Ester Tube Equalizer.
The original runs the signal through a valve on the way in and another on the way out, with the passive equalizer between them. ESTER puts what those valves do when you drive them - the density, the harmonics, the way the sound shifts under a push and takes a moment to come back - into one tube stage in front of the equalizer, like a preamp, faithfully for both tubes the original was historically built with.
That placement is deliberate. With the valve after the EQ, every boost would also drive it harder, and you would be chasing the saturation each time you touched a band. In front, colour and tone become two separate decisions: set the drive once with INPUT TRIM, then equalize freely. The amount of saturation stays where you put it, the curves stay exactly where you set them, and the EQ gets to shape the harmonics too - HIGH CUT can smooth the edge a hard drive adds, LOW CUT can tidy the weight it builds.
The lamp between the channel rows is the stage's own meter, reading the harmonic product actually being generated. SAT takes the whole stage out without disturbing a setting.
Two tubes, two chapters of history
The two tubes ESTER reproduces - 6072A and 6N1P
The cell in the top bar switches the stage between two tubes, voiced separately, and they drive differently. 6072A starts early and thickens gradually across the whole travel of INPUT TRIM. 6N1P stays clean for longer, then breaks up quickly and hits harder in the upper half. Both are matched in loudness, so switching changes the character, not the volume. A fresh instance opens on 6072A.
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