Eminent Technology ET-2 Tonearm Owners

11-28-13: Richardkrebs
Since the key to performance of the trough is to better keep the cartridge body still, it seems to be the place to position it.

This seemingly innocuous statement requires careful examination as it continues the flawed thinking espoused earlier in this thread.
If the goal were to keep the cartridge still, then one would never reach the end of the record. The record groove is not a straight line; it is a spiral with a decreasing radius that requires the cartridge to move to the center of the record as it plays.

Furthermore if the record is not perfectly centered, even by 0.01mm, then the cartridge is required to move in and out from the center approximately 660 times for a standard 33rpm record at Industry Standard or 0dB (20 minutes of music). This means that the arm will reverse direction 1320 times within approximately 20 minutes of music. (Is anyone here still of the view that adding lead mass to an ET2 that is reversing direction 1320 times per side of a record is a good idea?)

There are two goals which are in conflict with each other -
1. To ensure that the cartridge maintains a constant relationship with the groove the cartridge will be constantly moving to align itself with the groove.
2. To ensure that the recovery of as much information as possible which would suggest keeping the cartridge as still as possible.

On the one hand we want the cartridge to maintain a position that at all times it aligns the cantilever pivot point to the center of the groove. In order to achieve this, the cartridge must be able to move laterally freely and unimpeded whilst playing.

Any addition of mass or "apparent" mass by adding lead, stiffening the counterweight spring or adding fluid damping will increase the inertia and will reduce the ability of the cartridge to maintain the correct alignment with the groove instantaneously. The increased inertia will introduce lag to the response time of the cartridge tracing the groove and increase cantilever flex and distortion. Some may not hear this effect, but it is there and is readily apparent in a resolving system with good fundamental timing.

If you want to hear the concept proposed by Richardkrebs that the cartridge should remain still here is a link to the Transcriptors Transcriber. This turntable has a fixed arm which tracks linearly by holding the cartridge still while moving the platter underneath.
http://www.youtube.com/watch?v=IQ_r0Vk9Ct8
Have a listen. This set up has more WOW (as in pitch variation) than a wind up gramophone on its last legs. This is the sound you will end up with if you add enough lead, fluid damping and/or remove the counterweight spring as has been suggested.

As Frogman has confirmed with his experiments - when he decouples the spring and lowers the apparent mass, he gets a quicker and more tuneful bass response. Less weighty but better timing.

The use of fluid damping may ameliorate a resonance issue with some particular arm/cartridge combinations, but it comes at the cost of compromising the ability of the cartridge to follow the groove by increasing the resistance to tangential movement - it slugs the sound. A better solution is to ensure that arm/cartridge resonances are minimised such that fluid damping is not required.

I would also point out, since someone mentioned the Townsend Rock, I sold several of these when I was an importer/retailer in the 80’s. The use of fluid damping in this TT killed the sound so much, that cartridge differences were nullified. For example, one customer could not hear the difference between a Madrigal Carnegie and a Koetsu Red. I also ran an ET2 on the Townsend Rock for a while, with a Shure V15Vmr and can assure you the sound was much improved in speed, timing, articulation and transparency without fluid damping. Having dealt with Max Townshend directly, I should point out that Max’s reference cartridge, at the time he designed the Rock and the fluid damping mechanism, was the London Decca Gold cartridge, a poorly constructed cartridge with no cantilever and notorious for it’s poor tracking ability. It was in this context that he came up with the trough design.

H F Dover.
Still....relative to the groove.

Everyone else understood what I meant.

Hi Dover,

It would seem to me that the constant corrective motion of the arm to compensate for LP production imperfections, either lateral or vertical (warps), would involve some degree of "overshoot" and, thus, generate some stylus/groove misalignment due to inertia and that a properly implemented damping system would reduce this overshoot while having minimal impact on the initial transient response, ie using a minimal amount of the damping fluid such that the paddle only skims the fluid's surface (per Frogman).

I would not argue that the use of damping is a sonic tradeoff in practice and would not be desirable in a world of perfect LPs and ultra-stable resonance-free cartridges, but perhaps it is a desirable solution in our real world of neither?

Dave

Dlcockrum

Precisely

Dlcockrum
Yes I agree that damping may be required in some cases, and that running the paddle at the surface would be best. That is how I set the paddle with the Townsend TT.

However, the application of damping should be a last resort. In my experience many folk have applied damping to cure a "resonance" that has resulted from poor set up eg VTA, tracking force, etc and could have been removed by careful set up and in the case of the ET tuning..

I have used electromagnetic damping on my ET2 as discussed earlier in this thread. The damping is created by eddy currents which are only generated when the arm moves relative to the magnet.

I have run the ET2 for 25 years and found that the higher compliance cartirdges such as my Shure V15vmr benefitted most from electromagnetic damping.

With lower compliance cartridges such as Madrigal Carnegie, Koetsu, Denon 103 and Benz Micro fluid damping slugs the sound in my experience. Bear in mind that I run a decoupled counterweight assembly rather than a sprung counterweight - this has the advantage of keeping the ET2 horizontal mass as low as possible. As your friend Frogman has found, running the counterweight decoupled has produced quicker, more transparent bottom end in his system.The set up procedure he described above is the same as I have used.

A little history here -

If you read Bruces manual and patents he starts with a low mass arm, and then brings the effective horizontal mass up very gently by providing variable spring rates on the decoupled counterweight. This is formulated to keep the differential resonances between horizontal and vertical in sync with the compliance of the cartridge and the Q of the system. The Q is related to the dampening of the oscillation - the use of magnetic dampening will shift this slightly. Very small adjustments can give quite dramatic changes to the sound, especially in speed, transparency and articulation.

Krebs approach has been to load up his ET2 with 30+ grams of lead. He has also removed the decoupling spring from the I beam. Effectively he has added some 60g to the horizontal mass of the ET2. It is no wonder that he has changed his mind after 20 years and is now using fluid damping. Mass increases inertia and has no dampening properties. The high horizontal mass he is running has increased the side forces on the cantilever by over 300% when the arm moves back and forth increasing cantilever flex and distortion.

Quote from Thigpen

If the weight is coupled the system resonant frequency would be extremely low, a resonant frequency at 3Hz with a significant rise in response (6-12dB) results, which would affect tracking slightly because of the asymmetric position of the cantilever, we opt for splitting the horizontal resonance frequency into two points and lowering the "Q" which improves tracking.
More important than tracking, the intent was to reduce the modulation effects of low frequency energy (FM and AM) that increase distortion in the cartridge

I note that DGarretson has been experimenting with his Terminator tonearm. The Terminator in standard form has a much higher horizontal effective mass than the ET. DGarretson has reduced the horizontal mass quite substantially by reproducing some of the parts and yielded significant improvements.