"The SBEQ is an EQ Booster pedal, with some light distortion capability. EQ range is set in between that of most amps tone controls so as to make a good sound better.You can adjust the ranges that are unable to adjust with the amplifiers tone controls, you can both boost or cut the special high-end and low-end with SBEQ. It is meant to be used at the end of effects chain to fine-tune the sound and in this gives control over frequency ranges hard to control on most amps- the in between bands. It has a light ceiling-effect to the upper high treble so as not to boost the treble too much. In this it was tuned to some of the popular brighter amps. SBEQ can be used by itself as an EQ or booster to give a distorted edge to your tone as well as to overdrive an amp input. While boosting the distortion comes progressively rather than having a sharp overload point and point of noticeable overload and it distorts later up than conventional EQ pedals.
SBEQs main goal is to fine-tune response and in this have lower distortion than conventional Graphic EQ pedals especially lower phase distortion. It is also designed to be used with piezoelectric guitars and give control over ice-pick treble and general boominess. It can be used also on bass without losses but is mainly tuned for guitar. It can do boost and cut in mids, treble or bass or be used as just boost or damping."
Here's a demo video so you can see what it can do:
This one was purchased by the Tracers Fund at freestompboxes.org with a view to finding out what was inside, the schematic is drawn up by WhiteKeyHole:
JFETs are unknown but 2N5458 or 2N5452 bias to correct voltages.
As you can see it's a "James" style eq setup between a couple of Jfet gain stages. You could use opamps for the gain stage but you'd need to ensure that the output impedance driving the eq stage remains the same as any difference will alter the response of the tone section...
Here's a vero layout:
Here's the discussion on the freestompboxes.org: http://freestompboxes.org/viewtopic.php?f=7&t=13259