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Old 17th Oct 2020, 9:40 pm   #1
Michael Maurice
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Default Accuracy of BSR turntables.

I recently serviced a Ferguson radiogram fitted with a cheap and cheerful BSR autochanger, the one with the plastic turntable.

It was completely seized up so I cleaned it, lubricated it and re-assembled it. Nothing unusual there....

Except, the owner complained it was running very slightly fast, not very fast, but compared to an MP3 download from a mobile phone it was ever so slightly fast. It gained around 10 seconds over a 3-4 minute song.

i did explain that the speed was never that accuate, but he wasn't having it.

So my questions are

1. How accurate would the speed be on a turntable like this?

2. As the motor speed is tied to the mains frequency, how accurate is the 50Hz mains?

3. How accurate is the speed of music played on mobile phones etc?
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Old 17th Oct 2020, 10:47 pm   #2
Radio Wrangler
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Default Re: Accuracy of BSR turntables.

Question 2 is easy.

http://www.gridwatch.templar.co.uk

Gives you national grid statistics including national frequency at about 5 minute intervals.

Question 1 depends on machining accuracy, particularly of the step-'pulley' which is likely a diecasting in a BSR and liable to some shrinkage.

Question 3, I haven't a clue. It could be quite good - crystal controlled, but there may be software fudges galore.

Is it a real synchronous motor or just an induction job with uncertain slippage?

You could print a stroboscope and use a neon bulb. The mains is fairly accurate. For timekeeping, the number of cycles/day is controlled.

Shorter term, the frequency is varied, low to demand extra generating capacity comes on-line, high to shed capacity.

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Old 17th Oct 2020, 11:13 pm   #3
Michael Maurice
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Default Re: Accuracy of BSR turntables.

Its a standard induction motor with the stepped pulley interference fitted on the shaft.
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Old 17th Oct 2020, 11:26 pm   #4
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Default Re: Accuracy of BSR turntables.

It's only about 5% fast. I doubt BSR would be bothered!

You could try a W/W resistor in series with the motor- value selected on test

Next week (s)he'll be complaining it's slow......
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Old 17th Oct 2020, 11:38 pm   #5
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Default Re: Accuracy of BSR turntables.

I'm probably very ignorant in this area Michael but 10 seconds over 3-4 minutes doesn't seem very much. It breaks down as an1/8th or a 24th ie 4-5% spread out! I'm certain that a lot of players back then would have run a little slow or fast without notice. Does the customer have perfect pitch? the new advantage of digital monitoring? or some other problem? Did it sound "wonky" to you? I suspect not!

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Old 17th Oct 2020, 11:53 pm   #6
Michael Maurice
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Default Re: Accuracy of BSR turntables.

It sounded fine to me, considering it was an early 70's mediocre radiogram. you had to listen very very carefully to hear that it was running fast.
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Old 18th Oct 2020, 1:04 am   #7
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Default Re: Accuracy of BSR turntables.

This series of decks almost universally run too fast from what I've found.
As an experiment I once filed down the pulley to reduce the speed on 45 and 33!

This didn't bother people when they were new, but having something to compare it with such as MP3 files wasn't available of course.
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Old 18th Oct 2020, 3:09 am   #8
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Default Re: Accuracy of BSR turntables.

I have sometimes fitted a series resistor in such cases. If the radio chassis has a tapped mains transformer, say 200/220/240v you could try connecting the gram motor to the 200v tapping, I have done this with rc75/80 decks, which often are found to be running fast.
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Old 18th Oct 2020, 6:32 am   #9
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Default Re: Accuracy of BSR turntables.

I've used a phone app (Rpm Calculator) where the phone is placed on the turntable and it shows the speed in a static display. Used it to set the speed on a few turntables.
I suppose where theres no adjustment, it is what it is.
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Old 18th Oct 2020, 7:46 am   #10
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Default Re: Accuracy of BSR turntables.

Only BSR specification I can find is this one for a 1967 UA70 deck which was classed as one of the better ones.
Long term speed variation 0.5% for +-10% voltage variation.
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Old 18th Oct 2020, 8:00 am   #11
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Default Re: Accuracy of BSR turntables.

"i did explain that the speed was never that accuate, but he wasn't having it."

Considering the age of the deck, He seems an unreasonable customer - but they are always right, they say.
How about some fine emery paper to take a little off at a time.
Tedious, but may be the only way.
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Old 18th Oct 2020, 8:46 am   #12
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Default Re: Accuracy of BSR turntables.

