Eminent Technology ET-2 Tonearm Owners
Chris. Yes spring has sprung here. BBQ's, Boating, Fishing, and company with great friends watching long sunsets over a glass of wine. I suspect that it was the change in temperature that precipitated the o"ring failure. I am using a HP manifold at around 18 psi. HF Dover. I knew that you would bring up the added weight question inside the spindle. The 30 gm adder was a guess based on 16 year old memory. Clearly my guess was well overstated. I will be removing this when I do the swing arm counterweight test to bring the arm as close to stock as possible. The 95 gm total, arm and cart weight, is accurate. This depending upon c/weights and cart used by others, being more or less the same as a standard ET2 using a mag wand. For further discussion on how every ET2 on the planet requires the cartridge to push sideways the total arm weight when tracing an eccentric record, please read below.... > Bruce. > I have been thinking about the horizontal effective mass of your ET2 and have a question please. > The horizontal effective mass calculation you give in the tech section of the manual shows an arm mass of 30 grams which is then added to the weight of the cartridge to give total horizontal mass. This calculation ignores the weight of the counter weight since it is decoupled via the leaf spring. > > My question is around the horizontal effective mass seen by the cartridge when tracing an eccentric record. The resonant frequency of the counterweight spring assembly is 2-5 hz and the lateral tracing frequency of an eccentric record at 33 rpm is 0.55 hz. > At 0.55 hz the transmissibility would be approaching 1, even with a counter weight spring frequency of 2 hz. > > This would therefore mean that the cartridge "sees" all of the counterweight weight when tracing an eccentric record? > Thus the effective mass at this low frequency, 0.55 hz, would be the total weight of the arm and cartridge including the beam and the weights it is carrying. > > Many thanks > > Richard. > > Richard, Below the counterweight decoupling frequency cutoff ~ 2hz, the effective mass becomes the total mass. Then you have another resonance freqeuncy to add to the mix which is typically much greater than .55Hz. So yes, it sees all of the mass below 2Hz, but the combination of those masses results in a cantilever resonance above that frequency. You should see the arm move back and forth with the eccentricity of a record at .55Hz as opposed to deflection of the stylus. I hope this helps and thank you very much for the interest. brucet |
Frogman. I suspect that the check valve you refer to is actually a safety relief valve. And yes it could be the same thing that I am hearing. It may have an adjustment so you could, entirely at your own risk :-) increase its setting to see if the bleed flow could be stopped but still maintain the same pressure out of the regulator and on to the arm. Obviously I don't know what your surge tank can take in terms of max pressure, so be careful should you decide to do this. I read the TAS review and this could be a review of the changes I hear in my system. It is a significant jump in performance and ultra easy to do. The dimensions given for Motronix unit would imply that any surge tank, if included, would be very small indeed. So maybe it is simply two high quality regulators with a central bleed? It shows how sensitive the arm is to smooth air delivery. As per my earlier post, the compressor had cycled off, so the air supply was coming only from the reserve in the tank. The "noise" in the air stream could only be coming from the regulators and the associated hosing to the arm. |
Frogman. Look to the other end of the arm and compare the counterweight attachment. If you are using a low compliance cart on an ET2, this is the main cause of diminished bass extension. Calculate your FR using the ET2 manual formula. Around 7Hz or above and you are missing the lowest registers. The math on this is very clear. Further the quite flexible goose neck and arm pillar on the ET2 don't help. |
Gentlepeople. Just another take on the thoughtful input from Pegasus. Is it possible that the screw torque adjustment thing is at least partially due to the disruption of multiple mechanical paths? Lets look at the arm as a set of parallel mechanical conductors carrying current to "ground" (the plinth). In the ET their are multiple paths in the pillar and interface with the plinth. We have likely all experienced earth loops in our HiFi journey. Could this be something similar. Multiple parallel paths with slightly different propagation times, creating the equivalent of an earth loop. By disrupting, breaking, some of these paths are we actually building a single path to ground, hence cleaning up the mechanical earthing of the arm. |
Dover. Up till recently you have been telling us all repeatedly that the counterweight decoupling spring is active at eccentric record frequencies and that at these frequencies my arm is up to 300% heavier than a standard ET2. We now all know that you are wrong and that the spring is in fact rigid at this low frequency making the effective mass seen by the cart in standard ET2's in the same ball park as my arm with a fixed counterweight. The math which proves this effect, below FR, shows that above FR the decoupling spring is active and it dramatically reduces the arms effective mass. This is a brilliant solution if you are using a high compliance cartridge. But this same math shows that if the FR is around 7Hz or above, we get bass attenuation. Low compliance carts will exhibit a FR in this danger zone of 7Hz and above. If we fix the counterweight, to push FR below the danger zone, we unfortunately get a big, high Q peak at FR. Exactly what the leaf spring fixes for us. So there is a conundrum here. Live without the last bit of bass extension or fix the counterweight and experience bloated bass performance, not due to excessive bass but due to the FM phase problems propagating up from FR into the audible spectrum. On the bloated bass topic we agree. But there are solutions to this. Run the arm at pressures below design and dress the lead out wires to resist lateral movement. Not a very elegant solution but it kinda works. Or far more effective, ran at design pressures and use an oil trough. See BT's test data on this where he uses his arm "set up so that a high amplitude Q existed" (a fixed counterweight exhibits a high Q) and then adds the oil trough. The resultant response graph he publishes in the oil trough manual, shows a critically damped system with zero resonant peak and importantly he mentions "the ET2 with a damping trough will exhibit almost perfect low frequency phase response" No more bloated bass and with full LF extension. Lovely. |
Dover. Sigh.... You need to read my posts properly. This is taking us nowhere. Slaw. I checked out the M-30 and M-60 filter. That is most impressive... 0.1 micron. What regulator are you using? Testing with a small amount of air bleed in between my two filter regulators yielded strongly positive results. I suspect that this is due to some tiny instability in the regulators themselves. I may experiment with a second bleed in between the last regulator and the arm. The arm should be a constant load, so bleed there should not result in varying pressure across the arms travel. |
Slaw. Fear not your are not alone! Way back in this thread, I think, I talked about the connection with music being the key. The way it makes us "FEEL" I also talk about this on my web site. A system is just a collection of machines, sometimes this menagerie comes together in such a way that we connect directly with the music. It is a wonderful sensation and I could not live without it! cheers. |
The motivation for putting a soft tube between the two regulators was the finding that a small amount of bleed off between the regulators had a positive effect. This implied that the air pressure was not constant between the regulators. Or for that matter after the last regulator. More pressure equals more flow into the arm since it is not a compensated load and since a needle valve is not a compensated load either it will pass more or less air as the pressure increases or decreases. So the needle valve tends to smooth these pressure changes hence smooth out the air flow. The soft walled tube acts slightly like a balloon, it tends to absorb small pressure perturbations by expanding with increased pressure. The surprising finding was that this positive effect was present even when the pump had turned off. This points towards the regulators themselves creating tiny pressure changes which the softer tube helped to reduce. Acting in a way like a surge tank. If this is correct then it may be better to have the regulator remote from the arm. A long length of soft hose to the arm then helping to smooth out the regulator pressure irregularities. Obviously more testing is required. One test would be to fit a surge tank after the regulator in a rig with a regulator close to the arm. Or simply add another long length of soft tube which would be so easy to do....Chris. A small increase in regulator pressure may be required if this was done to compensate for the line losses. It is fascinating stuff. |
My thinking on why pressure irregularities have such a large effect is this. It is to do with the way the air enters the bearing manifold. This thru a small single hole. It then circulates around the sleeve and enters the 14, from memory, threaded and loosely plugged holes exiting around the spindle. Each bleed hole will see a slightly different inlet pressure because their is a dynamic flow around the manifold with associated pressure drops. If there are pulsations in the air stream this will be manifest as slightly different flow rates into the manifold and thus pressures seen by each of these holes and the flow rate thru them. This would cause the spindle to chatter. When I built the replacement manifold, I planned to interpose a finely sintered metal tube between the air inlet and the sleeve. The idea being to force the air to more approximately enter the sleeve area at all points simultaneously. I didn't do this because it made the diameter of the manifold too large and it would have fouled with the platter and I didn't think that it was a big deal. I do now. The walker arm manifold has 4 air inlet points. Maybe they have looked at this issue and used multiple inlets to help reduce its effect. |
