If you position a cartridge arbitrarily you will increase tracing distortion and promote uneven vinyl and stylus wear.
The goal is to have your stylus retrace the path of the cutting stylus across the record while maintaining stylus and cantilever tangency with the grooves at all points. (Perfect retracing and tangency cannot be achieved with a pivoting tonearm - cutting styli move across the record on a straight line radius, not on an arc - but you still need to get as close as possible.)
This is what alignment protractors are for. It is very difficult to mount a cartridge properly without one. Which protractors you can use depend on your RB600's mounting distance.
1) What is the distance (in mm) from your arm's pivot point to the center of your platter spindle?
2) Is this distance adjustable?
With that info we can recommend specific, compatible protractors. Without it we're guessing.
P.S. Mario b's description of overhang was the correct one. |
But if the cartridge can't be moved inside the shell, or it's a SPU type of cartridge, how can one get both the pivot-to-spindle distance and overhang right? You can't. Any parameter you cannot adjust forces you to rely on the accuracy of the manufacturer(s). There are no high end cartridges with SPU mounts AFAIK. Plug and play rigs are for users not interested in optimizing the performance of their systems. That's a perfectly valid approach of course. Different strokes and all that. There is one high end tonearm (SME) which does not allow adjustment of the cartridge in the headshell. SME does include a sliding base that adjusts overhang by changing the spindle-to-pivot distance. This still assumes a perfectly square cantilever, which is a bit optimistic IME. Some SME owners actually drill out their headshell mounting holes to give themselves some play. Sometimes you have to move the whole tonearm, but that would be a violation to the rule that for each arm there is one optimal pivot-to-spindle distance. There is no such rule. Where did you hear that? |
Robdoorack is correct. Like him I've mounted cartridges on several Rega type arms, some using the Rega (single point) alignment and some using Baerwald (two point) alignment. Baerwald results in lower overall tracing distortion, but it cannot be used on a Rega mounted at the specified 223mm. With the arm that far from the spindle most styli won't reach the two Baerwald null points.
Moving the Rega closer, to 219-220mm, does the trick. Of course this requires a table that allows moving the arm mount. Child's play on a Teres/Galibier/Redpoint or Raul's Acoustic Solid. Not so easy if the table has a fixed armboard. In that case drilling out the headshell slots, as Rob mentioned, is certainly an option. I prefer a pivoting armboard myself!
Dazzdax,
I'd suggest you pay an extended visit to the FAQ's section at Vinyl Asylum. There are many good technical articles archived there. Well worth the time. (Some of them contradict others, which makes it more fun!)
The goal, as I mentioned before, is to position and align the cartridge to minimize tracing error. A pivoting arm can be set up using any of several valid alignment schemes. Each scheme requires a different spindle-to-pivot dimension, so there is no magic mounting dimension. That of course means there is no magic number for overhang either. Each of these interdependent variables changes depending on the alignment null point(s) you choose.
Overhang,
Where are you? Have you measured your tonearm's mounting distance yet. |
Raul, I'm almost certain my friend's SME V slides toward/away from the spindle, but it wouldn't be the first time I was wrong. I'll have to check/ask him.
P.S. If you haven't checked my system in a while, take a look. Bad news: still plenty of "equalizers". Good news: no more SUT. I think you'll approve!
P.P.S. We went to the symphony the other night and I paid special attention to the kind of LF ambient info you described on your subwoofer thread. You hit the nail on the head amigo. Even with only violins playing the hall size was most evident from very LF info. Very astute observations you made. Gracias. (Now where am I going to put two subs?) |
Welcome back Overhang,
First of all, nice new rig! It should play some great music.
If you view the tonearm from directly above and swing the arm back and forth, you can visually imagine the exact point around which it swings. That is the pivot point, the only spot on the arm that DOESN'T move when you swing it.
There's no obvious visual spot at the pivot point on an RB600 so here's what I do: stick a small piece of Scotch tape on top of the arm tube, above the pivot point you just identified. Mark a dot above the pivot point with a pen. Swing the arm a couple of times to confirm the dot isn't moving. If the dot moves, change the position of the tape and try again. When the dot remains stationary you've marked the pivot point. Voila!
Now measure the distance from that point to the center of the TT spindle, in mm. Close counts, + or - 1mm is good enough. Let us know that dimension and we'll go to step 2.
Re: spacers
Once the Shelter is securely mounted and can drop it onto a record you can tell whether you need spacer(s) or not. Shelters typically like to have the cartridge body VERY SLIGHTLY tail-down. Use whatever spacers you need to achieve that orientation. |
Raul,
I must have been sleepy. Of course an SME IV/V changes mounting distance when moved on its rack.
In plain 2-D geometry the SME rack is a straight line segment. The TT spindle is a point. Any object moving along a straight line MUST change its distance from a fixed point.
The only path an object can travel without changing distance from a fixed point is a circle with said point at its center.
The SME rack is not a circle or any portion of one. If it were, moving the arm would not alter its relation to the platter or the LP. Such a mechanism would serve no purpose, the arm would literally be going in circles! |
Overhang,
AHA! Progress.
It appears your Gyro was used with some arm that needed a shorter mounting distance than a Rega. Fortunately, the Gyro's armboad is adjustable. I don't know the details but there are one or more screws you loosen, after which the mounting plate spins. You'll note the arm mounting hole is offset, so spinning the mounting plate changes the arm's distance from the spindle.
