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Old 14th Sep 2019, 2:09 pm   #21
Richard_FM
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Default Re: Question on Recording speeds

I've heard some early gramaphone discs could vary between 65 to over 100 rpm, possibly due to having a clockwork turntable drive or similar mechanism without a governor.
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Old 25th Sep 2019, 9:45 pm   #22
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Default Re: Question on Recording speeds

Both the Gramophones I remember from my Childhood & Teenage years had motors fitted with governors, and a speed control which was adjustable between about 65 to 90RPM or so, though all the records I remember my parents having, which dated from the 1920s onwards were nominally 78rpm, except for some Columbia discs which were marked 'Speed 80', over 2.5% faster than 78 of course.
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Old 26th Sep 2019, 11:48 am   #23
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Default Re: Question on Recording speeds

Just read in Wednesday Mail the answer to the original question.
Cheers
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Old 26th Sep 2019, 12:11 pm   #24
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Default Re: Question on Recording speeds

I, too, have seen the detailed answer in yesterday's Daily Mail which, among other things, points out the relationships between motor rotational speed, mains frequency and turntable RPM, giving examples of the calculations involved, something I, for one, had either forgotten or maybe never knew in the first place!
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Old 26th Sep 2019, 4:33 pm   #25
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Default Re: Question on Recording speeds

I find this rationalisation of the 78 rpm standard speed pretty puzzling. Maybe in the US there were fixed-speed synchronous phonograph motors back in the day, where 78.26 rpm could be calculated from 60 Hz mains and an integer gear ratio, but was there ever such a fixed-speed 78 rpm synchronous gramophone motor in the UK?

AFAIK all UK pre-LP 78 rpm gram motors used a governor-controlled variable-speed motor. Even the exotic Garrard 201 direct drive turntable had a speed control. So has the neat and tidy 78.26 rpm calculation ever had any relevance at all here in the UK?

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Old 26th Sep 2019, 11:45 pm   #26
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Default Re: Question on Recording speeds

78.26 rpm is for induction motors fixed speed 50Hz, and 77.92 rpm is the 60Hz speed.
According to "Hayes on Record" (EMI book) 78 was standardised by ca 1914, and this
era will have used clockwork and DC motors.
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Old 27th Sep 2019, 2:05 am   #27
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Default Re: Question on Recording speeds

Quote:
Originally Posted by Hartley118 View Post
I find this rationalisation of the 78 rpm standard speed pretty puzzling. Maybe in the US there were fixed-speed synchronous phonograph motors back in the day, where 78.26 rpm could be calculated from 60 Hz mains and an integer gear ratio, but was there ever such a fixed-speed 78 rpm synchronous gramophone motor in the UK?

AFAIK all UK pre-LP 78 rpm gram motors used a governor-controlled variable-speed motor. Even the exotic Garrard 201 direct drive turntable had a speed control. So has the neat and tidy 78.26 rpm calculation ever had any relevance at all here in the UK?
The attached Wireless World article (from 1931) indicates that gear-drive turntables were found in British practice.

But I doubt that the precise standardization, to 78.26 rev/min, had much to do with domestic turntables, which often had a variable speed facility anyway. More likely it came about because of professional transcription needs, where gear-driven turntables with synchronous motors were found, and where precise timing was needed. The latter indicated a need for precision with both recording and playback speeds. 78.26 rev/min was a 23:1 reduction from 1800 rev/min, the speed of a 4-pole synchronous motor operating from a 60 Hz supply. Also, where variable speed turntables were used for transcription purposes, 78.26 rev/min was easily set with a (60 Hz) stroboscope.

The 50 Hz case would give 78.95 rev/min as a 19:1 reduction from 1500 rev/min. Whether that was the actual recording speed in 50 Hz areas I do not know. But with stroboscope-equipped turntables, it would often have been the playback speed. The RCA 70-series synchronous motor, gear-driven professional turntables were available in both 60 Hz and 50 Hz forms. My best guess from the nature of the mechanism is that the “78” speed was 78.26 rev/min at both supply frequencies. (See: https://www.vintage-radio.net/forum/...0&postcount=59.)

(Typical stroboscopes also produced a slight error with the 50 Hz. 45 rev/min combination, “locking” at 45.11 rev/min.)

The old British Standard BS1928 for gramophone records – which I have not seen - might provide some clues, in that it probably specified actual recording speeds, and so might tell us whether late-era British 78s were recorded at 78.26 or 78.95 rev/min.


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Attached Files
File Type: pdf Gramophone Motor Design WW 19310325.pdf (523.4 KB, 29 views)
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Old 4th Dec 2019, 8:57 pm   #28
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Default Re: Question on Recording speeds

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Originally Posted by Synchrodyne View Post
Columbia chose the existing 33⅓ rev/min transcription speed for its LP. The readily available articles, such as that attached, do not explain why, although one may infer that the engineering analysis showed that there was no good reason not to do so. The full answer was probably provided in the article – which I have not seen - in the IRE Journal for 1949 August, available (for purchase) as an IEEE paper, at: https://ieeexplore.ieee.org/document/1698116, “The Columbia Long-Playing Microgroove Recording System”, by P. Goldmark et al.
The Goldmark et al paper on the LP is in fact readily available at the American Radio History site, which has some of the IRE Proceedings issues, see: https://www.americanradiohistory.com...roceedings.htm. The issue at interest is 1949 August. I have extracted and attached the article as a .pdf, heavily compressed, but still readable.

The reason for the 33⅓ rev/min rotational speed choice was not given explicitly, but one may derive from the initial conditions/constraints and the discussion on trades off that it was “in the ballpark”, if not precisely optimum. Thus we are left to conclude that Columbia found no good reason to deviate from this established speed. Not discussed in the paper, but the graphical data also show why 45 rev/min was a better choice for the 7-inch disc.


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File Type: pdf Columbia LP Microgroove IRE 194908 Compressed.pdf (1.23 MB, 29 views)
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Old 5th Dec 2019, 1:01 pm   #29
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Default Re: Question on Recording speeds

The more I read about this topic the more I appreciate the amount of research and development behind the Development of the LP. It must have been a wonderful time to have been involved in this subject and bring it to fruition.
Thanks for all the information provided it has certainly been interesting reading.
John
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Old 11th Dec 2019, 2:49 pm   #30
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Default Re: Question on Recording speeds

The postwar turntables used in Oz used induction motors, driving a cylindrical stepped driver wheel, which mated with a "rubber tyred" "idler wheel" which then drove the inner rim of the turntable.

The steps allowed the selection of the various speeds, eg., 78, 45, 33, & sometimes, 16.

All sweet, but in Western Australia, up to about the late '40s, early '50s, the Mains frequency was 40Hz.
Machine shops had a "nice little earner" making replacement stepped driver wheels, which were fitted by the local distributors of such turntables, with the originals saved for the day we would change to 50Hz.

That day came, & the distributors then sold those original driver wheels to those needing to update their equipment.
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