Chris. You have now given us all another area to pine over. Humidity.....thanks a lot! :-) I don't think that your test is quite representative of what I was suggesting, since you are disabling one regulator but leaving its body in circuit. If their is any instability in the regulator it could be caused by the its structure, since the air flow path is convoluted. For example the water separator function is achieved by creating a vortex in the bowl. I will have a play this weekend where I move the regulator close to the arm, making the adjustment for line losses. This will keep the arm pressure the same. I will use exactly the same hose and length so the only variable will be the reg position. BTW, I have a pressure gauge very close to the arm, it reads in bar. Setting the pressure by ear results in a reading of 1.25 bar which is a little over 18 psi, not the 17 psi I mentioned earlier. That said how accurate are the gauges we are using anyway? cheers. |
Ok Since I cooked dinner tonite, I got a leave pass afterwards..., Have just finished trying the second regulator close to the arm. There was just 3 feet of tube between it and the arm, the original configuration having 40 feet of tube. I adjusted the pressure to compensate for line losses. With the regulator close, the soundstage shrunk both in width and depth. There is a subtle veil over the sound with attack and decay diminished. The model of regulator I use is. Norgren B07-201-A1KG. Looks like a pretty standard unit and appears similar to the photos posted here by various owners. After an hour of going back and forth to confirm my findings, I couldn't wait to settle back to the original layout....... Compressor with built in regulator- 4 ft PVC tube- needle valve bleed off- second regulator- 40 ft PVC tube- pressure gauge- arm. The Norgren regulator does something to the air flow that the arm doesn't like. Having 40 ft of tube mitigates this. I would be curious to read findings from others where a significant length of soft PVC tube was used between the reg and arm vs a short length of the same tube. For my setup the long tube was clearly superior. |
Chris. "great crazy hobby this is. We are running two very different......" Yes but isn't diversity the spice of life! My pre is my own, all tube design, well actually my own unique combination of known gain blocks with some interesting P/S features. It exists in a family of one, world wide. I wish I did live just down the street. I suspect that it would be a lot of fun. Yes, I freely admit that the pressure disparity with and without the trough is interesting. Maybe I will revisit this, but the oil trough change was big in my rig even at 12 psi each way, it just got better, with the trough, as I pushed it up to 18. If your kids are like mine, they will continue to give you sleepless nights for many years to come....sorry about that! |
Chris. Back in the day, nearly 20 years ago, I took a piece of aluminium to a machine shop along with the original plastic goose neck, set at the mid position and said to the machinist "copy this please". I did ask him to make the part that slid into the wand one thou bigger in dia as I felt that it was not a good fit in the wand I was using. There was no drawing produced. Now days to get a part machined in my shop I need a CAD drawing at $150/hour to produce. A CAM program at $150/ hour to produce. Machining itself at $450/hour, plus material which actually is the smallest cost of the lot. If we were making 100's it would be viable, but a small number would be very costly. The best option is to find a local machine shop that has lathes and milling machines and take an original goose neck along "please copy this" I used the same aluminium as the wand, 6061 T6, from memory. This info is somewhere in the manual. Sorry I cannot be more helpful but, I would recommend that anyone interested goes through the effort. There is really a big jump up in performance when the quite flexible original is replaced. |
Chris / Ketchup Yes the numbers scare me, but they are necessary to cover even more frightening expense numbers. The beast, which is our business, roars out every minute of every day saying "feed me!" Absolutely, a mag wand is on the wish list for use with my MC cart. A mag or titanium goose neck, now that is an interesting idea. |
Chris. You must have time on your hands to produce such a lengthy thoughtful tome. I read it multiple times to try to get inside what you were saying. I think that you take BTs comments to mean that the o'rings will leak if a low pressure manifold is over pressured? I don't think that this is what he means. I suggest that BT adjusts the arm design pressure by manipulating the clearance between the spindle OD and manifold ID and/or the way the capillaries are set up. The push back at end of travel he talks about is due to excessive air flow exiting the gap between spindle and manifold bush, not due to the o'rings leaking. The shims I have added are in the gap between the manifold outer plastic shell and inner aluminium bushing. This is the gap where the o'rings sit. The 2 shims about 2x3x**mm thick, each end, are spaced at 120 degree increments. Completing the circle at 120 degrees each end is one M2 grub screw. It is gently tightened to make a solid mechanical link between the manifold outer shell and the inner bush. One would not consider removing the main arm to TT plinth mounting bolt and gluing the arm to the plinth with say rubber discs spacers in place of the three pointed screws, since this would be introducing a compliant joint between the arm and TT. But this is exactly what the o'rings do. They are a compliant joint. The positive benefits of adding the shims and grub screws is unambiguous. cheers. |
