as an exercise, but also because the construction of pots/shaft/knobs on them is not easily replaced.
first thing i tried was a ruby amp.
that didn't seem too happy about the speaker i wanted to use.
out of the parts bin came another contestant: the LA6500.
it would need a bipolar supply for extra headroom/volume, but i can live with that.
has the added benefit of not needing coupling caps -added one at the end for speaker protection, but don't think it's really necessary.
so i put in a transformer to power both the amp and the keyboard from the mains.
no more wallwart!some moons of testing later i installed this:
* a 071 preamp, with a fixed gain of about 700%.
the first pot (originally the tone control) is taming the input.
it can still do clean sounds, but when the output is hot enough, the signal gets clipped by a pair of back to back yellow LEDs. sounds really nice, and the signal never exceeds 4 - 5Vpp, which is very reasonable for the poweramp.
* lowpass, taking off some clipping harshness
*LA6500 poweramp, with the second pot acting as a master volume.
slightly amplifiying the signal further, and providing enough current for the speaker.
i mounted the LED clippers in front of the speaker, the cone of which i sprayed white.
now the speaker 'lights up' when the signal is clipping, which looks as ridiculous as that gooseneck led.
all in all it sounds great, looks nice and it's plenty loud.
not complaining.
