Do It Yourself

Get the Most Out of Modding Pedals Part 2: Big Muffs and Rats

  • By Nicholas Kula @tonereport
  • August 27, 2015

In the last installment, I talked about two mods that can be performed on 95 percent of pedals out there—the often-requested “more bass” coupling capacitor replacement and the “bias knob” voltage starvation knob, done three ways. These two simple mods can impact the sounds of your pedals in ridiculously toneful ways and cost under a dollar to implement. In this installment, I will talk about specific pedals and which components have the most impact on the overall sound.

Before I begin, I offer the same disclaimer I offered on the last installment:

Neither I, nor Tone Report Weekly bear any responsibility for any kind of personal or property damage that may occur as a result of the instructions provided herein. Legal mumbo-jumbo aside, we ask that readers be familiar with a soldering iron and its accompanying safety procedures before trying anything listed here. Furthermore, if a pedal worked before trying any mods and it doesn’t anymore, it’s through no fault of these instructions, as I’ve personally performed every mod listed, some several times over.

Big Muff: Emitter Resistors, Coupling Capacitors, Tone Stack

Have you ever stopped and wondered how the Big Muff has about 500 variants from its original manufacturer, and yet it’s still one of the most fun circuits to dissect and rebuild? The short answer: There’s so much going on in the circuit, and slight changes to certain values have massive effects on the sound. In particular, the biggest impact on the sound is found by swapping out only a few components. The Pete Cornish G2 is one of the definitive ultra-boutique overdrives, and it is even based on a Big Muff circuit. That’s right, messing with some of the components in a run-of-the-mill Big Muff can result in such an overhaul that overdrive occurs.

So yes, emitter resistors. The four little black things with three legs on a standard Muff circuit board are called transistors. These three legs correspond to three parts of a transistor: emitter, base and collector. That said, emitter resistors are those resistors that run from the transistors’ emitters straight to ground. On a stock Big Muff, transistor 1’s (herein referred to as “Qx”) emitter resistor is 100 ohms (brown-black-brown bands), and both Q2 and Q3’s emitter resistors are 390 ohms (orange-white-brown bands), and Q4’s emitter resistor is 2k (red-black-red bands). Decreasing all of these values leads to much more gain (be careful with Q4, though). In fact, one of the first-ever boutique Muff clones, the Sustain Punch Creamy Dreamer, omitted these resistors entirely and tied Q1–Q3’s emitters straight to ground for maximum gain.

Remember when I said “more bass” is achieved by upping the input and output capacitors? Well, that is still true, but Big Muffs have quite a few coupling capacitors in order to keep bass amounts level throughout. The Big Muff has six of them. On a current-issue Big Muff, these capacitors are all 1μF non-polarized (meaning there is no defined positive or negative leg) film capacitors. Luckily, there are only eight such caps in the pedal. The two capacitors that aren’t coupling caps can be identified by what its legs lead to; one leg should lead to the diode pair, the other should lead to a 470pf cap, a 470k resistor (yellow-purple-yellow bands), a 100k resistor (brown-black-yellow bands) to ground, and the base (center leg) of Q2 and Q3. These are DC blocking caps that set the frequency range to be clipped, and that’s a whole other story. In general, these will always be the capacitors touching the diodes with one leg and the transistor base with the other, regardless of which Muff type you’re working with. The thunderously bassy early-model triangle Muffs used huge 3μF coupling caps and the sound is as bassy as one would expect. Many doom players rely on the Black Arts Pharaoh to bring the brutal; the input and output caps on that pedal are a robust 10μF.

Thirdly, there’s one property of Muffs that everyone can agree on: Where’s the mids? Muffs typically have a scooped sound, but it’s actually very simple to “add mids” back in to the mix, so to speak. Placed between lug three of the Tone control and Q3’s collector (looking at the transistor from the top down, the collector is on the top when the curved part is facing left). Usually, this value is somewhere around 0.0033—0.004μF. Swapping it out for something bigger (try 0.01μF) results in a big mid push.

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  1. Paul Bowes

    “Take a look at the following diagram of a single-channel op-amp.” Ummm…where?