Choosing A Basic Telephone Recording Interface Circuit To Build ?

[R.T.Fex]

A friend asked me what telephone recording interface they could buy
to use to connect their pots landline to their digital voice recorder.

I thought of the old Radio Shack 43-2208. But I discovered that Radio Shack no longer sells it.

Searching on the web, most of the currently available devices are either
very overpriced digital recorders with an interface built- in,
or interfaces for a pc through the usb port.

Fortunately, there are still some interface circuits posted on the web.
I found two websites that have potential, I think...

https://www.sagebrush.com/phontech.htm

https://www.epanorama.net/documents/telecom/teleinterface.html#audioint

On the two websites there are about 10 basic circuits and a few more advanced circuits.

My friend does not need a circuit for a recording studio or a broadcast studio,
just a circuit that will yield relatively even volume levels for both the local and distant call participants,
and some overvoltage protection for when there is an incoming call ringing.

Could someone take a look at these circuits and give me a little guidance as to which one to build,
before I start looking for parts on MCM, Newark, Arrow, Mouser, Digikey, and Jameco's websites.

Thanks for any help you can offer.

 

[KlausST]

Hi,

A quick google search ( this is really easy) brings some results
* ISD1020, ISD2360, ISD2560, APR9600, APR33A3,

Are all these obsolete without replacement?

There are MP3 players with recording function, maybe one can modify them..

Klaus

 

[R.T.Fex]

Hi KlausST,

Forgive me for not expressing myself more clearly.

The chips you listed are to build a recorder circuit.

My friend already has a digital voice recorder. I do not need to build the recorder.

The Radio Shack device mentioned was an audio interface between the telephone lines and the mic input of a tape recorder.

The circuits listed on the webpages, I put up as links, are also interfaces between the telephone lines and the mic input of a recorder.

I just wanted to get an opinion from the folks here as to which of those circuits looks like it has the best potential for
yielding clean audio,
with even volume for both the person who is talking on the phone where it is recording and the person talking on the phone at the distant end,
and has sufficient protection to avoid damaging the audio input circuit built into the recorder when the ringing voltage appears when the telephone rings.

This interface will not be built into the recorder. It would be in a little box with wires going to the phone lines and to the mic input of the recorder.

I hope this better explains my question.

 

[bking]

Search for "Cermetek DAA". I've used them in the past. It will give you the line interface with the proper isolation for ringing, etc. Then it's just a matter of op-amps for getting the audio levels you need.

 

[R.T.Fex]

Thanks bking.

https://www.cermetek.com/catalog/telephone-line-interface/

It looks like the CH1837A , CH1840 , or CH1847 would be suitable since they do not have the Loop Current Holding Circuit that the XE series do.
I think such a module might lower the level of audio signal on the receive line.

Have you used any of these three DAA's ?

Could you recommend a basic op-amp circuit for getting even audio levels for local and distant participants?

Recorder input specs are 2.2k Ohm impedance, level -70 dBv

Thank you.