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Ceramic mic, 8 ohm speaker, 9v, in need of an amp circuit

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TechDude

New Member
I have a microphone from a pretty old phone that is ceramic. I have an old police speaker that has a resistance of 8 ohms. I would like to use 9 volts. I am in dire(?) need for a circuit that will amplify the sound produced when talking into the mic. I'm looking for suggestions or schematics on how I will go about doing this. Note: It does not have to be a 9v circuit. Another Note: I will be using this in an area where it may be quite loud, so the louder the better. Thank you so much!!!

P.S. Accidentally posted this in general electronics forum
 

audioguru

Well-Known Member
Most Helpful Member
Your choice of using a battery with only 9V (only when it is brand new) limits the power into the 8 ohm speaker.
An LM386 amplifier has an output of only 0.45W at clipping.
A TDA2822M is two amplifiers in a bridge and its output is 0.75W at clipping.
The battery voltage quickly drops to 6V and the output power will be less than half.
Both will be as loud as a cheap clock radio, not loud.

A car radio amplifier IC has an output of 8W at clipping into an 8 ohm speaker or 14W into a 4 ohm speaker at clipping when its supply is 13.2V. It will sound loud up close.

If the microphone can hear the speaker then the circuit will produce acoustical feedback howling.
 

TechDude

New Member
I'm pretty new to electronics. So you're saying that Watts is how you increase the sound? And do you have any suggestions of where to find a car radio amplifier IC? Thanks for your help though!!
 

audioguru

Well-Known Member
Most Helpful Member
Philips and ST Micro make at least 70 car radio amplifier ICs. Some are mono and many are stereo. A few have 4 amplifiers in the IC.
They are powered by the huge and heavy battery in a car. But they can be powered from 10 AA Ni-MH rechargeable cells for a few hours.

Their datasheets show an amplifier schematic and a pcb layout. They are available at most electronic parts distributors like Newark or Digikey in Canada and the USA.
 

TechDude

New Member
Thank you so much for the help. So I would just be able to connect my mic, speaker, and 10 AA battery (no capacitors, resistors, etc.) to the ports and it would amplify the decibels considerably? Also, could this blow out my speaker?
 

Chippie

Member
Thank you so much for the help. So I would just be able to connect my mic, speaker, and 10 AA battery (no capacitors, resistors, etc.) to the ports and it would amplify the decibels considerably? Also, could this blow out my speaker?
You need to study the circuit for which ever ic you select and add the necessary resistors and capacitors in order for it to function correctly...

You may need a small signal amplifier stage for the microphone too...

Again depending on which ic you select, there is a possibility of damaging the speaker if you over drive it..

Decide which chip you want to use a report back...We can take it from there..:)
 
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TechDude

New Member
Alright. I have chosen to use the TDA8580J IC. Can someone check it out and see if it will work for what I'm trying to do? Thanks for the help
 

audioguru

Well-Known Member
Most Helpful Member
The TDA8580 is a stereo bridged amplifier IC. I thought you wanted just one amplifier.

Its datasheet shows that with a 12v supply its output at clipping into an 8 ohm speaker is about 5.6W for each of its two bridged channels.

Its schematic shows no resistors are needed and three capacitors are needed for one channel.

A preamplifier circuit is needed for the microphone.
 

TechDude

New Member
I would like to just use one amplifier. Like i said, I'm very new to this so I may do things that don't make sense... haha. So do you have a proposition for an IC then?
 

audioguru

Well-Known Member
Most Helpful Member
A TDA7240A IC is a single amplifier with 7 pins. It needs a few resistors and capacitors. A pcb design is in its datasheet. it will need a medium-size heatsink with fins.
Its output into an 8 ohm speaker at clipping with a 12V supply is 6.4W.
A preamplifier circuit is also needed for your microphone.
 

TechDude

New Member
Cool cool!! And any simple preamplifier circuit should work?
 

TechDude

New Member
K. And you guys are sure this will work with my ceramic mic?
 
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audioguru

Well-Known Member
Most Helpful Member
Cool cool!! And any simple preamplifier circuit should work?
No.
The preamp must match a ceramic microphone. That microphone is obsolete so data is hard to find. I think it needs a low gain preamp with a very high input impedance. Maybe a FET transistor.
 

Chippie

Member
Use an op amp that has a J-Fet input stage....Make the gain adjustable from Unity to say 10 times...Go from there...
 

Chippie

Member
I found a preamp that should work. I'm guessing this circuit should work?
Ray Marston is pretty good on the money with this stuff... Looks simple enough provided it has sufficient gain it ought to work...

Much simpler than a J-Fet op amp circuit

Try it...:)
 

TechDude

New Member
Will do and thank you so much for all the help!!!
 
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