Making a 332 ring on stage

[Darren-UK]

Ah well, worth suggesting I thought. On b. I'd have suggested not plugging the 'phone in until immediately before the relevant scene but I understand your predicament now.

[Welsh Anorak]

Hi
I had to do this and used an old field telephone I had lying about and cranked the generator. Sounded very realistic except the operator had to be a distance away to avoid the 'whirr whirr' noise!
Glyn

[Jim_746]

Could I use a 16 Hz - 25 Hz sine wave on a computer as the ringing signal generator and connect it to a step up transformer connected to a bell set or phone? Would I connect the out put to terminals 6 and 18 in a 746 telephone?

[russell_w_b]

Originally Posted by model746

Could I use a 16 Hz - 25 Hz sine wave on a computer as the ringing signal generator and connect it to a step up transformer...'

You might have more luck driving a 100V line PA amplifier into your bellset, with your PC sine-wave driving the amp.

You could always knock up the simple circuit attached, for which I claim no originality, but which I have used successfully to ring telephone bells. All you need are:

* an old mains transformer with LV secondaries either centre-tapped or near-matched. In practice, it doesn't seem to matter if either side of the centre-tap is unbalanced (say 4.5V tap 1 - tap 2 and 6V tap 2 - tap 3), as all you'll get is a spikey waveform. It'll still work. You'll be connecting the transformer up so what is the mains side becomes the output to your bell, and the transistors drive the LV side. It seems to work best if you have a 110V mains tap.
* Couple of transistors, either sex will do (reverse supply polarity accordingly!), typically ZTX450 or ZTX551. You won't be drawing more than about 250mA from the d.c. supply.
* non-electrolytic capacitor (although electrolytics do seem to work without problems as well) 470nF - 10uF.
* Four resistors: couple of 100Rs and a couple of 1K - 1.5Ks.

Frequency seems to depend on transformer size (titchy transformers out of wall-warts give a higher frequency and may be unsuitable), though this can be 'pulled' by changing capacitor value or loading differently by using a different mains tap on your ringer supply output.

[arjoll]

I've just spotted this thread.

Dad used to do a lot of sound effects work for a couple of local theatre groups, and in the 70's built a mechanical phone ringer effort with an old tape recorder motor, telephone magneto and heaps of meccano! It used a rotating disc and microswitch, but the problem they had was that sometimes it would start up at the start of the 2 second gap in the cadence!

In the late 80's he picked up a ringing unit from an old PBX when his work had their phone system upgraded. It generated the AC at the correct voltage (the thing you'd do with a 555 and some meaty transistors), but didn't generate the cadence.

He worked out a circuit with a pile of 555's but never got it quite right - weird issues with cap charging messing up the timings etc. I was keen on 4000 series CMOS, so designed an alternative with a couple of 4017 decade counters.

If you clock them from a 555 monostable at 5 Hz and have two cascaded 4017's it should work about right. Take outputs 1, 2, 4, 5 from the first 4017 into a buffer and your relay controlling the AC out to the phone. Reset the whole lot with output 6 from the second 4017.

In the end he put some dip switches on his new 'ringer' unit so he could set the cadence and do a US ring as well!

[Malcolm G6ANZ]

Hi, I also provide sound fx etc for several am dram groups. For phone rings I always use pre recorded sounds via a local speaker. Two reasons, a) The prop phone usually is broken and without wires so making it work would be a nightmare b) I am in control of when to stop and start the fx. There nothing worse than having the phone continue to ring after its been picked up.
I've had no complaints yet from either the audience or the director
Malcolm