Electro Harmonix Signal Pad

Bought this unit to act as a 'boost' for my valve amp. I really like the sound of my amp but didn't want to chain together effects or spoil the tone I'm already getting. Another guitarist who gigs regularly introduced me to using a unit like this. The principle is that you set your amp to the loudest setting you need for your solo then use the pad to reduce the overall level to your crunch /clean volume. You click the pedal on to reduce the volume and click it off to raise it to solo level. The pedal doesn't need a battery or PSU so it can't fail on you mid-gig.
This means that you can effectively use your amp alone to give you your desired tone without having shedloads of effects in the chain.
I recommend you give this a try for yourself, I doubt you'll be disappointed.

This pedal is nothing more that a variable resistor that can be bypassed via the foot-switch.

The power supply is just for powering the ON/OFF LED indicator - the pedal works without power. However, that does annoy me a little bit because there are mechanical solutions that would do this job, even in the dark. I get that an LED circuit is probably cheaper to make if you're buying those parts in bulk anyway, but it still greaves me a little that EH chose to do this. The reason I got this pedal is because I'm front loading a 5151 overdrive with a Unit67 boost, and wanted to be able to replicate the overdrive's output attenuation when it was off. Now I have the overdrive's output attenuation at unity gain and this Signal Pad pedal does the real attenuation. This allows me to keep the boost engaged when the overdrive is off without overloading amp simulator I have later in the signal chain.

It's a pretty inexpensive addition to my pedal with lots of tonal benefit.