Here I present a simple reactive load project that simulates a 3-way loudspeaker. This can be very useful for a designer to bench-test the stability of an amplifier when faced with a “real” load, not a purely resistive one, without necessarily connecting the amplifier to an actual loudspeaker. During long tuning sessions, the continuous emission of tones, whistles and waveforms at high power for extended periods can become unbearable. The circuit schematic can be seen below.

The network of resistors, inductors and capacitors simulates an 8ohm load. The one I built can handle up to 200Watt RMS. To obtain the non-standard resistor values shown in the schematic it is sufficient to make series-parallel combinations as listed below. I used only 10 watt power resistors, since most of the current flows through the coils.

• 2ohm resistor = parallel 2.2 + 82 ohm
• 23ohm resistor = series 22 + 1 ohm
• 60ohm resistor = parallel 68 + 470ohm

I made the coils myself by printing the coil formers with a 3D printer and winding the required copper turns on them, all solenoids. However, they are easily available from various manufacturers of coils normally used in crossover networks. The RDC values are not critical, the coils I built all have lower RDC.

I assembled everything inside a box recovered from a faulty portable record player. The coils must be kept away from metal because it changes their value, so a wooden box was ideal. In addition, the suitcase-style construction makes the load easily transportable.

I brought the wires out with banana connectors for connection to the amplifiers and added two small terminals to conveniently connect the oscilloscope probe. Finally I reinstalled the original lid of the portable record player so the load can be stored away when not in use.