Microphone amplifier for speaker output.

Discussion in 'General Electronics Chat' started by dikidera, Sep 28, 2015.

  1. dikidera

    Thread Starter New Member

    Sep 6, 2015
    Hi all.

    I want to build an analog intercom system. At first I wanted to do it with just a few transistors and amplify the signal, but ultimately, it proved to be too difficult, as I am very new to electronics, in general.

    With those problems in mind I set out and bought a few IC amplifiers. All-in-all I have these components:
    9V battery
    8ohm speaker
    Electret microphone

    The goal here is to amplify the signal of an electret microphone(which is generally between 10-50mV), and output to a 8ohm speaker, all powered via a 9v battery.
    Upon further reading I was told that the order of amplification is LM741->LM386, because the LM741 has a max output current of 25mA thus can drive a very high load, whereas the LM386 has a high current and can drive a lower load like an 8ohm speaker.
    However, I am not sure if the distance will be problematic, the speaker itself will be connected via a 20m long cable. I don't know if this distance will lead to problems, the cable I have has virtually no resistance.

    Currently I am lacking a circuit for these, so I am turning to you guys for some help.
  2. AnalogKid

    AAC Fanatic!

    Aug 1, 2013
    There are dozens of different intercom circuits on the innergoogle, so a good way to start is run a few searches, notice that the many results settle down to a few basic designs, and get to understand them. After that you will have some questions, and be much better prepared to use the answers.

    The 386 is a classic choice for a small speaker amplifier, and you'll see it in many designs. The 741 has a couple of strikes against it for low cost circuit work. A big on is that while it can run on only one power supply voltage (and ground) like the LM386, its output voltage range is limited. Better to start with an LM358. It runs well on a single power supply (as does the 386), has reasonable gain and distortion for intercom work, and you get two in one package in case you want to do some extra signal processing, like a noise filter or AGC.

  3. Aleph(0)

    Active Member

    Mar 14, 2015
    I say you are right about totally use discrete components being too much unnecessary work, bigger issue is if not interested in study electronics why you not just buy intercom? They not expensive and you save time for enjoyed work! I say life too short for wasting over pocket change or proving DIY prowess to self:rolleyes:
  4. blocco a spirale

    AAC Fanatic!

    Jun 18, 2008
    Rather than just buying random parts; first, find a design then source the components. It can be done with a single integrated amplifier chip, switch the speaker between microphone and loudspeaker duties.