Question about audio amplifier

[Mac7978]

Dear all,

Can anyone explain to me why the input impedance of an audio amplifier is extremely high? Is it becuase of current saving?

Also, I have a 2-wire dual mode speaker with the differential impeance 32 ohm, and it will driving by a audio amplifier with the output differential impedance 8 ohm. My question is that how can i do matching between them to maximize the efficiency.

Thx

 

[Btrend]

1. the high impedance is for getting signal without attenuation. consider ur source has output impedance Zs, and ur AMP has ZL, the voltage u receive is Vo=Vs*ZL/(ZL+Zs). The higher ZL is, the higher voltage u receive. so the SNR will also increase . it's not for current saving .
2. maybe u need a tranformer for impedance matching

 

[Borber]

Input impedance of end stage is about 22kΩ to 47kΩ. The idea is not to overload preamplifier and attenuate signal. Preamplifier input impedances are different for each type of input signal MC, MM, mike, tape, tuner and aux.
End amplifiers has very low output impedances and are supposed to be voltage sources. No impedance matching is neccessary.
Amplifier has specified load impedance for rated power.
Problem is if speakers has different impedance than load impedance specified for amplifier. Thus you may overload amplifier if speaker has lower impedance as specified or you will get less power if speakers has greater impedance as specified.
You may need to use transformer to match speaker impedance to the rated one.

Your amplifier does not have 8Ω output impedance but at 8Ω load it delivers it's rated power.

 

[ttnknathan]

If your output stage drives the 32Ω resistance,you get the scale of the mos tansistor by the power which would be delivered.So for the same reason, you can get the scale by your specefications! By the way,I also want to know,if the scale of the output stage is decided,(I am sure the scale is very big ),how to control the output stage transistors,make it deliver small current while it doesn't work!

 

[leemarrow]

Hi to all,
anyone know a good ebook about audio power amplifier?
I need a ebook with formulas to project a audio power amplifier from zero.