Green Citrus

Here's a cool DIY design of a Green (Mutamp) amp emulator. Four JFET stages with a 2-band EQ and a Boost control. Should be a nice easy fit in a 125B with the board mounted pots. Here's the schematic for reference. Sound demo here.

Basic Audio Zippy

The Zippy is a silicon fuzz designed to give that vintage brassy sound. I've laid it out for board mounted pots and it'll fit in a 1590B or a 125B with top mount jacks. In the words of John Lyons...

Early fuzz boxes were designed to emulate the sounds of the saxophone.
The Zippy will allow you to channel your inner Coltrane with very reedy fuzz tones. Saxy and sexy.
At lower settings a nice musical razor blade fuzz sizzle.
Turn it up and it becomes an increasingly sharper toothed saw blade fuzz. It snarls. It spits. It goes from fat and thick to thin and cutting without losing it's signature top end sizzle and low end rumble.
The body control (bass cut) makes it easy to dial in just the right amount of beef. Zipper fuzz tones bloom and softly decay.

MI Audio Boost 'n' Buff V1

The Boost 'n' Buff is a simple little booster that doubles as a buffer when it's turned off (so it's not a true bypass effect). You should be able to squeeze this one in a 1590A. The FSw pads are for the bypass footswitch. If you want to build the second version of the Boost 'n' Buff, add a B20k to the output as a volume control.

Rothwell Love Squeeze

Here's a nice little compressor that should be a fairly easy build. It doesn't have the squish of a DynaComp, but goes for a more subtle compression like the Orange Squeezer. Board mounted pots and an easy fit in a 1590B. Here's the schematic for reference.

BearFoot FX Baby Blue OD

Here's Bjorn's Baby Blue overdrive. Fairly straight forward JFET circuit with hard clipping in the 2nd stage. The clipping diodes in the original are (massive) 2A1200s, but other silicon diodes will work–socket and experiment. The JFETs used in the original aren't confirmed, but I've laid it out for GSD pinout. Pots are board mounted and should fit in a 1590B. More info here.

Also, I've added extra holes on the PCB for the 470nF caps in case you want to use electrolytic capacitors.

Haunting Mids V3

Here a Black Friday Fuzz layout to compete with your Christmas shopping. The Haunting Mids is a one knob variation of a Big Muff. The Sustain control is a trimmer internally and the tone section and recovery stage have been removed. Great one for bass! Should be an easy fit in a 1590B or even a 1590G.

Spaceman Effects Saturn V

Here's the Spaceman Saturn V boost pedal. It's a pretty unique booster and uses depletion mode LND150N3-G MOSFETs. In original units, there are 2 resistors in series going to each drain of the transistors. They essentially create a 4.7k resistor using some really uncommon values. (It appears that the only reason for that is for more interesting guts. And lets be real, Spaceman has some of the best looking pedal guts around.) I've included room for the ferrite beads of the originals to fit on the board (these reduce RF noise) and if you wire the pots off board you can probably fit it in a 1590a. More info and schematic found here.