SoulSonic FX Hunny Bunny

Here's another design by Martin from Soul Sonic FX. Here's what he had to say about it over on FreeStompboxes:

It's a cool little hybrid combo of an opamp driving a MOSFET. It has a great range of drive, from light and crunchy to thick and heavy. At it's highest settings, some people might consider it a distortion, I guess it just depends on how hot your pickups are. You can see some fun tricks used in this circuit; subtle things that give it the special charm it has. 

Electro Harmonix Muff Fuzzes

Around the same time that the EHX Big Muff was first released in 1969, Mike Matthews also released the Muff Fuzz. It was unrelated to the BMP other than the name, and came in the same small enclosure as the LPB-1 that plugged straight into the guitar. Later it was re-released in a floor pedal as the Little Muff Pi and more recently as the Muff Overdrive. In the mid-70s, the circuit was updated, moving away from the Fuzz Face based transistor circuit to a design based around the popular JRC4558 op-amp. I've laid out both versions below and both should fit in a 1590a.

Mad Professor Sky Blue Overdrive

Here's another BJF designed circuit: the Sky Blue Overdrive. There are 4 controls: Z adjusts input impedance, Distort. controls gain, Texture adjusts the hard clipping, and finally the Volume. It uses 3mm LEDs in the feedback loop of the opamp, and then JFETs for hard clipping.

Catalinbread Katzenkönig

Here's a new one from Catalinbread for #fuzzfriday. The Katzenkönig–the cat king for those of you who don't sprechen sie Deutsch–is a silicon tonebender-type fuzz with some RAT features thrown in. Catalinbread was kind enough to publish the schematic in the manual for this effect. Pots can all be board mounted using right angle PCB pots mounted from the solder-side of the board. The exact transistors used in this effects weren't published in the manual schematic, but lower gain NPN silicons should do the trick. Socket and experiment with your favorites.

Edit Oct. 14: Original transistors are BC550B, in the 300-400 hfe range. 2N3904s will work well also.

Lovepedal Englishman

Here's the Lovepedal Englishman. It's claimed to sound like a cranked Vox (either AC15 or AC30 depending on which clipping diodes are selected). Like many of Lovepedal's offerings, this circuit is built around a single transistor. Unlike many of Lovepedal's offerings, it's not based off the Electra Distortion. Instead, it draws from the EHX LPB-1 booster with switchable diodes at the output.

BearFoot FX Sea Blue EQ

Here's a cool EQ/booster from Bjorn Juhl. If pushed hard, it will break up much like a tube EQ would, and adds warmth and clarity to your tone. It uses 2 JFETs and a James style tone stack.

SoulSonic FX Stage Overdrive

Here's a cool overdrive circuit designed by Martin from SoulSonic FX. It's said to be a "Klon Killer," so if you've been disappointed by that circuit, give this one a go. Signal goes through a buffer then is split between clean out put and the rest of the effect. So not a true-bypass effect, but having a buffer in your signal chain won't kill you. And the buffer on this thing is really top notch. For switching use one side of a DPDT for the effect, and the other for the LED indicator. For more info and the schematic, check out the thread on FSB.