Things That You Should Leave Alone

The SSM 2015 chip uses a resistor to program the first stage bias current, and in the SX202, this resistor is set to the maximum bias current that the 2015 can safely handle. Do not reduce the value of this resistor to increase this bias current, as you will probably damage the 2015 chip. These chips are very hard to find these days, so you will have to live with the extra distortion from a damaged chip for some time.

What's more annoying is that increasing the bias beyond the stock arrangement does not improve performance. I found this out the hard way, so leave the 27K bias resistor alone! There is some evidence to suggest that distortion might be improved by increasing the value of the bias resistor, thus reducing bias, but this increases noise, and the preamp is already on the noisy side. Leave the bias alone, as it already seems to be optimal!