amplifiers with telephone speakers n mouth piece

Hello sir,
I want to make a very very simple n cheap intercom system from the scrap of two telephones.i want a circuit diagram for the amplifier in which the mouth piece (mic) & ear piece (speaker) of handset can be connected directly so as to work as a complete audio system.Rest of the design & other connections i ll make of my own by applying suitable ideas but i want the amplifier simply so as to get the sound on the speaker from the mic or mouth piece . if it needs a simple pre amp then tell about it cause i will connect a simple amp using 820 ic circuit but if it requires some special one then i ve to go for it so please tell me details of the circuit diagram of that single amplifier.
Thanks

Hm, you may not need much of a circuit.
If it is a very old handset, then I think the mic contains carbon granules that change resistance with pressure?
So you would just stick the mic and earpiece in series, then to a battery. However, any phone that is not
very old will probably have electret elements, so this won't work, and you'll need an amplifier circuit.
However, you could not damage the phones (old phones are worth something if they are truly
ancient ; ) and connect them back-to-back like this.

ok sir thanks a lot but the phone set im using are 10 years old only & both of them are using electronic cicuit completly but all the the PCBs are damaged fully so of no use. i disposed it fully out of the public area so as to maintan green electronics but now i only have the chasis cables & mic speakers only so i have to work with it only.please tell me about that circuit diagram only.i ve 820 ic amplifier for now so can i connect a simple pre amplifier using 555 or 741 ? is it possible ?

At 10 years old, it is likely to be an electret element.
You could try any simple amplifier circuit. For example, an LM386 will be sufficient, I recall they have
quite high gain (not used one in years). TBA820 that you mention should also be fine, possibly sufficient
without any pre-amp.

If you find you do need a pre-amp, then the 741 would be ok but better to use a better op-amp.

As a side note, here is a typical late 1960's circuit for an intercom, using just a few transistors. It uses a speaker
as a microphone in reverse, the idea being that you'd use a switch to swap the position of the two speakers, so that
the intercom works both-ways.

ok sir the info is bright enough & i ll work on it definitly but tell me can we use 810 ic in place of 741 as u just told to use a better one ? i used 810 amplifier in my practical once found all the way enough to drive small speakers so i am asking as we are concerning with telephone speakers

An electret mic just needs some power through a resistor, see this thread.
That thread will clear it up for you. Your TBA820 will be fine. Not ideal but fine.
A 741 can only be used as a preamp (if needed). It won't drive a speaker. It may drive an earpiece (just), but the TBA820 will definitely drive it.
Use the TBA820. If you find you need a preamp, then use an op-amp, but hopefully something better than a 741.

Ok sir thats very useful one.Sir please let me have a proper circuit diagram of a pre amp circuit better than 741.which ic i ve to use & what's the circuit diagram for that ? i need a proper pre amp as you said

There are several ways to do it;
you could use a dedicated mic amplifier (which may implement features like AGC). An example is **broken link removed** but it may be hard to find.
Or, you could use a better op-amp, e.g. see the circuit **broken link removed** which uses
a low cost fairly easy to find op-amp, or use any of **broken link removed**.
None of them are particularly exotic to find, and will give good performance for an intercom.
Or, you could use a transistor preamp circuit, e.g. the one in the thread mentioned earlier.

ok sir thanks a lot i got it & now time to make practicals with it so as to make much better results thanks a lot once again sir

sir im getting distortion sounds too much with the following circuit designings

**broken link removed****broken link removed**

have a look & please tell why this going on ?
in ic configuration im getting too much several times much distortion than the transistor one im showing here , its too irritating im operating it on 9volts 250 mA .
thankssssssssssssss

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sir would you please let me know about an equivalent ic for MX 9812 if there is any , so that for time bieng i may work on it to observe results

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how its possible for me to get a proper pre amplifier designed homely for electret mics ? im frustrated already sir please help me :--x