Its a fairly long description in the manual but basically involves putting the second arm / cartridge on top of the first while playing a track and "listening" to it to hear resonances in the first arm.
It also includes a discussion of how materials change their physical properties at resonance and become much less rigid or stiff. |
If you want to experiment with really low compliance tightly coupled counterweight you could just wedge something like a tooth pick in the joint to essentially remove the spring from the equation. I think Bruce mentions this somewhere, in any event I didn't invent it, just passing it on. |
I have used an ET-2 since they first came out. It is now mounted on a TNT of early vintage (MK I, II??) which still has the spring suspension. I am about to convert it to the paddle ball suspension as soon as I can find some paddle balls and make up a few parts.
I recently plumbed it into my shop compressor so my tone arm is now driven by a 5hp compressor with a 50 gallon tank. I am running about 15psi but keep seeing 19psi as the sweet spot but I can't tell any difference. What is magical about 19psi? |
On weight placement: whether you want the weights close to the arm tube or far away depends on the cartridge compliance. Bruce has a pretty good write up in the manual which is available on the ET website. |
Thanks Ct, I seem to remember reading in past about the hose/ coupling limitation. I have read the comments and discussion on Salvatore's site and found them interesting.
I scanned the threads you linked and did not find anything about ET-2 or pressure. Perhaps I didn't look close enough.
I don't have my setup plumbed in a way that allows me to adjust it from the listening position but I should probably do that. From what I can tell so far I think at 19psi things seem to go a little dead but there seems to be a nice spot where things open up a bit at about 16psi.
I agree that filtration is an important part of the system and while my compressor is located a bit far away in a different environment I probably have more dedicated to filtration and drying than most as I also use the compressor for spraying finish so I have more traps and driers than most. I also have a regulator at the compressor for the turntable line and another filter and regulator at the turntable. The regulator at the turntable is a low pressure large diaphragm unit which may help a bit. I do not have a surge tank at the table however.
Also here in SoCal there is probably less difference between the indoor and outdoor environment than in many parts of the world. |
Frogman, do you mean 19 was a little too much and ...
I think I agree that 16 - 17 seems to be the sweet spot in my system.
Ct, that was an amazing setup on the Chinese thread. Do I understand correctly that he had mounted the arm from the top on a micrometer controlled X/Y stage???
I just got a post back from Mike at VPI with some suggestions so my next move will be setting up a ball suspension to replace the springs in my TNT. Apparently this will make a significant difference.
I just realized I can set up a system with pictures so I will try to get something posted. |
Chris, do you sill have the springs in your TNT? I have seen much discussion about different drive belt materials but I have not tried it yet. Perhaps it is time. From my perspective I don't see how the background is going to get much blacker as it is pretty much silent now if the record is good quality and clean. I gave up on the tripully setup years ago and don't miss it at all.
I am using the PLC drive and really should try a SDS. I think I may try to borrow one before I make the plunge. When you talk about speed stability are you talking short term or longterm, e.g. wow and flutter or pitch control?
I just splurged a bit on a new prepro so I'm not quite ready to invest more at the moment. |
Re I beam compliance
I think what Bruce is saying is he is using the decoupling of the balance weights to reduce the effective horizontal mass which allows the use of heavier arm components with their inherent increased stiffness. This seems to imply the use of the single leaf beam to provide the max decoupling, but the best answer is complicated by the compliance of the cartridge you are using.
If I understand correctly the selection of heavier weights close in or smaller weights further out also depends on cartridge compliance and can be verified by measuring the horizontal resonance frequency with a test record.
Changing the compliance of the beam will have a significant effect on the resonance with the stiffer beam increasing the resonant frequency. I may have that backwards but the idea that it changes with the I beam coupling is correct.
The stiffness of the component parts of the arm are physical factors that cannot be changed by anything attached such as I beam and balance weights. The amount of deflection in the arm components however will change with the change in weight and coupling of the I beam assembly. This deflection is however vanishingly small except perhaps at the I beam spring. |
The ears always rule. Didn't mean to suggest otherwise.
If things always worked as physics suggests then this treck would be much easier. |
C1 if you are really interested in visitors let me know, I would love to hear your Dalis.
Frogman the change in sound with changing pressure was fairly subtle prior to the suspension change and since the change is essentially nonexistent.