Try to make your spindle-pivot dimension 219-220mm. That's the optimum for a Rega to achieve 2-point Baerwald alignment, which is widely considered the best scheme.
If you can do that, visit www.TurnTableBasics.com and buy their $20 mirrored alignment protractor. The TTB is probably the most accurate protractor short of a $150 WallyTractor. You'll be all set.
Doug
P.S. Don't bother trying to align a cartridge using your Rega protractor with the arm at 216-218mm. It won't be possible. That protractor assumes 223mm. If you don't want to buy the TTB protractor and just want to use the Rega one, you'll have to swivel the arm's pivot point all the way out to 223mm.
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Plinko,
Glad that was helpful. Trying to measure/adjust the pivot point when you can't even see it is too tough for me!
Mario b,
IME Baerwald alignment cannot be attained with a Shelter cartridge on a Rega mounted at the standard 222mm. The stylus will not reach the null points. This is true of many cartridges, as explained on the instructions that come with most Rega/Baerwald protractors.
This is not a "flaw" of Baerwald protractors. It's a mathematical function that results from choosing a different alignment than the arm was designed for.
BTW, 60mm and 115mm are not the Baerwald-defined null points. You can use those points if you like, but you won't be following Baerwald's equations. The Baerwald null points are 66.0 and 120.9mm.
There is no reason to be nervous about changing your arm's mounting distance, especially on a table like Overhang's Gyro that's specifically designed for it. Deviating from Rega's specified 222mm to achieve a superior alignment has no down-side and no risk. Why would you be reluctant to do that?
One can certainly DIY one's own protractors of course, using any null point or null points one chooses. But a mirrored protractor like the TTB or Wally is more accurate for cantilever alignment than a piece of oak tag. |
After several months finally you achieve to convincing that the step-up transformer is not the best way to go, better say: is not the way to go, for amplified the signal on a phono cartridge. Welcome aboard!!!!!!!!!!! Raul, play fair! I never said an SUT was "best". I only said it was viable for those on a budget. I still believe that. Not everyone can afford a reference quality preamp. My old preamp/phono + SUT's can be bought for < $1,500. My new preamp/phono cost nearly $6K, and if sold through normal retail channels it would cost over $10K. It wins the battle easily, but at that price it should. Still, thank you for the welcome. You and Nick both insisted that FET's could significantly better our SUT's. It took us alot of money and him alot of work, but you were both correct. It does sound amazing. :-) You have to have [two subs]. When that happen you will be really happy about. From careful listening at the concert last week I believe you. Please order me a bigger house! ;-) |
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Mario_b asked: Why cant one set the cartridge overhang using linear measurements as per the arms manufacturer for the designed tracking arc: Then use compassed circles for Baerwald, Stevenson or whomever one divines to have the null points ones looking for, and use these to set just the stylus tangent? What am I missing? Here's what you're missing: this method assumes one can attain stylus-groove tangency at DIFFERENT pairs of null points with the stylus travelling on the SAME arc. That is not possible. On any given tracing arc, assume the cantilever is tangent at two points A and B. This is only possible because the cantilever is travelling through a given moment of arc, from which it receives a given angular shift. Now choose two new points, C and D, located on the same tracing arc but separated by a different moment of arc than points A and B. Make the cantilever tangent at point C and check its orientation at point D. It will not be tangent. Why? Because it experienced a rate of angular shift that was suitable for the (different) angular seperation of points A and B. Changing alignment schemes will always require changing the tracing arc. Tracing arc protractors (like the Wally or your proposed DIY) are wonderful and easy to use, but like any protractor they are specific to one particular alignment scheme. |
Mario,
That's the spirit! I first did this just like you're planning to do, by trial and error. I tried to set up my OL Silver/Shelter 901 at the OL-specified 223mm using a TTB protractor. No dice. The stylus couldn't be aligned at both points. I sat down and thought through the geometry, slid my armboard in a couple of mm and, bingo! Problem solved.
It was only later that I got my head around the theory (a little) by talking with real mathematicians on VA and reading some of the papers there. If you want real math, go there and search for posts by John Elison.
Again, anyone can choose Rega's Stephenson geometry and have no problems at 222-223mm. I just like Baerwald's theory (lowest total distortion) better and appreciate the greater accuracy the TTB's mirror makes possible. Frank Schroeder uses a DIY protractor he printed on a piece of card, so if you prefer that you're in the best possible company. I just like the mirror.
P.S. Whatever protractor you use, don't forget to disengage antiskating!
Bob,
Thanks for sharing that info. Null points at 64/120 are pretty similar to 66/120.9. I think the key is that you're at 222mm whereas my Rega style arm specifed 223mm, which definitely didn't work.
Another variable is the stylus-mounting screws dimension. The farther the stylus is ahead of the plane of the mounting screws, the farther the arm can be from the spindle. I don't know your BPS but ZYX's and Shelters are both about 7.5mm, which is on the short end of typical. Some cartridges run as long as 9mm, which would probably make adjusting the arm unnecessary.
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Bob,
That extra mm explains why you can reach null points similar to Baerwald's while shorter cartridges can't quite make it before hitting the front of the slots. (I assume you're pretty close to the front.)
Thanks for some interesting info,
Doug |
