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Re: [ARSCLIST] Mostly for laughs
From: Patent Tactics, George Brock-Nannestad
Philip Holmes wrote
> Yes, and I've never understood why you HAVE to track so heavy on those
> old 78s. Big, lazy grooves. Nothing that even approaches high
> frequencies (12k?). 78rpm just stretches out all the difficult stuff so
> nicely (compared to the inner grooves of a stereo microgroove). Also,
> they aren't known to have huge transients (bass drum whacks). It always
> seemed like tracing a microgroove was way more difficult.
----- there are several aspects here:
1) the deviation of the groove from the baseline (modulation, max. amplitude)
is much larger than on LP
2) the cantilever carrying the stylus is sitting in a springy mass - called
hence the work (being mass times distance) on the stylus is much greater,
because the distance is longer. It is true that the wavelengths are larger,
but the speed of the record below the cartridge is also much higher.
----- however, there are huge transients indeed in most shellac records: the
grit. The pickup will give a response proportional to recorded velocity
(which is inversely proportional to time, being the rate of change of the
deviation), and a particle of grit is so small that it only lasts a short
time, and hence gives a high velocity. It is so large that it can overload
the pre-amp, and this is one of the main reasons for obtrusive surface noise
on 78s. All the little grit particles merge into a continuous-sounding hiss
when the pre-amp is overloaded.
----- the stylus-groove contact is force-dependent, and this brings
acceleration into the discussion. Acceleration is the rate of change of
velocity, which means you have to divide by the time yet again. And with grit
particles, the time is very short, etc.etc., in other words, each grit
particle gives a huge acceleration that actually makes the stylus float most
of the time - this was demonstrated in the late 1940s by Cecil Watts. So, you
do need a large vertical playing weight.
----- if the weight is too large, the cantilever "bottoms" and the signal
becomes distorted. For this reason, when I use a stereo pickup for 78rpm
replay, I only load the headshell until the cantilever is centered in the
surrounding metal tube. That way, the airgaps are reasonably equal all
around, and the largest linear dynamic range may be expected.
----- to a later contribution: a centrifugal force can only be generated on a
body that rotates around an axis (apart from it being virtual). However, when
a record is played, the stylus does not rotate, so it is not subject to any
force like that
----- just to round this off: you can play a coarse groove (such as a 78) by
a microgroove stylus. It does not destroy the stylus, as many believe, but
you do need to push the cartridge towards one side of the groove to maintain
the contact. The reason you get such high distortion and swishing noise if
you just leave the tone-arm where it is, is that the bottom of the groove is
rounded and cannot push the stylus back and forth.
The above needs to be repeated from time to time.
> David Lennick wrote:
> > Don't know the weight, but as it turns out, this stylus is hardly a dud..I
> was using too
> > light a tracking force on it!
> > dl
> > phillip holmes wrote:
> >> How many grams is five cents? I'm surprised that Expert made a dud.
> >> They have two cartridges of mine being rebuilt.
> >> Phillip
> >> David Lennick wrote:
> >>> "From: "phillip holmes" <insuranceman@xxxxxxxxxx>
> >>>>> Absolutely. And I totally agree that actually building a listening
> >>>>> can be prohibitively expensive. Improvements are easily made with
> >>>>> adjustments. Too many people find some formula to use, set their
> >>>>> listening room up and never listen to the results. I've had
> >>>>> from moving the speakers a few inches.
> >>> Hey..I had an epiphany that cost me five cents. A 2.0 mil Truncated
> >>> stylus from Expert that I got a couple of years ago had never given me
> >>> fit, too much chatter, variable results, but as a last resort I tried it
> this week
> >>> on a difficult disc, and added a five cent piece to the tone arm (the
> >>> styli won't take that much extra weight). It played gorgeously. I ended
> >>> re-doing two projects this weekend because of the improvement.
> >>> dl