Resurrecting this old thread in hopes some of the LT regulars will respond. I participated in this and own a few LT’s myself, and I prefer my LT-30s, overall, but recently discovered an interesting issue with my two Revox B791s. (All my TTs have been serviced, recapped, belted whatever has been needed)
For the few warped records I actually play, the B791s are excellent with the LT-30s practically indistinguishable, mainly because, I feel, both B791s have a brush as part of their carts, ( though on each I have upgraded the actual stylus to a Jico SAS for the V15V, and HE for the TXE-SR) which definitely assists in warp tracking. The LT-30s are definitely quieter.
The issue that came up was on an otherwise excellent Feels So Good LP, one of the few of my original albums I didn’t sell when CDs came out, bought by me, when they came out in the 70s, and treated with Soundgard. A very quiet pressing, with excellent dynamics superb depth. BUT, on one side, the stamper pressing is 2-3mm off center. The hole is perfect and the other side is centered.
Played on my other TTs there is no problems whatsoever besides what would be an added W&F component of course, though I don’t hear it, possibly because all mine are DD. But on both the B791s, every revolution where the cart goes furthest towards the spindle and reverses there is a slight deep bass “thump”, inaudible when any music is playing but easily heard in the silent grooves. It tracks perfectly, and I think this may be normal. I searched for a few other off center albums, and they all do it if the off center is above a certain amount. Played on my pivoted TTs, or my LT-30s, there is no such thump, though on some records, there is an increase in groove noise at the same reversal point.
I have measured the TP1 voltage on the B791s during playback of various albums and adjusted the gain pot to minimize the voltage swings.
TP1 measures the voltage that is generated by the opamp to determine the final voltage and direction of the advance motor for the arm. The SM states that ~ +/-1V is normal with standard groove pitch, and the voltage increases with increased pitch, requiring the TA to advance faster. At runout, the voltage peaks past 3V, which triggers EOR and TA return before the limit switch is hit. So I know they are tracking optimally, and smoothly. It is only during an above certain amount of reversal, that this happens. I suspect it is simply the adjustment of the cart direction during a brief acceleration, which is verified by the voltage increases seen in TP1 at that moment. For instance, no such thump is heard when the cart accelerates in the runout groove and then lifts. Only in reversal movement. I have stared at the motor during this reversal and can BARELY see it turning in response. Originally, when I first heard it, and before I adjusted the opamp gain pot, the movement was more pronounced. But in reality, I heard and experienced no tracking error difference. The adjustment definitely reduced visual motor rotation.
I would just like to have someone else with the same table try an out of center LP on theirs and see if they hear the same.
I should mention that like many slight issues such as this, it is basically only heard when using quality headphones. I can hear it on speakers, but only if I crank them up between songs, to a level louder than I would comfortably listen to.
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