Had another go at trying to identify an "LP" sized disc I picked up somewhere. I found this reference
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"?Direct Cut Acetate? a system that used a cellulose acetate medium coated onto an aluminium disc which, though soft enough to cut, was sufficiently hard to withstand playbacks without excessive wear" is exactly this description, acetate film over thick Al disc. It has a small hole on the underside , presumably to drive the disc around and resist the cutting force. Unusually this is marked 50RPM, agreeing with the 120 band strobe ring (uk 50 Hz mains) and you play from the inside to outside, has some ragtime like piano music on it, well one track anyway, seems to be 2 tracks. Dated by rubber stamp and endorsing ink, 11 Dec 1944 and AY 1, may have had another letter beforethe A. There isa letter D impressed in the aluminium on the underside near the drive dog hole. I must get around to taking a recording off this disc by modding a vinyl record deck to play it properly. Did the BBC modify their ones to 50 rpm?
The Marguerite lathe offered 60 rpm as an alternative to 78. I have never heard of one running at 50 rpm. The strobe was sometimes marked "50 c/s", but the disc ran at 60. rpm.
Yes , the BBC did use 60 rpm for a while, but no disc from this era will have been recorded with the RIAA characteristic, so you will need specialist equipment for correct playback (initially try a Blumlein
300c/s characteristic, it suits most UK recordings of that era). More info on this wil be found at:
There was a later BBC characteristic known as the "D" system, but this did not come into use until 1949 (so the "D" stamped in the disc is unlikely to refer to this).
You will not get many plays before the quality begins to deteriorate, so make sure you have everything in place before you let a styus touch the surface, so you stand the best chance of getting a good transfer straight away. If the nitrate surface has deteriorated, there are ways of improving it by replacing the missing plasticiser molecules with other chemicals. (If the surface is mud-cracked or there is red powder on it, the disc will be in a dangerous condition and you need to seek specialist help to avoid starting a disastrous fire.)
Generally a 0.0028" stylus is about the right size, but if the nitrate has shrunk, you might need to try a range of sizes to get the best results - or to avoid 'bottoming' on the aluminium if the bottom of the groove has split. Deep spiral scratches are a nightmare because they drag the stylus across the grooves; there are a whole range of techniques for dealing with that situation, ranging from tiltng the deck or playing the disc backwards, to re-cutting the grooves by hand under a microscope.
There is some info about MSS in "Audio Biographies" by Briggs and I believe Cecil Watts's wife published a biography of the firm, although I have never seen a copy.
If you want more help with this, please contact me (I live in the UK).
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~ Adrian Tuddenham ~
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www.poppyrecords.co.uk
wow, what a lot of info that pdf would seem to be now on
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not read it yet. I'll take a pic of the label and also the reverse with spindle hole and the drive dog hole. Label says "SPEED 50 R.P.M" At the moment I was only trying to think how to fudge a deck to play it. Hang the motor upside down and a 50/45 scaled from the 45 pulley,replacement pulley, if I can find one. I seem to remember not only inside to outside but counterclockwse rotation. Hopefully minimum stylus pressure No idea about antiskating and handedness of the arm at the moment. May end up replaying in reverse and then electronically reversing it. No intention of even applying distilled water to the surface for the moment.
the third is the reverse, the label on the front is covering over the drive dog hole, viewed from the rear. The tearing around the spindle hole is the only obvious failing of the film, clumsy positioning over a spindle in antiquity? Film laid down like silicone slivers and resist etc in chippery production? spun at high speed with a dot of liquid on the disc? The colours are about right, plum-brown in flat light and coppery tone with slanting light reflecting off the aluminium. The apparent grooves on the rear is probably machining marks of the Al blank. Perhaps the 50rpm business was a "pirated" manufacturer trying to escape patent infringement, I suppose patent library is one route to look into. I'll check again , but the blank space between 2 tracks, with continuation groove, spirals in such a fashion that playing from sinside to out , the disc would be spinning normal clockwise , so hopefully normal handedness of the tonearm and normal antiskating weight.
Typical centre-start transcription disc of the period. Broadcasters sometimes used centre-start to make sure the louder climax of a performance was recorded at the highest surface speed to give best quality.
Common practice for continuous programmes lasting longer than one disc side was to use two recording machines (often with a single common amplifier). Sometimes thesae were set up so that one recorded outside-in and the other inside-out, this meant that the changeover on playback was less noticeable because the surface noise didn't suddenly change its quality. This system was not popular with the playback operators, who had to check each side carefully and often made mistakes.
The label suggest that there is no question that the intended playing speed was 50 RPM - but it is definitely non-standard.
