Digitizing vinyl and mixing my next album has inspired me to build the CMoy headphone amplifier.Â I’ve been taking regular walks to the bar with a set of headphones and a cheap MP3 player loaded with in-progress mixes.Â Since these are unmastered tracks, and thus uncompressed audio signals, the little USB-charged MP3 player doesn’t have the juice to bring the tracks up to normal listening level.Â The more complex the track, the greater the build-up of transient peaks and the quieter the mix.Â Vinyl tracks are also uncompressed, which means there’s more difference between the loud parts and the quiet parts.Â The CMoy amp adds an extra 18v of power, which means I can plug in the MP3 player and leave it at its default volume, using the amp to drive the headphones.
I’m almost done.Â The tutorial I was using suggested a dual pot with a built-in power switch, which I had to order separately from the other parts.Â This particular pot works so that when you turn the volume all the way down, the power clicks off.Â It’s a wise feature considering that you can seriously damage your hearing with this amp.Â This way, it’s always turned all the way down when you power it up.Â I tested it out before I housed it (in the standard Altoids tin) and it got pretty loud with one 9v battery.
I took another look at the looper project I’ve had put off to the side for about a year:Â three toy sound samplers with pitch shifting that you can hack into and add to a simple mixer circuit to create a lo-fi, multi-channel looping effect.Â I drew up a wiring diagram, planning on using a chunk of steel stud to house it:
I decided instead on an enclosure from an old whatever-the-hell-it-was from ax-man.Â You can buy old machines for $5-$10, take the guts out and use the case for new stuff, which is cool because electronics enclosures are really expensive.Â The drawback is that it’s harder to get a space efficient design since the housing was meant for something else, but I’m starting to realize that I like things to be life size, sturdy and clunky with plenty of soldering room.Â The last looper circuit I built, I think I fried the chips because everything was crammed too tight on the board and I couldn’t troubleshoot it.
All the knobs are where the pots will go.Â The nuts represent toggle switches, the plastic grommets (LED holders) represent LEDs, the washers represent momentary switches, and the pots represent foot-switches.