Servo Controlled Arm

Kirkus, thank you for your insightful comment. Very informative on the shortcomings of these servo arms regarding the cartridge mass interacting with the arm mechanism.

You are also correct on the linear tracking servo arms like the Rabco and Goldmund. I used to object to such design for the same reasons the above members mentioned but I have since revised my thoughts on them. Doing away with anti-skating and tracking consistency across the entire side of a record and less stress and wear on the cartridge cantilever are all positive features to me. After all Goldmund is planning to release their $30,000 Reference 2 table with a linear tracking servo arm, T-8, a T-3 arm on steroid.

Sorry to the OP for my generic response, not related to his arm. I read "servo controlled" and assumed we were discussing a linear tracker. "Servo dampened" would have clued me in to googling first. Thanks to Hiho and Kirkus for addressing the real question.

I also wonder how an active servo mechanism could respond effectively to the varying resonance damping characteristics of different cartridge suspensions. Every adjustment it would make would be after the event.

A servo could be adjusted to control horizontal and lateral resonance frequencies of the whole arm, but that doesn't address the real challenge in cartridge/tonearm interaction - controlling internal resonances that feed back into the cartridge and alter the signal it generates.

The internal energies in a cartridge/tonearm occur at all sonic frequencies and with constantly varying amplitudes, all at the speed of sound. Quite a challenge for an active system to deal with.

I have my suspicions about this approach. The easiest way to "break" this concept is to put on an LP that is not perfectly centered. Each time the eccentricity comes around the stylus gets slammed from one side to the other because the servo cannot react properly. Now it may very well play perfectly pressed LPs beyond amazement, but the design does seem to limit what LPs could be enjoyed.

To all who have responded,

Thank you for the time and education. So much to learn....

Sincerely,

The internal energies in a cartridge/tonearm occur at all sonic frequencies and with constantly varying amplitudes, all at the speed of sound. Quite a challenge for an active system to deal with.

Actually, not a problem at all . . . there are countless electronic products around you every day that use electro-mechanical servo mechanisms that respond several orders of magnitude faster than the speed of sound. Think about the focus servo on your CD-ROM drive, happily maintaining a lock on a target the size of a few smoke particles, with the disc careening around at 48x speed.

A servo-damping system is basically an electronic implementation of the typical gooey-fluid tonearm damping trough - and likewise can only affect a very limited set of tonearm performance parameters. And similarly, the shortcomings of these servo-dampened tonearms isn't necessarily the servo . . . it's the tonearm.