To vary the speed without a lot of butchery, connect the turntable motor through a step-up auto-transformer to the 100v output of a large P.A. amplifier. Feed the amplifier from an audio signal generator and adjust the frequency to get the required speed change. Carefully monitor the motor current and adjust the amplifier gain so that it is maintained at a similar value to the normal 50c/s current, otherwise you will burn out the motor at low frequencies.
Alternatively, look out for a secondhand Lenco turntable with infinitely variable speed.
No, these discs weren't played many times, so it is more likely to be caused by shrinkage of the laquer film pulling away at the centre. It also appears to have delaminated at the rim for the same reason.
...or edge dipped into a bath of laquer whilst rotating slowly. Both techniques were used.
They weren't usually machined, the blanks were stamped out of sheet aluminium. Without examining this one closely, I wouldn't like to guess at what caused that.
No chance, hardly anybody but the BBC and GPO could get hold of MSS blanks during the war; the GPO ran the factory. By 1944 aluminium was in very short supply, so private recordings, when they could be made at all, were being made on glass and even galvanised iron blanks (they were heavy!). The BBC monitoring services recorded onto wax cylinders.
A centre-start disc still rotates in the conventional direction, it is one of the few conventions in the recording world that never seemed to be flouted. The only time you would need a reversing turntable is if you needed to play it backwards to recover a lost turn because of a jumped groove.
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~ Adrian Tuddenham ~
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www.poppyrecords.co.uk
I think I'll go with the larger pulley, even if not giving exactly
50rpm it will be constant at a measurable speed. The other letter in front of AY 1 may be a J, so JAY 1, a ragtime pianist of 1940s called Jay Something ? The blemish at the rim on the front face is a splodge of powdery paint or tippex, easily removable if/when I dare to clean the disc. No damage on the active face film, a few spots missing on the rear. I'd played it sometime for about 5 seconds, the track stayed intact, played well enough to tell by my nonmusical ears it was a pleasant piece of ragtime piano or some such style of music. I suppose they were double sided discs but only one face recorded on this. But the exposed Al on the rear near the spindle hole does not show machining marks. Perhaps there was an attempt at recording on the rear, but at too low a pressure, it feels smooth to the touch, and the film patterning goes right to the centre. I wonder if the use of Persian blue, endorsing ink (stains well into paper fibres for legal document use) is relevant or that is just the ink pad they had there then. Another recovery program I must get back to sometime is 3 spools of used taperecorder wire that came with a rusted up Magnetophon , circa mid 1950s. one of these
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Hardly anyone could afford one of those pocketsize (well greatcoat pocket) covert recorders, then. It would be unlikely they were erased (unless it was a dismissible conduct if not erased before disposal ) as required the use of batteries only, and no fast erase. 3 batteries to power the peanut valves and motor. I got the motor and mechanics free running again, but ran out of time , before cross-connecting the head to the head wiring of the R/P head of a modern cassette recorder, to hear what,if any, is recorded on the wire.
Found a pulley to give +0.5% of 50 RPM, so within normal mains f variation. I intend to record on minidisc as stereo from a magnetic pickup. At this stage not playing around with the EQ of the phono amp, any recommendations for setting the normal domestic amp bass and treble controls for this first (only?) recording . After a second or 2 at inner and outer posistions to check antiskating weight and stylus weight is ok
Record in the highest possible uncompressed quality. This may be the only surviving recording and you don't want to screw up the sound wih the artefacts of Minidisc or any other compression format.
Even with a high bit-rate digital format, it is best to put right everything that can be done in the analogue domain before digitising it; once digital artefacts have been created by digital equalisation or speed changes, they can never be undone.
--
~ Adrian Tuddenham ~
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www.poppyrecords.co.uk
I could certainly take the 1V "L & R" audio feeds to other recorders, but the only analogue recorder I have is an ordinary domestic cassette recorder of dubious quality other than it works, no 30 IPS R-R recorder, plus wav file on a laptop?
Stereo WAV file on a laptop is your best option. If you were able to equalise it and get the speed exactly right before digitising it, you could used 16-bit 44.1k sampling, but if you intend doing any digital manipulation, a higher resolution is preferable to keep the artefacts to a minimum.
If you know what format your processing software needs, record in that format to avoid the artefacts of conversion - but it is better to eliminate all that nonsense by getting the analogue signal right in the first place.