I don't think the manifold is clogged as the pressure is in the correct range with the original pump. I have had the manifold out and cleaned it but it was some time ago.
If I get bored perhaps I should do it again just to be sure. |
Can anyone describe the symptoms / downside of over pressure?
Initially (recent history as I have had this arm since '85) it seemed that the music dulled a bit above 16 psi.
After replacing the spring suspension in my TNT mk 1? with delrin cups and racquet balls I don't think I can hear any difference between 15 - 19 psi. |
Since no one has responded I will post my thoughts and see if anyone comments.
I think of it this way:
As the pressure is increased the volume of air used increases and this is dependent on the clearance between the manifold and spindle. At some point that escaping air will become obvious in two ways, one being the noise created and the other will be horizontal force on the arm at the end of travel.
The increase in pressure will also make the tube / manifold interface stiffer and I think this is what causes the increased performance. It seems to me the the stiffer the better as long as other factors such as oscillations, vibration etc. from the escaping air don't rise to a
level that they cause problems.
My arm is a very early version, so certainly not optimized for higher pressure, and I can feel the air escaping at 19 psi but I can't hear it yet. I have not tried to determine if it introduces significant horizontal force. As I stated in my post I could hear some of the life or vibrancy go out of the music when I increased the pressure but since I have tightened up the suspension I no longer notice this change.
It would be interesting to ask Bruce about this. I suspect that as the pressure increases he reduces the clearance between the manifold and tube. There must be a point of diminishing returns and I wonder where he thinks it is.
As I think back on what I did I also made some adjustments to tighten things up on the arm / mounting board around the same time I changed the suspension so that may also be a factor.
I should plumb the pressure regulator so I can sit at the listening position and adjust the pressure so it is easier to evaluate changes.
|
Frogman I do remember having an issue with air loss from the manifold due to a cap screw leaking. I don't remember which one it was, I resolved it by using Teflon plumbers tape on the cap screw.
Conversations with Bruce T implied that some have had problems with stripping the threads in the manifold where the adjustment block attaches.
I also think that if these screws are too loose it allows the arm to flex quite a bit which would seem to be very counterproductive. |
I have a very early ET2, so early in fact it came with an ET1 manual. Why would I mention this? Because there is a very interesting technique Bruce describes using a second tone arm and cartridge to measure arm resonance. Have any of you folks heard of this, especially those who have removed the damping materials? |
An interesting set of articles on the ET2 with a little discussion of resonance in tone arms.
http://www.stereophile.com/content/eminent-technology-two-tonearm |
I have not thought much about the actual mechanics and physics of turntables and arms but some of what I read does not make much sense to me. Perhaps someone can help me understand better.
Folks talk about "draining" energy to the earth or some other place of stability as if it somehow removes the effect. This does not make sense to me. If a tone arm resonates at some frequency it seems to me that it must be moving. That movement will eventually be damped by some mass, i.e. the movement will become undetectable. The resonance will if no longer being excited die out as the energy is dissipated as heat energy raising the temperature of the resonating part.
The damage from an audible perspective would seem to me to come from the movement. For the cartridge to reproduce what is in the groove it needs to be absolutely fixed relative to the groove. If it moves relative to the groove then that movement becomes part of the electrical signal as there is no way for the cartridge motor to know if the cartridge is moving or the cantilever is moving.
What I think Bruce is saying with his measurement technique is that if you can sense movement in the headshell of a tone arm, which is what you are doing by placing another stylus / arm on the headshell as it plays a record, that movement has to be counterproductive to the faith-full reproduction of the information in the groove. |
Well I finally got around to trying the dual leaf I beam. I went back to the single leaf as I liked the bass better. |
Chris,
The cartridge that I use has medium / low compliance (15x10-6) or thereabouts.
I am using three small or one large weight and it is in the area of 5 on the beam.
I did notice a little leaner sound with the double leaf spring but found a loss in bass so I went back to the single leaf. For what it is worth I play and listen to a lot of live acoustic music (I play guitar and upright bass in a bluegrass / old time setting several times a week) and I am not a fan of the lean hard sound some folks claim is "Hi Fi".
I did change the VTA a bit but my cartridge does not seem to be terribly sensitive to VTA. |
Chris, I can't get the correct tracking force with only two small weights. |
