Too bad the schematic isn't on the Captain's website, but you should be able to work it out from Brendon's handy photo work with some careful tracing. If you're interested, There are a number of sample schematics on the website which appear much simpler as they are OP-AMP based rather than discrete transistors. Setting gains would be much simpler as you'd only need to change one resistor value in each of the driver and recovery amp sections. They provide both voltage and constant current type drive amp designs. The only downside is that you need a bipolar (+/-) power supply, but, with some simple circuit tricks, you can go single supply by using a virtual ground reference at 1/2 the single supply voltage, and AC couple the signals into and out of the amps.</p>