I was going to build the Cmoy circuit myself, but after pricing it out I found it was cheaper to buy a completed circuit (without enclosure, jacks, or potentiometer)on e-bay than it was to build myself. This also works out as I get to add my own jacks, it seems every prebuilt pocket amp uses 1/8" jacks for both in and out and I wanted a 1/4" jack for my SR125. As this circuit smartly has the opamp set into a socket instead of directly soldered, I can switch out the opamp chip. I may try the OPA2134 chip, but as it is, this is a pretty nice sounding portable setup. I use it mostly with my MP3 capable mobile phone. (LG Chacolate)
System edited: While adding a portable 12V power supply I accidentally reversed the polarity to the circuit. This damaged the OpAmp. I replaced the LM chip with the OPA2107 chip. The LM chip was warmer and would hide some of the shrillness of my MP3 player and my desktop PC. The OPA chip is very up front and doesn't hide anything, which in this case is a little annoying because of the source.
I normally power this off of either a 9V battery, as seen in the pictures. If I have a chance to plug it in, I have a small 12V AC/DC adapter that I use. However, I seem to get the best sound when I power it with a 12V source I made using an old PC power supply. I built this for my other hobby, remote control aircraft. I use it to power the hobby charger I use for my batteries.
