where should i add diodes to this opamp booster to get distortion?

[ljoe1969]

i found this schematic for a clean boost on the web and i built it and i like it.
i would like to change it to add distortion for heavy metal sound. so can i just add a couple of diodes after the output cap and have a distortion unit, or would it take more modification to make it a distortion booster?

http://www.jer00n.nl/2010/07/28/clean-boost-for-guitar-or-bass/#comment-1405

thanks,

joe

[amptramp]

You have a choice here.  You can add diodes in parallel but facing in opposite directions across the output pot from top to ground (not connected to the slider) to give you a sound similar to a DOD 250, which clips the oputput to a fixed level above the threshold or you can put diodes in parallel but facing in the opposite direction across R2.  This will be more like a tube screamer with unity gain for the signal above the clipping threshold.  Either way, you may want to make R1 variable to change the gain which changes the drive to the diodes.

Since clipping adds harmonics, you may want a capacitor across the diodes to keep the clipped signal from sounding too bright.

Additional note: diodes across the output pot will pull a lot of output current from the op amp, so you may need a 1K resistor in series with the output electrolytic cap.

[Mark Hammer]

Don't.  It is a clean booster with a gain of 3.2x.  That will likely push your amp ito clipping a little easier.

If you really want the distortion to come from the pedal, I recommend making a Distortion+, which you'll recognize as being very similar to this circuit.

[ljoe1969]

basically i just want to make this into a headphone amp with distortion.

i gonna keep one clean for the pedal board.

thanks for the replies.

joe

[Mark Hammer]

If yu want a nice little headphone amp with distortion and EQ, this is pretty decent: http://hammer.ampage.org/files/PocketRockit.PDF

[ljoe1969]

i just built it. almost works.

it works for about 30 seconds or so, then it dies. change the opamp, used a socket good thing, works for a few seconds then dies again.

thanks for all the help.

i guess i will build something different.

thanks for the pocket rocket schematic.

joe

[ljoe1969]

got it to work. sounds good to me.

now, what do i need to change to run 2 of these in series from one battery?

one with the distortion added and one without. when i add the diodes for distortion the volume is very low so i need to add another one without the diodes to boost the volume back.

i would like to use a TL072 dual opamp.

ljoe