What is it? I took the Solaris pcb (a deluxe germanium Fuzz Face circuit from Aion FX), and added a few extras, according to my own needs/wants as a guitar player:
A second footswitch for a preset. This allows you to switch between two different fuzz sounds (set with two "Input" knobs, which act like guitar volume knob cleanup when turned down).
A germanium boost. A germanium Rangemaster style boost, modified to be a full range boost rather than a treble booster. It allows you to get some more extreme fuzz sounds, similar to playing a fuzz face through a cranked amp.
An external bias. This alters the character and texture of the fuzz. It’s biased “correctly” at 12 o’ clock, but changing it allows you to get those more gritty or gated sounds.
I used two carefully selected germanium GT402B transistors (reportedly used for the Analogman BART Sun Face), and a germanium GT308V transistor for the boost.
 
Why a preset? Because it’s like two Fuzz Face pedals in one. I’d played (and built) various Fuzz Face style fuzzes, but I’d always felt like I wasn’t using them to their fullest potential. I loved the gritty overdrive sounds, and I loved the huge fuzz sounds. But messing with the guitar’s volume knob in the middle of a song didn’t feel precise or instantaneous enough. The second footswitch solved these problems: Now I can dial in 2 completely different sounds and switch between them.
 
“So many knobs and switches, where do I start?"
Start with the Input and Body controls. These are the most powerful controls, and the most crucial for getting the fuzz sound you want. You can forget all the rest for now (leave them on max, except volume + bias).
I recommend leaving "Fuzz" on max, or near maximum, and controlling the amount of distortion with the "Input" knobs (it’s like turning down your guitar volume knob, which is what all well known FF players have done to get good tones). This is why I added a second Input control. Input B, next to the footswitch. This means you can switch between a big wall of fuzz and a gritty overdrive.
 
Body controls the amount of bass / treble. You can start with it in the middle and adjust it to taste. The Body Switch is a second body control, but just for the blue mode. It has 3 modes. Left is the default/standard position which bypasses the switch and uses the original body knob. Middle = bassy. Right = trebly. Note that the body controls make the most difference at high input settings.
Next, look at Boost and Bias. Boost activates the germanium Rangemaster boost. Bias changes the texture of the fuzz, giving you those more gated or spitting tones. 12 o’ clock is biased “correctly”.
 
Pickup switch should be turned off if the pedal is first in your signal chain, and turned on if the pedal is anywhere else.
This pedal has no battery snap for a 9V battery. I put so much into this enclosure that there’s actually no space for one.
 
Here is the description of the original Solaris, taken from the Aion FX website:
The Solaris Germanium Fuzz is an adaptation of the classic Dallas-Arbiter Fuzz Face circuit from 1966. The Solaris is a “deluxe” version of the Fuzz Face that adds 3 new knobs and a switch for extra flexibility. Added controls include an Input attenuation control (similar to using the volume control on a guitar to control the gain), a Body control to filter the amount of bass that is fed into the circuit, and a Contour control to tweak the midrange emphasis. (If you just want a no-frills Fuzz Face without the extra mods, the Proteus project is a stripped-down version of the Solaris.) There is also a charge pump allowing for -9V operation from a normal +9V supply.
New in [this] version of the Solaris is a switchable pickup simulator at the input. The Fuzz Face was originally designed to connect directly to an electric guitar, and as a result it is notoriously picky about where it’s placed in the signal chain. If it’s fed a low-impedance signal (e.g. if there’s another pedal before it) then it loses much of its character.
The pickup simulator solves this problem by adding a transformer, resistor and capacitor to convert the source signal into the higher impedance that the circuit likes. It was invented by Jack Orman of AMZ and has been used in commercial versions of the Fuzz Face such as the Earthquaker Devices Erupter.
It won’t provide the same interactivity with the guitar’s tone & volume as if the pedal was connected directly to the guitar, but it will allow the circuit itself to retain the tonal character. You should only use it if you want to place the Solaris in a position other than first in your signal chain.
USAGE
The Solaris has five controls and one toggle:
Fuzz controls the amount of gain from the second transistor where the clipping occurs.
Volume is the output volume of the effect.
Contour affects the midrange by varying the changing the Q2 bias.
Input allows you to attenuate the input signal, mimicking the effects of turning down your guitar volume. This way you can get similar volume-knob tones even if the fuzz is not the first effect in your chain. Joe Gagan, who came up with this control, recommends turning the Fuzz knob all the way up and using only this knob for the amount of distortion.
Body is an input capacitor blend, which controls the amount of bass.
Pickup enables or disables the pickup simulator.
 
One more note (from me, not Aion FX): In building this, I used only high quality components. This pedal has been hand made with the greatest care and attention to detail. I take an ongoing interest in my pedals - if you manage to break it, you're welcome to send it back and I'll be happy to repair it, free of charge.