Making a 332 ring on stage

[Stockden]

This afternoon I was approached by one of our local Am-Dram group clutching a 332 style phone, who wondered whether I'd "be able to rig this up so it will ring". The catch of course is that the performance they want it for starts next week and the dress rehearsal is tomorrow afternoon...

Now it's about 35 years since I did my telephony theory but, if I remember correctly, the ringing signal is 25Hz at somewhere around 50 volts. My initial plan therefore is to feed the thing with un-smoothed, half wave rectified DC at around 24 volts via a "push to ring" button. Is that going to work and (much more importantly) is it going to harm the phone?

I know that whoever rings it will have to do the "pulsing" manually but that's the price they're going to have to pay for giving me no notice!

Hugh

[Boom]

You'd think with the money Channel 4 has got that they would be able to get a ring tone right but no, Deal Or No Deal gets it totally wrong and sounds more like a US tone than a UK one.

50Hz feeding a divide by two followed by a 3055 or similar should be easy enough. Chuck in a simple 555 timer circuit and it should give perfection.

It would probably need two 555's as there seems to be a gap between each pair of rings i.e. ring-ring gap ring-ring.

[Dave Moll]

As far as I recall, the circuitry of the GPO box which I have for generating a ring current (without cadence) along with 50VDC creates the 25Hz supply similarly to how Hugh describes - half-wave rectifying mains before feeding it into a transformer arrangement. The circuit diagram in the referenced PDF explains better than I can.

Alternatively, if you had access to a linesman's telephone with a "CB/LB/ring" button...

Either way, I'm sure that that the back-stage man can make a better job of the cadence manually than Dave's description of Deal or No Deal above - never actually listened to it myself, and even less inclined to now!

Best of luck at such short notice.

[Stockden]

Thanks for the suggestions chaps,

I was aiming to keep it simple (not least because I'm under pressure to mow the lawn this afternoon!), hence the transformer and rectifier suggestion. I can see the benefit of the transformer - rectifier -transformer approach as explained in Dave's PDF and I think I can lay my hands on the bits to replicate that without any problem. I'm sure that the FX man can sort out the cadence.

Off to warm up the soldering iron .. (and hide the lawnmower )

Hugh

[llama]

I think the GPO box in the PDF looks to be fairly critical regarding the transformers. Plus the unspecified "filter" could be a problem. I don't understand where 25 Hz comes from - half-wave rectified AC (50HZ) is still 50Hz. Maybe the capacitor in the T2 area makes T2 ring ('scuse the pun) at 25 Hz(?).

I'd be tempted to use a relay with one of its normally-closed contacts in series with the coil. That could run off say 50 Volts and a further contact on the relay interrupt the 50 Volts. Simples.
Graham

[AndiiT]

Hi,
If you aren't too bothered about the correct ringing pitch simply use a transformer which gives around a 40 to 60 Volt ac output, these can sometimes be obtained from scrap video recorders and, providing the telephone is wired as a "two - wire" device, (diagram here) just connect the AC supply, via some kind of push to make switch to instigate the ringing, to the A and B terminals.

Any of the methods described here should not cause any damage to the telephone

Regards
Andrew

[Stockden]

Yes, my experiments have revealed that it's more complicated than it looks. Certainly you get a distorted 50Hz out not 25Hz. Voltage seems to be more important than I'd though as well. I've tested the ring with 25Hz at 33v RMS from a signal generator and the ring is reasonable but not as loud as I'd expect.

If I had more time I'd play more but I think I'll suggest that they either use a recorded ring sound or follow Andrew's suggestion of ringing it with 50Hz.

Thanks for the suggestions,
Hugh

[dseymo1]

I've created the correct cadence before using a motorised cam / microswitch arrangement, but found that a phone isn't really loud enough for on-stage use. If you need to mike it up, you might as well record the ring in the first place!

[Boom]

Extremely interesting:-

'In Australia and the UK, the standard ring cadence is 400 ms on, 200 ms off, 400 ms on, 2000 ms off.'

http://en.wikipedia.org/wiki/Ringtone#Ringing_signal

[McMurdo]

Using 50Hz to ring a mechanical ringer is hit and miss and depends largely on the adjustment of the bell/clapper to ring at all (as opposed to just vibrating).

BT ren boosters use a split rail +/- 48V supply that is swapped in polarity by a couple of 24V changeover relays connected as a flip-flop. This gives the correct waveform to ring a bell reliably.

[Paul Stenning]

It may be easier for them to play something like this http://www.freesound.org/samplesViewSingle.php?id=28353 through an amp and speaker.

