Extensive compressor reviews and FAQ

Morley (Tel-Ray) VCO: This is a vintage gem from the early days of classic rock. It's a giant shiny chrome-plated volume pedal combined with a compressor. I have to admit I am predisposed to love this thing just because it looks so cool.
It uses an optical element for the treadle control, instead of a gear or pulley like many other wah/volume-type pedals. This means it is not subject to the same type of mechanical wear-and-tear as those others, and it will never get the scratchy sound of a dirty/worn pot. There is an on/off toggle switch for the whole thing, but there is no separate bypass for the volume control--when the unit is switched on, the volume pedal is always engaged. And it's an active device, so your signal is buffered whether the compressor part is switched on or not. The volume control is great: smooth and with a useful, natural sweep. The only problem is the treadle's pivot position relative to your instep makes it painful to do fast tremolo-like sweeps. But it's good for slow swells and fadeouts.
The compressor part is not optical, it is an OTA using a CA3080 chip like the Ross/Dynacomp family. However I've been told that the circuit is closer to one of Electro-Harmonix's older designs, and not a copy of the Ross/Dynacomp circuit. It only has two knobs: one that increases the level of your signal going into a fixed threshold (this controls the amount of compression), and the other is make-up gain. The preset attack and release times are both a lot faster than the Ross/Dyna types have, so it has a very smooth note attack and then it lets go quickly. The fast release, combined with the high noise floor, means it "pumps and breathes" quite a bit. There is a footswitch for dis/engaging the compressor, but it's not really a bypass exactly.
The bad news is that the compressor is very noisy, very hissy. However it's about 30 years old, so I suspect that replacing and upgrading the 5 electrolytic capacitors, 3 chips, and 3 transistors would cut the noise down dramatically. I didn't end up doing this myself, as I have too many projects already, but it seems worth doing if you have the inclination. The good news is that the tone is fantastic! Warm, clear, and full-sounding. Additionally, it does not seem to lose any lows or highs--which is remarkable considering the poor frequency range I expect from most "vintage" pedals.
The construction is extremely rugged, designed to work hard and last pretty much forever. The only fragile part is the lightbulb that is used in the optical control circuit, but those bulbs are fairly cheap and easy to find. It has a permanently-attached AC cord, so it will not run on batteries or a typical wall-wart supply. As noted before, there is no bypass switch.
Basically, if the noise problem can be solved by replacing some degraded old components with new ones, then this pedal is a serious contender, with better tone and wider frequency range than the Ross/Dynas or Orange Squeezers--plus it's a good volume pedal, and it's a burly chrome beast like a Harley or a muscle car. Classic.
Price in USD: $100-$200 used, no longer available new.