The Load-Invariant Power Amplifier: 2.0
The Load-Invariant Power Amplifier PCB has been redesigned to use the latest output transistors in either TO3P or MT-200 packages. There have been many other improvements; see below.
A Load-Invariant power amplifier is one that is specially designed to give exceptional linearity into low impedances. The ultimate aim- for perfect Load Invariance- is a distortion performance that does not worsen at all as the load impedance falls from 8 Ohms to 4 Ohms and below. No amplifier currently exists that is perfectly Load Invariant, but in this design Douglas Self approaches closely to the ideal
One of the ways in which Load Invariance is improved is by the use of multiple output devices with carefully-chosen characteristics. This technique has the great advantage that it also reduces the crossover discontinuity for operation into loads of 8 Ohm or less, reducing the distortion produced. The Load Invariant amplifier therefore gives superior performance into 8 Ohms as well as 4 Ohms.
PCB 004: £33:00 each.
This graph shows the typical amplifier THD when running from +/-24V minimum supply rails. Performance at higher supply rails is somewhat improved.
Measurement system Audio Precision SYS-2702. Measurement bandwidth 80 kHz