PPihkala May 30, 2017 | 14:26 Why to use NPN (Q1, BD139) as control element, since it's base current will create an error at the output current? I think this should work at less current error with N-MOSFET at Q1. If needed for stability by IC1 just add extra load resistor from it's gate to ground (1-5k ?). If power rating of single resistors is not enough, then use more in parallel, with bigger values of course.  I also find it odd that you have the value setting resistors at the power path, which makes you to use all these relays.  

There will be a calibration menu in the upcoming update somewhere in June. But you will need your own equipment to calibrate against. The new software will contain default calibration data tested with my equipment up to 1.01 GHz with a 1dB accuracy.

How did you created the frame variable? More speciffically, how did you created the bitmap? What hex convertet tool you used?

Hi Ton, Thanks for the reply and clarification of the use of the toroidal core. In reading other texts, polypropylene capacitors have less distortion than polyester - but these texts refer to low voltage use - the text refers to no distortion for polypropylene - book i refer to is Design Of Active Crossovers. I did notice that the inductance decreased with an increase in current - but the maximum current is assumed to be a lot less than 15amps - for domestic listening levels. The inductance versus current curve is reasonably flat up to 5 amps for the inductor mentioned. I will continue to search and post any findings. The datasheets for components never seem to provide the required details - such as inductance expected for capacitors, or capacitance expected for inductors etc. , however low that they may be. Price is not guaranteed to obtain the optimal component either. Regards, Richard.

Test with more than 70mA, shows the resistors with 125mW less power tolerate. I think for 0805 resistors is from 0 to 25mA in 100uA steps better, for more power, use bigger resistors.