3 watt Amplifire problem

[Avidestroyer]

I made an 1 watt amplifire. Diagram is shown below link.
https://sci-toys.com/scitoys/scitoys/computers/solderless/small_1_watt_audio_amplifier.jpg
this amplifire is worked well but it is not suitable for huge bow. So I am intend to create 3 watt amplifire.
But when I add 6 transistor to this circuit instead of two, this amplifire not work, just the speaker make a sound noise. My power supply was 6 v. Why this problem occure? Plz tell me anyone.

 

[sky_123]

A classic example of why not to trust everything you read.
This has got to be one of the most 'interesting' circuits ever.
You have to use some common-sense. When you buy an audio amplifier, does it consist of a single transistor and three resistors?
That alone should send alarm bells ringing in your head, and that's without any further knowledge of electronics.

Use the circuits shown on this site.

 

[BradtheRad]

The sci-toys.com circuit is okay as a demonstration of a simple low-power audio amplifier. However it exposes the speaker to a DC component. You will risk ruining the speaker if you increase the current too much.

Just for curiosity, here is a screenshot of my simulation.

I had to reduce the upper bias resistor to 27k. This lifts the output waveform into the DC range, so that it resembles the entire range of the input signal.

 

[sky_123]

Ah - I didn't spot the 50-ohm resistor (which will at least save the transistor).
However, I suspect in a real circuit, it would be very distorted because of the offset (maybe pushing
the cone to it's limit).
EDIT: Sorry, I see you've made the same point about the DC component too.

 

[Avidestroyer]

Oh! It's also not work. I put 6 v instead of 9 v. Is it a reason for not work?

 

[BradtheRad]

A 6V supply can still power the amplifier. However to get sufficient loudness you'll need to adjust some of the component values.

Here is a screenshot of my simulation.



I reduced the 50 ohm to 15 ohm.

I placed the speaker closer to the transistor.

I added a potentiometer so that you can fine-tune the bias current to the transistor. The idea is to raise or lower the operating range, so that all of the waveform appears just above the zero V level.