An easier way to set VTF/VTA/SRA? Perhaps....


I've occasionally advocated the need (over at Vinyl Asylum) for an additional alignment parameter in order to more easily find the desired tracking force (VTF) and stylus rake angle (SRA) interaction and easily adjust for changes in suspension elasticity. I refer to it as Weighted Cantilever Angle (WCA) which is the angle of the cantilever (from horizontal) where the manufacturer intended the cantilever to be positioned within the cartridge generator. (This would of course require manufacturers to provided the intended WCA for each cartridge.)

To align for WCA, a small angle gauge would be placed on the record surface to determine the cantilever angle as tracking force and tone arm height are adjusted to keep the headshell/cartridge body level. When the combination is found whereby the cartridge body is level and VTF and VTA/SRA provide the recommended WCA, then the optimal vertical cartridge alignment should be very close and only need fine-tuning.

The weighted cantilever angle could be easily checked periodically to see if there have been changes in the suspension.

Do you think this idea has merit? If not, what are the flaws in my thinking?

Tom
tketcham

Showing 6 responses by nsgarch

"WCA"? Do we really need another acronym? What you appear to be talking about is finding the VTF (within the manufacturer's prescribed range) which will put the plane of the coil windings (basically the plane of the coil former) at a right angle to the lines of the magnetic force field generated between (or 'around', depending on the design of cartridge's magnetic generator) the magnetic pole(s). (In the case of MM cartridges, it's the reverse.)

The easiest way to determine this is to listen for or to measure (your ear will work just fine) the cartridge's maximum output at two or three nearby VTF settings (before making other adjustments.) Some tips: 1.) Do this with a mono record and (if it has one) your preamp set on 'mono'. Why? You may have harmonic distortion or minor tracking issues at this point before setting all the other parameters - but it's still important to set this one FIRST! 2.) If your cartridge is a new MC, delay all but a rough setup until after a minimum of 50 hours, AND for that first 50 hours, set the VTF to 1/4 gram OVER the manufacturer's recommended maximum. Why? First don't worry; you won't hurt the cartridge or the suspension running the VTF a bit high (and you should own an accurate digital scale by now ;-) This will result in a suspension (when break-in is over) with a 'Q' (elasticity factor) that remains constant just BEYOND the normal operating range -- otherwise, the 'Q' can be non-linear just at the point most MC cartridges yield their best output (the high end of the VTF range.)

After doing this, you can move on to setting the SRA and other alignment parameters; EXCEPT: forget VTA, which, if you give it a minute's thought, you'll realize is a totally useless concept. If everyone's cartridge's dimensions and angles (ALL of them!) happened to match EXACTLY all ALL of the cutter-head's dimensions and angles, there might be a case made -- and even then it would be philosophical at best, because you could only reliably play records made with THAT cutter-head/operator! And besides, lathe operators make adjustments too!! And cutter-heads generally are cantilever/suspension-less!

AND, if you have a stylus with a spherical or elliptical tip, you needn't worry too much because how it fits in the groove is pretty much the same over a range of SRA. A micro-ridge or line-contact stylus is just the opposite and SRA is extremely important. Here is the most accurate way to do it I've found to do it: Basically, you have to find the point (after finding/setting the optimum VTF) at which the stylus is perfectly vertical in the groove (looking from the side, not the front.) This is different for every cartridge (even among the same model/manufacturer.)

Once you've found that baseline, you can go from there. I've provided detailed instructions here: http://forum.audiogon.com/cgi-bin/fr.pl?eanlg&1140840022&openmine&zzNsgarch&4&5#Nsgarch
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Tom -- finding true vertical for a line or micro-ridge stylus, as I outlined, is actually quite easy, and many people have done it with great results once it was explained. And there are only three stylus geometries, if what you mean by "geometries" is stylus 'shapes'. There are: spherical, elliptical, and line/micro. There was also the Shibata which was an attempt at making a line-contact but before laser cutting techniques were available. After finding zero SRA, it's nice but not mandatory, to have an arm with vertical height adjustment "on the fly" (while the record is playing) so you can experiment easily once you know where true vertical is for your stylus.

As for your statement
I refer to it as Weighted Cantilever Angle (WCA) which is the angle of the cantilever (from horizontal) where the manufacturer intended the cantilever to be positioned within the cartridge generator.
I think you are using the wrong terms, which is what's getting you into conceptual trouble. It's not the CANTILEVER which is positioned WITHIN the generator -- since the GENERATOR consists of the coil/armature positioned inside the magnetic field. The cantilever is completely outside that area. And frankly, I don't think cartridge makers are much concerned with cantilever angle, so long as it allows the cartridge body and front pole piece to clear the record surface. What cartridge makers ARE interested in doing is making the cantilever as SHORT as possible to eliminate resonances. The van den Hul Colibri doesn't even HAVE a front pole piece in order to facilitate an EXTREMELY SHORT cantilever. And DECCA cartridges have no cantilever whatsoever!

