to sweep.”
“The range control adjusts the lowest frequency that the filter settles back to as the input signal decays. If the sensitivity control is turned counter clockwise, the range control can manually adjust the filter frequency, like putting a wah pedal in a fixed position for tone coloration.”
“A mini jack has been included for power adapter operation and disconnects the battery when in use. A well filtered 8-10 volt, negative ground power supply is recommended. Battery drain is 1.5 mA.”
Versions of the 440 Envelope Filter (subject to revision and further validation):
- 1977: Red version, wires soldered to circuit board, components facing up. This version may have been manufactured into the very early 1980s;
- 1979: Green version, wires soldered to circuit board, components facing up;
- 1981: Blue version (week 1-12), wires soldered to circuit board, components facing up;
- 1996: Green reissue with printed circuit board, wires connected with a pin connector, components facing down.