The Audio Technica VM670SP is a mono moving magnet cartridge. The stylus has a 3.0 mil (thousandth of an inch) curvature radius suited for playing 78s.
I recently purchased one of these from Vinyl Revival in Melbourne to replace an Ortofon Type C cartridge originally purchased circa 1970 (see text box “The Ortofons Reach their Use-By Date”).
The VM670SP manual specifies a tracking force of 4.5 to 5.5g (5.0g standard).
I want to show, with accompanying photographs, that:
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A tracking force of 5g causes the cantilever to deform such that the bottom of the cartridge body can foul on the record surface on anything other than a perfectly flat record.
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Reducing the tracking force significantly reduces cantilever deformation and provides adequate separation of the cartridge body from the record surface.
Observed Behaviours
With 5g tracking weight, bottom of cartridge touches record surface
Many 78s, be they shellac, acetate or vinyl, are not perfectly flat — causing the disc surface to move up and down as the disc rotates.
The VM670SP tracking weight was set to 5.0g and confirmed with an electronic stylus balance.
On a not-perfectly-flat disc, this tracking weight caused the bottom of the VM670SP cartridge to scrape cyclicly or bounce on the record surface (an effect that is sometimes audible as a thumping sound in the cartridge output).
Vinyl 78s (often used for production music in the 1960s) can have a raised ridge around the outer rim of the disc and this also can foul on the bottom of the cartridge.
Supplied headshell tilts cartridge back
The VM670SP cartridge was mounted in an Audio Technica AT-HS6 headshell. This headshell appears to tilt the cartridge back slightly from the (horizontal) plane of the tone arm.
This tilting makes worse the problem of the cartridge bottom bouncing or scraping on the record surface (see diagram and photo).
Tests with lower tracking weight
Dialling the tracking weight back to less than 5g makes a noticeable difference. The stylus cantilever does not bend up as much and hence the bottom of the cartridge is well clear of the disc surface.
At this lower weight, the cartridge appears to still track satisfactorily on the records tested. Of course results may be dependent on the particular characteristics of the disc being played (in particular, the modulation level).
Conclusion
Although the cartridge printed instructions nominate a tracking weight of “5.0g standard”, this clearly makes the cartridge susceptible to scraping on the disc surface. On “bumpy” discs the compliance of the stylus cantilever causes the cartridge to bounce on the disc surface.
Running the cartridge at a reduced tracking weight, say somewhere in the range 2.0–4.0 grams, avoids the scraping/bouncing problem. The cartridge appears to track satisfactorily at this reduced weight.
Is the 5.0g recommendation intended as a maximum value perhaps?
The Ortofons Reach their Use-By Date
The two Ortofon Type C standard play and microgroove mono cartridges had become progressively dysfunctional, refusing to track records (stay in the groove) even with a few grams of stylus force. It was clear that the rubber parts in these cartridges had hardened and lost their compliance.
What to do? Ortofon offers a refurbishment service at an exorbitant price, but these cartridges were already 50 years old and there were newer cartridges available from Ortofon and Audio Technica. So I replaced the “78” cartridge with a new model VM670SP from Audio Technica.
