Vox V830 Distortion Booster

Yes. It is big. I've omitted the complex power supply, but left most of the noise reduction measures in tact. Transistor controlled LED circuitry is also gone. With dual gang gain pot and the board size, this will be a tricky but doable fit in 1590B.

Marketing spiel from ten years ago:
Attention: Guitarist who want the fattest distortion. 
Classic distortion, warm tone and high gain. The V830 delivers distortion that goes from 'just enough" to blistering. And its VOX, all analog circuit ensures that your guitar's sound is always warm and natural - no matter what level of distortion you dial in.

Versatile, to fit your style and the way you want to play.
Whether you're into low string riffs on an axe tuned down to D, or paint peeling high notes, the V830's unique design gives you great distortion without losing it's edge and becoming muddy. Even power chords never loose their harmony. The VOX Distortion Booster, for guitar with an attitude!

Three controls - that's all you need. 
The Distortion Booster's DRIVE, LEVEL and TONE knobs give you all the control you need to get the tone you want. It couldn't be any faster or easier to get the sound you need. And, VOX's true-bypass switching ensures that your direct sound is unaltered when you hit the footswitch and bypass the pedal's circuitry.