Is it possible for the center image to drift from lp to lp?

Another factor I forgot to mention was the recording itself, which might be found in the original master tape or could be a pressing issue.  I have tried multiple copies of the same recording and the center image is skewed one way, and when subsequently playing another recording the center image is in the middle. 

Get a preamp with a balance control!

I do not know why any home audio system would leave that out!

Recording engineers don't always put the singer centre-stage. More often than not, but not always. Sometimes they will alter the singer's volume on one channel so that they're slightly off. You can hear this on side two of Shriekback's Big Night Music: On the first song the singer is centred; on the second he is off to the right; on the final song he starts off to the left and drifts slightly towards the centre as the song progresses. I also have an album by Luke Hurley where both him and his guitar are off to the right throughout the entire album. God knows why they made that decision, but there you go.

Number 4 is, incidentally, impossible with a single close-mic which is how the vast majority of music is recorded. The only time this would happen is during an intimate live performance recorded with two extremely well placed microphones. This almost never happens.

I had recently been having this same problem. Solution in my case was from none of the possible causes you mentioned. It came down for me to speaker placement alone. Due to a slightly lackluster overall sound and the same kinds of center imaging problems you mentioned, I, too, was experimenting with placement. For example, set one way, the speakers imaged a little to the left. After widening them apart a bit they imaged even more to the left and after widening a bit more, then they imaged to the right...clearly something was going on. My room is a bit irregular making adjusting by measurement fairly unreliable when trying to zero in on the sound with any exactitude. So I decided I had to roll up my sleeves and arrive at best position by ears alone...a gruelingly painstaking and time consuming (but, time-honored) process.

After several straight days of learning my way around with it, and countless wild goose chases, I began to realize that while distance between speakers and from speaker to front and side walls are indeed very important, what is really even more critical is rake angle vs toe in. I suspect everybody gets toe in, but they may tend to forget about rake angle...and I happen to think that deferring to the manufacturer on that is usually a mistake anyway. But, rake angle, when improperly set between the 2 speakers, can result in a skewing of the center image height in which there is an apparent vertical *leaning*, or slanting, of the vocalist to one side. Toe in more commonly affects the size of the center image.

To make it short, when all these speaker angles have been dialed in by ear to the point that the overall image And center image is coherent enough, then, I’ve found, that all those center image vagaries (like the ones I believe you have described) completely disappear - especially including all the apparent, indefinable drifting of channel balance from recording to recording.

At the very least, rake angle must be taken into account by ear. Once you’re in the right ballpark of speaker agreement, very small amounts of misalignment can have a noticeable impact on the center image.

Hope this helps.

Similar experience with CD and SACD. SACD's center almost always shifts to the right. My guess is that my right ear is more sensitive to higher frequencies. But that's just a guess. I just move the chair a little.