TUTORIAL Mini Muffin Fuzz - EHX Muff Fuzz (Opamp Version)


Breadboard Baker
This is a quick and simple build. This is more of a distortion than a fuzz so I don't know why EHX called it a 'fuzz'. Anyways, here is the schematic and link to the build doc. I'm going to go a bit faster than my first few tutorials for 2 reasons. If you've been following the first few tutorials you should have a general understanding of my build process and if not please ask below. The second reason is that there aren't that many components to explain 'this one goes here, that one goes there.' I tried to take better pictures this time to help with that.


7 resistors, 4 capacitors, 2 diodes, a 4558 opamp, and a A100k pot.

Let's get started.

First, let's set up the opamp and complete the power section. Shout out to @fig for showing me a different way to hook up C100 and save some real estate on your board: simply put the filter cap in between the two power rails, longer lead to red. 2 680k resistors act as a voltage divider (one coming from power and the other going to ground. This is common in opamp builds. From this voltage divider C101 goes to ground and 2 jumpers need to go to the opamp: one to pin 5 and the other to pin 3. Pin numbers start at the top left and go CCW. Pin 4 of the opamp to ground and pin 8 gets the full voltage from the power rail (red strip).

Now let's focus on the input section. My input is a yellow jumper from my guitar. From here a 1m resistor goes to ground to help with 'popping' when stepping on a footswitch as well as increase the input impedance. A 10n cap should also be put in the input section too.


Now let's put some more resistors in here (R2, R3, and R4). R2 goes from the 10n cap to pin2 of the opamp. R3 goes from Pin 1 to Pin 2. Note: the relationship in values between R2 and R3 here set the gain of the opamp. More on that later when mods are discussed. R4 will 'link' the 2 opamps in this one chip together and goes from pin 1 (an output) to pin 6 (an input). Right now it's looking a bit messy, but I wanted to show a more compact layout than previous tutorials if you want space to mod this circuit.


Ok. Now the diodes. The schematic calls for 1n34a diodes (germanium). Unfortunately I don't have any in my supply so I chose to use 1n4148s. You may put in whichever diodes you'd like and this would be considered MOD 1 to this circuit (substitution). I chose to put one end of the diodes right into pin 6's row and jumper them back from the other side to pin 7 like so.


2 more hookups and we're done. A 100n capacitor comes out of pin 7 of the opamp. I had to bend the leads a bit to allow the other side of the cap to not go back into the opamp and decided to go south on my board. From here goes the volume pot: pin 3 to the capacitor, pin 1 to ground (not shown in this pic), and pin 2 to output. One more quick jumper from ground on one side of the board to the other and we're done!


Here's a pic of my whole rig right now including my test box. It will be expanded shortly when my tayda order comes in next week. :) Here's a link to my test box build report https://forum.pedalpcb.com/threads/test-box.5092/.

You can also get instructions how to build your own from here. Mine is slightly modified, but the general concept is the same: http://tagboardeffects.blogspot.com/2014/09/test-box-20.html


Let's talk mods for a minute here. Here's another copy of the schematic above:

MOD 1: This was explained above, but you may substitute whichever diodes you'd like for D1 and D2. They all have different characteristics, so experiment til you like it.

MOD 2: When I fired this up I noticed that the sound was a bit too treble-y for my taste. How can you give this circuit some more balls? Change out C1 for a higher value cap. I chose a 100n, but you can use whichever you'd like for your taste.

MOD 3: Remember I mentioned the relationship between R2 and R3? This relationship sets the gain of the opamp. To get a direct, yet tweakable (somewhat oxymoronic) gain stage, simply swap out R3 put in a 500k pot. Lug 1 of the pot to pin 2 of the opamp and Lug 2 of the pot to pin 1. It is common practice to link lugs 2 and 3 together, but you don't have to. We're simply swapping in a variable resistor.

MOD 4: Want even more gain in this circuit? Try putting in a 1m pot instead of the 500k pot. Or if you'd like you can add a resistor or potentiometer in parallel with D1 and D2 greater than 10k. This would make this circuit a 2 gain stage circuit. Too much gain (is that even possible? lol) will make the circuit not sound that great, but experiment all you'd like with the gain mods to see what you like best.

MOD 5: You can have even hard-er clipping (see what I did there?) by moving the diodes from pin 6 to ground. It may be worth your while to put in a relatively small resistor (1k-10k) from pin 7 to the diodes, so you'll have to move the diodes a bit. This resistor will help protect the diodes from burning out.

MOD 6: Even HARDER clipping! Keep the original diodes in place and add an extra set of diodes to ground after pin 7's added resistor.

MOD 7: This circuit is calling for a tone control or tone stack. I will be posting soon a tutorial of the PedalPCB Pedal Block Tone Control which is a very simple Big Muff tone stack. I'm going to be a little lazy since I've already discussed this mod in a separate thread here. Just scroll toward the bottom. You will want to add a low pass filter right after pin 7 or your hard clipping diodes. Here's a link to the cutoff frequency calculator if you're interested http://www.muzique.com/schem/filter.htm
There are many other mods out there (common and/or uncommon), but here are a bunch to get you started.