The Fat Gett (2) – Sorting the tone stack and other issues

In part 3 you’ll see why I came back to messing about with Muffs. But for now let’s just go over how I got things righter this time.

I started with the stock Black Russian values. I even tried using the original BC549C and C547C trannies, but they just lacked the punch that I wanted, so I went with 2N5089s. I remembered to take out the second clipping stage, and did a little work biasing the transistors. The collector voltage seemed a little high so I got them closer to 4.5V. I should add that the instruction PDF on the Fuzzdog multimuff kit is absolutely spot on. It gives all the values you need for pretty much every Big Muff you can imagine. His PCBs and kits are top notch. Highly recommended, he’s a proper sound lad to boot.

Of course I couldn’t get it quite right, and I forgot about the pap tone stack I’d put in the original, you’ll see in video below. I also put those wrong values in Project 1B (coming soonish). Only when it was complete, and turning the knobs did very little did I realise that it was definitely duff. I’ll sort that soon enough (but that’s not soon enough! ). You’ll probably see a post on how to desolder when I go back to it and put the right bits in.Here’s the sweep from that original tone stack.

mids switch off
mids switch on

Since that slight oversight I remembered that AMZ has a really good big Muff tone stack that I should have used. I adopted version 2 of the AMZ tone stack with two slight tweaks, I used a 330K resistor instead of a 470K to maintain a bit more bass. Instead of using a 25K body pot in parallel to the 3K3 resistor I use the 12K/27K/SPDT combo from the original, which was the only part worth keeping from the original tonestack I had. Having said that I may well swap back to a B25K pot in the future depending on how I feel. Here’s how the sweep of the new, improved tone stack looks.

mids switch off
mids switch on

You can see straight away that this one has the capability of cutting more bottom end, whilst retaining more treble. Anyway here’s the vid comparing the two. sorry.


Next time I go back to tinker with the tone stack calculator, I’ll definitely bear in mind that you can choose the taper of the pots as well, and that’s going to have a sizeable effect on the tone curves it generates. **see notes below**

If you’re not familiar with the different tapers of pots here is an image I borrowed from Kitrae’s Big Muff Page to illustrate the difference between a linear taper ‘B’ pot, and a logarithmic/audio taper ‘A’ pot.


The taper basically equates to how much you turn the pot and how much resistance there is between legs.

a B100K and an A100K pot will have the same resistance at extremes (0 and 100K), but the way we get from 0 to 100K differs due to the taper. Why the different pots? Basically because of the way we hear things. Our ears are very strange instruments and we hear loudness increases logarithmically. That’s why we generally use A pots (audio) for volume and gain. Ever had an amp or pedal where 0 to 1 is very quiet, then as soon as you get to between 1 and 2 it’s rather loud? That’s because they didn’t use an A pot. Be aware that there is a third type called C, which is reverse log. They are also used but less common.

If you want to learn more about pots, this is an excellent article from Geofex, there’s no point trying to rehash it and ballsing it up. Plenty more great articles on there too.


**I’ve left this post as is, but there’s actually a couple of errors here, which I realised after doing my first run of Fat Getts. I’ve left my mistakes in here, because I made them at the time. I was so busy at the time working on getting Champion Leccy and this website set up that I didn’t consider a couple of rather simple things I should have spotted at the time. See Fat Gett (7) for updated, accurate info on the Big Muff tone stack  **


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