Cassette tape speed adjustment

none at all.

Tape speed depends on the rotational speed and diameter of the capstan. On a properly maintained deck all other factors are irrelevant.

Ron(UK)

Excessive take up reel torque can result in unacceptable wow and flutter. Same with the supply reel. I don't think the thickness of the tape has much to do with anything.

I just use a speed test tape from Konig. It has a strobe wheel behind what would normally be the tape viewing window. Very easy to see an accurate setting for the speed, and virtually instant comparison between forward and reverse. Also easy to see any cyclic variations in speed, or long term drift.

Arfa

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correct?

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and

Strobing of what rotational part against what reference? How do you know if the tape is stretched?

It doesn't matter if the tape is stretched, the tape speed is governed by the rotational speed of the capstan. If the tape were stretched you would have to adjust the capstan speed to get the right playback pitch on that particular tape tho I doubt it would be very noticable. Somewhere I still have a cassette with 100 hz on one side and 8k on the other, plus a strobe disk visible through the window on the 100 hz side. You set the capstan speed by measuring the 100 hz on playback. The 8k is for head alignment. The strobe disk is driven by the capstan.

Quite often the playback speed would be adjusted to be correct, followed by complaints from the customer that all his tapes now seem to play at the wrong speed!

Ron(UK)

be

is

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so

C30

what

Whatever touches the capstan spindle could wear and if the reference source for stobing is a mains lamp, that is only set for (UK) 50x60x60 cycles per hour (for synchronous clocks) and short term only +/-0.5 percent targetted frequency.

I have the related problem of someone who says he has perfect pitch.

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?

Has anyone ever heard of a tape stretching enough to be detectable? I find that very hard to believe. Far more likely that the motor's speed control is off.

Do you have another deck you can use? Record 5 minutes on the reference deck and then compare the time to play the same on the test deck. I've used a CD recording and then played the CD at the same time as playing the tape on the test deck. If they fall out of sync then the test deck is running at a rate different than the reference deck.

That's exactly the way I have (occasionally) adjusted the speed of a tape deck.

Record a CD track on a known (or hopefully) good deck, and play it back on the suspect deck, while simultaneously re-playing the CD. A bit of skilful nudging of the tape deck 'pause' and 'fast-forward' buttons will be needed to get the audio adequately synchronised.

As you tweak the tape speed control, you will may get the two tracks in almost perfect synchronism (producing a pleasant echo effect!). However, this condition will probably hold for maybe only 10 or 20 seconds, after which the tape audio will start to creep either 'early' or 'late', and may even wander between the two.

At the end of a typical 3 minute track, the audio may be a a few seconds out, and no matter hard you try, you are never going to do better. But not even the most ardent audiophile with perfect pitch could ever detect that the speed was incorrect.

--
Ian

You underestimate audiophiles sir! ;)

answer

pi times diameter gives the circumference of the capstan.

1 7/8 ips divided by circumference gives the required revolutions per second. You can measure the RPS of the flywheel, but that does not guarantee that the tape is traveling at 1 and 7/8. The bottom line is that you need a calibration tape and a frequency counter. You can measure the frequency at several spots on the tape to see if the tape pack and such, has any effect on speed. BASF used to make an excellent calibration tape. I do not know if they are still available, and they are not cheap.

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 //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

JSB

spindle

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speed.

Wokingham, Surrey, UK monitored mains frequency, is instructive, try it in the middle of a national televised football match or similar

spindle consistency Not from my random sample of 8 audio cassette capstan spindles, all were

1.9mm or a bit lower say 1.89, with no cleaning etc, just as found. If 1.9mm then rotational speed of 478.72 rpm and if the specified diameter (cannot even find that) is 0.075 inches (bit less than 1.9mm) then speed is 477.46 rpm for 15/7 ips. Googling including "478" or "477" throws up nothing, googling on rev/sec not possible in like manner

-- Diverse Devices, Southampton, England electronic hints and repair briefs , schematics/manuals list on

But compact cassette was never intended to be a precise method of recording, almost everything about the system is inexact - the recording medium itself is hardly a precision piece of engineering. The whole system was designed for convenience over performance. Admittedly, there are/were some very very good machines available which I`m sure way outstripped the original design specs.

Cassette machines intended for 'homestudio' quality recording generally run the tape at a faster speed and have a facility for varying that speed. they still tend to use a crappy brushed dc motor and rubber belt drives though.

Ron

JSB

spindle

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that the

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speed.

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.

speed

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Konig

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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.