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Mod 5: Install a Variable Mid Control in Your TS9 or SD-1
Tools and Parts for This Mod
• Two 10k Ω 1/4-watt resistors
• .0068 μF capacitor
• .0047 μF capacitor
• .033 μF capacitor
• B100k Ω alpha single-gang 9 mm right-angle PC mount linear potentiometer from SmallBearElec.com
• Pot knob
• Three 3" pieces of wire
• 1/4" drill bit
• Marking utensil
Our final mod gives you control over the nasally mids that have long plagued the Tube Screamer and Super Overdrive. Be aware, though, that you’ll lose quite a bit of volume with this mod due to insertion loss. To make up for this volume loss, I recommend you also either replace the original diodes with LEDs or wire the original diodes in series (neither of which is covered here).
Fig. 7: Reference schematic for the TS9 and SD-1 variable-mid-control mod.
1. TS9: Remove resistor R8.
SD-1: Remove resistor R7.
Photo 22 (left): Remove R8 in your Tube Screamer. Photo 23 (right): Remove R7 in your Super Overdrive.
2. Twist one leg from each of the two 10k Ω resistors together so that their bodies are almost touching.
3. Wrap one end of a 3" piece of wire around the connected resistor legs, solder the joint (see Photo 24), and put electrical tape or a heat-shrink tube around the joint (not shown).
Photo 24 (left): Twist together your 10k Ω resistors and one end of a jumper wire, then solder the joint. Photo 25 (right): Solder your .0068 µF cap to the 10k Ω resistors and attach a jumper to one of the resistors.
4. Twist the legs of your .0068 μF cap onto the long legs of the joined 10k Ω resistors and solder the joint, then twist the end of another 3" wire onto the long leg of one the 10k Ω resistors and solder that connection. See Photo 25.
5. TS9: Place the long leg of the
resistor that has the 3" jumper in
the hole from R8 closest to the
dot (pin 1) on the IC chip. Place
the other resistor’s leg in the hole
vacated by R8. Solder the legs in
place. See Photo 26 and Photo
22, if necessary.
SD-1: Place the long leg of the resistor that has the 3" jumper in the vacated R7 hole that is closest to the IC chip. Place the other resistor’s leg in the other vacant R7 hole. Solder the legs in place. See Photo 27.
Photo 26 (left): Install the 10k Ω resistor with the 3" jumper in your Tube Screamer. Photo 27 (right): Install the 10k Ω resistor with the 3" jumper in your Super Overdrive.
6. Solder your .033 μF cap to lug 1 of your B100k Ω pot, then solder the last piece of 3" wire to lug 2 of your pot, and then solder the .0047 μF cap to lug 3 of the pot. See Photo 28.
Photo 28 (left): Solder the .033 µF cap, a 3" wire, and the .0047 µF cap to the new pot. Photo 29 (right): Solder the wire from pot lug 2 to the diode near your Tube Screamer’s power jack.
7. Solder the wire attached between the two 10k Ω resistors to the remaining leg of the .033 μF cap that’s soldered to lug 1 of the pot.
8. Solder the remaining wire attached to the long leg of the 10k Ω resistor to the remaining leg of the .0047 μF cap that’s soldered to lug 3 of the pot.
9. TS9: Solder the 3" wire connected to lug 2 of your pot to the leg opposite the stripe of the diode located right next to the power jack (see Photo 29). Test the pedal and be sure that your modifications worked.
Photo 30 (left): Solder the wire from pot lug 2 to the sleeve of your Super Overdrive’s 1/4" output. Photo 31 (right): Measure and mark the drill hole for your TS9’s new pot.
10. TS9: Measure 5-6 mm
(about 1/4") from the upwardly
angled part of the case and
draw a horizontal line from the
right side of the case to about
where the tone knob is.
SD-1: Measure 1 cm to the right or left of the edge of the 9V adapter jack on the front of the case. Draw a vertical line there.
11. TS9: Draw a vertical
line starting smack dab in the
middle of the volume pot’s hole
until it intersects with the line
you just drew. This will be the
center of the hole for your new
pot (see Photo 31).
SD-1: Draw a horizontal line 1 cm above the bottom of the case until it intersects with the vertical line. This will be the center of the hole for your new pot (see Photo 32).
Photo 32 (left): Measure and mark the drill hole for your SD-1’s new pot. Photo 33 (right): Make sure the pot lugs face the top of your Super Overdrive enclosure to avoid shorting the circuit.
12. Drill a 1/4"-diameter hole in the marked spots.
13. Wipe the lines off of the enclosure, secure the new pot, reassemble the pedal, and enjoy your new variable-mid control! Note: On the SD-1, be sure to install your pot so that the lugs face the top of the case so they don’t get grounded to the back plate (see Photo 33).