[prepress]

Okay, I have just completed another test session, and things are closer to normal. BTW, the TT is a Sota Sapphire VI with a SME 309 arm, if that matters; tonearm cable is Van Den Hul. Here's what happened:

First, I re-oriented the turntable's PC so that it doesn't touch or isn't near any other power cords. It did run perpendicular to a couple and may have been touching them. I relocated the TT's power supply recently, which brought its PC much closer to other PCs. Yesterday was the first time I tried playing any records with it in the new spot.

Second, I switched from the MM to the MC input, turned everything on, then raised the volume without a signal to see what I'd get. With my ear about 3 inches from the speaker, I began to hear hum at about step 39, which increased with volume. Then I went back to zero volume, put on the LP and increased the volume gradually; I didn't hear any hum with the volume up to 36 with my ear right up to the speaker.

Third, I turned everything off, moved the phono cables back to MM input, then repeated the procedure. This time, with no signal I began to hear hum at about step 48. Playing the LP again I was up to step 45 and couldn't discern any hum, even with my ear almost on the speaker. I didn't try the "Mono" setting.

While I'm thinking the power cord adjustment is the main contributor to the improvement I heard, I also changed the settings for the two inputs which has gotten me closer to a volume level comparable to my other sources as well as the Sonata3's specs, as best as I understand them. I'll try dialing that in a bit more now that I have an idea of how to do it. And if the hum problem resurfaces, I'll report it.