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In Reply to: RE: Fremer's ZENITH ANGLE CORRECTION or have we all gone crazy. posted by ecl876 on February 08, 2021 at 21:09:26
The article is a thinly disguised advertisement/infomercial for the Wallytools service and assumes that perfection is possible.
There are quite a few issues to comment on in that article.
Fremer's method of setting SRA is flawed to begin with - you can't set it "accurately" statically. It must be done dynamically to factor in the effect of drag and presumes that the optimum VTF has already been determined to set the operating VTA. If the SRA doesn't match the reference VTA for the coil relationship to the groove, then simply adjusting arm height to achieve the desired SRA will simply introduce an error in the coil alignment.
Secondly, the cutting angle (as defined in the standard) is between 0 to 5 degrees with DMM set at 0 degrees so it is pointless to slavishly set 92 degrees.
As for the merits of having Wallytools tell you the correct azimuth? Well that assumes that the horizontal bearing is perfectly normal to the plinth and platter and that the set offset angle matches the horizontal bearing offset for the arm. The arm height must be set correctly (i.e parallel to the record for the pre-determined Wally Azimuth to be valid. However, if you are going to adjust the arm height to "fix" a perceived SRA issue, then you will simply introduce an azimuth error. This is the reason that adjusting arm height in miniscule amounts results in an audible difference - multiple parameters are changing simultaneously including azimuth, offset and overhang with the resultant change to skating force. It is not simply due to the tiny change in angle which is inconsequential with respect to the record to record variation in cutting angle.
Lastly, whilst correct zenith IS important and the benefits are clearly audible, it is more important that the coils/motor be aligned for minimum tangential error to the groove rather than introducing an error in the generator alignment to correct any stylus zenith error.
It is all very well to have software that allows you to draw reference lines on an image to do calculations, but unless the stylus tip is perfectly normal and central in the image field, parallax will introduce errors in the calculations. The same issue applies to the measurement of tip rake angle.
The mounting tolerance for the zenith of a Shibata tip is +/- 5 degrees. You would not be successful in arguing that a zenith error of 4 degrees (as per Fremer's image, but assuming a Shibata tip) was defective since that would be argued to still be within specification. The manufacturer might replace the cartridge to maintain goodwill, but chances are zenith is almost never "perfect" if such large tolerances are allowed. A 1 degree error would be very hard to discern reliably.
If this weren't the case then a conical stylus would be unusable since the contact positions on the scanning surface are continuously shifting in a manner equivalent to a zenith error.
As it is, the tolerance for cantilever skew is (claimed to be) within 1 degree for AT and that is all but invisible given that this represents a displacement of the stylus tip of 0.1mm assuming a cantilever that lies perfectly on the centreline.
Still, I'm sure there are plenty of audiophiles with deep pockets who would happily part with their money for the Wallytools information and who believe that "perfection" could even exist for vinyl replay when in reality there is no such thing as perfection with vinyl replay given the myriad of variables involved and the effect of stacked tolerances.
To me the Wallytools service is pointless and a waste of money which is better put elsewhere. It would make more sense to send the cartridge to a retipper such as Peter Ledermann and actually FIX the problem if indeed it is determined that a problem even exists.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
Follow Ups:
Do you play records? If so, how do you set up your turntable and cartridge? What setup tools do you use?
Thanks!
John Elison
Anthony,
you bring up a bunch of great points, I'd like to dig deeper into the one below.
it is more important that the coils/motor be aligned for minimum tangential error to the groove rather than introducing an error in the generator alignment to correct any stylus zenith error.
I'm not exactly clear what you are saying. The important relation of the coils to the groove are with respect to azimuth. I was made aware of this whole Zenith issue setting diamond cantilever combos a number of years ago. 1-2°+ of rotation was obvious and given the ±5° tolerance it was all within spec of the parts I was buying. It wasn't until recently that I stumbled across an electrical test that was really dominated by an incorrectly set zentih. When I would align the cartridge for minimum Zenith error independent of how crooked the cantilever looked, not only did the sound improve, obvious inner / outergroove distortion seemed to disappear. Below are two pictures of cartridges aligned for minimum IMD distortion electrically.
What I find most interesting about the analogplanet bit is how the "Hero" picture showing an askew zenith has some sincere parallax issues and when you add the precisely measured numbers up, 18 minutes (0.3°) are missing. If the goal is 15' accuracy with a 95% certainty, how can an amount greater than the alleged precision go missing?
dave
Hi David
Just to reiterate, I am in complete agreement that zenith is important and the effect is audible.
However, my view is that the importance does not override the conventional wisdom to optimise cantilever alignment.
Indeed, the process of aligning the cantilever is already subject to large uncertainties depending on the tools used and patience of the user so even if one were to know the zenith error, it is highly unlikely that the correct compensation could be achieved by the average person and that in most situations, many users are probably completely unaware of the magnitude of the errors were they not told about them. In the first image you showed, I already observe that the cantilever is not aligned correctly. The question is how one can perfectly align offset with existing techniques which all rely on visual judgement which is at best unreliable and subject to repeatability issues and why I think that the Wallytools service is of limited value.
