The Grump - Bass Fuzz

Current Stock:

HEY YOU KIDS, GET OFF MY LAWN! The Grump Bass Fuzz is so grumpy that it has five knobs, just to be a pain about it.

Note: I may be able to send out one of these immediately, but usually I'll need anywhere from three to five days to assemble and test one. See the 'Ordering' page on the website for details.

Another note: The Grump does come with an external power jack, even though the unit in one of the photos above doesn't have one.

Yet another nother note: The Grump comes with one red knob and four black ones, not all black knobs like in the videos. The red knob makes it sound much better. Heh heh.

MrExcane demonstrates The Grump. See the 'Video' tab for more.


The Grump has five, count 'em, five knobs:

Input Turning this knob clockwise will attenuate the input signal, which can be useful for basses with active pickups or if the signal strength has already been bumped up by, say, a boost or a compressor or something.

Gain Sets the amount of gain, which in turn sets the amount of fuzziness, somewhere between "old combo amp that's been sitting in the garage for fifteen years " and "grotesque."

Bright Sets the high-frequency response, independently from Tone. With the Gain knob turned down, the effect of this knob will be less noticeable.

Tone Clockwise: more highs, less lows. Counterclockwise: more lows, less highs. 

Vol Controls, you guessed it, output volume. The Grump is shipped with this knob turned all the way down, because the output can be rather loud compared to the original signal.

The clipping is symmetrical, which means that the positive and negative duty cycles of the square wave are roughly equal. Traditional fuzz is asymmetrical, but I call this "fuzz" because it has a cloudy, squishy quality rather than the sharp, focused tone of traditional distortion.

The Grump doesn't use op amps - the clipping and distortion come from medium-gain JFETs and a pair of diodes.


If you're wondering, the little blue trimpot on the circuit board biases the transistor right next to it (lower left in the photo of the circuit board). Before a Grump unit ships, its little blue trimpot is set by Igor so that the voltage at the two measuring points, marked BX and BY, is about 5.1-5.3 Volts. In general, that's the "sweet spot" for the best tonal response and smoothest clipping. By "sweet spot" I mean where Igor hears the biggest, fattest low-frequency response with the Gain knob turned all the way down.

You can change the value of this trimpot if you want to (by turning the white center part with a screwdriver). You'll find that the sound gets pretty thin or cuts off completely, at extreme values. At ~= 7.5 Volts, you might get more dirt at the cost of less low end.

To set the trimpot back to "factory default", turn the pot until you measure somewhere around 5.1-5.3 Volts at the measuring points. At that position, you should hear strong lows with the Gain knob turned down. Use your ears, too - you might like a slightly different bias.


The Grump features:

  • True bypass switching
  • Hammond enclosure
  • Metal film resistors, 1% tolerance
  • Switchcraft jacks
  • Heat-treated silkscreened graphics

All TH Audio pedals are handbuilt and tested in the United States of America.