The FSM 3 is a 3 band EQ isolator and comes in two versions, the standard (or A version) has pots with centre detent which is OdB and each band is adjustable between +6dB and full kill. The B version has no centre detent, OdB is fully clockwise and fully anti-clockwise is full kill.
Each band (bass/mid/treble) of the EQ uses an 8 pole filter which gives a theoretical roll off of 48dB/Octave, to achieve the required precision when the three bands operate together, the capacitors of the EQ filters are measured by hand and selected to give the best response we can achieve.
The noise floor is below -100dB, on the B version with each of the 3 bands set to full kill the signal disappears into the noise floor which is >-1 OOdB.
There is an EQ bypass switch (front panel push button) which will bypass the EQ section and route the input straight to the output.
There is a sub bass output and its rolloff frequency may be set to one of five frequencies between approximately 70 Hz and 225 Hz.
Alternatively there is a pot may that may be enabled (shown by lit LED on front panel)
which will vary the roll off frequency from 70 Hz - 225 Hz.
The headphone output can be set to monitor input, output or a combination of the two using the two selection buttons on the front panel.
The output level is indicated by a 5 LED level meter on the front panel, also there is a
LED indicator if the input level is clipping.