21st century problem

[Johny B Good]

Turntable strobe markings are also included for use with a 60Hz driven lamp source (120Hz flicker) as well.

[F Murtz]

Well they come from such good British stock.

[polygonum]

Fair enough.

[Martin Brown]

Lights never did flicker at 50Hz. Incandescent lamps vary with the power dissipated in the filament so that they flicker at 100Hz.

Neon indicators still flicker as you want them to.

These days you can get cheap precision LED strobes and cheap crystals for spot frequencies that are accurate to ~2ppm (which is probably a fair bit better precision than the spot frequency on the mains).

[Martin Brown]

Yes. But for comparison an untrimmed cheap crystal oscillator as used in a wristwatch is typically better than 30ppm (and

[PeterC]

So what reference would the rotating corpse use?

[Dave Plowman (News)]

Think you have to be careful how you word this. Hz refers to a complete AC cycle. A lamp may well produce 100 peaks of light per second when driven by 50 Hz - but doesn't flicker at 100 Hz. 100Hz would mean 200 flickers per second.

[Tim Watts]

I'm going to disagree with this.

Why is a rectified 50 Hz sine not regarded as a 100Hz waveform - waht used to be a single asymmetric wave has been converted into a pair of identical symmetric waved - I would argue that therefore it is now 100Hz

- as would the resulting lamp flicker.

[tony sayer]

Actually we had a Edison Phonograph in our local community radio station and it did, for a recording over 100 year old, sound surprisingly good.

A great deal of discussion went on with the appropriate way to "mic it up" carbon mikes almost won the day;)!...

The man who owns it takes them out, he's got a pair, CJ'ing sometimes rather then DJ'ing! At such events as "Bestival"..

And like the 78 RPM which was a nominal speed, they were much the same in speed variation..

[charles]

He doesn't live in Cobham, Surrey, does he? If not there's someone else who owns two.

[John Williamson]

The frequency of the neon or old style fluorescent lamp flicker is

100Hz, according to a photocell connected to a frequency meter, as you get two flashes per cycle of mains unless you rectify it. In this case, the cycle is from zero output to full output and back again. Filament lamps also flicker at 100Hz, but the amplitude is reduced by thermal inertia, and I doubt anyone without the right lab could detect the flicker from an HF ballasted fluorescent lamp, due to the persistence of the phosphor used.

[Martin Brown]

Hz refers to the repetition frequency. The voltage varies at 50Hz with average zero, but the power dissipated in the filament varies from 0 to a positive quantity irrespective of the direction of current flow.

This results in some mean amount of light output from the hot filament with a 100Hz variation in intensity and colour temperature superimposed on top of it.

[Johny B Good]

I'm surprised they didn't round the price up to £78.00 to match the nominal rpm. :-)

At 75 quid, it's a snip for a Russ Andrews product.

I've considered replacing the mains driven strobe on the TD125 MK1 with a crystal referenced 100 Hz strobe driven white LED (on a 5 or 10 percent duty cycle to 'sharpen up' the strobe markings).

Sadly, in the short term, it's the turntable that's acting as a measuring reference for the mains frequency variations being applied 3 or 4 times per minute to make sure the total cycles per day remains within about 1500 of its exact value, midnight to midnight for days, weeks, months and years.

The very slight 'drift in speed' mimics the behaviour of the hum bars that only became visible on 625 line TV transmissions in the early 80s in the days before 24 hour broadcasting at the end of the 'broadcasting day' before the TXes were shut down (if ever - I have a feeling they left them running for the lousy 5 or 6 hours break in TV programming even way back then).

The pattern was quite distinctive so I know the speed variations were from the mains and not the turntable itself.

[Johny B Good]

...at 100Hz, same as incandescent, striking at 90v on the magnitude 'up slope' of each half cycle of mains and likewise, extinguishing at

60v on the magnitude down slope.

It's fairly trivial to knock one up from a 32768Hz clock crystal and a bit of cmos TTL. However, I'll have a google for such 100Hz strobe generator boards (or something I can canabalise a board from).

