Anyone using Amp to ring phone?

[GovCampbell]

I've seen several threads on using an amplifier to help generate a ring signal to old style rotary phones. I've looked at the circuit diagram here: Telephone ringing circuits

I have an amp, a Sony. I have a transformer, a Radio Shack model: 6v or 12v to 120v (mounted backwards). I have a soundfile on my computer, sine wave at 20hz. I have some resisters, (not the exact ones called for in the above diagram, but close).

But try as I might I can't make it work. Does anyone use this method? Can anyone help me figure out what I'm doing wrong?

 

[Nelson]

I've never thought about using an amp to ring a telephone. Novel idea, though, just don't know how well it would work. At minimum, you would need a transformer to match impedance s (8 ohm for the amp and 600 ohm for the telephone, +/- a few percent), which the transformer in the diagram appears to do. Ring signal is typically at least 90 volts, so the transformer output will need to be fairly high. Doesn't really need to be 90 volts, but that's what telephones are designed for.

Also, be sure the telephone ringer works by hooking the phone up to a standard, analog telephone line and calling it. In very rare cases, old telephones were set up for selective ringing at non-standard frequencies, but as I said, that is unusual.

 

[SweetBennyFenton]

That sounds like a pretty cool project.

Personally, I don't have the electronics knowledge needed for this kind of thing. I bought a Tele-Q a few years ago and it's served me really well. They're not cheap, but they work well.

Tele-Q: Operating Telephones for Stage and Screen.

 

[Nelson]

Do let us know if you are able to get an amp to ring a telephone, I'm intrigued now! Might even try it myself sometime if I find an amp that I don't care about in case I burn it up

 

[FMEng]

I've seen several threads on using an amplifier to help generate a ring signal to old style rotary phones. I've looked at the circuit diagram here: Telephone ringing circuits

I have an amp, a Sony. I have a transformer, a Radio Shack model: 6v or 12v to 120v (mounted backwards). I have a soundfile on my computer, sine wave at 20hz. I have some resisters, (not the exact ones called for in the above diagram, but close).

But try as I might I can't make it work. Does anyone use this method? Can anyone help me figure out what I'm doing wrong?

In theory, it should work. You need to check voltages with an AC voltmeter to see what's going on. I would drive the 6V winding on the transformer with the amp. You need about 90V AC on the secondary to the telephone. You may not be driving the amplifier hard enough. I would also test the telephone on a working phone line to make sure it works because an old telephone could be broken.

It could also be that your transformer isn't beefy enough. Pretty much all transformers we can get our hands on are designed for 60 Hz. A small transformer might lose too much efficiency at 20 Hz because it doesn't have enough iron. A bigger transformer (rated for more current) will work better. Or it might just need more voltage swing from the amp than one would expect from the turns ratio, due to the efficiency losses.

 

[65535]

A 100V distribution transformer should work.

 

[Lambda]

It never occurred to me to use an amplifier as a phone ring simulator.
Today, I tried this experiment. I didn't have an old phone handy, so I used an old ringer I had lying around that was pulled from a model 220 phone. Its impedance was 1.6k ohms. I used a nice hefty transformer with a 1 ohm primary and 5.2 ohm secondary. I put a resistor in series with the primary to bring the total impedance to 8 ohms. The ringer bell was connected directly to the primary.
The amplifier I used was an Akai AA-R20, capable of 26 watts. The maximum open-circuit output voltage without clipping was 20 volts peak-peak.

When I fed the amp a 20hz sine wave, the bell DID RING. Quite nicely, too. It sounded best at 100v p-p out of the transformer secondary. The contraption drew 0.78 amps from the amplifier.

So, I'd call this one confirmed. You can indeed ring a phone with an amplifier and suitable transformer. But if you plan to try it, be sure to have a nice big transformer. With the one I was using, at 20hz the sine wave looked pretty destroyed.
If anyone wants, I can post pictures of this setup.

 

[TimmyP1955]

So long as the load on a solid state amp is above the recommended minimum, it doesn't matter what it is - 10 or 10k, whatever, so no transformer is needed (unless you want to increase the output voltage of a small amp). We drove a ringer with a Crown K1 in bridged mode (for the larger voltage swing - IIRC 80V did the job - right at clipping). The sound source was a sine wave, X seconds on, Y seconds off, X seconds on, ...... (I can't remember what the frequency was, and I can't find the file.) We had it on a USB stick and played it on the LS9's MP3 player, starting and stopping it with a UDK.

