SND FB-14 Extended Range Fixed Filter Bank

via this Noisebug auction
"special audio filterbank with coils and discrete class A circuitry

- classic class-A circuit design using coils, which have to be hand-made and thus are costly, but sound just so much better. Only 4 transistors in signal path, 2 of them being selected germanium types, which behave somewhat similar to vacuum tubes.
- 14 bands with 2-pole-filters. Center frequencies are 35, 65, 105, 160, 240, 360, 540, 800, 1200, 1800, 2700, 4000, 7000 and 12000 Hz.
- The choice of the frequencies in (nearly) fifth intervals avoids a false ´tonality´ (that is an unwanted emphasis or attenuation of the same musical tone in different octaves) that can be found on all octave, semi-octave, and one-third-octave filterbanks.
- The control range per band is +/- 20 dB (!). This corresponds to a ratio of 1/100 compared to 1/16 (+/- 12dB) available on almost all other equalizers and filterbanks. So even drastic sound manipulations are possible that normally require two chained EQ´s. The q-factor of the filters gradually increases from 0.7 at +/-10 dB to 6 at +/- 20 dB.
- The individual filters are not decoupled from each other. Thus all kinds of - wanted - phase changes and cancellations occur. Normally this circuit design has the disadvantage of a very non-linear control curve (all relevant changes happen within a few degrees at either end of the pot´s turn). To compensate this, sealed conductive plastic pots with a special curve are used, custom-made for us by ALPS.
- Input gain and output level controls. Input gain can be set from - 20 to +20dB. Due to its special circuitry, overdriving the unit produces much more interesting results than standard rc-filters using op-amps.
- Frequency range 20-50000Hz +/- 1.5dB, Signal-to-noise ratio 90dB.
- 1/4” jacks for input and output. Internal ground-lift for separating chassis and audio ground. A special summing Y-cable can be ordered for connecting stereo sources.
- Bypass (using a sealed relay) through frontpanel push-button and automatically when power is disconnected ("hard-wire bypass").
- 19”, 1 unit, depth (behind frontpanel): 58mm + plugs, external power supply."