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In Reply to: RE: Has anyone used an oscilloscope to align for zenith and azimuth? posted by John Elison on November 29, 2015 at 20:18:22
Okay. It looks like I was on the right track for azimuth. I do have a storage scope so that will help. I thought zenith could be done. IIUC, zenith is the measure of the rotation of the stylus with respect to the groove, when looking straight down from the top of the cartridge body.
http://www.theanalogdept.com/2_pt_align.htm
I thought that if zenith were perfectly set, when looking at the Left and Right channel traces from a monophonic sine wave signal you'd see them perfectly in phase. If the zenith was off you'd see the sine wave from one channel leading or trailing the other.
I normally use either a DB Systems alignment tool or the Hoffman DIY arc alignment tool, but I've been curious to see whether I could do better using a scope.
Follow Ups:
Whilst in principle, using phase measurement of a mono signal could be used to determine zenith, and indeed I have toyed with this idea myself...Unless you had a tangential tracking arm and was confident in a perfect tangential relationship, with a pivoted arm checking zenith would require a considerable number of repeat measurements to determine reliably, given the possibility of cantilever skew either dynamically during play due to the effect of reaction forces on the cantilever due to eccentric grooves/off-centred records or a fixed skew due to a manufacturing defect. Secondly, the wow induced frequency shifts would result in a degree of uncertainty on the measured phase error.
It is my understanding from reading about Soundsmith (who take great pride in only providing the highest quality of alignment, that zenith errors are rather more common than one would like to think!
Certainly this is the point behind square or rectangular shanks for the stylus in aiding consistency in alignment.
Thereafter, the mounting method either results in precise SRA alignment at the expense of tip azimuth accuracy, or the other way around according to an article I read interviewing J Carr of Lyra.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
I haven't tried this, but it should be easy to determine whether or not interchannel phase shift can even be detected when altering zenith on-the-fly while observing the oscilloscope phase measurement. This would be fairly easy to do with an SME V tonearm because overhang can be changed on-the-fly while playing a test record. As I said, I haven't tried this, but maybe I will try it one of these days just to find out if it's possible.
Best regards,
John Elison
You'd probably want two locked grooves for zenith, one at each null point. Otherwise, I suppose you could digitize the output of a test record as is passes through the null point. Either way, you'd probably need a special record with a HF tone at those two points.
I'll be interested to find out what you discover regarding using an oscilloscope for zenith alignment. My experiments didn't reveal any correlation between zenith alignment and inter-channel phase, but I didn't spend a lot of time on it. Therefore, it will be interesting to see what you come up with.
Thanks,
John Elison
I would agree given the difficulty in separating the effect of zenith errors from cantilever skew.
As for tip azimuth, the audibility very much depends on the tip design (especially bearing radius / contact design) and the magnitude of the error.
One of my Denon DL301/II cartridges has a tip azimuth of 1.4 degrees. This is not (of itself) audible given the tip profile. We've speculated on this in the past, and I agree that it is probably a variation on a "hyperelliptical" or somesuch line contact tip. Getting the electrical azimuth correct is more important and is what I focus on with this cartridge and my DL304.
However, for other simpler tips such as a conventional elliptical, tip azimuth is very audible to me and results in noticeable increase in sibilance and image smear.
Same with radical line contact tips with very large bearing radii eg Soundsmith OLC or VdH. There is a limit with these as to how much you can rotate them before they touch a portion of the groove that results in them not fitting in the groove as intended! The OLC sounds absolutely awful if you have a gross azimuth error with terrible sibilance and distortion. Once correctly aligned it is a superb sounding tip.
If one considers a simple elliptical cut (front and back face cuts), then the resultant footprint on the groove wall is an inverted pear shape. If the tip is rotated, then the contact area will gradually increase in one wall with the net effect that the scanning loss will increase in the channel with the larger scanning radius.
For a parabolic line contact stylus utilising a cut such that the bearing radius is in line with the shank/tip axis, small errors are less detectable since the line may be sufficiently long that the (possible change in the length of the contact line) does not audibly affect the frequency response or frictional force. However, it will be apparent from a thought-experiment that the contact area will gradually decrease on one wall resulting in possible differences in wear. On the other hand, a parabolic cut such as a Shibata cut results in a curved contact line which is forward of the central shank/tip azis and it will be readily seen that tip azimuth will have a profound effect on IMD given the change in effective SRA on each wall and the induced zenith error.
Regards Anthony
"Beauty is Truth, Truth Beauty.." Keats
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