The tone keeper is a six knob optical compressor based around the EQD Warden ™ and lifts every slightly hit note right into your face. A compressor with so many features usually reserved for studio gear and work equally well on bass guitar. A build-in charge pump brings the unit up to 18v while you only need 9v to power it but still get the maximum clean headroom and sustain without getting noisy at all, thanks to the opa2134. (This chip is a bit more expensive but I really recommend it every time you want to make a build less noise – for instance, ace had great results in my personal BE-OD.)
If you want to try your build first and order that chip later from a trusted source you can replace it with a TL072 – but keep in mind, backgrounders noise will increase by doing that.
But let’s get back to the topic: tone, attack, release, level, sustain, and ratio gives you every control in your hand you could need to get the maximum out of every note. For tweaking a compressor the first time, start with all knob at noon and adjust from there while switching the pedal on and off from time to time so your ears get a better chance to hear the difference. Led is a clear white, no. Red to angle it, I had around 2-3mm distance to the LDR that faces the direction of the led. You can use sockets if you want to try different LEDs but keep in mind that this raises your led and the legs of the LDR should stick out far enough to compensate for that.
For further analysis on this circuit take a look at this thread on Free Stomp Boxes Forum