# Class B Audio Amplifier

#### BigglesPiP

Joined Apr 1, 2006
3
I built the circuit from this website in MultiSim

I'm going to:

Measure the voltage theat my mp3 puts out.

Measure the current when it's playing into my car stereo with the cassette tape adaptor. At normal voltage (FM radio @ good volume) on the stereo and full on the player (too quiet).

And through V=IR and P=I(squared)R calculate the power (Whatts) that it is right now and use that in the simulation

This should give me a good guide of how much amplification I'll get with various values of resistors etc. THen I can confidentely make 2 of them (stereo sound) on soldered breadboard.

Also this will be the 1st circuit I've ever soldered to breadboard.

Please do poke holes in my plans,

Cheers,
Bracken

Joined Jan 10, 2006
614
Is this for in the car..??
Some things to keep in mind, most cars are only 12 volt and don't possess a "dual 12 volt battery with centre tap at earth" system.
You can also Quadruple the power output into a given load by bridging 2 amplifiers into that single load. Another way to increase power is to use an inverter to step up the 12 volts into a higher voltage split rail supply..(this is how most modern high power amps work).
I might also check for crossover distortion on that design, as it is normal to fit emitter resistors on the output.
And whats the deal with the linear pot..? Is it some form of variable negative feedback..?
The design looks a little unconventional, but without trying it myself, I cant offer any further insights.

#### BigglesPiP

Joined Apr 1, 2006
3
I'm going to switch to 2 PP3's for power.

I just measured the Resistancwe of the cassatte adaptor in use to be 150 Ohms

the linear potentiometer is the volume controll.

I'm not sure about the crossover distortion but the page i got it from on this website said it can be used as is for an amplifier.

Anyone know the mean pk-pk voltage a portable audio player puts out?

#### mozikluv

Joined Jan 22, 2004
1,435
Originally posted by BigglesPiP@Apr 2 2006, 08:59 AM
I'm going to switch to 2 PP3's for power.

I just measured the Resistancwe of the cassatte adaptor in use to be 150 Ohms
the linear potentiometer is the volume controll.
I'm not sure about the crossover distortion but the page i got it from on this website said it can be used as is for an amplifier.
Anyone know the mean pk-pk voltage a portable audio player puts out?
[post=15732]Quoted post[/post]​
hi,

the term you use "portable audio player" is quite vague. pls. be specific so we can give a an educated guess or a specific answer.

moz

#### n9352527

Joined Oct 14, 2005
1,198
Originally posted by BigglesPiP@Apr 2 2006, 02:59 PM
I'm going to switch to 2 PP3's for power.
[post=15732]Quoted post[/post]​
It wouldn't last long with 2 PP3s.

#### BigglesPiP

Joined Apr 1, 2006
3
I've found out that the headphone soket on a Mac G4 is about 1.4v Pk-Pk. So I'm running my simulations based on that.

I only need the volume to nearly double.

But with the volume quadrupling I'm only drawing about 150mA from each PP3 cell.

Surely that must last long enough.

#### n9352527

Joined Oct 14, 2005
1,198
Originally posted by BigglesPiP@Apr 3 2006, 02:22 PM
I've found out that the headphone soket on a Mac G4 is about 1.4v Pk-Pk. So I'm running my simulations based on that.

I only need the volume to nearly double.

But with the volume quadrupling I'm only drawing about 150mA from each PP3 cell.

Surely that must last long enough.
[post=15753]Quoted post[/post]​
Duracell Plus is quoted at 550mAh and I would think that this is measured under less than 150mAh current drain. Anyway, simple calculation and ignoring the effect of high current drain would result in around 3.5 hours of battery life.

Btw, when you said doubling or quadrupling the volume, did you actually refer to the Vpp/power of the signal or the actual dB of the sound? Of course you have to realise that relationship between Vpp/power and sound loudness is not linear.