Circuit description
From
the main foot switch, the signal enters the input buffer. From there it
goes to the Lead Drive. The Main Drive gets its signal from one of two
places, the Lead Drive or directly from the Input Buffer. This is
selected by activating and deactivating the LEAD foot switch. The lead
drive has two controls, a front-panel DRIVE knob and an internal volume
trimmer, which controls the level that gets passed to the Main drive
when Lead is activated. This affects the amount of volume boost in lead
mode, and it also affects how the two drive stages (Lead and Main) stack
together. Standard setting is for a moderate level increase, around
11:00 on the internal blue trimmer. The Main drive has front-panel Gain
and Tone controls. The Tone control is a basic Bass/Treble circuit.
After the Main drive, the signal goes to the Voice circuit. The Voice
circuit is comprised of two static phase shift stages. This idea comes
from the original Foxrox ZIM pedal - these are the first two voice
selections on ZIM's voice selector switch. The Voice switch functions
like a bass boost/cut switch, but there is more going on than that. The
phase shift stages create a musical shift in tone, giving the low
setting a a fat, smooth tone, and the high setting a clear and slightly
resonant quality. The middle setting is the output of the main drive
with no voicing applied. Next is the volume control. The output level
of FR100 is set to be within a reasonable range, unlike some pedals that
are way too loud even with the volume knob barely turned up. A linear
taper pot is used, which makes the typical volume range arrive between
10:00 and 2:00.
FR 100 Daughter Board
FRDB
This board contains all of the overdrive circuitry and part
of the signal switching circuitry.
Blue Trimmer: This
trimmer controls the volume of the lead drive. Lead drive is always
going into the main drive, which further clips the signal and compresses
the dynamic range. Changes in Lead Drive level affect both the drive
characteristics in lead mode and the amount of volume boost. Normal setting is around 11:00.
Signal switching - A solid state relay is used to switch the
Lead Drive in and out of the signal path. The logic circuit that controls the
relay is on the mother board. This approach keeps high-gain signal runs to a
minimum inside the pedal and makes the Lead mode switching silent.
Overdrive circuit - There are two separate overdrives on the
FR 100 daughter board. Dual/double sets of clipping diodes each on each drive maximize
the amount of dynamic headroom and allow hotter signals in the circuit before
clipping. There's a total of 8 clipping diodes. The Main drive has an inverted mid-range feedback circuit that gives
it a clear, natural sound. The Lead drive has a strong mid-range and plenty of
gain, which is amplified when stacked with the Main drive.
People wishing to modify the overdrive circuitry can do so
by downloading the FR 100 DAUGHTER BOARD SCHEMATIC (coming soon).
FRDB circuit boards are available for hard-core experimenters who wish to create their own overdrive.
Plug it into FR 100 and you're in business! Mess the card up? Order another one and you're good as new.
