How many whatts is this person using?

I want to build this amplfyer but have no idea what wattage speeker they are using. Can any one tell me (I already know it is 8ohms)?

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I played with this circuit a while back. With a 50 mV input, you get 5 mW output with a chopped sine wave through an 8 ohm speaker. If you use a 32 ohm speaker, you can get somewhere in the neighborhood of 25 mW.  Extremely low powered. (mW is milli-Watt, 1/1000th of a watt). It is okay for private listening in a quiet area, but the fidelity is not very good and the battery life will suffer due to the waste of electricity through the speaker since it runs in "Class A" mode. If you want better performance, try a LM386, MAX4410, or look at my thread over at Nuts-n-Volts magazine that was inspired by BrunoIP's project.
....and therefore there's DC in the speaker...
Yuck.

Steve
Yep, Class A will do that. But this is a very dirty Class A, not good at all. AND, very anemic. Very low power. It is only good as a learning experience, IMO.

Qa
Well, it will unless its capacitively coupled.
Check my thread listed above. It tells what happened when I tried that. It's all on page 1.

Qa
David97 (author)  Quercus austrina6 years ago
I have been thinking about using a IC to make somthing like this. What would be the easyest one to use?

The 386, usually prefixed with LM or JRC (LM386 or JRC386). Anywhere from 250 mW to around 1 W, depending on actual chip designation. Easiest of the low power, 1st time builder chips to work with. The datasheet will show you everything you need to know about it. You can also search Instructables for the many projects built around the IC. Also search Answers for previous help on it.

Remember, this is a mono or 1 channel amp. If you want stereo, you'll need to build 2 circuits. If your input is an Ipod or similar player, use the "Gain = 20" circuit. That should be sufficient.

Qa

David97 (author)  Quercus austrina6 years ago
Im geussing that the
Amplifier with Gain = 20 Minimum Parts
dyagram
Vs and Vin is the signal input and pin 2 is - and all others are + (apart from unused pins).

Yes, Amplifier with Gain= 20 Minimum Parts

Vin (pin 3) is your signal input, Vs (pin 6)  is your positive from the power supply/battery, pin 4 is the ground/negative from your power supply/battery, you need the 220 uF cap (250 uF is very hard to find, 220 will do) at pin 5 oriented with the positive side toward the chip, the 0.05 uF and 10 ohm resistor combo is only needed if you get oscillation. All ground symbols can be tied together. Unused pins are left alone (1,7,8).

Qa

Less than 0.5W, and its a poor circuit, because you end up with DC in your speaker.

Steve
Kiteman6 years ago
Working it out in my head, I think it's about one Watt.