15IPS less distortion (30IPS mod)

A single resistor sets the amount that the diode ladder will clip the signal. In the 15IPS mkII this is R6, in the 15IPS mkIII it is R7. Increase R6/R7 for more distortion or decrease it for less.

To dial in the exact amount of distortion by ear, replace R6/R7 with a 1k trim pot.

One engineer who uses a pair of 15IPS for mastering sets his R6/R7 to 180R and calls it the "30IPS" mod.

The resistor specifications are through-hole, metal film, 1% tolerance, 1/4 watt.