Chris. Sometimes these posts can be unintentionally blunt. re the time thing. I meant that you always seem to be prepared to spend your time researching and sharing your extensive knowledge on the ET arms. I personally have learnt much from your input, which is most appreciated. I look forward to the brothel post! cheers |
Pegasus Yes air supply is grounded by earthing the brass threaded part of the pressure gauge that touches the air stream. I have tried this earthing remote from the arm and close to the arm. Close is best in my setup. Theory is that the air builds static as it flows thru the tube. A second test, recently repeated was to place a large ferrite bead over the air tube close to the arm. This caused a dramatic negative change. Go figure. Cheers |
Dover. For the sake of brevity I left the word "vertical" of the tracking angle. Pretty sure that this adjustment is applicable to a linear arm. My point was...if the spindle is NOT parallel with the platter, the VTA will change as the arm moves across the record. Bigalt. Agree 100% a level platter and a level spindle go hand in hand. Perhaps I misinterpreted your earlier post. I took it to read that you make this adjustment from time to time. Assuming that the plinth is not in some way distorting over time, I would expect this adjustment to be a set and forget one. Thereafter any shift in level of the whole TT system, say with seasonal movement of the floor/wall, would be corrected by re-levelling the whole TT. |
Slaw. Taking a look at your systems page, I see a nice compressor setup with aux receiver. A few questions please... What is the total volume of the two receivers? You get impressive cycle off time, more than a typical LP side, which has to be a good thing. Also, is it an oil less compressor? If not, any concerns about oil vapour getting into the arm? Obviously the filter and separator are inline to protect against this, but we worry about such things don't we. Many thanks |
Slaw. Many thanks for sharing the info on your compressor set up. Most interesting. Also good luck with your TT project. Just a comment on the idea of using lead shot. I have had mixed results using shot. Both in loose form and epoxy glued. In some installs it seems to create a smearing effect, however using one piece lead in sheet or rod form has always been positive. This provided it is not inserted into the energy loop we are trying to damp. That is, I have found it beneficial if the loop is laminated with lead. As always YMMV cheers. |
Slaw In my experience using solid lead never over damps the structure provided it is adhered to the structure with a glue that is of equal or higher hardness than the structure. Do not use glues like Ados! Using lead in this way actually increases the vividness or presence of the sound. Try a small sheet of your chosen plinth material. Listen to it thru a stethoscope by tapping it with something hard. Now epoxy glue a sheet of lead to the parent material. Try the tap test again. You will likely hear a sharper but much shorter "Tic". Think of speaker waterfall plots here, we want rapid dissipation of the energy. IMO the same applies to TTs as well. Next load another sheet parent material with a bag of lead shot. Tap test again. It will likely not be as sharp but will be a longer slurred sound. I think that the lead shot actually rattles and this is what you are hearing. Some years ago I made a TT stand. The vertical colums were 2" ID aluminim tubes. I tried filling these with sand, lead shot and a combination of both. Finally used solid lead rods inside the tubes. This was easily superior to the other iterations. Cheers and good luck with the project! |
Frogman. I agree 100%. IMO it is impossible to over damp, if our objective is to keep the piece of gear or part "still" and there are very few pieces of the audio chain that aren't meant to be still. It is however very easy to incorrectly apply materials in an attempt to damp that just shift the movement signature of the piece, often making it move for longer after the initial excitation. The method of bonding the damping material to the structure is critical in this. I experimented with hardener and adhesive ratios on my TT build to find the best hardness of the epoxy. It appears that the optimum is when the adhesive is more or less equal in hardness to the parent material AND when the absolute minimum amount of glue is used. |
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. |
