Roland AS-1 Sustainer

Roland AS-1 Sustainer: This is one of Roland's earliest pedals, before they created the Boss brand name. It combines optical compression with transistor distortion, for a long-sustaining singing tone with minimal dynamics.
 
It actually has a beautiful tone, with lots of bite. The distortion is very natural and light, not over-the-top. There's no loss of highs, but the lows are gutted completely. This sound was meant for lead guitar tones flying over the band mix. Because the dynamics are flattened, it also brings all of your hammer-ons, light strums, and other small notes to the forefront. Surprisingly, it's not all that noisy on its own, but it definitely amplifies any noise that's already in your signal path.
 
It has all the flaws of so many older pedals: it has a tiny circuitboard in a giant cast-metal housing, the bypass switching is a bad tone sucker, it only runs on batteries (two of them), there is no on/off LED or threshold LED, and the jacks are reversed (input on the left). So on the one hand, those are plenty of reasons not to buy it. On the other hand, if you are interested in doing some modding, this pedal is just begging to be your next project. You could easily rehouse the circuit in a much smaller box, with proper switching, LED, and DC jack. Or you could make those improvements inside the existing cool-looking large body, and have plenty of room to add extra circuits, like a clean blend or an EQ. And in all honesty, I like the tone and the effect enough (for what it is) that I do think it would be worth the work.