I have two tube amps, a kit-built VTA ST-120 and a Yaqin MC-30L. I recently took the Yaqin out of storage to alternate it with the ST-120. The Yaqin has separate 4-ohm and 8-ohm speaker connectors. I've always used the 4-ohm connectors on the Yaqin and I wired the 4-ohm transformer tap to the positive speaker connectors on the ST-120. However, in hooking up the Yaqin I inadvertently used the 8-ohm speaker connector. I am using some Polk SRS SDA-2.3 speakers that have a nominal rating of 4 ohms.
I was somewhat surprised that using the Yaqin 8-ohm connectors gave me what I perceived as better and tighter bass. With that in mind, I decided to hook up the 8-ohm transformer leads in the VTA-120. Again, with my speakers I think the bass is more pronounced and drum attacks sharper. But, I also think at the same preamp setting I lose a little volume through the VTA-120.
So, is this all in my head or is there some realistic basis for these observations?