Please help with simple Amplifier circuit modifications

[timeisthefourthdemension]

Hello,
I am trying to cut out the distortion channel on a fender frontman 15, and and also add an insert FX between the Preamp and Power amp. http://www.thetubestore.com/lib/thetubestore/schematics/Fender/Fender-Frontman-15G-Schematic.pdf

With the help of this, http://www.diystompboxes.com/smfforum/index.php?topic=3102.msg18257#msg18257 , I believe to have done the first by removing R7 and R25.

For the second task, should I place the insert point before or after R38? Or somewhere else? What is the role of R38?

Thank you,
Rodrigo

[PRR]

Q1 against R38 appears to provide a power-off mute.

Between U3A and R38 may work OK.

As general best practice, signals sent outside or brought back into the box "should" have series resistor and capacitor to protect from ugly loads and stray DC.

I don't see why you have to snip R7 R25. Can't you just jam a toothpick in the switch?

[timeisthefourthdemension]

thanks,
reason I am not using the tooth pick approach is that I am going to use the switch for something else I plan to add to the circuit, a tremolo effect.

could you give me some insight on where to look for  theory on how to calculate  the value of the R and C I should use for the out  and  in?

thanks

[mth5044]

I don't know about theory, but you could look at a couple of amps with the function you want and swipe it!