Hello. There has been some private questions about the design of my modified ET2. I have included here some more photos for those who may be interested. The target design brief was to - eliminate all unneccesary joints. - minimise different material count - eliminate any unneccessary components that could move - make it as rigid as possible - make it as inert as possible. These took precidence over convienence of use. http://cgim.audiogon.com/i/vs/i/f/1370870032.jpg The main pillar and manifold are acrylic, since the decission to make the TT plinth out of acrylic was already made. This allowed me to fuse the arm pillar to the TT chassis eliminating one joint. No allowance is made for making the spindle parallel to the platter, after the fact, but I decided to machine the bottom of the pillar should this be required. Measurements showed that this was not needed. Two cavities are milled into the pillar. In one is glued a lead billet, the other is filled with sand. 4 X M5 capscrews in machined slots pass thru to the manifold. These are loosened and the removable VTA screw is turned to raise or lower the manifold. One turn is approx 1/2 mm (20"). Tightening the cap screws creates a very strong joint. The manifold is indexed to the pillar with a lug each end to keep it level. The pillar manifold interface is not curved. This because I did not have the machining capability at the time of build. 2 x M2 grub screws pass thru the manifold and contact the bearing sleeve pushing it slightly towards the pillar. At 120 degree increments there are 2 small pieces of shim metal inserted in the gap between sleeve and manifold. Tightening the grub screws presses the sleeve against these shims removing the compliant o'rings from the loop. Arm lifting is done by hand and the wand rests on a piece of foam at the cartridge end, when off the record. The goose neck is solid aluminium made from the same grade as the spindle. The oil trough paddle is attached to the goose neck. This is a 15 year old design, if I did it today there would be a few changes, but the fundamental architecture would be the same. As you can see my ET has had a little surgery :-) |
Frogman and Slaw. You planted a seed when talking about the Montronix regulator and controlled air bleed. I have just teed off a 1/4" needle valve in between the compressor regulator and the second in line regulator. The tee is configured such that the compressor output is fed straight to the needle valve and the second regulator is connected at right angles. Such that the air going to the arm has to turn 90 degrees. The needle valve is just cracked open, bleeding only a tiny amount or air to atmosphere. This does not alter the pressure at the arm since there is a significant delta P between the two regulators. If your regulators are of similar stability as mine you can expect greater solidity and dynamics and just plain better sound. This test was done when the compressor was off so the air supply was ex the high pressure storage tank only. Theory is that the regulator must be dithering about its setting. The needle valve, being non compensated clips the peaks of this pressure perturbation. |
Dover. "yet again you miss quote me" I think not. See your post 03-13-13. Where you go to great lengths to show, incorrectly, that when tracing eccentric records, my arm is 300% heavier than a standard ET2. The leaf spring is inactive at eccentric record frequencies. ALL ET2's and my arm are of similar effective mass as seen by the cartridge under these conditions. I am on record stating the clear superiority of the oil trough over my previous low pressure damping method. Dover "provide damping in the vertical plane and less in the horizontal" Wrong. A quote from the oil trough manual "The design of the paddle and its position mean that it will be much more effective for damping horizontal resonances than vertical" This is a simple paddle shape and lever effect. The arm has no leverage over the oil paddle in the horizontal plane but has the full length of the arm wand in the vertical. The target is horizontal damping. This is why BT publishes the before and after responses of horizontal resonance. Where the nasty high Q resonant peak is effectively eliminated. Frogman. If you are using a low compliance cartridge, have you tried a properly stiff fixed counterweight with an oil trough fitted? Disabling the leaf spring(s), say by wedging match sticks in the gaps, gives a hint at the effect, but the counterweight I beam is too flexible (it was never designed to be stiff) to show the true differences. |
