Well, I've constructed the tester as described with a 1.5V battery and the photodiode from an old Mac mouse. It DOES move the signal strength indicator in Adobe Audition, but not nearly sensitive enough to produce a blip in the record mode. Looks like I'm going to have to step up to a 9V battery and put in a pot, till the signal strength is enough to be useful. I wonder why the designer gets away with 1.5V and I have to go through this ordeal of rewiring mine for a 9V. Seems nothing works out as described.