Cassette tape speed adjustment
in [Repair]
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From: Ron on 9 Dec 2009 07:38 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... >>> Assuming my test tape is stretched (I doubt it , as it would have to be >>> even >>> stretch the whole length). >>> I normally test speed monaurally so the beats are unmistakable. That is >>> 1KHz >>> test tape output and floating accurate 1KHz sine signal both fed into > one >>> headphone cup. Easily gives 0.1 percent resolution (assuming test tape > is >>> ok). >>> >>> If I record accurate 1KHz tone onto a blank tape for exactly ( to human >>> reaction time accuracy) 100 seconds. Then replay for beats of 1Hz or so >>> and >>> output lasts for 100 seconds +/- reaction time then is the speed > correct? >>> I >>> suspect that repeating this process with the speed regulator changed , > say >>> 5 >>> percent, would also give "correct" speed, that time also >>> >>> >>> Does anyone know how much effect types and thickness (play duration C30 > to >>> C90) have on replay speed perhaps in conjunction with too soft or too >>> hard >>> pinch wheel rubber ? >>> >>> >> 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 >> >> > > > 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)
From: N_Cook on 9 Dec 2009 08:33 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... > >>> Assuming my test tape is stretched (I doubt it , as it would have to be > >>> even > >>> stretch the whole length). > >>> I normally test speed monaurally so the beats are unmistakable. That is > >>> 1KHz > >>> test tape output and floating accurate 1KHz sine signal both fed into > > one > >>> headphone cup. Easily gives 0.1 percent resolution (assuming test tape > > is > >>> ok). > >>> > >>> If I record accurate 1KHz tone onto a blank tape for exactly ( to human > >>> reaction time accuracy) 100 seconds. Then replay for beats of 1Hz or so > >>> and > >>> output lasts for 100 seconds +/- reaction time then is the speed > > correct? > >>> I > >>> suspect that repeating this process with the speed regulator changed , > > say > >>> 5 > >>> percent, would also give "correct" speed, that time also > >>> > >>> > >>> Does anyone know how much effect types and thickness (play duration C30 > > to > >>> C90) have on replay speed perhaps in conjunction with too soft or too > >>> hard > >>> pinch wheel rubber ? > >>> > >>> > >> 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 > >> > >> > > > > > > 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) 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.
From: Ron on 9 Dec 2009 09:22 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... >>>>> Assuming my test tape is stretched (I doubt it , as it would have to > be >>>>> even >>>>> stretch the whole length). >>>>> I normally test speed monaurally so the beats are unmistakable. That > is >>>>> 1KHz >>>>> test tape output and floating accurate 1KHz sine signal both fed into >>> one >>>>> headphone cup. Easily gives 0.1 percent resolution (assuming test tape >>> is >>>>> ok). >>>>> >>>>> If I record accurate 1KHz tone onto a blank tape for exactly ( to > human >>>>> reaction time accuracy) 100 seconds. Then replay for beats of 1Hz or > so >>>>> and >>>>> output lasts for 100 seconds +/- reaction time then is the speed >>> correct? >>>>> I >>>>> suspect that repeating this process with the speed regulator changed , >>> say >>>>> 5 >>>>> percent, would also give "correct" speed, that time also >>>>> >>>>> >>>>> Does anyone know how much effect types and thickness (play duration > C30 >>> to >>>>> C90) have on replay speed perhaps in conjunction with too soft or too >>>>> hard >>>>> pinch wheel rubber ? >>>>> >>>>> >>>> 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 >>>> >>>> >>> >>> 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) > > > 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
From: N_Cook on 9 Dec 2009 10:42 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$1(a)news.eternal-september.org... > > Set up a sig genny and test him out Much easier to say the test tape is stretched. Perhaps perfect pitch testing would only work by playing the likes of JSB Tocatta and Fugue in D major, not pure tones How come I cannot google the rpm of an audio cassette capstan? A calibrated strobe and tipex mark on the capstan periphery should give a definite answer (assuming the spindle is clean and not worn). It should be determinable from tape speed of 1 7/8 in per sec and spindle diameter, that is about 1.9mm, but what should it be to 0.1 percent accuracy?
From: AZ Nomad on 9 Dec 2009 11:12
On Wed, 9 Dec 2009 15:42:00 -0000, N_Cook <diverse(a)tcp.co.uk> wrote: >Ron <ron(a)lunevalleyaudio.com> wrote in message >news:vZCdnX7J1q8uL4LWnZ2dnUVZ7rVi4p2d(a)bt.com... >> N_Cook wrote: >> > Ron <ron(a)lunevalleyaudio.com> wrote in message >> > news:0dednd3AmaG0B4LWnZ2dnUVZ7tqdnZ2d(a)bt.com... >> >> N_Cook wrote: >> >>> Arfa Daily <arfa.daily(a)ntlworld.com> wrote in message >> >>> news:vbKTm.64350$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 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. |