help! in need 10 watts (or more) audio amplifier schematic transistor based

[Mr RB]

What we were trained to do was to put 10 ohm or 22ohm resistors in the supply rails (often in place of the fuses), then if the amp had a fault or severe bias arror etc a resistor would start to cook and make a bit of smoke, but no transistors would be killed.

Once the amp had been tested with a sinewave and no load (or a light load) the resistors would be replaced with fuses and a proper load connected. Often smaller fuses for the first tests!

If people in your school are destroying FETs all the time the teacher might need to suggest a better methodology.

 

[Cluene]

The 10W Mosfet amplifier has C3 connected wrong. Its (-) wire should connect to the positive wire of C4 so that it "bootstraps" R4.

If the bias adjustment pot is set at a low resistance then the Mosfets will not be turned on and will not burn. It is adjusted for an output bias current of maybe 40mA which will not cause the Mosfets to burn unless their heatsink is not big enough.

The transistors amplifier is extremely simple and old. It uses C1 to "bootstrap" R1 and R2.

The value of audio coupling capacitors is simply calculated with the lowest frequency you want. 1000uf will cause the output power to be half (-3dB) at 20Hz into an 8 ohm speaker.

www.redcircuits.com has many audio amplifier projects.
www.sound.westhost.com/index2.html also has many audio amplifier projects.

Thank you very much for the links . I found one schem which used an all BJT transistor. I think I'll try that one up. Hope all the parts are available in our stores. (45 watts class B Amplifier)

By the way, its okay to supply the circuit with a (33+ and 33- Volts and 3 A) transformer or (30+ and 30- volts, 1 A) transformer right? it wouldn't fry up or anything.... Sorry, I really just want to make sure to lessen expenses and all and deadline is quite near.

 

[audioguru]

A 45W audio amplifier has an output of 45W and produces heating of about 35W. Then a total of 80W is used from the power supply.

The project uses a 25V-0V-25V transformer to make plus and minus 33V. The maximum current drawn by one amplifier at its maximum output power is 80W/66V= 1.2A.

If you use a plus and minus 30V power supply then the maximum output power will be reduced to about 36W and the max heating will be about 28W for a total of 64W. Then the maximum current drawn by one amplifier at its maximum output power is 64W/60V= 1.1A.

Of course something will fry if you connect something wrong. But that amplifier circuit uses Q8 and Q9 to limit the maximum current.

 

[Cluene]

Good news everyone the original circuit that I made already worked. Thank you very much for all your help! I will still make the 45 W class B amplifier for my personal use ... I find making amplifiers really interesting now .

The problem laid under the following:
1. wrong positioning of our BC547 transistor.
2. short circuit between heatsinks (took a very long time to see that)

Though there is still a problem with one of our mono amplifier (I made 2 for stereo) which doesn't produce a very smooth sound like the other one. Perhaps this has to do with a defective capacitor?

 

[Mr RB]

...
The problem laid under the following:
1. wrong positioning of our BC547 transistor.
2. short circuit between heatsinks (took a very long time to see that)
...

Both are common problems on a hobby amp build, congrats on finding the faults and getting the amp working.

And as I said before, if you had put 10 ohm resistors in the fuse holders you could have caught both those faults with no damaged parts (except maybe the 5 cent resistors).