Pumbaa Distortion

[Roscoe]

Build Rating

5.00 star(s)

Hi all. I've built a bunch of stuff over the last few years. Been lurking for a while but decided to start posting some of my more recent builds. There's good inspiration to be had from the Build Reports section, and hopefully I can contribute!

Built the Pumbaa a few months ago. Great distortion, plenty of sounds to be had. The Caliber knob is interesting, but I usually wind up setting it around 11 o'clock and forgetting about it. Oh well. Someday I'll broaden my tonal pallette.

Pretty straight forward build. Had to get creative with a few resistors. Looks like the op amp is scheduled for obsolescence by TI. Enclosure was heavily inspired by the original.

I think chicken head knobs need more love.

 

[dcfvgb]

I think chicken head knobs need more love.

+1

 

[Bret608]

Looks great and yes on the mini chicken heads! I was not aware of this PCB so will have to check it out.

 

[BuddytheReow]

I usually wind up setting it around 11 o'clock and forgetting about it

That's most of my pedals. Set it and forget it!

 

[dot matrix madness]

The requested OPA 604AP Op-amp has got a hefty price tag. Are the 25 V/µs specs a must for this purpose,
or would a TL 071, TL 051, LF 411, or OPA 347 do an "acceptable" job instead?

 

[Roscoe]

The requested OPA 604AP Op-amp has got a hefty price tag. Are the 25 V/µs specs a must for this purpose,
or would a TL 071, TL 051, LF 411, or OPA 347 do an "acceptable" job instead?

My gut would say a crazy slew rate like that is not necessary for this circuit. This is just a real fancy Rat-style pedal. The OPA347 puts you in regular rat territory, but all of those other op-amps you listed will keep the op-amp gain stage from causing slew-limited distortion as effectively as the 604AP (at least I think). The 604 also appears to nominally have a rail-to-rail output swing.

Not sure how noticeable that kind of distortion would be when you consider the clipping distortion caused by the LEDs and hitting the supply rails on the two gain stages. There's always the good old socket and swap method. Differences between most of those op-amps would probably be negligible at best.