EH 7811 Stereo Memory Man

EH 7811 gave the Memory Man “stereo” output.  How can a mono signal become stereo?  In this case, it’s all about the phase.  The “main output” has both the dry and wet (echo) signals summed “in-phase.”  The “stereo output” has the dry and wet summed “out-of-phase.”  When the two outputs are sent to a pair of speakers placed significantly apart from each other, a pseudo-stereo effect should be heard.

An interesting article about the pseudo stereo effect.

The plain 7811 has an extra 741 op amp that is deleted on the 7811B board.  The plain 7811 also lacks a LED indicator.

The bypass scheme is unusual on the 7811 models.  The footswitch is wired up SPST and works to mute the compander circuit.  This could have been an evolution from the “squelch” function from the EH 1307 / EH 7500 circuits.

This idea was expanded upon to light up a LED at the same time.

See the EH 7811B page.

At this time, I don’t have a record of any 7811A boards.

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.

Schematic

I have not seen a factory schematic for this variation of the Memory Man, but the EH 7811B schematic should be a close enough guide.  I have an example with 1980 pots that I plan to trace at some point to verify this.