SRV Special...The SRV Special is a modified Tube Screamer Circuit. Some capacitors and resistors are left, to make the sound more pure. Furthermore 1M or higher is used for the GAIN pot to increase the GAIN range of the pedal.
The pedal is an approach to get closer to Stevie Rays Sound...
The Mods have been invented by JC Maillet in 1997.
Read the whole story here:
SchematicCompared to the original Tube Screamer Circuit, the input capacitor has been increased from 27nF to 10uF (this is also known as Fat input cap Mod).
The 1uF and the 10k resistor before the + input of the first OP amp are gone. Also the 51nF capacitor parallel to the diodes has been removed.
The Gain Pot has been increased to 1M or 2M for more gain.
The 1uF after the output of the second OP amp disappeared, also the cap and the pot before the base of the second transistor.
As Transistors 2SC1815 or 2n5210 are common. I tried also BC549 and couldnt recognize any difference.
As OP amp IC, you can use a classic JRC4558 or also TL072 (more clarity)
My BuildI used a TS808 Kit from uk-electronic.de
When assembling the PCB I used jumpers for the parts that are missing in the SRV special or I just didnt assembled anything.
Exactly I did the following:
-) Omit 51pF capacitor (parallel to the diodes)
-) Replace both 1uF caps with jumpers
-) Replace the input cap (27nF) with a 10uF elecotrolytics (- side points to the input)
-) Omit 10k resistor at the + side of the first OP amp
-) Omit 510k resistor at the base of the second transistor
-) Replace the 100nF cap at the base of the second transistor with a jumper
-) Jumper 100R resistor in series to the output cap
For the enclosure, I used the pre-drilled 808 enclosure from uk-electronic and just placed a label there (OK i was too lazy to design an enclosure there)
DemoHere you find a demo of my Build: