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In Reply to: RE: 78 rpm stylus for 33 rpm records? Can it hurt? posted by coffee-phil on March 14, 2017 at 09:43:46
> What we think of as a "modern" microgroove 33 1/3 RPM Lp started after WW2 and at first
> had a 1 mil groove. About the time stereo came out the groove width became 0.7 mil.
You are referring to the radial dimensions of conical styli. The groove is V-shaped and does not have dimensions of 1-mil or 0.7-mil. Here is the DIN specification for the V-shaped groove:
The width of the opening at the top of the V on the Hi-Fi News test record appears to be slightly less than 90-microns or about 3.5-mil.
I do like to speak precisely, so thanks for clearing that up. It appears that if we are talking conical styli, the 78 stylus will just ride higher in the groove of the Lp and should work better than we might expect.
In your first post on this you stated that with the 78 stylus on an Lp one would lose high frequency response. That is what I would have assumed, but in the light of what you just pointed out I have to wonder why a 78 stylus would be any worse than a conical stylus intended for Lps.
> I have to wonder why a 78 stylus would be any worse than a conical stylus intended for Lps.
The larger tip won't fit into high-frequency groove undulations. Although the groove is V-shaped, the radius of curvature of groove undulations become smaller than the radius of the stylus when the frequencies get higher. Therefore, the larger stylus simply passes over the high-frequency undulations. That's the whole point of line-contact styli and other more sophisticated stylus shapes, which allow the stylus to follow high-frequency groove undulations more accurately.
I think you have presented the case for elliptical and line contact styli.
The question remains: If both a conical 78 styli and one made for Lps are intended for a 90 degree groove in the record why won't the 78 stylus just ride higher in the the groove of an Lp with the part in the groove essentially identical?
By the way Esoteric Sound has elliptical styli for 78s and they provide sound samples comparing them to conical styli. They almost have me reaching for the plastic.
I don't know why you would think that something the size of a beach ball would follow an undulating surface with the same accuracy as something the size of baseball when the undulations have curvatures closer to the size of the baseball. A beach ball will simply roll over them but the baseball will maintain contact with the undulating surface. The 78-rpm stylus is analogous to the beach ball whereas the 33-rpm stylus is analogous to the base ball. Each groove wall is an undulating surface.
A 78-rpm record spins more than twice as fast as a 33-rpm record. Consequently, the curvature of the undulating groove is larger for the same frequency on the 78-rpm record as on the 33-rpm record. Therefore, the larger 78-rpm stylus can follow the faster groove on the 78-rpm record with greater accuracy than it can follow the slower groove on a 33-rpm record.
At any rate, if you can't visualize the problem of tracking a microgroove record with a 78-rpm stylus then perhaps someone else can explain it to you better than I.
Yes of course I get that when the wavelength of the signal approaches the dimensions of the stylus things are going to fall apart. The first thought would be that a 78 stylus is larger than one for microgroove records and therefore would have a lower high frequency cutoff for any given record speed.
Looking at the picture which you posted, which I'm assuming is for Lps, it shows a groove which has its sides at 90 degrees from each other. Now I don't know but I'm guessing a standard groove 78 has a similar 90 degree groove but cut deeper into the surface of the disc. Now confining the discussion to conical styli, I would expect the the cone to be a good fit to the 90 degree groove. If that is so should not the tip be identical regardless of the overall size of the cone. Now perhaps standard groove styli are truncated above the tip such that the minimum width is too large for a microgroove. Without being truncated at the bottom I would expect the standard groove and the microgroove styli to be identical up to the point where the cone is truncated at the top.
You are asking about the included angle of the tip? Typically this should be "no more than" 60° but is normally 55° for "modern" tips. The tolerance for the groove angle is actually 90±5°in the IEC 1987 standard. The 1981 DIN standard actually has a finer tolerance of ±0.7°.
I don't know what the included angle is for a 78rpm tip and it might be larger than for a microgroove tip. If you look at the collector pages, there are lots of discussions around optimum stylus dimensions. It is all on a record by record basis and you can't rely on label or era.
For a stereo record, the maximum groove width is 30um and a mono record is 51um and the stylus bearing radius is chosen so that the contact point is about 60% of the way down the groove away from the shoulders.
My point to the OP (who curiously hasn't responded to anyone suggesting he just wanted moral support encouraging him to conduct his experiment in futility.... which he didn't get!) is that the tip is intended for Monophonic replay and the manufacturer is very careful to NOT provide a channel separation specification which implies that there is either NO vertical compliance or "very little" vertical movement. Either way, as the compliance of the 78rpm stylus is necessarily low (laterally) to remain in contact with a groove moving at a considerable speed, the OP is running a significant risk of damaging his records to say nothing of the erasure of the HF undulations he will be doing in a very short space of time.
"Beauty is Truth, Truth Beauty.." Keats
I'm going to have to study this some more.
The spherical tip of the stylus is the only part that rides in the V-shaped groove. For a given frequency, the curvature of the groove-wall is smaller for a 33-rpm record than for a 78-rpm record. Therefore, a larger spherical tip can be used with a 78-rpm record. If you try to use a 78-rpm spherical stylus on a 33-rpm record, it will not be able to track the higher frequencies.
However, there is no sense in explaining this to you anymore. What you need to do is try it and you will understand immediately.
I had regarded you as one of the more knowledgeable people on this forum.
The question I was raising is whether the spherical tip of a conical stylus intended for standard groove 78s is indeed smaller than that of a conical stylus which is intended for microgroove Lps.
You apparently are not carefully reading what I wrote or not fully comprehending it.
Your responses have become somewhat insulting.
> The question I was raising is whether the spherical tip of a conical stylus intended for standard
> groove 78s is indeed smaller than that of a conical stylus which is intended for microgroove Lps.
Is this a joke? If this is your question, then you are the one who can't read or even remember what you've written. The original post states that 78-rpm styli have 2.7-mil to 3-mil tips. You yourself wrote that microgroove styli are 0.7-mil to 1-mil. You know as well as I do that these are the radial dimensions of the spherical tip of conical styli.
> Your responses have become somewhat insulting.
Really? Well, this is my last response so you should be happy.
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