Preamp perfboard
I perfboarded my preamp circuit for my thesis project, the EM Brace. I’m using this circuit to boost the electromagnetic frequency signals before they are sent into the larger 40-watt amp that I’ve showed in previous posts. The circuit uses two OPA134 chips, which are really great audio preamp chips, so the mono signal is getting boosted twice. I based the circuit on the original Chu Moy headphone amp & used this site for help with the power supply, which requires negative and positive voltage (+4.5v and -4.5v). On the chu moy circuit, I changed the feedback resistors from 10k to 100k on the first chip and 1M ohm on the second chip. This yielded substantially greater amplification. My initial signals are weaker than signals that would come out of, say, an iPod or computer, so I don’t think I would change these resistors if I was building a headphone amp, as the original schematic yields plenty amplification to drive a pair of headphones.