The purpose of optimising the cartridge alignment is to enable accurate tracing of the signal wavelength which requires that the cantilever is allowed to oscillate symmetrically about the mean centre position and the groove modulation is traced with the lowest distortion.
Consider a tangential cantilever alignment initially; this requirement becomes compromised due to the effect of (zenith related) phase error once the groove wavelength decreases and the radius of curvature of the groove approaches the stylus scanning dimension (i.e frequencies above a critical value and velocity). However, below this critical frequency, stylus zenith has a gradually reducing impact until the groove wavelength becomes sufficiently long that stylus zenith has little effect. However, cantilever alignment is still important for determining the phase relationship for lower frequencies.
I acknowledge that my use of the term 'coil alignment' is confusing - rather than orthogonality to the groove wall, I am referring to the relationship of the coil motion to the symmetry of the oscillation due to the lateral movement - it is important that the cantilever is moving symmetrically about the reference "zero" position where the amplitude of stylus displacement is greatest. Since zenith error introduces a phase shift at shorter groove wavelengths relative to the groove velocity, we have the situation of varying phase shift as a function of frequency in addition to that introduced by tracking error. So the question is whether the phase shift at shorter groovelengths approaching the scanning dimensions is more or less important than maintaining tangentiality of the cantilever as closely as possible. It doesn't seem sensible to me compromise the symmetry of the stylus displacement at low frequencies which impacts on tracking ability of large amplitude signals particularly when we start adding in the complication of tracing vertical modulation to recover stereo information.
The other reason why I am sceptical about prioritising zenith over cantilever alignment is based on the groove contact characteristics of a conical stylus (or larger cut elliptical).
You will no doubt have seen the graphic provided by JICO illustrating the contact positions on the stylus as the groove is traced which they use to highlight the advantage of the SAS. Ignoring the pinch effect which is also illustrated, we see that the contact position varies greatly with the conical stylus around the scanning surface. Although this produces an inherent distortion, users of the DL103 do not seem bothered by this!
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
My take thus far on this is quite different and only a hypothesis at this point so apply salt to what follows.
I suspect that the idea that incorrect zenith simply effects phase is flawed. The Electronic measurement I use is measuring the IMD of a 60Hz+7kHz tone with a 4:1 ratio. You then filter out the 60Hz and look at the FFT of the signal and the level of the sidebands at 6940Hz and 7060hz tell you the amount of IMD. If those levels are 40dB below the 7kHz fundamental then the IMD is 1%.
This is not a new testing concept. The Ultimate Analogue Test LP has instructions and a test track for setting VTA using this exact procedure and both the CBS STR-110 and the Shure TTR-103 lay out this test for mistracking. I stumbled upon this using Analog Magic's VTA setup and quickly realized that the zenith if slightly misaligned dominated the distortion measurements and a zenith error of 1.2° assures that a null point will never be hit on the playable record surface.
In trying to use this test to set VTA, The distortion was high and I could never obtain meaningful numbers by any amount of VTA change. I saw reference to try another alignment geometry so I twisted the zenith a bit and was shocked how much the measured distortion numbers changed. After a few I then began initially setting the Zenith first by using the VTA test outlined above. After a null in distortion was located in the vicinity of where the null point should be I them proceed to using the track to set VTA as it was intended.
here are the plots of IMD distortion vs. Zenith angle for a conical and a micro-ridge.
I have used this approach for electrically setting zenith on more than 20 cartridges and once you get the feel for it, it is a quick and effective way to get repeatably good sound across the entire side of an album.
I decided I should document this more fully as I typed this so I made a forum post about more of the details and to better document the whole process. It will be linked below and to avoid any appearance of being a shill I will say that I am a dealer for analog magik and while it is entirely possible to measure IMD by other means, I find it to be a simple and reliable tool for electrically aligning zenith. I would be all for any discussions on alternative methods of easily measuring IMD with a test record and a scope.
dave
Hi Dave
That's very interesting!
I was just having a good think about the point you raised about the issue of phase vs tracking error over the last few days.
If I may just go back to the issue of tracking error in relation to a long groove wavelength (relative to the radius of curvature for the scanning surface) and how it causes distortion - if the cantilever axis is not tangential to the groove then the movement of the cantilever is not perpendicular to the groove and this results in a distorted waveform with an FM-like distortion that is related to the groove wavelength. With a conical stylus, the points of contact are such that the line joining them is always perpendicular to the direction of the record motion and matching the cutter. I am sure that this is why a cartridge such as the DL103 has such ardent fans. With an elliptical or line contact stylus, the contact points are no longer perpendicular to the groove wall except at the null points and tracking error introduces the phase component which makes these styli far more sensitive to tracking error.
So the question is if, for a groove wavelength that is very much longer than the radius of curvature of the scanning surface, the tracking error due to cantilever alignment still dominates? It is not until the groove wavelength decreases sufficiently that the phase error due to the zenith compounds the problem. However, nulling a zenith error doesn't solve the distortion due to the cantilever tracking error and that you are still introducing an FM distortion to the signal.
