Eminent Technology ET-2 Tonearm Owners
Richard, My ET 2.0 versus the ET 2.5 – both have high pressure manifolds. First an observation as I read what Ketchup and yourself said about the compliance in the air bearing spindle. Ketchup do you notice any difference in force required to move the spindle in your ET 2.0 and ET 2.5 with no air on? My ET 2.0 spindle can be forced through the manifold with no air. There is quite a bit of resistance but it can be done. This is normal according to Bruce. And its anodized coating prevents any damage. My ET 2.5 spindle will not move – it is really tight. There is not much movement at all without air. It has to be really forced. Bruce built it a few years ago for me. It was designed to run at 19 psi. Unlike my ET 2.0 which will run at 19psi and a low 3 psi as well, my ET 2.5 will start binding up if I drop the pressure – not sure what the actual PSI number is. The spindle starts resonating above a certain psi. We have discussed this here before. The consensus seems to be this PSI number varies just like our individual setups. For me its 19 psi and the reason I had the arm made for that psi. Richard as far as sonic differences with me. Let me use an analogy. We have all seen those graphs that show motor oil and the difference between lets say 5w30 and 10w30 motor oil at different temperatures. http://i36.photobucket.com/albums/e29/2002neonrt/35graph.jpg Lets assume lower temperature represents lower compliance / heavier cartridges – that is the ET 2.5 5w30 and the ET 2.0 is 10w30. Both overlap and work well within a large range for both MM and MC. But when the setup is tweaked/improved I think the ET 2.0 works a tad better with MM and ET 2.5 with MC. Does that analogy make any sense? People assume the ET 2.5 is better because it is (.5) the next newer version. It depends. It came after so the obviously the parts themselves are newer but as far as sonics go ? well we know the smaller diameter 2.0 spindle according to Bruce resonates at 5-6 hz. The 2.5 resonates at 2-3 hz. The armtubes are the same as far as I know for both versions. Aluminum original one better with higher compliance, CF – middle ground – Magnesium – for really low compliance. This is the advice from Bruce with the testing he has done. The ET 2.5 sucks more air – has more volume. When they were in the same room I remember how the pressure gauge when I unplugged one for other would move by a few PSI. Ketchup’s graph shows this too. The ET 2.0 was around when vinyl was in its heyday along with MM cartridges. Then came MC cartridges and BT adjusted (I guess) to the time and introduced the 2.5 with its lower resonance. Just an opinion. If all things were the same – apples to apples - We know that will never happen. The ET 2.0 seems to handle a little better with lighter higher compliance MM’s. Like a lighter sportscar with great handling. But add a bigger motor to the sportscar (heavier MC/stiffer/lower compliance ) and I feel the ET 2.5 handles a little better. Bigger diameter spindle along with the lower resonance. A very rigid spindle to manifold coupling in my 2.5. The differences are not day and night. The MM 420str sounds great on the 2.5. Its just seems to be a little more ease on the 2.0. Bruce’s review of the 420str kind of confirmed this to me too. So I use MC on my 2.5 and MM on the 2.0. The rooms are adjacent to one another in the basement. Hope that helps. Richard you mentioned that you studied the Dynavector arm. Did you take any measurements of it - Impressions ? Cheers |
Chris. Thanks for the comparison notes. I now have a clear picture of the differences. The Dynavector arms have always been fascinating to me due to their radical design. Magnetic dampening and for a pivoted arm the unusual idea of deliberately different effective mass in the vert and horiz planes. Both of these features being recently discussed in this thread. Have only listened to 2 of these beautiful arms and in systems that I am unfamiliar, so cannot draw any concrete condclusions. I have included a quote here from their manual on the 507 should anyone be interested. • 3 Bi-axis inertia separation for accurate signal reproduction and superb tracking ability "Bi-axis inertia separation" may sound complex but it simply refers to a tone arm having two arms which operate independently in the horizontal and vertical planes. In contrast, a conventional tonearm has only one arm which moves both horizontally and vertically. This is called a gimbal type tonearm and the inertia for both planes is the same. The DV507 bi-axis tone arm has a large inertia for horizontal movement and a very small inertia for vertical movement. We shall now explain the reasons why this is advantageous. It is well known that a cartridge generates an audio signal by the differential motion between the cantilever and the cartridge body. Consequently, if the supporting point of the cartridge (the tonearm) vibrates, the tonearm motion affects the audio signal. In these conditions, the signal, which causes the tonearm to vibrate is of low frequency and large amplitude. In the currently used 45-45 stereo record cutting procedure, low frequency signals are almost entirely recorded in a horizontal direction. This means that the low frequency signal, which can cause vibration in the tone arm, exists only as a horizontal force. The tonearm therefore must have sufficient effective mass and rigidity in the horizontal plane in order to provide a stable platform for the cartridge. On the other hand, for the mid to high frequencies, the effective mass of the tonearm should not be too large since the combined mass of the cartridge and the head shell need to be taken into account as well. In particular, where records have a warped surface, the vertical effective mass needs to be small enough to ensure a good tracking ability on such surfaces. To summarise, the tone arm should have a large effective mass and enough damping in the horizontal plane and at the same time a small effective mass in the vertical plane. These conditions are almost impossible to achieve with a tone arm of conventional design using a simple gimbal pivoting system. To solve the problem, Dynavector designed a bi-axis, inertia controlled tonearm where the shorter and lightweight vertical sub arm is placed at the end of the horizontal main arm. This is the special feature of our design. |
Richardkrebs/Chris : Magnetic Dampening vs Mass. I have been away on business and my responses have been brief. I can now expand on my previous comments. With a lower mass the arm will move more rapidly initially to align with the eccentricity of the record, minimising cantilever flex. The magnetic dampening only commences its action once the arm starts moving, and is proportional to the rate of movement. I should point out that the dampening is created by eddy currents which are only generated when the arm moves relative to the magnet. By contrast, adding mass means the arm will not move until the driving force from the eccentricity is enough to overcome the higher inertia. This increased resistance to movement from the added mass means that the cartridge cantilever is forced to deflect to keep the stylus in the groove. This defeats the purpose and advantage of an air bearing tonearm - the uninhibited degree of freedom to accurately track the groove. This higher mass is not dampening, it is increased inertia - a resistance to movement. Magnetic dampening is dampening the arm motion once the arm has commenced movement. I'll restate this : Magnetic dampening allows the cartridge to move to the correct position in a damped fashion. High mass means the arm wont initially move, inducing the cantilever to bend. Any excessive cantilever deflection in a moving coil will result in phase anomalies as the coils attached to the cantilever are driven into a position where the response becomes non linear. Furthermore, with the higher mass, once the arm starts moving, the lateral movement is undamped. Cartridge overshoot and more cantilever flex is inevitable. With magnetic dampening the lateral movement of the arm is always damped when moving. |
