The Megalith Delta high gain distortion pedal design came from years of R&D of our MI Amplification high gain amplifier, the Megalith Beta. It took some time for me to really understand the variables behind great high gain tones. But by designing the amplifier from the ground up, I was able to really grasp how to make a complex, sophisticated high gain sound that kept all the nuances, huge bottom end and the clarity and character of the top end.
The Megalith Delta pedal is a solid state 'model' of the Beta preamp, using JFETs to simulate the gain stages of the preamp valves. The transfer characteristics of FETs are very tube-like, so it seemed that this was a great place to start.
This, of course, is not something revolutionary. A quick peruse of the pedal market and various DIY sites will reveal various FET renditions of valve circuits. However, digging a little deeper shows somewhat limited implementations of these circuits. Often, it's just the exact same circuit as the 'simulated' amp, but with FETs instead of tubes, adjusted source or drain resistances, and 9V operation. Little or no thought it given to the operating points, dynamic range, scaling of clipping thresholds, output impedances, and intrinsic capacitances due to things like the miller effect etc.
As you can see, making a FET stage behave like a particular tube stage is actually a very complex affair. One thing which differentiates our endeavour from others' is the fact that the amplifier in question is our own. I designed every single aspect of the Megalith Beta, and have insights into its working you can't get by simply looking at the schematic. I know what I wanted every tube stage to do, the logic behind each stage design,... even things like the effect of track and cable capacitance. Because of this, I was able to feed all these parameters into the design, and come up with something which is as close as humanly possible to the original.
Now the controls,...
The GAIN control offers a wide sweep in gain, from low-mid gain rock tones, to serious crunch, to every dark shade of brutal imaginable.
The three-band EQ and EQ SHIFT are taken straight from the amp as well. The EQ SHIFT allows three different voicings by shifting the response of the tone stack.
One of the challenges of doing the Megalith in a pedal format was how to integrate the CONTOUR control into the design. The CONTOUR control, which changes the response of the phase inverter, is what really gives the Megalith amp its flexibility. If you want a loose, fatter, vintage high gain sound - turn up the CONTOUR. If you are after a more modern, tighter and cutting high gain tone - turn down the CONTOUR. So in order to mimic this response, I designed a phase-inverter like stage, and integrated the CONTOUR control into it. The combinations of the EQ section will give an impressive number of high gain sounds, just like the Megalith Beta amplifier.
A BOOST mode was added to the pedal as the amplifier really steps up going from "mid" gain mode to "high" gain mode. I thought by adding this as a foot switch, it gives you the option to really step up the crazy. I also figured that mid to high switching was a lot more useful than low to high, as there are already plenty of great options out there for the lower gain sounds. Lets face it, someone interested in the Megalith isn't going to be too stressed about missing the low gain mode!
A big part of the Megalith Beta amplifier's huge gain sound is the 160 Watts of headroom! Of course, this would always be the limitation in trying to emulate a high gain amplifier to stomp box form. But by adding voltage doubling circuitry in the Megalith Delta pedal, it allows the 9V supplied by battery, or DC adaptor, to be increased to 18V within the pedal's circuitry. This has the advantage of producing the crushing low end without mush, much like the 160W output of the Megalith Beta does at the amp level.
Now, the biggest challenge was working out how to fit it all into a case, and keep it stable. For those of you who haven't strapped yourselves in for a Megalith ride,... let me tell you, it's one seriously high gain amp. It's the only amp I'm aware of that doesn't need to be driven with a pedal to get a super-tight saturated gain tone. So packing all that gain into a modest pedal enclosure is not only challenging in terms of layout (there are 110 components in the circuit), but also in terms of stability. After a few failed attempts, I moved to a 4 layer layout, with top and bottom ground planes for shielding. This also necessitated a few circuit tweaks to take into account the extra capacitance to ground.
Finally, I designed an output section which is designed to 'compensate' for the standard guitar amp's clean channel response, so that when you plug the Megalith pedal into a 'reference' clean amp, you get something close to the feel of the Megalith Beta. Having said that, one of the main aspects of the Megalith Beta's 'presence' is the sheer headroom and output power it has. So no, you probably won't unleash carnage and devastation plugging a Megalith Delta into a 5W lunch-box amp. That's just the physics of it,... a reality more inviolable than the existence of fragile harmonics in a crystal lattice.
I feel that, although it may sound cliché, the Megalith Delta high gain pedal is unlike any high gain pedal out there. It came off the back of a complex amplifier design in the Megalith Beta, that already pushes the standard in metal amplifier tones. By emulating the preamp of the Beta, it truly captures the essence of the amp with response and character retained.
Below is a quick demo of the finalised design. It goes quickly from clean, to crunch, to the heaviest of metal tones in under two minutes.