personal audio amp

[audioguru]

Isn't the internal circuit of the chip wrong as well?, the input is shown connected to the non-inverting input of BOTH amps.

It works fairly well when the gain is high. The 1st amp has a gain of 26, and the 2nd amp has a gain of only 24 which isn't too bad a difference.
If the gain was only 1 then the 2nd amp wouldn't have any output.
Actually, with a gain of one then the output of the 2nd amp would be only the distortion products of the 1st amp.

The amp can be setup with an inverting input and with a low input impedance. Then the output level from each amp is the same.

I don't like the 2nd amp amplifying the distortion from the 1st amp, but it sounds OK with its very high amount of negative feedback cancelling the distortion. :lol:

 

[Nigel Goodwin]

Isn't the internal circuit of the chip wrong as well?, the input is shown connected to the non-inverting input of BOTH amps.

It works fairly well when the gain is high. The 1st amp has a gain of 26, and the 2nd amp has a gain of only 24 which isn't too bad a difference.
If the gain was only 1 then the 2nd amp wouldn't have any output.
Actually, with a gain of one then the output of the 2nd amp would be only the distortion products of the 1st amp.

You appear to have missed the point?, as drawn the inrenal circuit wouldn't work - the input is applied to BOTH non-inverting inputs, so the outputs will be in phase, so no sound at all from the bridged speaker.

I'm also pretty sure no body would design a bridged IC with different gain values, presumably another mistake on the diagram?.

The amp can be setup with an inverting input and with a low input impedance. Then the output level from each amp is the same.

I don't like the 2nd amp amplifying the distortion from the 1st amp, but it sounds OK with its very high amount of negative feedback cancelling the distortion. :lol:

It doesn't matter much when it's done that way, because the distortion is reduced by the attenuation factor corresponding to the gain of the second amplifier.

Sorry, just looked back at the circuit, it's not done that way, the second amp is just a unity gain inverter - so the non-inverting inputs definitely shouldn't be connected!.

 

[baftab]

stop making fun of it...
am already so dishearted...
i was making a power amplifier 80 watts!!!!!!
and here i am...making this crap
but i have to submit it day after tomorrow..and am fasting...and tomorrow is friday so all shops will be closed
so i AM sticking to this design...

but atleast my teacher will b happy to see so many capacitors and transistor...am telling you guys...he knws NOTHING...he even told us tht when u supply DC voltage to a capacitor....the circuit becomes short :shock: ..and i thght it behaaved as an open circuit :lol:

and the best part..."if the resistance on emitter is grounded....there will be no voltage drop across it"
lolz

 

[audioguru]

You appear to have missed the point?, as drawn the internal circuit wouldn't work - the input is applied to BOTH non-inverting inputs, so the outputs will be in phase, so no sound at all from the bridged speaker.

Hee, hee. :lol: Stick it on a simulator that works, and you'll see the 1st amp with a gain of 26 and the 2nd amp out-of-phase with a gain of 24. :lol:

I'm also pretty sure no body would design a bridged IC with different gain values

Motorola did.

{quote]the second amp is just a unity gain inverter - so the non-inverting inputs definitely shouldn't be connected!.[/quote]
When configured as an inverting amp, the non-inverting inputs are bypassed to ground.

 

[audioguru]

Just trying to delete my duplicated post.

 

[baftab]

it works...lolz
you were right....though
sounds as if someone is strangling Jon Davis...lolz
but who cares...as it it gives me an output....
thnx thnx thnx thnx thnx both of you

 

[audioguru]

Congratulations, Baftab, it works! :lol:
Give your little amp some power supply volts, like from a 9V battery and it will be much louder.

 

[baftab]

okay
i will try 9 volts..AFTER i have my project checked
thnx again

 

[audioguru]

Hi Baftb,
Yeah, it's better to be safe than sorry. Your little amp with many parts would be a power-house with a 9V battery and might destroy itself.
I figure that it would have an output into 8 ohms of a whopping 60mW.

Transistor circuits like the 1st and 2nd transistors in your circuit would need a biasing resistor changed to be used with a higher supply voltage than the original 4.5V. Also, emitter resistors could be added to them to cancel some of their high distortion. The collector resistors could be increased in value.

If you were a gambling man, you could re-bias the 2 transistors and try a 36V supply. The little amp with many parts would have an output of nearly 1W, and I think it would not smoke but actually last a while.
You could add emitter resistors to the 1st and 2nd transistors, bootstrap the bias for the output 2N4401 and add negative feedback from the output to the new emitter resistor of the 1st transistor. Then it would sound wonderful, but its gain would be only about 20 so it could amplify very well only the output of a CD or MP3 player.
Your teacher would be very impressed!

Of course you might get addicted to making the little amp work better, and add real power transistors to its output, combining with the existing output transistors to make compound complementary followers. You could also change resistor values to make it better like reducing the value of its output emitter resistors, and increasing the value of its collector resistors. With a 36V supply, it would have an output into 8 ohms of about 18W or about 36W into 4 ohms.

If you really get carried away with modifying your little amp, you could make two of them and connect them in a bridge like the IC I showed.
With a 36V supply, it would have an output into 4 ohms of about 100W! :lol:

 

[baftab]

thnx
i have my project checked
now i'll improve it the design you gave is awesome
it'll b like transforming a car into a jet..lolz
sure i'll start working on it from monday...as soon as i get the components
thnx

 

[audioguru]

i have my project checked
now i'll improve it the design you gave is awesome
it'll b like transforming a car into a jet..lolz
sure i'll start working on it from monday...as soon as i get the components
thnx

See, now you are addicted to electronics like me! :lol: