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Push Pull Arrangement

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Suraj143

Active Member
I need to boost the sound of UM3561 circuit.I have added a push-pull amplifier to it.

Is my diagram ok?

Thanks.
 

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ronsimpson

Well-Known Member
Most Helpful Member
No.
1) The output of the IC only swings from 0 to 5 volts. The output of the transistors can not swing more than the input of the transistors. So the signal at the speaker can not swing from 0 to 12 volts.
2) The transistors you have will cause distortion. The Base-Emitter voltage of a transistor is about 0.65 volts. With two transistors there will be a 'hole' in the signal of 1.3 volts. see https://en.wikipedia.org/wiki/Crossover_distortion
 

audioguru

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Most Helpful Member
You do not have an amplifier, an amplifier has voltage gain. Yours has emitter-followers so it has no voltage gain. Since the transistors are not biased then the p-p output is 1.4V LESS than the input. The useless 2.2 ohm resistors also reduce the output level.

The datasheet of the toy sound generator does not show its output level since it is designed to drive ONE COMMON-EMITTER TRANSISTOR that you do not have. A common-emitter transistor has a lot of voltage gain (your circuit has voltage loss, not voltage gain).

If the output from the IC is 1V p-p then your transistors do nothing.
If the output from the IC is 1.6V p-p then the output of your transistors is 0.2V p-p which is almost nothing.
Your 12V supply is not being used since the output from your transistors is so low.

There are THOUSANDS of audio amplifier schematics in Google. Use one.
 

Suraj143

Active Member
Hi guys I understood what you mentioned.Yes there is no any amplification thing.

I think better to place a single common emitter transistor.

Here is the one I'm going to use.

Is this ok?What about using a D313?

Sometimes I may use a horn instead of a speaker to get more sound.
 

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MikeMl

Well-Known Member
Most Helpful Member
You do not have an amplifier, an amplifier has voltage gain. Yours has emitter-followers so it has no voltage gain. ....

I guess you never heard of Power Gain. His emitter follower arrangement will have a power gain of ~50 (17db).
 

audioguru

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Most Helpful Member
I guess you never heard of Power Gain. His emitter follower arrangement will have a power gain of ~50 (17db).
But will produce a low amount of sound. The original circuit on the datasheet using a single common-emitter transistor has plenty of voltage gain.
IF the IC has an output of 5V p-p (it might be much lower) then the unbiased emitter followers will have an output of about 3.6V p-p.
The total output power (squarewave including all harmonics) is only 0.4W into 8 ohms. The fundamental frequency will have an output of only 0.2W.
 

MikeMl

Well-Known Member
Most Helpful Member
According to the data sheet, the Absolute Max Vdd is 5V; recommended operating voltage is only 3.5V.
 
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