Ron wrote in message
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N_Cook wrote:
Ron wrote in message
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N_Cook wrote:
Arfa Daily wrote in message
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"N_Cook" wrote in message
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Ron wrote in message
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N_Cook wrote:
Ron wrote in message
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N_Cook wrote:
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"N_Cook" wrote in message
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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


Far simpler, find a known good machine - your chum with perfect pitch
will help here - record a known frequency on a tape which you know to
be
good. Play said tape back on customers machine with freq counter hooked
up to the headphone socket and adjust for same frequency - sorted.


My test tape is 100hz, I spose the higher the frequency, the better
accuracy you can get. Don't expect miracles.


Things counldn't be easier with a "known good machine " .
My 3 test tapes were created on what was supposed to be such a machine
in a
pro AV studio.
One tape got knackered at one point but rest of tape agrees with the
second
one. The third remains unused while first 2 agree with one another,
using
any old speed consistent machine for cross-comparison, in relative
rather
than absolute terms.


So you are saying that you already have a test cassette?


3 of them made on the same batch of tape and on the same machine but more
than 15 years ago. As they are all stored in the same environment they could
theoretically all have chemically degraded/stretched to the same degree. I'm
trying to find some process that gives an independent verification that does
not require a know good machine.
eg quartz controlled (so low tens ppm) f-meter coupled strobe fed to
rotating capstan if diameter/s of the spindles are manufactured to specific
dimensions of precisely known tolerances. Perhaps 1.9 +/- 0.002 mm and 2.4
+/- 0.002mm say, no such data found googling. I can only measure to +/-0.02
mm and no slip gauges for absolute calibration.
+/-2 in 200 or so, is not accurate enough