Dan Armstrong Red Ranger

Here's a classic circuit from Dan Armstrong–the Red Ranger. It's a booster with a switch for boosting treble, full range, or bass. Original units didn't have a volume control, but it could easily be added to the output.

Heavy Darling Fuzz

Found this one over on DIYSB and thought it'd be a good Fuzz Friday layout. It was designed by Dragonfly for the old FX-X contests. Here's what he had to say about it:

The Heavy Darling is a SIMPLE fuzztone that cleans up great, has old school character, and good sustain...pretty much ANYONE who can solder should be able to build this one. It uses a MPSA13 Darlington transistor in the 1st stage that pushes the 2N3904 into full saturation. The 220k resistor limits the amount of saturation, and you could certainly experiment with values here. A pot could also be used to give some variable gain, and you could even set up the pot in a similar manner to the Orpheum, Fuzzrite, and Shin-Ei style fuzzes.

Red Llama + BMP tone stack

I drew this up last month on a whim, built it and it actually sounds pretty good. It's just a Red Llama with a Big Muff tone stack tacked on to the end. Ripe for tweaking to your own taste, especially with the values of the tone section. I changed the values to give boosted mids, but those are easily changed (consult google for different tone stack values), and I used 47n caps instead of 68n and 33n that are normally in a Red Llama (only because I have a ton of that value in my parts stash haha).

Electro-Harmonix OD Glove

Here's the Glove from EHX's nano series. Essentially, it's an OCD with a switchable charge pump. On originals the voltage switch is internal, but external makes more sense to me, so wire that to your preference. Here's the schematic for reference.

Skreddy Top Fuel

For Fuzz Friday, here's another fantastic Big Muff variation from Skreddy–the Top Fuel. It replaces the input stage with a MOSFET-based stage, and uses an interesting diode array for the 2 clipping stages. There's also a fabricated version of this layout in the store here.

Black Cat OD-1

This one's pretty simple, but is really versatile going from light overdrive to fuzz levels of gain. Originals use an OP275, but other dual op amps can be used (1458, 4558, TL072, etc.). It's should be a nice fit in a 1590a.

Catalinbread Naga Viper

Here's a versatile boost from Catalinbread. It has its roots in the classic Rangemaster treble booster, but with a silicon transistor, the Range pot varying the input capacitance, and the Heat pot controlling some of the gain. Check out the thread on FSB for discussion, schematic, etc. This is laid out for board mounted pots with the board mounted vertically.