Amplifying a phone signal

[Todd David]

Strange DIY topic, I know, but here goes:

I want to amplify the built in speaker of a phone system to be heard in a noisy area of my shop.

The phone is a network system and is 24V.

The speaker in the handset is 42ohm resistence.

Can I simply hook up the wires going to the handset internal speaker to the line-ins of a home receiver to amplify the signal?

Any general help appreciated...

Todd

[hermanv]

An interstage transformer is the best answer if you want to run the signal to the input jack of a receiver. There is no guarantee that the speaker in the phone is isolated from the phone line (it probably is but it might not be) your receiver is unlikely to enjoy having ringing volatge (90VRMS at 20Hz) applied to an input.

The transformer should be around 10 to 1 with the 10 side hooked to the speaker.

If you can't get one of these, go to the local electronic surplus store a get a speaker line transformer or as a last resort a tiny AC power transformer 115V to 12V windings (NOT a DC wall wart). Hook the 115 side accross the telephone speaker and the 12V side to your power amp input. Put a 1K resistor accross the 12V winding to knock down the high frequency peaking that will result.

You will need to use shielded wire.