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Audio power apmplifier

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samEEEf

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Audio power apmplifier for my pc

I have two unused speaker at home. These were in old cassette player. I want to use these speakers with my PC. Could anybody help me to make a good amplifier for my PC?

Impedance: 3 ohm
Peak input power: 20W (confused :-?, what is the output power)

These ratting is written on the BOX

Could anybody please show some calculation (related to power, impedance etc) with some suggested IC?
 
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alexan_e

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You can make an amplifier using LM3886, you can find many projects if you do a search

Point to point wired LM3886 chip amplifier with a hi-cap snubberised PSU.
LM3886 Gainclone 2x68 Watt Full Amplifier Project

As an additional comment the 20W peak input power of your speakers can't be translated to RMS watts, your speakers may easily be 5W or lower.
The amplifier above has a very respectable output and very good sound quality but it bay be too much in your case, a simple 10W amplifier will be more than enough
10W Mini Audio Amplifier
a-netz.de - Audio Amplifier with TDA7240

Alex
 
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samEEEf

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Thanks a lot Mr. alexan_e for referring such simple circuits. I need to know about the 3 ohm impedance. What is the impact of a speaker impedance with a designed amplifier circuit having other value? If a amplifier circuit is designed with 8 ohm impedance value and somebody connect a 4 ohm speaker what will happen? Is there any chance of burning the speaker? In this case, of course, output power will be changed. What will be the actual output power?
 

alexan_e

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The speaker is not a resistive load so the reported resistance is usually a mean value, the impedance graph is something like


Amplifiers usually report the watt output for 8ohm, ideally the amplifier should be able to provide twice the power in 4 ohm , four times higher in 2 ohm and eight times higher in 1 ohm (with the same low distortion).
Not many amplifiers are able to do that because you need more current as the resistance gets lower but the majority of amplifiers work fine with 4 ohm, they can't provide twice of the 8 ohm power but still work fine.
A speaker can only be damaged if you drive it with a power rating above the specification (you will probably hear it distorting when you go to that point unless you provide heavy bass) so don't worry about the speaker being damaged because it is 3 ohm, it just give a harder time to the amplifier connected to it.

you can read Home Toys Article - Speaker Impedance, Your Amplifier And You.

Alex
 

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