Wednesday, March 23, 2011

Discrete SS Mini Amp

Do you have a desire to build a fractional-watt miniature solid-state guitar amp? Apparently many people do, since there are several schematics out in the wild on the DIY discussion boards. For some reason, they tend to be built around little "chipamps" like the LM386 and its successors. They work off a 9V battery and are pretty easy to build. Make magazine even featured one version that was assembled into a cracker box.

I'd bet (though I haven't done any "reverse-engineering" to verify) the mini-amps from the big name makers are not much more—they probably just have an op-amp distortion and tone control circuit ahead of the chipamp.

Seems like it would be better to do it with discrete transistors so that some of the magick-mojo properties of tubes could be included, e.g. low parts count, no negative feedback.

There are some good JFET-based overdrive/distortion stompboxes out there, so that part should be doable. JFETs still seem like a good fit for the power amp, since the low voltage and power demands are well within their typical rating, their transfer curves are pentode-like, and (unlike MOSFETS) the gate draws current when driven positive, just like a tube grid (not the same characteristics as a tube grid, but some current does flow.)

Tuesday, March 8, 2011

BoxHead Amp - Recording

The first commercial recording using this amp was released on 3/8/2011:

I play rhythm guitar for this track on my Yamaha RGZ-211M through the BoxHead, mic'ed with a Nady ribbon.