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STUTTER TREMOLO BUILD
INSTRUCTIONS
By FF_Pedals 2011
Layout by Culturejam 2011
There are two ways to build this effect. The JFET can be
used in series or shunt. The board was designed for series
connection (original youtube demo). I tried modding it for a
shunt connection and it sounds even better (signal based
noise occurs in series mode as signal builds charge on C2). I
will give the instructions for the shunt version. I highly
recommend you build it like this. It sounds very good. See
Appendix for original schematic and bill of materials. In the
shunt version you do not need a switch for smooth mode,
just a 100kB pot. You will also need a 1M resistor, 2 x 47k
and a 330k resistor (compared to original BOM). Follow
these instructions carefully. This is a SQUARE WAVE
tremolo, make sure you twist all your offboard wiring for
best noise performance.
How it works:
Q4 is the LFO from the EA Tremolo. Q5 is a BJT inverter that
creates a square wave. R15, R21 and the “Cycle” pot set the
DC bias on the base of Q5 which adjust the threshold voltage
of the inverter to vary the duty cycle (off/on time of pulses).
Q1 is an amplifier with a pre-gain cut volume pot. You could
increase the gain by decreasing R4. You could eliminate the
pre-gain volume and put a volume on the output (R23) if
you prefer. R5, R6 and C3 set the signal ground and DC bias
for the JFET. Q3 is an output buffer. In shunt mode the
JFET dumps the signal between C2 and C4 to the signal
ground (4.5V DC) through the low impedance path to
ground of C3. When the depth pot is cranked (0 ohms) it is
in full stutter mode. Increasing the resistance between the
JFET source and the signal ground increases the “off”
volume and gives a smoother more normal sounding trem,
even though it is hard switching between two volumes. By
adjusting the duty cycle in smooth mode some great trem
sounds can be made. Compared to series mode, in shunt
mode there is a little signal bleed through during the “off”
cycle which is combated by adding in the 100k resistor in
series with C2.
SHUNT Schematic:
There are MANY ways to mod this effect. These values are
just my suggestions to get you going. Experiment and have
fun.
Parts list:
C1 100n
C2 100n
C3 100u
C4 10n
C5 39n
C6 100n
C7 100u
C8 100u
C9 1u
C10 1u
C11 1u
C12 10u
CYCLE 1M B (linear)
D1 1N914 or 1N4148
D2 4001 or other 1N400x
D3 LED Standard red diffused
Q1 2N3904
Q2 J201
Q3 2N3904
Q4 2N5088
Q5 2N3904
R1 1M
R2 470K
R3 10K
R4 2K7
R5 47k
R6 47k
R7 1M
R8 100k B Depth pot
R9 1M
R10 1M
R11 1M
R12 10K
R13 100R
R14 10K
R15 1M
R16 10K
R17 2M2
R18 100K
R19 1K
R20 15K
R21 330K
R23 1M
RATE 100K C Rev. log
VOL 500K A log
Shunt Build Instructions (highly suggested)
1. Locate the trace from the bottom of C4 to the source
(middle pin) of the JFET. Cut it with a utility blade
right under R11 so it’s hidden. Should be very easy.
Check with multimeter to make sure you have broken
the connection:
2. Install all of the resistors and diodes EXCEPT R8 and
R22. Put a 100k resistor standing up where the switch
SW1 was supposed to go. (ignore my 330k resistor
standing up, I had to use a 1/2W...)
3. Install C2 from the top hole of C2 to the left hole where
R22 was supposed to go. Make sure the lead does not
short against the bottom hole of C2. Steps 2 and 3 let us
install that 100k resistor between C2 and the JFET
drain...
4. Install C4 but DO NOT CLIP THE LOWER LEAD. Bend
the lower lead of C4 towards the drain of the JFET (top
hole) do not solder it to anything yet.
5. Install the rest of the caps.
6. Put the JFET in and wrap that lower lead of C4 around
the drain before soldering.
7. Solder in the transistors or transistor sockets,
whatever you feel comfortable with.
8. Wire the pots, they are all variable resistors and you
can just use lugs 2 and 3 if you want, they are all the
same configuration. The depth pot goes where R8 was.
Twist the wires and put them in where R8 was
supposed to go, the order does not matter. Wire the
volume, and rate to the appropriate holes (Volume 2
and 3, Rate 2 and 3...). In shunt mode the duty cycle
works backwards so you have to connect lug 3 where
lug 1 was supposed to go.
9. Install the LED on the board.
10. Do your offboard wiring, available online
elsewhere. For a bypass indicator, solder a current
limiting resistor and length of wire to the longer leg of
an LED and heat-shrink it. Solder a length of lead to the
shorter end of the LED and heat-shrink. Connect the
side with the resistor to the 9V lug of the DC jack
(center lug) and the other lead goes to the 3PDT (see
offboard wiring diagrams online).
Here’s how I drilled and built my Stutter Trem:
Appendix
Original schematic. JFET is used in series. Small signal based
charge builds on C2 and gives a little bit of ticking. Not
always noticeable but annoying when it happens.
Original Bill Of Materials:
-Enclosure
-3PDT stomp switch
-SPST toggle (Smooth mode)
-DC Jack
-9V Battery clip
-9V Battery
-1 1/4" Stereo Jack
-1 1/4" Mono Jack
-1 Red diffused LED (Rate indicator)
-1 LED of your choice with appropriate resistor (Bypass indicator)
-1 1N914 or 1N4148 Diode
-1 1N4001 or equivalent 1N400x series Diode
-2 1M B Linear Potentiometer (one for optional smooth depth control)
-1 500k A Log Potentiometer
-1 100k C Reverse Log Potentiometer (50k C optional faster speed)
-1 2N5088 BJT Transistor
-3 2N3904 BJT Transistor
-1 J201 JFET Transistor
RESISTORS:
-1 100ohm
-1 1kohm
-1 2.7kohm
-1 4.7kohm (optional faster speed mod)
-4 10kohm
-1 15kohm
-3 100kohm
-3 470kohm
-6 1Mohm
-3 2.2Mohm (2 of these were changed to 47kohms R5 and R6)
CAPACITORS:
-1 0.039uF (0.033uF could be substituted)
-1 0.01uF
-3 0.1uF
-3 1uF 16V Electrolytic Radial
-1 10uF 16V Electrolytic Radial
-3 100uF 16V Electrolytic Radial