[russell_w_b]

Originally Posted by Stockden

If I had more time I'd play more but I think I'll suggest that they either use a recorded ring sound or follow Andrew's suggestion of ringing it with 50Hz

A telephone with a 59A bell in it can be adjusted for 50Hz - doesn't sound as good as 25 or 16 2/3 hz, mind! See here.

Your 'am-dram' group wouldn't have a BT line on the premises, would it? You could then rig it up as a 'proper' telephone and call it from a mobile (as long as you don't get an unwanted call).

I'd use a linesman's instrument or an old field telephone, me. The 400ms - 200ms silence - 400ms ringing cadence, followed by a break of 2 seconds equates to a couple of bursts of ten 'tings' and ten 'lings' and is pretty easy to emulate with a wee bit practice. Two steadily executed complete revolutions of the magneto broken with an ever-so-slight pause, say, repeated as necessary. You'll get a decent voltage as well, so a good ring. Pimp your bells to maximise the volume.

It needn't be sinusoidal either; better, actually if it is 'peaky'. As suggested elsewhere, a 555 timer cct with a jaggedy output should do the trick.

[Kat Manton]

Hi,

I've used/abused solid-state 100V-line public-address amplifiers in all manner of ways (including using three of them to drive a three-phase motor.)

If you have one available, it may be worth trying such an amplifier fed with 25Hz from an AF signal generator. (I suspect it would work and it doesn't involve building anything if you already have the amplifier and generator.)

Cheers, Kat

[kalee20]

I hade to sort out a 'phone bell for my local group, too. As it didn't need to mimic the exact sound of the telephone, I used a DC bell screwed to the wall in the auditorium (which sounded like any GPO extension bell anyway).

The cadence was generated by the attached circuit, which is designed so that as soon as the switch is operated, a double ring-pulse is generated immediately.

In place of the bell, you could use a relay to switch in any AC supply to your phone, as others have suggested, and have it sound authentic.

[Station X]

I can mimic ringing by pressing my back door bell push. Getting the cadence right is no problem. It's many years since most people had phones which "rang" as opposed to warbled and the average audience probably won't be able to tell a telephone bell from a door bell.

[Lucien Nunes]

I have used Kat's method before to generate ringing current. I had about one hour's notice and could only use whatever I could find lying around at the venue. So I played a test tone off my Sound Check CD into an ordinary 300+300W PA amplifier, which in bridged mode would supply 100V from its 8 ohm loudspeaker output. Having checked the bell operation, I recorded the cadence of the tone to cassette, so that I didn't have to stand there repeatedly pressing the button during the cue. (Crikey, cassette? must have been a while ago!)

If you haven't got a high power amplifier, you could use a wall wart transformer in reverse to step up the output of even quite a modest amp. Shunt some resistive load across the primary though to avoid accidental spikes at the amp during experiments!

Regarding the GPO unit yes T2 is a specially made transformer used in a semi-resonant arrangement.

The worst hack I've seen of a stage telephone had mains and low voltage control run via the four cores of its original line cord. Needless to say I took the plug off and made some disparaging noises. I never looked inside to see what evils lurked there!

Lucien

[Dave Moll]

Originally Posted by Station X

the average audience probably won't be able to tell a telephone bell from a door bell.

At a recent production by our local am-dram outfit, they used the door bell arrangement. No doubt, I was the only member of the audience cringing - even though the 'phone in question was a modern cordless one for which an electromechanical ringer was completely wrong.

[Stockden]

Thank you all for your suggestions, the director was mightily impressed when I told how much discussion her request had generated. In the end they've decided to go with a recorded sound effect and I've passed them the one at freesound, which Paul highlighted.

I've made the point about "more notice next time please" so, if this surfaces again, I'll revisit this post. Thanks again for all the ideas.

Hugh

[Darren-UK]

I'm a tad late on this one, but does the building the play is taking place in not have a telephone line installed?

If it does, then why not simply plug the telephone in (using an extension to reach the stage if necessary) and make it ring from a mobile with the number pre-entered?

[Stockden]

Originally Posted by Darren-UK

I'm a tad late on this one, but does the building the play is taking place in not have a telephone line installed?
?

Ah, if only it were so simple. The venue is the large function room at the top floor of what was once the Town Hall. There is a phone line but it serves the club also housed in the building. This means that the line is:

a. Too far away to reasonably run a cable.

b. Liable to be rung at any moment by someone wanting to talk to the club manager or barman.

I suspect that b. would prove to more of a problem than a. but thank you for the suggestion. In any reasonable sort of a venue it'd be the ideal answer!

Hugh