Cassette tape speed adjustment
in [Repair]
|
From: N_Cook on 11 Dec 2009 05:47 Ron <ron(a)lunevalleyaudio.com> wrote in message news:CPOdnaXSau0Hj7_WnZ2dnUVZ8uCdnZ2d(a)bt.com... > N_Cook wrote: > > Ron <ron(a)lunevalleyaudio.com> wrote in message > > news:79mdnU8QxrtKk7_WnZ2dnUVZ8u-dnZ2d(a)bt.com... > >> N_Cook wrote: > >>> Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message > >>> news:wRYTm.105473$iT5.66666(a)newsfe12.ams2... > >>>> "N_Cook" <diverse(a)tcp.co.uk> wrote in message > >>>> news:hfoghs$f07$1(a)news.eternal-september.org... > >>>>> Ron <ron(a)lunevalleyaudio.com> wrote in message > >>>>> news:vZCdnX7J1q8uL4LWnZ2dnUVZ7rVi4p2d(a)bt.com... > >>>>>> N_Cook wrote: > >>>>>>> Ron <ron(a)lunevalleyaudio.com> wrote in message > >>>>>>> news:0dednd3AmaG0B4LWnZ2dnUVZ7tqdnZ2d(a)bt.com... > >>>>>>>> N_Cook wrote: > >>>>>>>>> Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message > >>>>>>>>> news:vbKTm.64350$Dl4.48926(a)newsfe08.ams2... > >>>>>>>>>> "N_Cook" <diverse(a)tcp.co.uk> wrote in message > >>>>>>>>>> news:hflv4c$p04$1(a)news.eternal-september.org... > >>>>>> 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
From: bz on 11 Dec 2009 11:31 "N_Cook" <diverse(a)tcp.co.uk> wrote in news:hft7vv$nsr$1(a)news.eternal-september.org: > 3 of them made on the same batch of tape and on the same machine but > more than 15 years ago. As they are all stored in the same environment > they could theoretically all have chemically degraded/stretched to the > same degree. I'm trying to find some process that gives an independent > verification that does not require a know good machine. > eg quartz controlled (so low tens ppm) f-meter coupled strobe fed to > rotating capstan if diameter/s of the spindles are manufactured to > specific dimensions of precisely known tolerances. Perhaps 1.9 +/- 0.002 > mm and 2.4 +/- 0.002mm say, no such data found googling. I can only > measure to +/-0.02 mm and no slip gauges for absolute calibration. > +/-2 in 200 or so, is not accurate enough > Suggestion: Google for guitar tuning meter There are meters available for ~20 bux and even some 'on line' meters. Record a known good 'string note' frequency and use it for your standard. Should get you close enough for any audiophile's ears -- bz 73 de N5BZ k please pardon my infinite ignorance, the set-of-things-I-do-not-know is an infinite set.
From: bg on 11 Dec 2009 12:11 N_Cook wrote in message ... >Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message >news:wRYTm.105473$iT5.66666(a)newsfe12.ams2... >> >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message >> news:hfoghs$f07$1(a)news.eternal-september.org... >> > Ron <ron(a)lunevalleyaudio.com> wrote in message >> > news:vZCdnX7J1q8uL4LWnZ2dnUVZ7rVi4p2d(a)bt.com... >> >> N_Cook wrote: >> >> > Ron <ron(a)lunevalleyaudio.com> wrote in message >> >> > news:0dednd3AmaG0B4LWnZ2dnUVZ7tqdnZ2d(a)bt.com... >> >> >> N_Cook wrote: >> >> >>> Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message >> >> >>> news:vbKTm.64350$Dl4.48926(a)newsfe08.ams2... >> >> >>>> "N_Cook" <diverse(a)tcp.co.uk> wrote in message >> >> >>>> news:hflv4c$p04$1(a)news.eternal-september.org... >> > >> >> >> >> 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
From: N_Cook on 11 Dec 2009 12:31 bg <bg(a)nospam.com> wrote in message news:hftuf0$od4$1(a)news.xmission.com... > > N_Cook wrote in message ... > >Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message > >news:wRYTm.105473$iT5.66666(a)newsfe12.ams2... > >> > >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message > >> news:hfoghs$f07$1(a)news.eternal-september.org... > >> > Ron <ron(a)lunevalleyaudio.com> wrote in message > >> > news:vZCdnX7J1q8uL4LWnZ2dnUVZ7rVi4p2d(a)bt.com... > >> >> N_Cook wrote: > >> >> > Ron <ron(a)lunevalleyaudio.com> wrote in message > >> >> > news:0dednd3AmaG0B4LWnZ2dnUVZ7tqdnZ2d(a)bt.com... > >> >> >> N_Cook wrote: > >> >> >>> Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message > >> >> >>> news:vbKTm.64350$Dl4.48926(a)newsfe08.ams2... > >> >> >>>> "N_Cook" <diverse(a)tcp.co.uk> wrote in message > >> >> >>>> news:hflv4c$p04$1(a)news.eternal-september.org... > >> > > >> >> > >> >> 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
From: Arfa Daily on 11 Dec 2009 19:57
"N_Cook" <diverse(a)tcp.co.uk> wrote in message news:hftvlm$nii$1(a)news.eternal-september.org... > bg <bg(a)nospam.com> wrote in message news:hftuf0$od4$1(a)news.xmission.com... >> >> N_Cook wrote in message ... >> >Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message >> >news:wRYTm.105473$iT5.66666(a)newsfe12.ams2... >> >> >> >> "N_Cook" <diverse(a)tcp.co.uk> wrote in message >> >> news:hfoghs$f07$1(a)news.eternal-september.org... >> >> > Ron <ron(a)lunevalleyaudio.com> wrote in message >> >> > news:vZCdnX7J1q8uL4LWnZ2dnUVZ7rVi4p2d(a)bt.com... >> >> >> N_Cook wrote: >> >> >> > Ron <ron(a)lunevalleyaudio.com> wrote in message >> >> >> > news:0dednd3AmaG0B4LWnZ2dnUVZ7tqdnZ2d(a)bt.com... >> >> >> >> N_Cook wrote: >> >> >> >>> Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message >> >> >> >>> news:vbKTm.64350$Dl4.48926(a)newsfe08.ams2... >> >> >> >>>> "N_Cook" <diverse(a)tcp.co.uk> wrote in message >> >> >> >>>> news:hflv4c$p04$1(a)news.eternal-september.org... >> >> > >> >> >> >> >> >> 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 > > This is becoming bizarre ... Konig strobe test tape. Good enough. End of. If not good enough for your very discerning customer with "perfect pitch", then it is he who is at fault, for believing that the cassette medium is sufficiently good to serve his needs, and you for allowing him to continue believing this ... Arfa |