The Super Hard-On's name gets lots of chuckles but the sound it extracts from a fine vintage guitar and amp certainly elicits amazement. The input impedance of this device is 5 million ohms, which means it lets the guitar pickups coast along effortlessly without dampening the high end like a normal pedal or amp. The SHO (as we fondly call it) can boost like crazy too, naturally saturating a vacuum tube amp. The absolute loudest, shiny-ist, cleanest boost with the highest possible headroom... hey, don't blow up that amp!

This pedal will make your guitar "schwing!". It is a clean pre-amp that has such a super high input impedance (>5 Meg) that your signal will be purer than you have ever heard. Also can get VERY loud to give your amp enhanced overdrive and volume. Your guitar will really project in live situations.
One knob :

CRACKLE OKAY : Volume. Negative feedback control like old 60s recording console inputs which crackled when you adjusted them too. So don't think the pot is noisy if it makes noise when you turn it, the crackle is OK.

Zachary wrote : The super hard-on has an input impedance of 5 million ohms and delivers up to 8.5 volts peak-to-peak, making it the loudest box available with a 9V battery. It uses no bipolar, fet, or op-amp devices, but rather a mosfet switch. Try listening to one turned down low with a strat. When it is on, you can clearly hear the pickup "open up" as the load is taken off by the very high input impedance.

Starting 7/98 made with 2 output jacks, slightly higher price. Starting in mid 2002 they now have an LED, and a bit higher price again. They also have a power jack now, so no power plate is needed.

More info on the Super Hard-On