Dover. I quote directly from your post of 03-13-13 *********On an eccentric record the acceleration will be the same for each arm – 0.0024metres / (1.8 sec x 1.8sec) = 0.00074 metres per second squared The horizontal effective masses of the 3 arms mentioned in this thread are: Kuzma has been quoted as 100g Terminator 80g ET2 25g The force on the cantilever is as follows: Kuzma = 0.1kg x 0.00074m/s2 = 0.000074 Newtons Terminator = 0.08kg x 0.00074 m/s2 = 0.000059 Newtons ET2 = 0.025kg x 0.00074 m/s2 = 0.000018 Newtons Summarising then you can see that the increased mass of the Terminator and Kuzma arms increase the lateral forces on the cantilever by 300-400% over the ET2. Now Krebs has modified his ET2 by adding 30gm of lead to the spindle. This adds 30g to the effective mass of the "ET2. Krebs also couples the counterweight ( no spring ) which adds another 30g to the horizontal effective mass. So Krebs has increased the horizontal mass of the original ET2 from 0.025kg to 0.085kg. The Krebs modifications have increased the lateral forces on the cantilever by over 300%********** Dover You stated in this post that the ET2's effective mass as seen by the cartridge WHEN TRACING AN ECCENTRIC RECORD was 25 gms. This is not true. The effective mass of an ET2 below FR is the total mass of the arm including the weight of the counterweight. Depending upon cartridge and wand used this will be in the order of 75 to 95 gm. I say again, the leaf spring does not flex due to the action of tracing an eccentric record, so it does not lower the effective mass at these frequencies. The lateral forces imposed on my cartridge due to tracing an eccentric record are much the same as those imposed on a cartridge mounted in a standard ET2, Terminator and Kuzma. If the cantilever is flexing when tracing an eccentric record in my set up it is by definition flexing with a standard ET2 as well. I am sure that others are finding this line of discussion tedious and for that I apologise. Slaw. Thanks for the info. I will take a look at M-30 M-60. Does this have an air bleed as well? I am already using a combination 3 micron filter and water trap. |
Further to the quality of the air supply. My current air rig is.. Compressor with storage tank and built in regulator.. 4 feet of 1/4" tube, tee to bleed off needle valve and second regulator with filter/water trap.. 40 feet, soft clear PVC 1/4 " tube....arm. Compressor cycles off at preset pressure. The 4 foot tube was black hard plastic. What type of plastic? I don't know. I have just changed it to 1/4" PVC soft clear plastic. Testing with the compressor cycled off showed an improvement with the clear PVC. This was a little surprising to me so as a backup I inlisted one of my sons to do an ABAB test. I just asked him to tell me if he could hear a difference and if yes, which he preferred and why. He did not know what change I was making. Note as above. The compressor pump had cycled off for these tests so the air was being drawn from the tank only. He told me that he could hear a difference and he preferred the soft PVC. Stating it is "much clearer" Regulator instability? Go figure! |
Dover Below is a copy of a mail I received from Bruce T many months ago. You might find it enlightening reading. "Richard, The resonance of the air cavity is over 500Khz and does not manifest itself on the surface of the bearing, it is a well damped liquid bearing. A statement - " the air gap allows movement at audio frequencies" - shows a lack of understanding regarding how a tonearm works. In two out of three degrees of freedom (x,y, & z axis) a cartridge is completely free to move in any tonearm. How can it not move in the X & Y axis but magically pull and push in the constrained Z axis? The record is encoded in and the forcing functions greatest in the X (vertical) and Y (horizontal) axis. A tonearm works because of mass present in all three axis with the forcing functions above the systems natural frequency. The tonearm components headshell, arm wand, are thousands of times heavier than the cantilever and stylus, so by a ratio of masses, they sit still. To put this in perspective go run back and forth and jump up and down on a several hundred thousand pound untethered barge and watch the displacement of the barge, while it will move, its motion will be extremely small relative to yours and proportional to the ratio of masses. I used three measurement methods when developing the tonearm, accelerometers, strain gages, and the simplest and most effective was the use of a second tonearm to play parts of the tonearm under test while playing a record. Measurements at the air bearing are more than 60dB (1 million times) below signal levels, lower than the pivoted tonearms I used for comparison. In reality the ET-2 has its highest inertia in the Z axis and appears rigid to the cartridge. If a tonearm moved at audio frequencies it would reveal itself as dips in frequency response. brucet" The arm IS rigid at audio frequencies, however it is sensitive to supply pressure irregularities. These are two completely different phenomena. re pressures. In my rig, I found 12 PSI to be optimum without an oil trough, 17 psi with one. There is no inconsistency. |
