# Amplifier problem

Discussion in 'General Electronics Discussion' started by Avidestroyer, Jan 23, 2013.

1. ### Avidestroyer

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Jan 11, 2013
http://sci-toys.com/scitoys/scitoys/computers/solderless/small_1_watt_audio_amplifier.jpg
this amplifier is worked well but it is not suitable for huge bow. So I am intend to create 3 watt amplifier.
But when I add 6 transistor to this circuit instead of two, this amplifier not work, just the speaker make a sound noise. My power supply was 6 v. Why this problem occure? Plz tell me anyone.

Last edited by a moderator: Jan 23, 2013
2. ### Harald KappModeratorModerator

12,465
2,987
Nov 17, 2011
The two transistors forma a darlington pair. That is for higher current gain.
Using more transistors in this setup doesn't necessarily create a "better" or "stronge" amplifier (btw: that has nothing to do with fire - note the spelling).
Btw: that circuit you linked is not a prticularly good design. Maybe good for a toy but way off from HiFi.

It you need a higher powered amplifier, it's not only the number of transistors that counts but also a different circuit. Google is your friend.

3. ### BobK

7,682
1,689
Jan 5, 2010
Looking at that circuit I seriously doubt that it puts out anything like 1 Watt. There is a 50 Ohm resistor in series with the speaker. If the speaker is a standard 8 Ohms, it sees only 8/58 = 14 percent of the voltage swing, and that is limited to 9V p-p or about 3V RMS. So the speaker sees 0.4V RMS and the power into it is V^2 / R = 20 mW. If the speaker was 50 Ohm, it would see half the voltage or 1.5V and a power of about 45mW.

Bob

4. ### Miguel Lopez

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67
Jan 25, 2012
Class A amplifiers are not known precisely by their efficiency. Why don't you try a simple push-pull complementary amplifier? An LM386 can also do the job easily.

5. ### Avidestroyer

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Jan 11, 2013
Because here IC is often not available. Therefore, I want to make by bjt.

6. ### Miguel Lopez

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67
Jan 25, 2012
I love BJT's amplifiers. You can do it as simple or as complex as you want (or need) and performance will be affected in the same way. But I have to confess that I have never built a Class A using transistors. In the search provided by Harald on post #2 there are good examples of push-pull.

First of all, enjoy and have fun as you work with electronics.

7. ### (*steve*)¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥdModerator

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Jan 21, 2010
Where is "here" (out of curiosity)?