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Cheap Chinese Audio Amp: How can I reduce the noise? Answered

I have a $2.50 audio amp from China.  It's what you'd expect: some rusted components, some scratches on the PCB, and yet it still works.  I use it with a 9v battery, my phone, and a big, repurposed car speaker.  It get's loud enough I think it can easily destroy the speaker with that 9v.  

My question: At any volume worth using that amplifier for, there's noticeable noise.  What can I do to remove this?  Some research shows that a capacitor may help, but where would it go?  Thanks

Tags:noise

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iceng

Best Answer 2 years ago

What Downunder is trying to explain to you is that the 9V fails to deliver the instantaneously needed energy for a Loud or heavy Bass note peak causing the waveform distortion you call noise... If you know better and do not take our advice on using a power supply to improve the sound them at least add a 15v or 25 volt DC 1000uF electrolytic polarity sensitive capacitor at the PCB site where the battery wires are attached. The capacitor stores energy that supplements the fly-power 9v battery when the amplifier needs to drive the speaker coil with some heavy sound.

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bobdabiuldericeng

Answer 2 years ago

Thank you, you made it much clearer. What would constitute a power supply in this case? A repurposed printer wall wort?

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icengbobdabiulder

Answer 2 years ago

Just about anything that is rated 500ma or more and a regulated dc output voltage 9v volt up to the amplifier board max voltage less 10% for safety.

Beware of the unregulated wall warts, they will usually inject 120 cycle hum into your sound which does not happen with batteries or audio power supplies. This low cost $6

http://www.mpja.com/12-Volt-Adapter-Power-Supply-1...

or this lab supply 12V at 2A capable for $12

http://www.mpja.com/3-12V-2A-Selectable-Output-Sup...

Not knowing where you live there ma be closer sources then Florida.

eBay has dealers who have free shipping

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bobdabiuldericeng

Answer 2 years ago

Iceng, idk what you're on, but I definitely do NOT need an 80W power supply. This is a 15w, dual channel amplifier. I only use one channel of audio, so it's not like I need the second channel. Don't need a small fan either.

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icengbobdabiulder

Answer 2 years ago

Then forget getting the fan too.

But you should read specifications where it does mention the maximum is twice 30W, peak is twice 25W and continuous output is twice 15W

-----------------------------------------------------------------------------------------------------------

Features:

1. 100% brand new and high quality

2. AC / DC, 2.0 / dual channel / stereo,12V/2A when using, the output power of 15W +15 W, peak up 25W +25 W

3. Can be accessed by two 4-8Ω 10-50W speakers

4. A large volume of small size

5. High signal to noise ratio

6. Upgraded version of the radiator, wider and thicker, better cooling effect


7. Fit for Bookshelf speakers, CRT televisions, radios, and other small amplifiers



Specifications:

1. Working voltage: DC 9-15V

2. Power: 15W +15 W

3. Maximum power:30W+30W

4. Output Impedance: 4-8Ω

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bobdabiuldericeng

Answer 2 years ago

Thanks man. I have a 7805, but that is 5v and might not work well. Alternatively, I could try a 7812, but i'd need two 9Vs to do that. I am aware of unregulated supplies, thanks for reminding me :) (and the links)

Also, I'd probably get a regulated supply from SFE, they have a good selection. And I believe the printer PSU/cord combo is regulated.

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steveastroukbobdabiulder

Answer 2 years ago

Its a 30W amp, it wants nearly 3A from the supply. Find a 12V 3 A wall wart.

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bobdabiuldersteveastrouk

Answer 2 years ago

Fair enough. So I guess the main issue is just getting it all the power it needs from a non-battery, because the volume is perfect. And that will get rid of the noise, right?

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Downunder35m

2 years ago

A 9V battery is lucky to provide you with 100-150mA, I doubt that is enough for a car speaker.
With no real info given I can only assume the 2.50 result in low power class A amp.

Get a proper power supply and speaker and give the thing the juice it needs before messing with the circuit ;)

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bobdabiulderDownunder35m

Answer 2 years ago

It is a ~5.5" car speaker, and the amp is as listed here: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItemVersi...

It gets plenty of juice, and while I understand that you didn't have all the details, I can assure you that while this thing is rated for more than 9v, the speaker can easily get loud enough that it is obviously strained and pushed to it's limit. Also, it hurts my ears at that point. So, it gets plenty of juice and significantly improves the volume over my phone's output. The question is more about noise, if you'd like to try to answer it again, go ahead :D

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icengbobdabiulder

Answer 2 years ago

Your link is not available any more.