Simple Audio Preamp for Mobile Phones/iPod

[ladyphoebe15]

I am planning to built a simple two-stage preamplifier. The speaker will be 8 ohm and 5-10 W and a VCC of +9v. I planned to use a voltage divider for the first stage and an emitter follower for the second stage. I'm quite confuse of what are the values of Vs and Rs ( coming from Mobile Phones/iPod). Any advice on how i should do it and if my planned configuration are okay?

 

[Nigel Goodwin]

I am planning to built a simple two-stage preamplifier. The speaker will be 8 ohm and 5-10 W and a VCC of +9v. I planned to use a voltage divider for the first stage and an emitter follower for the second stage. I'm quite confuse of what are the values of Vs and Rs ( coming from Mobile Phones/iPod). Any advice on how i should do it and if my planned configuration are okay?

Sorry, but there's nothing there that makes and sense at all

You need a power amp, NOT a preamp - absolute minimum would be four transistors (more would be better).

Also there's no way to get 10W in 8 ohms from a 9V supply.

I would suggest you:

1) Use an IC rather than make an amp, as you don't have the skills to make an amp.

2) Increase the power supply substantially if you want 10W (you need 30V - or 15V if using two bridged amplifiers).

3) Drop the power requirement greatly if you want 9V.

 

[audioguru]

Phoebe,
An audio power amplifier has a voltage loss. Use an imaginary amplifier that is perfect with NO voltage loss and use a 9.0V power supply, not a little 9V battery (that becomes 6V soon).
Then the maximum voltage swing into a speaker is 9V peak-to-peak. 9V peak-to-peak is 3.18V RMS. Then the maximum power into an 8 ohm speaker is 3.18V squared/8 ohms= 1.26W.
You will be lucky to get 0.5W from a real amplifier.
It will sound slightly louder than a cheap clock radio.

I bought a new clock radio for $1.75 a couple of years ago and it is LOUD but it sounds awful! I disconnected its cheap tiny Chinese speaker and connected a good little hi-fi speaker system instead then I increased the value of its output coupling capacitor to 4 times and now it sounds excellent.