@neonknight
I'm using Bob Carver VTA-180 monoblock amplifiers. Rated for 210 watts. The mentioned anomaly occurred (or at least noticed) when I had replaced the termination of speaker cables. The speakers were connected to the 4 ohm outputs on the amplifiers. Not sure if the break in on the speaker termination exaggerated the issue but when I checked the bias voltage on the amplifiers, I noted fairly violent changes in the bias voltage under normal listening volumes. I was concerned enough to contact the manufacturer. I was given some ideas to try to isolate the problem since one of the amps seemed more unstable than the other.
None of the tube swaps or other swaps had any impact on the issue. I do have some electronics background so while looking at schematics for the amplifier, I decided I may be over thinking the issue and decided to measure the actual resistance of the speaker, Mine were wired to be able to be bi-amped and have jumpers supplied by Eric (wanted to leave my options open for the future).
I measured again this morning to verify my findings. My MOABs measure 3.2 ohms. This is the load seen by the amplifier. When I checked the manual, it stated to use an output terminal on the amplifier that is less than the load (3.2 ohms). I moved the speaker wire to the 2 ohm output on the amp and voila, rock steady bias voltage even at high volumes.
IMHO, it seems that the MOABs are efficient. I love the sound. I replaced some Cornwall IIIs with the MOABs. They are sensitive to system changes. I missed the dynamic sound of the horns so I added some Stein Harmonizers. Also upgraded to all silver interconnects (thanks @Eric_squires, your posts and suggestions about cable to use led to some nice sounding DIY cables. Much more transparent than the Audioquest cables I was using).
If I were looking for some SS amplifiers to drive these speakers, I would want to ensure they are capable of efficiently driving low load speakers.
