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Personally, I don’t worry too much about the stylus shape when playing my 78s, but I’m just putting them on for fun, not to digitise them.
There are some things to consider when playing 78 rpm records on a “modern” turntable (I use the word “modern” to mean anything younger than about 60 years old…)
The stylus (because it’s much smaller) will sit down in the very bottom of the groove. This means that it is down there with the dust and dirt, so it will have more high frequency noise than, say, using a sharpened Burmese Colour needle in a wind-up gramophone.
On the other hand, if you’re playing a well-loved disc, then the modern needle is sitting in the groove wall in a different place than all of the steel needles that have been there before. So you might be playing on a “virgin” surface. (The same thing can happen when switching to a stylus of a different lateral grind radius on a new turntable.)
Another possible issue with the different stylus radius is that you’ve got a (comparatively) tiny needle sitting down in a big trough. (Imagine a marble travelling down a human-sized waterslide for a gross exaggeration for intuition’s sake.) Since there isn’t as much lateral control of the needle from the sidewalls of the groove, you will lose high frequency content. I’ve attached a scale drawing from the Beogram 4000c manual that shows the difference between the grooves on a 78 rpm and a 33 1/3 microgroove LP. A steel needle has a typical tip diameter of about 150 µm, whereas an early spherical tip stylus for an electrical record player would be in the range of something like 20 to 50 µm.
However, many / most 78 RPM records were made before the RIAA equalisation curve was standardised. Later 78s would have used some kind of equalisation, but there’s no real way of knowing for sure what the EQ curve should be. Some early electrical phono preamps had two dials for manually selecting the low frequency boost and high frequency roll-off that sounded most appropriate for a given record. Early 78s had no pre-emphasis at all, since it wouldn’t have been possible with a fully mechanical recording system.
So, given the uncertainties associated with these issues, combined with the level of production quality of the discs themselves, I would suggest an informed level of strategic apathy.
Of course, one thing you MIGHT choose to worry about in earnest is the wear on your stylus. 78s were usually made of a combination of shellac and clay, which made them tough enough to stand up to a steel needle with a 0.5 – 1 kg tracking force. However, this also makes pretty good “sandpaper” that might be less than friendly to your pickup.
Cheers
-geoff
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