--
~ Adrian Tuddenham ~
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www.poppyrecords.co.uk
So assuming Blumlein 300Hz recording characteristic. I'll feed a few uV from an audio sig gen parallel with the cartridge and adjust treble and bass to try to get something like
3dB down at 300Hz , flat between 600Hz and 3KHz, +3dB broad hump between
3 KHz and 7KHz and as little as possible above 8KHz. Whatever it graphs out as, record the details. Try a couple of seconds recording at centre, mid and outer, to check for enough but minimum stylus weight and antiskating , then review those recordings before going for a full run on 3 recording media. I've not set modified the deck yet, I'll time the revs when done, but it should be 50.3 RPM assuming 50Hz mains
For archive work, don't throw away anything you don't have to. Keep it wide open and flat (or "Blumleined") from 20c/s to 20Kc/s unless somethng is overloading. The 300c/s characteristic is easily achieved with a single RC time constant in a feedback loop (the time constant is
531 microseconds) giving bass bost. This should be sensibly limited by another pole that comes in around 20c/s, because you do not want to be calling for infinity gain at D.C.
A straightforward variable circuit that can be connected directly to the pickup is shown at:
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The time constant can be read directly off the dial of the multi-turn pot.
If you want something more elaborate, try:
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When you have made your 'Archive' copy, you can play that and then limit the bandwidth or do whatever is necessary to produce a 'Playback' copy that sounds easier on the ear.
It is a pity you are using a radial arm, but you can usually get away with it if you use a conical stylus (rather than truncated elliptical, which will emphasise the playback 'azimuth error' between the two points of contact on the groove walls). Do you have a stylus in the correct range for coarse-groove recordings? A microgroove stylus will give useless results (unless you happen to be incredibly lucky)
Why not use the 45 rpm speed and run it from a 56c/s supply? That will save a lot of hassle - any well-designed amplifier rated at about 100 watts, fed through a suitable reversed mains transformer, will do the job.
If you live anywhere within travelling distance of Bath, you could bring the disc here and I'll see what I can do with it.
(By the way, I'm beginning to have my doubts as to whether the blank was a genuine Marguerite product or whether it was made by some other company.)
--
~ Adrian Tuddenham ~
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www.poppyrecords.co.uk
Adrian Tuddenham wrote: "(If the surface is mud-cracked or there is red pow der on it, the disc will be in a dangerous condition and you need to seek specialist help to avoid starting a disastrous fire.)"
If the disc is old enough that the cutting surface was celluloid, or cellulose nitrate (rather than the cellulose acetate used in later years) then it might be bad juju!
Celluloid deteriorates with age - the camphor escapes and you're left with just cellulose nitrate, which becomes increasingly brittle.
Cellulose nitrate is known by another name - "guncotton". Also "flash paper". It's a primary ingredient in smokeless gunpowder.
If something made of celluloid or cellulose nitrate has deteriorated to the point where it's forming a powder... well, that powder might be touchy enough that even a static-electric spark might ignite it, and FOOM.
I'd also be concerned about diamond-stylus-to-groove friction - there's a *lot* of pressure on that tiny contact surface. I've heard that the heat generated during playback of an LP is actually sufficient to melt a very thin surface layer of the vinyl!
On the other hand, if it's a true "acetate" disc (made with cellulose acetate rather than cellulose nitrate) the flammability problem would be much less. If this material is deteriorating there might be a distinct odor of vinegar, as the acetic acid dissociates from the cellulose.
As to playing the disc... the cat's meow might be to gain access to an ELP laser turntable, which doesn't use a physical-contact stylus at all. No wear... but not cheap nor common.
It won't be. Cellulose Acetate can only be embossed, not cut. It was not used for direct-cut discs. (The manufacturers sometimes called their nitrate discs "Acetates", but this was deliberately misleading because of the bad reputation that nitrate had gained.)
Not all that effective; it plays every bit of dirt the same as solid groove wall, whereas a stylus will scrape the dirt away as it plays.
A stylus will also scrape the wall away if you get it wrong , so the optical system has the potential to do less damage; but the cleaning process needed before optical playback will probably do as much damage as the stylus. Swings & roundabouts.
--
~ Adrian Tuddenham ~
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www.poppyrecords.co.uk
The critical factor is the bottom radius, if it is very small you might be able to play it with a microgroove stylus; direct-cut discs often have a smaller bottom radius than pressed ones, so you might be lucky. If the bottom radius is larger than 0.001", a microgroove stylus will skate around all over the place.
The picture only shows the width of the grooves at the top, to find the bottom radius you either have to section the disc or play it with a variety of styli and listen for the smallest one where 'skating'* stops. The optimum size will usually be a bit larger than the bottom radius, so that the stylus tip is located positively between the groove walls away from the bottom. If it is too large, it will sit much higher and then it will encounter surface scratches and other damage near the top of the groove wall.
*Skating can be identified by distortion and a hollow burbly quality to the surface noise, not unlike the effect that bad digital de-noising has on the music.
--
~ Adrian Tuddenham ~
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www.poppyrecords.co.uk
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