edited and posted Jan 8th 2018, backdated June 18th 2017
When I was developing the Fat Gett, I used a modified Black Russian Big Muff circuit I had been working on as the fuzz section. Shortly after, I produced a handful of these as individual fuzz pedals.
The original Gett had a few tweaks from the original Black Russian.
- I swapped all transistors for the more readily available 2N5089.
- I changed the first clipping stage to a combination of 1N34A (germanium) and 1N4148 (silicon) diodes.
- I took out the second clipping stage entirely.
- I played with a couple of resistor values too.
These changes made the Gett more open sounding and bassier than a traditional Big Muff. It was also significantly louder. The extra volume and less compressed feel largely came from removing the second clipping stage. It sounded particularly good for detuned guitars, and doomy chords. When you moved to higher single notes it becomes more like a boost or an overdrive than a fuzz.
Since developing the fettle boost which serves a similar function I decided to revisit the circuit recently. I love a good, heavy, gnarly fuzz, you know, like a proper smash your amp doomy fuzz, but this first version didn’t quite tick that box. I plan on making more interesting and experimental stuff, but I feel like a really good solid fuzz is a must, so I went back to breadboard.
I did a lot of reading about various changes people have made to the Big Muff circuit, and tried a few that sounded most suitable. I was aiming for more gain, more fuzz and a bigger more powerful sound.
In the end I made 4 major changes, and 5 more minor ones to get it just right.
Most DIYers said changing Q1 (the first transistor) or Q4 (the last transistor) had the largest effect on the overall sound. So firstly I decided to swap out Q1 and try a few other options. I settled on darlington transistor after a wee bit of re-biasing. This certainly got me a lot closer to what I was after.
The next change was the tone stack. I originally used an AMZ style tone stack with an A250K pot. On paper, this seemed like a good idea, and it was an improvement on an earlier version I’d used (you can read about this in the blog posts about the Fat Gett). The problem with a logarithmic (A) taper pot, which I realised after putting a few together, is that when the pot is rotated halfway, the pot is only at 10% of its resistance, all the action happens after that. For this reason it made more sense to go back to a linear taper to get an even sweep.
I also decided to approach the tone stack in a more logical manner. The Big Muff control allows you to move between a low pass filter and a high pass filter. With that in mind, I thought about what those filters should look like by themselves, rather than just playing with values in the Duncan Amps tone stack calculator. I decided that as these filters would overlap, it would be best to have a small hump around 1 KHz – 3 KHz, to boost the mids a touch. I worked out the values for a 1 KHz high pass filter and a 3 KHz low pass filter and inputted the values into the calculator as a starting point. Like the Fat Gett, I wanted to include a switch to alter the tone curve, providing a bigger mid hump. I played with the initial values until I found something that gave more functionality. In the new tone stack, at mid rotation the response is fairly flat with a slow roll off from about 2 KHz. At around 60% rotation, the response totally levels out with a slight hump from 1 KHz to 3 KHz. With the mids switch on, this hump becomes much more pronounced.
Here are the sweeps, with and without the bulge (mids switch).
The third change was the small addition of a switch to provide the option of LED clippers as a second clipping stage. This is a more subtle change. As the clipping threshold of red LEDs is much higher than silicon diodes, they just clip a wee bit off the top, and don’t compress the fuzz as much as the standard Big Muff clipping section. I decided to call this control ‘fluff’ because it adds a soft fuzziness.
The last change was the most significant. It’s also a secret for the time being, because I don’t think anyone else has discovered it. I’ve certainly never seen it in any of the Big Muff based circuits I’ve studied. It’s really simple, and only involves one component, but this is the ‘dunsh’ function that really sets the Gett apart from other pedals. The dunsh is so strong that you won’t be able to hear the fluff when it’s on!
At this point I’d prefer to keep my secret under wraps. If it gains enough popularity then someone will reverse engineer it anyway. If you’ve put the work in to reverse engineer it, get in contact and I’ll let you know if you’ve cracked it!
At this point I realised I was most of the way there, but when you get playing around, it’s always fun to carry on and see what you can learn. So, I made a few more smaller tweaks, which are as follows,
- I upped the feedback resistor on the second gain stage from 470K to 1M. The theory being that this pushes more signal into the clipping diodes, as well as offering a touch more gain by reducing negative feedback returned to base.
- As a start point I had a 10K resistor to ground from the gain (sustain) pot. The Muff circuit has a 1K resistor as standard. I originally upped the value, to add a bit more gain to the circuit. As the new version has a load more gain, I found that on rotating the gain pot, it went from quite a lot of gain to a bit more gain. I returned to the original 1K value, which made the pot far more functional.
- The third tweak was also due to higher levels of gain. When I was testing it out on the breadboard, I started picking up radio. I added a small cap to ground after the first series resistor on the input, creating a low pass filter. I originally found 330pf to work best (roughly 12 KHz low pass filter), though I may up that value to 390pf (roughly 10 KHz) later, as there’s not much guitar we need after that point.
- I also found that when you lower the volume you lose more of the top end, so I added a capacitor between pins 1 and 2 of the volume pot offering a bypass for the higher frequencies, keeping the roll off more even.
- The last thing, was simply using monolithic ceramic caps throughout, with the exception of two film caps on the tone control. It’s widely reported that monolithic ceramic caps give a grainier sound, in the few side by side tests that I’ve done, I’ve found that I prefer ceramic caps. There are also theories that the materials used play far less a role than the difference in tolerances. I’d be perfectly happy to concede that point after further more scientific testing, but for the time being, the ceramics sound good to me.
Anyway, as far as I’m concerned this is the final version of the Gett, at least for the foreseeable future. It’s exactly what I’d aimed for, and I’ve got my eyes on more interesting designs and experiments.
I am planning on doing a double foot switch version called ‘the Bloody Gett’ which will have a separate foot switch for the dunsh, and a second volume to manage the volume disparity.