More Than You Ever Wanted to Know About Electrical Engineering: A Simple Amplifier Model
We’re going to be looking more closely at amplifiers in the coming weeks. The specifics of how an amplifier is built can get pretty complex, so we’re going to want some kind of model that approximates the overall behavior of an amplifier and is simple enough for us to analyze relatively easily. Here’s a general one we can use:
This looks like a mess at first, but when you break it down, it’s not
so bad. The left side is the input to the amplifier. v_s is the signal
coming in. C_in and R_in represent the input impedance to the amp - that
is, the impedance the signal sees on its way in. v_in is the signal the
interior workings of the amp actually sees.
right side is the stuff coming out of the amp. The triangle on the left
is an imaginary voltage source that stands in for a lot of complicated
amplifier stuff for us. All it does is produce a voltage equivalent to
v_in multiplied by some internal gain, g. C_o and R_o here represent the
output impedance of the amplifier.
We’ll be doing a lot more with this model and others like it.
So three years ago my friend brought me a badly modded Fender Super Six Reverb that he found in his dad’s garage, who had probably picked it up at a yard sale. It had been pulled from its original unit (just the head unit and the reverb tank) and put together inside a makeshift cabinet DUCT TAPED together.
We brought it to my favorite local amp repair tech (big shoutout to Rootbeer Audio in Philly) and he cleaned up the guts and recapped and retuned it and got it working again.
Fast forward a bit and here we are. Finally just about finished. Built a new solid pine cabinet for it and wired it to two 12" Jensen speakers. It’s loud. It’s mean. It’s honestly Stevie Ray Vaughan in a box.
Hopefully he doesn’t want to stay with this grill cloth but we’ll see what he comes up with this weekend.
Give me a shout if you are local to South Jersey/Philadelphia and you have a similar project you need help with.