yuckyamson
pfm Member
Is that him on the side? He looks like the one giving the demo, if anyone.
Is that him on the side? He looks like the one giving the demo, if anyone.
Hi Richard,
I have PM’ed and emailed you since Monday about the Supatrac arm and have yet to receive a response.
Please let me know if there is a problem with the shipment so that I can contact the courier.
Thank you.
out of curiosity, can you summarize what the azimuth issue is in simple terms? As the cart travels inward towards the record center the arm tends to tilt....which way?
The variation is quite hard to see, as my photos above show, but when it is discernible the cartridge tilts very slightly towards the centre at track 1 and slightly away from the centre at track 5. In a well configured arm I believe that the amount is more or less negligible, but I would certainly prefer if this error never occurred and I take customer criticism very seriously.
As far as I understand it, the reason for it is the hoist suspension underhang which means that the vertical axis for yaw movement is slightly tilted towards the cartridge, specifically at the equilibrium position. The natural arc of the cartridge is therefore on a circle which is slightly lower at track 3 than at tracks 1 or 5. This resolves as a very slight change in cartridge lean as the arm swings across the record. I emphasize that the effect is of a scale to be nearly invisible on my decks, and sonic performance remains unprecedented across the entire record.
The solution is a vertical hoist plane so that the normal to the record is perfectly parallel to the yaw axis.
So if I have it right, because the Hoist assembly can only be exactly evenly hung (i.e. both the right hoist and the left hoist's threads have equal pressure applied to each side) at the center of the record's playable area (i.e. midway through the record), because ultimately the hoist is a thread that his hanging on a hook an the hook itself doesn't rotate left/right (which, if it would, would create another movable part), the hoist pulls somewhat torquing IN at the start of the record and, after the swivel has achieved equilibrium in the hoist at the middle, proceeds to pull and torque OUT as the hoist turns past equilibrium? Is that right?
I thought the issue created would be SKATE or anti-skate, but I could understand if indeed it's actually create a YAW issue. Unless I'm way off base. Feel free to correct me.
This is exactly correct, but not the issue under discussion. Your point concerns residual skating forces in the bearing design. The Blackbird has an anti-skate mechanism which compensates for the bearing's residual skating forces when it is configured correctly. The anti-skate mechanism allows you to adjust both the difference between applied anti-skate force at the beginning and end of the record, and independently, the average anti-skating force. When you configure it correctly it will apply very little anti-skate force at the end of the record, since the bearing already applies some, whereas at the beginning it applies significantly more than would normally be required because it also needs to oppose the additional skating force residual in the bearing. For this reason I always test skating at the beginning and end of the record to ensure that both are in the good zone. Always remember that anti-skate force is never really right on any pivot arm because it is signal/drag dependent. Deviation in lean (azimuth) is a separate issue.
I use 'yaw' to refer to the correct movement of a non-tangential arm across the record. The issue in question is lean (azimuth) deviation as the arm yaws in the required way. I hope that's clear. I know it can be difficult to discuss these things without animated diagrammes. 3D dynamics can be a bit mind-boggling.
I think we are saying the same thing. For me YAW = AZIMUTH, i.e. that if the arm rotates ever so slightly on it's length-wise axis (as in, to restate, azimuth).
"When I use a word," Humpty Dumpty said in rather a scornful tone, "it means just what I choose it to mean -- neither more nor less."
"The question is," said Alice, "whether you can make words mean so many different things."
So as the hoist is out of equilbirum (either being at the beginning of the record, or the end, essentially either side of midway through the record) the thread hoists, resting on a hook
which when the hoist threads wind around (this way or that, again away from center position), adds a bit of "tilt" to the arm, this way or that.
Effectively the hoist hook is acting as a bearing of sorts. Richard obviously I'm not an engineer or designer, but it strikes me that this may very well be the compromise of the design and one worth living with. I'm not sure how you could fix this issue without creating another issue somewhere else or of some other nature. Let's say for example that the hoist-hook was itself allowed to rotate....it would alleviate the YAW/Azimuth and skate/antiskate issue caused or influence added to those areas, but now you'd have a bearing, subject to noise, resistance, chatter, vibration, etc. So that's the point?
It may be something to look at as your design develops but I'm just not sure how you'd work around it. The Underhung nature of the hoist is what puts forward pressure on the arm to push the thrustplate into the pivot-point.....so why ditch that? as you say when the stylus drags it helps the overall design concept as opposed to hurting it. How far out is the azimuth as of right now, at the extremes?
But that's not yaw. I don't think it helps to redefine well-established words as something else. The meaning of yaw is very clear in boats, aircraft and many other uses, so let's keep its traditional meaning with tonearms. The world is already enough like Alice's wonderland:
There is no hook. The hoists convene at a 1mm diameter downwards facing hole.
No, they don't.
The issue before us is azimuth deviation due to the tilting of the bearing's yaw axis. It arises only because the arm is configured with a tilted axis. You can also configure it with a vertical axis in which case there is no azimuth deviation. Contact pressure at the bearing is easily supplied by magnetism instead of gravity, therefore underhang isn't necessary, the yaw axis can be vertical, and azimuth deviation is avoided. No yin-yang required.
In order for the threads to "convene", the "downward facing hole" in effect acts as a hook. The bottom line is that as the hoist twists away from center there are some side effects.
I am not, unfortunately, fully understanding the solution to the issue, perhaps not the issue at all. But I get from Adam's video that azimuth is off both at the entry of the record groove and at the end, in opposing directions. If you have a way to solve it without compromise, hats off. Would love to understand it more.