My progress:

Current Limiting - used the oscilloscope in Visual Analyzer. The test requires the amp be driven hard to check for asymmetrical clipping. Channel 1 clipped evenly, then 8 ohm 200 watt dummy load started making funny noises. I rechecked both channels with a 12 ohm 1100 watt hot plate (complete with tea kettle), both looked good. Now I get to build a proper water cooled 4 ohm load with water heater elements and repeat check by the book - yay!

LF cancel and bias - I think both can be checked with free software. The brainstorm:

SweepGen sine wave > sound card L out > amp/dummy load > voltage divider (100k lin pot) > sound L in > Spectrum Lab super-dooper notch filter > sound R out > sound R in > Visual Analyzer o'scope

Spectrum Lab allows for building custom filters - the bad news - it's been almost 20 yrs since I've fired up a C compiler. If I fail as a code jockey (highly likely), I'll probably build Rod Elliot's DA design posted above with only two filters - 60Hz and 1k.


Visual Analyzer - Visual Analyser 2011 XE

Spectrum Laboratory - DL4YHF's Audio Spectrum Analyser

SweepGen - Audio Tools - from David Taylor, Edinburgh