I truly wish people would stop using that "SRA/VTA" term as if they are the same thing -- THEY ARE NOT!! Further, VTA can be pretty much any angle between too low (the back of the cartridge hitting the record) and too high (the front of the cartridge or front pole piece hitting the record) and so what!? What IS important, is to let the VTA chip fall where it may, while instead MAKING SURE the stylus' edges slant forward at exactly the same angle as the forward-slanting groove undulations - thus locking them together.

Sorry for the long post but I'm afraid we have little to agree on at the moment ;-)

Neil
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I wish I could agree with more of what everyone is saying, but most of it is wishful thinking. For instance
I assume that the stylus is properly mounted to the cantilever and that the manufacturer knows the angle of the cantilever when the stylus is at an optimal rake angle. Wouldn't it be much easier to measure the angle of the cantilever rather than a tiny stylus?
All I can say is I wish it were true but it's not. It's hard enough to mount a stylus to a cantilever. Expecting to mount the diamond at the same angle to the cantilever time after time is simply not possible. Even the solid one-piece diamond stylus/cantilever cannot be fabricated identically time after time. Thus the need for calibrating the initial zero SRA point for each stylus-cantilever assembly. Thaough statistically possible, no two can ever be assumed to be the same. As for
Well, the cartridge manufacturers do already provide the parameter to set the VTF right: - their recommendation of the range the VTF have to be set in.
There's a reason for specifying a 'range' and it's this: there is only one VTF setting for an individual cartridge at which the suspension will compress just the right amount to place the coils at exactly 90 deg. to the magnetic force field. If you look at a mechanical drawing or exploded view of a typical MC cartridge, there is a tension wire attached to the coil armature on the opposite (back) side from where the cantilever is attached. This wire is carefully pulled to a certain tension and locked with a set screw. This "pre-compresses" the suspension rubber; otherwise applying the correct VTF would just collapse the suspension and the cantilever would 'retract' up into the cartridge body ;-) Further, that wire is not pulled straight back, but slightly upward and back, forcing the coil armature to sort of 'tilt' forward and putting a little "downward English" on the cantilever - then, when the stylus contacts the record at the 'perfect' VTF, the suspension compresses and the coil armature tilts backward slightly, bringing it into proper right angle relationship to the force field. It's the trickiest of all the steps in making a cartridge and each cartridge will have a specific VTF setting (within its specified VTF range) where that alignment is correct. As far as I'm concerned, each cartridge has one absolute VTF setting at which this perfect alignment occurs. (It also happens to be the one where the cartridge sounds its best ;-) The SRA setting is not absolute. It will vary +/- a half a degree from the average 1.4 degrees as a result of two factors out of our control: record thickness and the whims of the lathe operator. Which is why SRA on the fly tonearms are preferable. And why I'll either eventually sell my SME V or get so old I just don't give a rat's a-- anymore!

Then you have to get the other geometries right on the money. Overhang, offset angle, azimuth. The only setup parameter that will usually vary (SLIGHTLY) from the theoretical ideal, and therefore a bit open to musical "taste" is cartridge loading. That variability is due to differences in tonearm mass/damping, cables, phono preamps and/or SUT's, or other room and/or hardware factors. It's where you get to tailor (if only slightly) the sound of your cartridge to suit your sonic preferences.

The other settings are pretty much absolute if you take the time to discover them. One can't (or shouldn't!) just go and "de-tune" a cartridge in an effort to change its sound ;-). You can try fooling with loading, cables, pre-preamp equipment, even different tonearms; but finally, if you don't dig the sound, it's just not the cartridge for you.
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Tom, you have the sequence reversed. There should be no tail-chasing ;-) ! You first MUST wait 50 hours (100 if you can stand it) until the suspension is settled in; a term I prefer to broken(!?) in ;-)

And forget some manufacturers' claims (like Immutable Music who made my Transfiguration for instance) about their new "space-age" suspension elastics. Maybe they ARE less susceptible to deterioration, however, there are NO supensions/cartridges that I've so far used, or more broadly, heard about or read about from their users, that didn't change quite audibly after the first 50 - 100 hours. Which is another reason why running-in a new cartridge at .25 grams OVER the max. recommended VTF (as I described earlier) for the first 50 - 100 hours is IMO essential for the long term stability of all other settings, including SRA.

