Chuck D. Bones
Circuit Wizard
I was chatting with BuGG about the MOSFET Driver circuit and he encouraged me to have a go at a redesign, so here's my first stab at it. The original had a Whole Lotta Gain and this version is true to form on that front. With everything dimed, the end-to-end gain is 115dB. I got rid of the extraneous opamp buffer up front and added a Timmy-style BASS control to the 1st stage. I also added LED soft clippers to keep the opamp from saturating. Q2 will saturate long before the LEDs turn on. U1 has the same gain range as before, from 0dB to 49dB. I used an LF356 for U1, but any FET-input opamp will work. In place of the Bias1 trimpot, Q1 now has a VOICE switch. In the left position, Q1's gain rolls off below 600Hz to give it a Bright Channel tone, good for humbuckers. In the center (off) position, Q1's gain is lowered to 12dB for a cleaner, low-gain tone. In the right position, Q1 runs wide open at over 40dB gain. Q2 has a Gain Trim, similar to the Bias2 trimpot, but now the bias is constant. Q2's gain is adjustable from 17dB to 40dB. That's followed by a Timmy-style TREBLE control and a source-follower output buffer. The MOSFETs run on +25V for HUGE volume and headroom. The max output is 20Vp-p. Take that, tube amplifiers! The two MOSFET gain stages are reminiscent of the Box of Rocks, so for now I'm calling this the Box of Timmys.
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