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.  

Parts: Relais from german shop Pollin: No.  340 781 with 2 reed contacs uA723H maybe from ebay round about 3€ or ask me. Resistors from Digikey.... All other parts are quite normal.  

First test circuit run on single side board, an old 8051 set the current. Output with out thermal stabilisation better then +/- 50µA. All curent measurment resistors 0805 0.1%. Output 1....40mA with out heatsink.

hi joost, how to calibrate? thanks. regards, ervin