EH 7811B Stereo Memory Man with Chorus

EH 7811B - Stereo Memory Man - 3 knobs - Red and Black - Chorus Switch - MN3005 - Compander - LED

Above: Trace of EH 7811B with LED and 1983 pots. 1x MN3005 delay chip. See factory schematic below.

This version of the Memory Man appears to be unique in how it uses an "effect cancel" scheme instead of a typical bypass. The footswitch is wired SPST and mutes or unmutes the expander (delay output) side of the NE570/571 (pin 16, rectifier capacitor) with a LED in series to provide some indication as well. Pretty clever.

(The EH 4600 Small Clone also uses a SPST footswitch to light up a LED and activate a FET gate to allow the delay signal to come through.)

Power supply is unique with its 78L15 +15V regulator (TO-92 package) plus -15V zener regulator. Like EH 7810, this Memory Man has a full 30V (+/-15V) power supply.

This also has some actual pseudo-stereo action at the outputs instead of just a "wet/dry" type "stereo."

It appears that "OUTPUT" has the dry and wet summed in-phase (and phase is inverted with respect the actual input signal), while "STEREO OUTPUT" has the dry and wet summed out-of-phase. This idea is as old as the hills. On an old vinyl record, these in-phase and out-of-phase signals correspond to lateral and vertical movement of the stylus. Look up how a stereo turntable works for more info. Also related is the mid-side method of microphone recording. MS is very popular with recording engineers and there's plenty of info out there on the subject.

The original idea is at least as old as Alan Blumlein's 1931 patents on stereophonic recording and reproduction.