The sequence I recommend (to avoid tail-chasing) is:

1.) Install your new cartridge in the TA and make the various geometrical settings as reasonably accurate as possible without being obsessive about it (there will be plenty of time for obsession later on ;-)

2.) Set the VTF to .25 grams over the max. recommended, for the first 100 hours.

3.) Play records for 100 hours. You don't HAVE to listen to them, but definitely play them. I emphasize that because some folks think you can "season" a suspension by just leaving the stylus/arm/cartridge sitting on a record for 100 hours without the platter revolving. I don't know about that one, but it just doesn't feel right to me!

4.) After the initial 100 hours, re-set the VTF for the loudest output. Let the high frequencies be your guide for "loudest", because they are the first to disappear when the coil isn't in the perfect position. You may have to do a few trials before you can decide. Use a mono record as I described earlier. That setting should be good for a long, long, time.

5.) Set the SRA as I described elsewhere.

6.) Level the platter using a small spirit level. Check with the level oriented in opposite directins. Average if you have a crappy level. Then, make sure the headshell is level along the spindle-to-stylus line.

7.) Set the azimuth (if your headshell or tonearm tube allows) using the mono record technique.

8.) Check stylus overhang and cartridge off-set settings from Step 1. But FIRST, note your VTF, because if the overhang needs more than 1 mm adjustment fore or aft, you'll need to reset the VTF to what it was before you reset the overhang.

9.) Set the anti-skate to ,3 to .5 times the VTF as a start. Line contact styli produce so little frictioon in the groove that using any anti-skate is probably gratuitous as far as differences in sonics is concerned -- but it does tame the TA skidding toward the spindle at the mopst inopportune moments!

10.) Set the loading (for MC cartridges) starting at 15 times the cartridge's internal impedance, and raising it slowly until the bass 'tightens up', but before it diminishes any amount in volume; and before the treble gets glaring (the bass will usually go first though.) If your phono preamp has only fixed load settings, 100 ohms will usually work very well for most MC's.

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Dertonarm, I never question the reports of others' personal experience(s) except in those (extremely rare) instances when I've had the same experiences only with quite different outcomes ;-)

I also think people need to be careful when assuming certain cause-effect relationships; and that they are responsible for the things they observe.

Because you observe that some cartridges you've worked with perform to spec right out of the box, doesn't disprove my assertion that there is a change, over time, in the elastomers; which there most definitely is, even in modern suspension materials, and especially for the cartridges you mention.

Most new (or even old) MC cartridges, unless they're defective, will perform "within a very narrow window within specs", as you put it, at a variety of loads and VTF settings. So what? I can easily make a brand new cartridge sound 100 hours old by loading it too high and applying a bit more VTF which will increase frequency response at the top and bottom until the suspension limbers up. I choose not to do that however knowing I'm going to have to do it all over again in 100 hours ;-) And because I enjoy hearing a cartridge going through its changes.

None of the three cartridges you mention are typical MC cartridges. They ALL have extremely LOW compliance, even for a MC (5 as opposed to 30 for most MC cartridges) and they all have HIGH VTF specs (3.5 to 9 grams!, as opposed to 2 grams for most MC cartridges.) So it's unlikely you'd hear any performance difference between brand new and 100 hours old, with any of those cartridges. In addition, those three cartridges are very low output and IMO not up to current performance standards ;-)
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Tom, I always wondered exactly HOW people (who cared to ;-) actually measured cantilever angle. One dare not risk damage to the cartridge by trying to put an instrument of some kind near the delicate cantilever mechanism while the stylus is resting in a groove - yikes!!

I guess one could take a macro picture using a telephoto lens (to minimize parallax error) and then measure the angle from the photo. But it seems like a lot of effort just to obtain anecdotal (read: useless ;-) information.

Sounds like you'll be ready to go once your new TA arrives. Take all the time necessary for you to feel confident you've zeroed in on the best VTF setting, before going on to establish the vertical SRA point. Do not worry that later, dialing-in the VTF just a little better (like even as much as +/- 0.1 gm) is going to screw up your SRA setting. Why? Because it won't affect it up anywhere near the amount a slightly different record thickness or slightly different cutting angle (as favored by various lathe operators) will. I already stated that SRA can't be an absolute for those reasons -- so don't sweat it. Just get it in the 1.4 degree ballpark and then (hopefully) your new TA has 'on the fly' tonearm height adjustment so you can adjust the SRA slightly for each recording. One of our members, dougdeacon, does that all the time using his Triplanar arm. He even notes the correct arm setting on each record!
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