TT057: Weitz 4-channel M-DAC

This replaces a previous piezo amplifier box which had 4 independent manual gain pots, with an version where gain is controlled by a 4-channel M-DAC, and adjusted either with a single manual pot, or remotely over USB.

The box is a TipTop1550K with a TTM0 board in slot 1, a TTMDAC board in slot 2, blank slot 3, and a TTPiezoPreamp board in slot 4.   System bandwidth is DC to about 1 MHz.

Pics:

First stage is a simple non-inverting preamp with a gain of 26:

The M-DAC is a variant of TTVersaDAC, where the reference voltage is replaced by a signal path.

Arduino code: