> >
> > N_Cook wrote in message ...
> > >>
> > >> >> N_Cook wrote:
> > >> >> >> N_Cook wrote:
> > >> >
> > >> >>
> > >> >> Set up a sig genny and test him out
> > >> >
> > >> >
> > >> > Much easier to say the test tape is stretched.
> > >> > Perhaps perfect pitch testing would only work by playing the likes
of
> > >JSB
> > >> > Tocatta and Fugue in D major, not pure tones
> > >> >
> > >> > How come I cannot google the rpm of an audio cassette capstan? A
> > >> > calibrated
> > >> > strobe and tipex mark on the capstan periphery should give a
definite
> > >> > answer
> > >> > (assuming the spindle is clean and not worn).
> > >> > It should be determinable from tape speed of 1 7/8 in per sec and
> > >spindle
> > >> > diameter, that is about 1.9mm, but what should it be to 0.1 percent
> > >> > accuracy?
> > >> >
> > >> >
> > >>
> > >> The rotational speed of a cassette capstan is not a fixed given. The
> > >> diameter of capstans vary from machine to machine, and the correct
> speed
> > >of
> > >> tape transport is then a function of how fast you drive the capstan
> > round.
> > >> The reference in my strobe tape, is indeed the mains. I have been
using
> > >this
> > >> tape for many many years, and I have file://never// had anyone
complain
> > >that the
> > >> speed of their machine is off, after I have used it to set one up.
> Konig
> > >> must think that the mains is a good enough reference, otherwise,
there
> > >would
> > >> be no point in them marketing the tape for the purpose of setting up
> > >speed.
> > >> Exception to this. As Ron said, very occasionally, when an owner has
> > >> recorded tapes when the machine was running at the 'wrong' speed ...
> > >>
> > >> Arfa
> > >>
> > >> Arfa
> > >>
> > >>
> > >
> > >I've since found 2 capstan spindles of 2.4mm diameterm so no fixed
> > >specification for cassette tape dynamics.
> > >
> > >Another possibility as a test tape - record some constant tone, any f,
> on
> > a
> > >few minutes of tape, pull out a long length and pass a magnet over two
> > parts
> > >a measured distance apart. retract, and then time the interval between
> > dips
> > >in play mode
> > >
> > >
> > You are assuming that if the capstan rotates at the correct RPM , that
the
> > tape speed will be correct. The proper way to do this is to measure the
> > playback frequency of the tape which gives you the tape speed.
Obviuosly,
> > the accuracy of the test tape, the accuracy of the counter, etc all come
> > into play to add errors. The industry standard is to use a wow and
flutter
> > meter in conjunction with a test tape. The test tape is recorded at
3000hz
> > on a reel to reel recorder and then loaded into a cassette shell because
> > there is no cassette recorder on earth that can produce a test tape with
> the
> > 10x or 5x accuracy needed as a standard.
> > Wow and flutter meters are basically frequency meters. They are like
> guitar
> > tuners, but the output is weighted to breakup the frequency variations
> into
> > long and short term changes.
> > If you can find a calibrated wow and flutter meter with a test tape, I'm
> > sure the cost will far exceed what your client is willing to pay. The
> > technology is at least 20 years old, and there really isn't a market for
> > anyone to make this equipment available.
> > The bottom line -------- Even if you go through the time and expense to
do
> > this right, what good is it if your client's tapes are not recorded at
the
> > same precision? You and he will be better off if you add a front panel
> speed
> > control so that he can dial in the speed to match the tape being played
> >
> >
> I found a large quantity of salvaged capstans+spindles.
> 26 off on my mike (rather than callipers before) measure 1.99 +/-0.01 of
> reading accuracy and 2 nearer 2.00
> 5 off measure 1.79mm
> 1 at 2.19mm
> 9 measure 2.49mm
> So I will give a few to my engineer mate and ask him what they measure and
> the temperature at the time.
> The machine in question uses 2.49.
> Assuming it is actually 2.5mm then doing the maths and strobing with
quartz
> f-meter calibrated strobe then my test tapes are 0.4 percent out from
> calculation via 15/8 ips etc.
> spindle rotation speed of 6.05 rev per second with an error of about 0.4
> percent , needs longer gate time or repeating more times to bring that
> accuracy up (rounding errors? so probably longer gate time required than
my
> meter has).
> If 2.49 diameter then 0.6 percent out
A rather belated follow up, just got the representative measurements back
from the
mechanical engineer.
1.99 +/-0.01 of
reading accuracy (measured at 62 degree c) and 2 nearer 2.00
5 off measure 1.79mm
1 at 2.19mm
9 measure 2.49mm
Either spindles or bearings would have to
be an off-size for free movement, so presumably sintered metal bearings
are (easier?) made round number size and spindles made 0.01mm smaller
diameter and
speed of rotation adjusted just as easily to that as any other speed.
--
Diverse Devices, Southampton, England
electronic hints and repair briefs , schematics/manuals list on
http://diverse.4mg.com/index.htm
> > N_Cook wrote in message ...
> > >>
> > >> >> N_Cook wrote:
> > >> >> >> N_Cook wrote:
> > >> >
> > >> >>
> > >> >> Set up a sig genny and test him out
> > >> >
> > >> >
> > >> > Much easier to say the test tape is stretched.
> > >> > Perhaps perfect pitch testing would only work by playing the likes