I don't know the answer. Maybe zenith distortion dominates particularly for line contact styli and this IS the right approach, but I can't help thinking that "two wrongs don't make a right" and I think that shifting entirely to nulling zenith at the expense of the longer wavelength FM distortion due to cantilever tracking angle doesn't solve the problem. I have a number of styli that have a zenith error, I may do the experiment. However, I have not found setting the offset to be particularly consistent and I normally consign faulty styli/cartridges to the reject pile and move on to suitable candidates that are worth the time and effort!
The test method you described sounds a clever way to determine IMD.
I have the Ultimate Analogue Test LP and also didn't find the VTA test terribly useful given that the VTA is essentially pre-determined by the cartridge manufacturer and is also has a fixed relationship to the SRA.
One thought came to mind in relation to the position on the record for the VTA test - it is centred at a radius of around 100mm. For a typical 9" arm set to the standard 66/121mm nulls, the tracking error is about 0.9° with a estimated distortion level of about 0.5%. Therefore wouldn't adjusting zenith for the minimum distortion not be changing the alignment completely? Surely one would be trying to set the distortion to the equivalent value based on tracking error? If on the other hand, the you had a suitable test tone centred around the nulls, then perhaps your method applies directly.
The original Ortofon (0001 and 0002) test discs have a difference-tone test stepping down from 20/19 kHz down to 8/7kHz which enable stylus condition to be monitored using the level of IMD as a metric. These are still available on discogs and I can recommend it to you as I find it the most useful of all my test discs (which includes the CBS STR-110 and 112 as well as the Telarc Omnidisc). In particular it has a white noise test tone which makes doing frequency response checks a breeze!
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
> In particular it has a white noise test tone which makes doing frequency response checks a breeze!
Wouldn't pink noise be the type of test required for phono cartridge frequency response? I thought white noise would have a 6-dB per octave increase in amplitude when played with a velocity responding magnetic cartridge.
Thanks!
John Elison
If you use a flat gain amplifier then a pink noise test tone would be applicable. However, most consumers would likely be using a conventional phono stage with RIAA EQ in which case the output signal being measured will have the pink 10dB/decade drop requiring the user to either interpret the response as is or apply a 10dB/dec gain to analyse the deviation from flat.
In the case of the Ortofon test disc, the test signal is pre-emphasised for RIAA therefore the output of a phono stage would be a flat signal within the tolerancing of the phono stage EQ.
In practical terms, it isn't validating the phono cartridge in isolation, it is only validating the combination of the phono stage and cartridge response, but most decent phono stages have gain topologies and fine component tolerances to give an RIAA response typically better than ±0.5dB which is better than most cartridges so the white noise output can reasonably be taken as being that of the cartridge.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
White noise has equal intensity at different frequencies. In other words, the energy of white noise in-between 10-Hz and 20-Hz is the same as the white noise energy in-between 1000-Hz and 1010-Hz. Because of this, a phono cartridge will have a 6-dB per octave increase in amplitude when reproducing white noise.
Pink noise, on the other hand, has equal energy per octave. This means that the pink noise energy between 10-Hz and 20-Hz is the same as the pink noise energy between 1000-Hz and 2000-Hz. Therefore, pink noise produces a flat frequency response when reproduced by a velocity sensitive phono cartridge.
RIAA equalization is different from either of these. The RIAA recording curve and the RIAA playback curve are pictured below.
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I thought my reply to your question was very clear, but I will repeat the key sentence but this time with capitalised words of importance in case you missed them the first time around...
"In the case of the Ortofon test disc, the test signal IS PRE-EMPHASISED FOR RIAA therefore the output of a phono stage would be a flat signal within the tolerancing of the phono stage EQ."
Secondly, as I pointed out, the test discs in question assume that a conventional phono stage is being used, therefore pre-emphasis is typically applied to the signal whilst proper test discs made to the DIN standard are linear cuts without pre-emphasis at a reference amplitude of 11.25um for 0dB.
Pink noise is typically used for testing loudspeaker sensitivity and subjective response balance because the 1/f spectral noise power is closer to that found in natural systems to which the human auditory system is attuned to. Hence, sound engineers use pink noise to evaluate room response.
White noise is an equal amplitude signal and is therefore ideal for analytical measurements not involving the subjectivity of the auditory nerve centre. Pink noise is derived by filtering white noise with a 10dB/decade attenuation characteristic.
Your statement that a pink noise test tone will give a flat response with a magnetic phono cartridge is incorrect for the commonly available consumer test discs such as the HFNRR and AP Ultimate Analogue Test LP which assume that the user will play back through a standard phono stage.
Using the pink test signal from the AP Ultimate Analogue Test LP, the spectrum on the left is with flat gain and the spectrum on the right is the RIAA equalised signal with the frequency range zoomed into just below 1kHz to just above 10kHz. You will note that with flat gain the response is up ~4dB at 10kHz with respect to 1kHz. When RIAA EQ is applied, the response drops by the expected 10dB/decade and the cartridge tested shows a fairly linear response of the Pink Noise test signal
The RIAA emphasised white noise test signal yields a flat response as expected from the "equal amplitude" characteristic of white noise.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
The language seems somewhat familiar, but I can't for the life of me understand it! 🤔🤔🤔
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