Linear tracking turntables, whatever happened?

@ct0517, to add to Dave’s excellent comments, and in the cause of clarification, let me say no, record changes are NOT made by sliding the LP under the cartridge/stylus (and the arm wand onto which is mounted the cartridge). At the end of an LP side, the wand is returned to it’s rest position, at the far right end of the arm’s manifold, where it is out of way of the LP. The LP DOES however need to be slid under the manifold, which is locked in position over the back of the LP, about half way between it’s center hole and it’s perimeter. Other linear trackers avoid this by having a longer arm wand, making it possible for the arm’s main structure to be located beside the table’s platter, not positioned over it.

The manifold being suspended over the LP makes possible a shorter arm wand, which has benefits (lower mass, inertia, and resonances) and one penalty (greater changes in VTA and SRA when navigating warps, resulting in possible "warp wow"; a table providing LP flattening---via vacuum hold down or a clamp---is good for the arm). One thing I like about the Terminator is the arm wand/cartridge/stylus facing the operator, rather than being 90 degrees perpendicular as with other linear-tracking arms; makes cueing much easier!---Eric.

Hey slaw, I guess you have your ET on a VPI, not your Townshend Audio Rock 7, ay? ;-) What arm is on your Rock? My Rock Elite (Mk.2) was made with it’s damping trough having an arc diameter appropriate for the shorter-than-usual Townshend Excalibur arm. The Zeta I use with my Rock is very close to the Excalibur in that regard (pivot-to-stylus distance), but has much better bearings (and a great stiff arm tube).

The Helius Omega arm has found favour amongst UK owners of the Rock 7. The Silver/Ruby version is especially nice, but at a not-so-nice price ;-) . Townshend Audio and Helius just happen to share the same U.S.A. distributor. Tim de Paravicini also recommends the Omega for use on his EAR Disc Master turntable, the table Audiogon member folkfreak owns (I saw and heard it in his music room last year), though he uses different arms (two) on his.

My knowledge of physics is rather limited, so let me ask those of you who finished high school (;-) if the following is correct:

To achieve higher moment-of-inertia (same as mass?) in the vertical plane, the mass of a counterweight should be located as near as possible to the line described by the arm tube running through the arm’s bearings. In other words, extending left and right of that line in the lateral (horizontal) plane as little as possible, i.e. as close as possible to the arm's bearings laterally. The opposite of that is the Groovetracer counterweight made for Rega arms, which is in the "longhorn" style---extending a couple of inches to the left and right of the rear stub onto which it is installed.

If the above is true, I can envision, say, lead weights being attached to a counterweight above and below the hole running through it for the arm tube’s rear stub, but not to either side of that hole. Correct?

@ct0517, I attributed the "The best bass comes when the tonearm is setup for the highest vertical inertia" statement to you. Does your "It's not really my assertion" statement mean that it is actually that of Bruce Thigpen in regard to his ET arm specifically (but not necessarily universally)?

Regarding the price of the London cartridges, the Super Gold Mk.7 (line contact stylus) is around US$1500, a little more with the Decapod mount. When I got a Decca the second time (in the early 90's, the first time being in '73), its' North American distribution was being handled by a Canadian company. I would say that would have been a good time for a Canadian to have bought one, but the Londons are definitely an improvement on the Deccas, well worth the difference in price between the two.

Chris’ (ct0517) assertion that high vertical moment-of-inertia produces the best bass is to me, a user of London (Decca) cartridges, VERY interesting. That cartridge exhibits far lower vertical compliance than horizontal, which aligns well with a pickup arm exhibiting higher vertical m-o-i, no?

@analogluvr, I’ve said it before, and I’ll say it again---Eminent Technology’s Bruce Thigpen is as brilliant a hi-fi designer as there has ever been, including Peter Walker!