Sunday, October 12, 2008

My Simple FET Booster

Here's my extremely simple FET booster circuit. It's so incredibly simple, anyone can build it, and it's cheap, while offering great results.




















I've used the 2N5485 and the 2N5457 interchangeably ( I hope I got those numbers right, I'm typing this from memory ) I use an axial electrolytic cap for the bypass on the 100 ohm resistor, and tantalum for the other two, because they're small, no other reason I could think of. Confession: 3k came out to be a great load resistor, but I didn't have a 3k, so I put a 1k and a 2k in series). I really think I could hide this in my Les Paul control cavity if I wanted to, and definately could put it in my strat, if I were to forego a couple of trem springs for battery placement. Hmmmmm . . . but that won't happen. This is going to be the first gain stage in my TUBE HOTTIE real tube distortion pedal. You can see waveforms of this preamp in the post below, the first pic being this preamp running on a 9V supply.


















I used half of one of those Radio Shack experimenter's circuit boards, the one designed for a 16 pin DIP IC, I simply cut it in half on a band saw at work. The 9V battery is shown simply for size comparison. I could probably put in on an unclad breadboard the size of a dime if I had to. The wires are color coded so I don't have to think about them a second time. Red and Black are obvious, the blue is input, and the yellow is output. Think about this: Which signal will be hotter, and which color is hotter? This makes things a little more fool-proof when final assembly comes. I started this habit when I was the electronics designer at Conklin Guitars back in the 1990s. Any of you that have ever heard the Conklin On-board Parametric EQ are proof that this simple philosophy works. I label all my pedals this way too, simply because I can hook them up in near darkness.

I measured an input and output signal with a true RMS Fluke multi-meter, and after doing the math, it looks like I'm getting nearly 16 dB gain at 5kHz. Holler at me if you have any questions.

Jim

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