Actual speed was always a variable. The motor had to contend with a single 45 that weighed almost nothing to a turntable full of heavy 78 rpm discs that weighed a lot more. I understood that the estimated speed was about +3% empty and -3% with a full load. This is also subject to the motor and turntable bearings together with the idler drive all being in new condition.
It would seem that your customers TT is behaving normally and within specification. The details in post #9 covers variation with voltage difference not the actual turntable speed.
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Old 18th Oct 2020, 9:14 am   #13
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Default Re: Accuracy of BSR turntables.

Comparisons are odious, as the bard said. If the thing is within 1% of nominal speed under ideal conditions, I'd say that's good going. I have detected something under 1% slow in isolation, but then I have absolute pitch as well. In juxtaposition, just about anybody can detect the minutest difference, by phasing if nothing else - the human senses are very good in this regard. Historically, professional tape machines and cutting lathes themselves weren't always perfectly on speed, particularly constant angular tension transports like the Ampex 300 series. The deck is within spec, and that should be the end of the matter.
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Old 18th Oct 2020, 9:19 am   #14
Edward Huggins
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Default Re: Accuracy of BSR turntables.

Customers do have high expectations of these volume produced basic decks and many queries are Posted here - and it seems, more of late. The earliest BSR Autochangers had sturdy fully shielded induction motors and quite heavy steel platters. These were needed in order to cope with varying weights - indeed up to a load of ten 12" 78s. Years later the rather nasty BSR C109 model, and it's later variants, usully had a "stack" of maybe just three 110 gram LPs - if that. I would not attempt to faff with it. Such a deck was entirely suited to a mid-range Stereogram. We had a trade account with BSR (mainly to replace old 78rpm units) and they always quoted us a + or - 3% speed variation.
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Old 18th Oct 2020, 9:27 am   #15
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Default Re: Accuracy of BSR turntables.

The comments in post #12 are very true, the difference with 1 record and a full load would alter the speed.
Perhaps load the TT up with a few LP’s and see what the difference is.

As Ted states, the deck is within spec.
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Old 18th Oct 2020, 10:20 am   #16
Michael.N.
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Default Re: Accuracy of BSR turntables.

If the customer has perfect pitch just say that the orchestra/band/group are playing at
A= 443 Hz.
Comparing old budget gear with modern digital equipment, asking to be disappointed.
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Old 18th Oct 2020, 10:31 am   #17
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Default Re: Accuracy of BSR turntables.

I would always differentiate between a standard induction motor (with capacitor) and
the shaded pole motor fitted. In the latter I have traced major speed error down to
a defective weld on one of thick copper rings on the stator.
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Old 18th Oct 2020, 10:36 am   #18
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Default Re: Accuracy of BSR turntables.

People who have only known digital systems all their lives are much less tolerant of speed and pitch errors. As others have implied, a 5% error is on the high side, but would have been acceptable from a basic consumer deck in the 60s.
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Old 18th Oct 2020, 10:51 am   #19
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Default Re: Accuracy of BSR turntables.

As others have said these BSR decks were cheap and cheerful it's probably always been like that. I had one that ran too fast on 33 it was a build up of rubber on the motor pully , just a tiny ring but it was enough. I always run the motor and apply a little emery paper to the pully just to be sure.
Otherwise as it has been suggested try taking a little off the pully , or try another motor if you have one?

Customers can be really unreasonable, I sold a Dansette to someone who "really wanted one" I advised them in advance that they were cheap and cheerful , not hi fi just aimed at teenagers wanting to play pop music. That was accepted until the player arrived then we had all sorts of "problems". suspect wow and flutter... on Opera music..? The main problem was background hum during quiet passages of music... I had it back to check it over, the hum was negligible in fact low for a Dansette. I just took it back and sold it to someone who liked Elvis...
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Old 18th Oct 2020, 12:35 pm   #20
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Default Re: Accuracy of BSR turntables.

As has been indicated, the speed 'slip' in a shaded pole motor - or indeed any non-synchronous induction motor is dependent on load.

It sounds like your efficient cleaning and lubrication has maybe reduced the motor load to less than it would have seen when it was new when everything was a bit 'tighter'. It's also worth bearing in mind that tracking weights used to be pretty heavy: 10 grams wasn't unusual. I guess you've got less than that now, so the motor is slipping less.

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