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  • Valves in Guitar Pedals

    by Guest Author April 01, 2021 4 min read

    Valves in Guitar Pedals | Boost Guitar Pedals

    Duncan MacKinnon, founder of Stompnorth Pedals, knows a thing or two about valves (AKA tubes) in guitar pedals. Below, he dives into how they work and why we love them...

    My introduction to building guitar pedals was a Build Your Own Clone – ESV Fuzz. The ESV stood for Extra Special Vintage on account of its Phillips Ac127/01 germanium transistors. Its sound is amazing and is indeed as old school as its name suggests, but I wanted to take "vintage" even further, so I started looking for valve kits and soon found a booster that used a single 12ax7 valve.

    I loved the way it sounded and the response it gave, so I knew that valves were the way I wanted to go with my own projects. As a synth player first and foremost, I was used to manipulating waveforms and textures, but even from this hi-tech perspective I still found vintage hollow-state circuitry [i.e valves] offered more pleasing sounds and possibilities than the more modern solid-state, transistor and op-amp driven circuits - which, of course, are also tremendous.

    The sensitivity and flexibility of a valve is, in my opinion, unrivalled in guitar pedal building where subtlety, response, transparency and sound quality (not necessarily fidelity) are the aim. A valve in low voltage "starved plate" mode offers a certain type of response and transparency which is different to the more full-on high voltage valve circuits. You can max-out a 12au7 pedal and still know which guitar you are playing. I also think they have a really pleasing and unique sound all of their own. This is the reason I designed one of my own pedals around a 12au7 running 9 volts.

    Stompnorth Clipshear Getter Drive

    The Stompnorth Clipshear Getter Drive combines a 12au7 valve with a MOSFET transistor and silicon and germanium clipping diodes.

    How a Valve Works

    A valve can be thought of as a glass tube, with an anode (plate) at the top, and a cathode at the bottom. Electricity in a valve flows in the opposite direction to the accepted norm of positive to negative, and it does so in a wash of electrons called space charge; this is the bit I love the most! When you turn a valve on, the cathode has to warm up, and then space charge is produced. This flows from the cathode to the plate through a vacuum. Not carried by radio, or wire of any kind, but literally floating through space, a tiny bit of outer space, (with flying saucers and ray guns), right there in your pedal.

    Your guitar signal enters through another internal component, the grid, which sits in between the plate and cathode. When a signal with positive potential enters the grid it gets caught up in, amplified by, and carried in the flow of space charge all the way to the plate, then on into your amplifier in an awesome shower of tone-bearing electrons.

    Another fascinating thing about valves is their sheer theatre. They are huge in comparison to other components - you can see the internal workings through the glass. Also, each one is slightly different inside. The getter flash (silver cap) is another brilliant factor of valves. The science is fascinating and they look great, but this subject is best saved for another occasion.


    In short, I think valves are magnificent, eloquent, and beautiful pieces of engineering that have un-reinventable qualities, which I think is why they are still so commonplace in guitar gear (and high end audio gear) today. They were not replaced by the transistor as we were told they would be - valves are here to stay.

    Shop Stompnorth Pedals

    The Stompnorth Midgie Booster Overdrive is built around a MOSFET transistor, known for their amp-like feel and here offering 21dB of boost. With selectable silicon or germanium diode clipping, this is a serious workhorse pedal getting you from boosted cleans to vintage crunch. The Midgie Booster Overdrive is handwired point-to-point and features high quality components, including Alpha pots and the large Jupiter capacitor which takes pride of place. This is a superb, super-stackable pedal which works really well in tandem with other pedals. Oh, and the power indicator glows to showcase several of the finest Inner Hebrides midges, personally collected by Stompnorth founder, Duncan!

    The bass-tuned Stompnorth Bass Midgie Overdrive is in similar tonal territory to the Electro-Harmonix Bass Muff - but that's where the similarities end. Its handwired point-to-point circuit is built around a single Darlington transistor and symmetrical silicon diodes. This is a great pedal to enhance your bass tone and get it growling. Use the toggle to switch between silicon diode clipping and "Fauzz" (faux fuzz derived from transistor feedback) to get your preferred flavour of drive tone. The power indicator features several Inner Hebrides midges, personally collected by Stompnorth founder, Duncan! They won't bite, but this pedal will.

    Stompnorth's Fishmoth Vintage Fuzztoner is based on the classic silicon Fuzz Face circuit popularised by artists such as Jimi Hendrix and David Gilmour. Built around low-noise, sweet-sounding foil capacitors, this very useable fuzz takes the Fuzz Face circuit and beefs it up with some very welcome extra features. The A/B toggle not only switches between brighter and livelier, and mellow "vintage" frequency response; it also alters the dynamics of the entire pedal. The Bias control enables you to adjust the response of the BC108 silicon transistors, providing access to a range of fuzz tones plus a gated, dying battery character. Turned all the way down, you get bucket-loads of bass and thick, wooly fuzz. Turned all the way up is glitchy and spitty.

    Stompnorth's flagship Clipshear Getter Drive combines two separate boost/overdrive circuits with optional silicon and germanium clipping diodes to achieve a multitude of low to mid-gain tones. Stompnorth founder Duncan MacKinnon designed the Clipshear Getter Drive to be an integral part of your rig, an "always on" pedal that enhances your core tone. It provides up to 17dB of clean boost that can push the input of your valve amp. The first circuit is a MOSFET transistor which gives amp-like response and overdrive characteristics. On its own it provides clean boost through to mild crunch. The MOSFET feeds into the 12AU7 valve circuit, which has a warmer, sweeter character and gets into full overdrive territory. The clipping diodes are the final section of the pedal and add distortion to the signal if engaged.


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