[sm_jamieson]

I like their terminology:

Play 78s? Our 78 RPM strobe disc allows you to set the speed of your turnta ble for playing older records. Having the correct speed means that your Included: The Zapper strobe light music won't sound overly dynamic because the record is spinning too fast, o r too 'flat' because the record is spinning too slowly.

The words "dynamic" and "flat" are rather vague and subjective words that a re not even used consistently by good old Russ. A record spinning too fast can make the music overly "dynamic" but so can one of those nasty transisto r amplifiers ! He is lucky that "flat" is in fact the correct word to use in its musical s ense. There is many an argument regarding some given singer, due to the mus ician using "flat" to mean poorly pitched in the downward direction, and th e non-musician meaning that the performance was dull and/or boring. It happens all the time on the X factor ... oh did I just admit I have been watching it ... Simon.

[polygonum]

Rotisserie

[tony sayer]

In article , charles scribeth thus

No it's Dr Greg Butler the odd geezer in the black hat with "Kipper the cat" who follows his master around everywhere;!...

[Johny B Good]

Well, I've googled around and the best 'readymade' solution I've found so far is the "Pocket Turntable Strobe" here:

This might well appeal to the OP (Richard Tobin) as a solution to his problem. I'd recommend the "60Hz" version for two reasons. Firstly, you'll be able to use the "60Hz" strobe marks and be able to adjust to

45rpm exactly (the "50Hz" strobe marks are set to 45.1rpm on account that's as close as you can get them to 45rpm) and secondly, on account it should help avoid confusion in the presence of room lighting with a pronounced 100Hz flicker.

The price is quite reasonable at $12.00 (£7.46). Unfortunately the shipping to the UK is another $8.00 (£4.97) taking the total order price up to $20.00 (£12.43) and Gawd only knows how long for delivery across The Pond. However, it's still only a 6th of the price of that Russ Andrews item.

Since I've already got a sizeable collection of crystal reference oscillator modues (DIP) and cmos TTL chips and pieces of veroboard (and even copper clad board - if I care to make up another batch of etchant) and I have considerable room for a much bigger PCB (damn, the crystal I used for a similar project 30 odd years ago was as big as, if not bigger than, the whole PCB used by the Pocket Turntable Strobe module!), I rather fancy designing and making my own superior (of course! :-) version so I'm not particularly tempted to place an order.

Interestingly, the picture reveals the use of a 12MHz crystal. I suspect the "50Hz" board would have revealed the use of a 10MHz crystal. It would seem that they've opted for a decades divider chip rather than using binary division and gating to get oddball ratios (no worries about getting TTL logic to divide by 11 or 13 or whatever I deem is best for whatever I think is the best crystal oscillator module frequency I have to hand for the job - given enough circuit board real estate and suitable TTL chips, I'm sure I can create a

120Hz pulse source from whatever is already in my possesion).

[Clive George]

Is that the 50Hz marks on a particular device, or in general?

Surely if you have 200 pips evenly spaced on your turntable edge, they appear stationary in a 50Hz strobe at 45rpm? Each pip would move three along per flash.

200, 270, 160, 216 pips would seem to be right for 45rpm@50Hz, 33 1/3rpm@50Hz, then the same at 60Hz.

[Johny B Good]

The error in this case arises out of the fact that they use 133 strobe lines or pips when, in theory, it should be 133.3333 to match the 100p/s strobe lamp

It is possible to get a stationary strobe pattern for 45 rpm using

50Hz mains driving a neon or tungsten filament lamp but you'd have to use 400 strobe lines (less than 1 deg seperation). As you say, each strobe line will move _exactly_ 3 places along for each flash of the strobe lamp which will make the pattern appear stationary when moving at exactly 45rpm with a 100 pulses per second strobe light source.

I think the main reason for accepting the slight error by using 133 strobe markings is simply to retain visibility of the stationary pattern under tungsten lighting. I suspect the motion blur with a 400 line strobe would make such a pattern all but invisible.

Of course, when a built in neon strobe light source is used, the use of a 400 line strobe pattern using very narrow lines probably would be usable (and extremely usable with a modern low duty cycle crystal referenced 100 p/s LED strobe illumination source - but, if you're going for _that_ option, why not go for a 120p/s strobe source using a

160 line strobe disc and keep it simple?)