 

[FMEng]

So long as the load on a solid state amp is above the recommended minimum, it doesn't matter what it is - 10 or 10k, whatever, so no transformer is needed (unless you want to increase the output voltage of a small amp). We drove a ringer with a Crown K1 in bridged mode (for the larger voltage swing - IIRC 80V did the job - right at clipping). The sound source was a sine wave, X seconds on, Y seconds off, X seconds on, ...... (I can't remember what the frequency was, and I can't find the file.) We had it on a USB stick and played it on the LS9's MP3 player, starting and stopping it with a UDK.

Using a transformer is a simple and cheap way to get the voltage swing necessary for the telephone ringer from a small audio amplifier. A larger power amp, such as your K1, can sometimes do it without a transformer but using an expensive, 1000 Watt amplifer (it would take one that big, driven to near clipping) to ring a phone isn't always the best use of resources. I guess it just depends upon what's available for the task.

 

[TimmyP1955]

Using a transformer is a simple and cheap way to get the voltage swing necessary for the telephone ringer from a small audio amplifier. A larger power amp, such as your K1, can sometimes do it without a transformer but using an expensive, 1000 Watt amplifer (it would take one that big, driven to near clipping) to ring a phone isn't always the best use of resources. I guess it just depends upon what's available for the task.

All true.

The K1 was one of three monitor amps that were not being used on the show, which made it simple.

I wonder if the output transformer for a small tube amp would have the necessary turns ratio to be usable?

 

[David Ashton]

A word of caution, telephone coils can produce very high back EMF voltages, capable of taking out the amplifiers output transistors, check on what circuitry you need to absorb this.

 

[Lambda]

All true.

I wonder if the output transformer for a small tube amp would have the necessary turns ratio to be usable?

I just tried it and it didn't work. The output level of the tube amp was only a couple of volts at maximum volume. The amp I was using was a very small one, so maybe one with more power would work. I'd be hesitant to try this with a really nice one, though, I know that tube amps don't like having their outputs open-circuit and 1.6k ohms might be too much.

A word of caution, telephone coils can produce very high back EMF voltages, capable of taking out the amplifiers output transistors, check on what circuitry you need to absorb this.

I didn't see any signs of high voltage spikes on either the primary or secondary when I tried it with a sine wave. A square wave, however, did produce some kickback, but not enough to damage the amp. Still, I wouldn't risk it with an amp you care about.

 

[FMEng]

I just tried it and it didn't work. The output level of the tube amp was only a couple of volts at maximum volume. The amp I was using was a very small one, so maybe one with more power would work. I'd be hesitant to try this with a really nice one, though, I know that tube amps don't like having their outputs open-circuit and 1.6k ohms might be too much.

The output of a tube amp isn't any different than that of a solid-state amp in terms of voltage. TimmyP was suggesting to remove the output transformer from a tube amp and driving the secondary from another amp to step up the voltage in the same manner as described at the beginning of the thread. It should work, but I don't imagine too many people are willing to harvest parts from a tube amp to ring a telephone.

 

[Lambda]

The output of a tube amp isn't any different than that of a solid-state amp in terms of voltage. TimmyP was suggesting to remove the output transformer from a tube amp and driving the secondary from another amp to step up the voltage in the same manner as described at the beginning of the thread. It should work, but I don't imagine too many people are willing to harvest parts from a tube amp to ring a telephone.

Oh, ok, I didn't think that through.

 

[echnaret]

I was actually trying to figure out how to do this a couple months ago. I was able to make a phone ring with an amp I had in my room. To do so, I loosely followed the instructions here:

How to ring a phone

Here are drawn instructions from the same site:
http://wandel.ca/homepage/phonering-instructions.jpg

Instead of trying to run his programs, I used Audacity to create the track for the CD (generate a 20 hz sine wave for 2 seconds, then 4 seconds of silence, and repeat for as long as you want the track to run. That was used for the left channel; the right channel was the same, except 180 deg out of phase).

After I burned the above track to a CD, I hooked up my CD player to an amp, and connected the phone wire to the amp as illustrated (I did not have the mentioned resistors, but made sure to not lift the phone off the hook while the CD played). After I cranked up the amplifier a bit (a Carver PM-1200 for anyone interested), I was able to get the phone to ring.

Both the telephone and amplifier I used were expendable, so I wasn't particularly concerned about damaging anything. That being said, do everything at your own risk.