Chris. The config was not quite as you wrote. In both iterations I used two regulators. The one in the compressor and a separate stand alone Norgren model. Basically I slid the second regulator along a 43 foot length of clear soft PVC tube to position it either within 3 feet of the arm or 40 ft of the arm. This to test my theory that regulators themselves introduce tiny pressure perturbations which can be smoothed by the long run of flexible tube. So, yes I believe that I have introduced a more consistent air delivery to the manifold. The key though for owners that have in-room regs close to the arm, is that the regs may be doing harm to the sound. Note I made no change to the air supply circuit, just its configuration. The pressure gauge is right next to the arm and I adjusted the second regulator pressure output such that the arm received the same pressure for the two configurations. So a spindle resonating problem would have shown up in both configurations. Further I know what excessive pressure sounds like and this was not what occurred last night. The arm has a high pressure manifold. What actual design pressure? Don't know, but 17 to 18 psi with an oil trough works best. Yes I tried different records and VTA settings. I did not remove the oil trough. Findings were consistent across all the tests. This would be very easy for you to try. Just significantly increase the length of clear 1/4" PVC tube from the outlet of your in-room regulator to the arm. You will need to slightly (very slightly) increase the reg pressure to ensure that the arm sees the same input pressure due to a small line loss in the longer tube. Now I know that this is not quite the same test as I did since you will be adding extra tubing but it will, I'm sure be informative. Yep, I am well aware of the "better equals worse" scenario. Have gone down that dark alley many times. Pretty sure that this is not one of those. Their was no ambiguity at all with my findings in my rig. Also just adding another finding from some years back. The air stream needs to be earthed close to the arm. In my case, I earth the body of the pressure gauge which has a metal sensor that touches the air flow. Static build up? cheers. |
Chris. Having owned power boats pretty much my whole adult life, I am very familiar with the effect you sight. There is a "golden" set of adjustments, propeller angle, trim tab setting, RPM, weight distribution, where once optimised, the boat becomes quiet, travels faster, the ride is smoother and it burns less fuel. It is I believe a good analogy for a tone arm set up. There are many individual adjustments that combined correctly can result in "golden" performance. It is probably difficult to compare oil trough settings. I am using a different oil and different paddle at the other end of the spindle. Further I have a fixed CW which means that the physics of the arm are quite different. The undamped resonant peak is higher on my arm, so it would need more damping to bring it under control. mlswgdtftwg |
Hi All. I have been experimenting with the air supply again. This after earlier experiments implied that the output pressure from the regulators I am using oscillate around their setting. The change I made was simple taking a few minutes but furnished a worthwhile improvement. initial setup was... Compressor, inbuilt regulator, 6feet soft PVC tube, 1/4" needle valve vented to atmosphere (barely open), second regulator water trap, 30feet soft PVC tube, arm. The new configuration places the needle valve immediately after the second regulator. The theory being that both regulators are unstable and bleeding some air to atmosphere via a non compensated needle valve will smooth the regulator perturbations in the air stream to the arm. I had to increase the setting on the second regulator a tiny amount to bring the pressure seen by the arm back up to the pre change figure. The hissing of the needle valve is not an issue since this setup is in another room. The result is an increase in "tightness" notes are more visceral and solid. Soundstage larger in all directions, greater differentiation of the sound between records and individual tracks of the same record . An agreeable result. All testing was done with the compressor cycled off. |
Hi All I have just finished testing a precision pressure regulator in the air supply for the arm. I replaced a Norgren B07-201-A1KG reg with a Norgren 11-818-101 Findings in my rig..., Was there an improvement? Yes. Things were a little clearer, more three dimensional and impactful. A big change? No, but worthwhile. All comparative testing was done when the compressor had cycled off, drawing air from the reservoir only. The old reg has a built in filter/water seperator the new reg doesn't, so a seperate filter/ seperator was also installed before the new reg. So technically two things were changed. Did this have an impact on the results? Maybe Whatever, the new configuration is staying firmly in place. The bleed off needle valves before and after the reg, that I posted some time ago, were retained and their beneficial impact confirmed. It shows all over again that the arm is very sensitive to the quality of the air supply. Cheers |
Chris. I can relate to the water in the air comment. Here in Auckland, New Zealand, it gets pretty humid in the summer months. Many years ago I was listening with a few Friends and we all commented on the sound quality being sub par. It was put down to the high humidity pulling down the bias voltage on the stats, a known issue. But then the ET locked up and it began spitting out water. Quite shocking to see this in action. I have used a water separator and drainable tank ever since that night. cheers . |
