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Vinyl Asylum Welcome Licorice Pizza (LP) lovers! Setup guides and Vinyl FAQ. |
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In Reply to: True mono cartridges, damage modern mono records? posted by jtycho on July 27, 2014 at 09:41:04:
As the stylus tip traces lateral mono groove modulation there is some vertical motion due to "pinch effect". This is primarily at the higher frequencies, and is due to the effective groove width being reduced by the modulation peaks. All quality mono cartridges allowed for this by providing for some vertical tip displacement. Otherwise, serious groove damage would occur. (Even the early acoustic phonographs had a bit of vertical compliance due to the needle being slanted backward.)
Vintage examples of mono pickups I'm familiar with include the GE VR RPX series, the ESL MCs, and the Weathers FM pickup. These all had some degree of vertical compliance, but did not produce any ELECTRICAL output from vertical motion. This is as desired, since the vertical pinch effect motion is dominantly second harmonic distortion. [By listening only to the difference between left and right outputs of a stereo cartridge (i.e., making its output sensitive only to vertical motion) while playing a mono record, one can hear the pinch distortion.]
Stereo groove modulation in the horizontal direction (center-stage sounds) also produces pinch effect distortion, which does appear in the left and right channel electrical outputs. A reduced tip scanning radius (i.e., 0.7-mil or smaller) minimizes the pinch effect distortion. This is the reason for playing stereo records with a smaller tip radius.
I have no first-hand experience with modern "mono" cartridges, but I hope they have SOME vertical tip compliance -- while being electrically insensitive to vertical tip motion. Otherwise, it would necessitate the entire arm to move vertically to accommodate the pinch effect – the vinyl would give way first! However, the pinch motion is predominantly at higher frequencies and of low amplitude, so the needed vertical compliance is required only for small displacements.
Personal opinion: As far as groove tracing, I see absolutely no technical disadvantage to playing mono LPs with a stereo cartridge, provided that the left-right outputs are summed to mono somehow to cancel sensitivity to vertical tip motion. Indeed, at least one modern so-called mono cartridge is really a stereo generator design with the left and right channel generators internally strapped together.
Incidentally, my recollection is that the Library of Congress is digitally archiving their collection of historic mono records (both LPs and 78s) using stereo cartridges (fitted with appropriate radii tips).
Charlie
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Follow Ups
- Pinch effect and vertical compliance - Charlie S in Maryland 18:44:45 07/29/14 (0)
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