frequent noise from basic TDA2822 audio amplifier I built

[Willen]

Recently I build an audio amplifier (schematic attached) based on TDA2822 8 pin DIP. But it's generating a kind of loud noise like "TaDat! TaDat!! TaDat!!!......" frequently twice or thrice in a second, almost louder than audio output. +5 volts is supplied by laptop USB and audio source is same laptop's headphone output.

It's amazing that it works so nice if I used same USB supply (from laptop) but my cellphone as audio source. What could be the reason and what can I do for further calibration?

Here's what I made exactly- (attachment)

 

[moty22]

Check that the earth of the headphones is 0 ohm to the negative of the 5V from the USB.
This circuit is wrong on the datasheet. pin 8 has to go to earth and C1 has to be between pin 5 to pin 1. You probably don't believe that the datasheet is wrong, look at other datasheet of similar amplifiers for example LA4525 or ask the member audioguru.

 

[tronitech]

Your circuit looks fine as long as RL is in the region of 32R?

Is your cellphone ground connected to your amplifier ground?

 

[Willen]

Yes, ground is common to USB negative and cellphone's too. I will correct as Moty suggested. This morning I added a 10k resistor from 3 to 7 (maybe like negative feedback?) then noise reduced but IC got so hot!

 

[audioguru]

Moty did not look at the datasheet that shows exactly the same bridged amplifier circuit.
Moty does not know about a bridged amplifier that uses a separate amplifier (there are two amplifiers) to drive each wire of a speaker with opposite phase so it effectively almost doubles the amplifier's supply voltage producing almost 4 times as much power as one amplifier. The Sanyo amplifier IC he mentioned can also have its two amplifiers bridged but differently to the TDA2822M dual amplifier.

Tronitech also did not read the datasheet where it shows almost 1W into 4 ohms with a 5V supply, or about 0.6W into 8 ohms.

When you added a resistor from pin 3 to pin 7 then there was too much negative feedback that probably caused the amplifiers to oscillate at a very high frequency that made them hot. DONT DOO DAT!

I think the TaDat! TaDat!! TaDat!!! noise comes from the laptop audio or its power supply.
1) Disconnect the inputs. Does it still make the noise?
2) Use a battery to power it and see if the inputs from the laptop produce the noise when they are connected.
Maybe the noise is the cell phone transmitting, "I'm here, I'm here, I'm here".

 

[Willen]

Hi AG,

It's little complicated matter than you said, because I tried all as you said.

1) It's not cellphone's effect: I tested its performance by turning OFF the cellphone. Noise is very accurate in timing (almost twice or thrice in a second) and in very same level loudly always.

2) It's not noisy audio from laptop: I tested by using battery to power the amplifier and used laptop as a audio input= It's working VERY nice!

3) It's not noisy power supply: I tested by using Laptop's USB as a power supply and used cellphone as an audio source= It's working VERY nice!

4) BUT if I used same laptop as a power supply (USB +5V) and same laptop as an audio source then it starts 'tadat! tadat!! tadat!!!' as mentioned in first point.

5) This particular one laptop has no problem because I tested on another a desktop computer and same thing/same type of noise exist there.

It has some interesting black hole there. If you made same thing which I made, you will also have same thing like howling feedback.

 

[audioguru]

My second thought about the noise is maybe the USB supply is overloaded and shuts off for a moment and repeats it over and over.

EDIT: I guess the ground for the audio and the ground for the power are different and cause the noise when they are connected together in the amplifier.

 

[Willen]

Then do I need to test continuity (in DMM) between Gnd of USB and Gnd of audio to see they are same or have some resistance?

There was a $4 cheap Chinese computer speaker and which has a USB plug for power supply and 3.5mm plug for audio. That worked very well in every computer, I don't know how.

 

[chemelec]

What does your Circuit Board look like?

Maybe you have Ground Loops, causing osillations on the board.

 

[flat5]

How much peak current does the amp want?

 

[audioguru]

How much peak current does the amp want?

If the speaker impedance is 8 ohms then the TDA2822M bridged amplifier with a 5V supply produces an output of about 1W at 10% clipping distortion or about 0.8W at maximum linear output. It is class-AB so its maximum heating will be about 0.7W. Then its maximum continuous current from the 5V supply is (0.8W + 0.7W)/5V= 300mA. Its peak current is 424mA.

 

[flat5]

"The USB 1.x and 2.0 specifications provide a 5 V supply on a single wire to power connected USB devices.
A unit load is defined as 100 mA in USB 2.0, and 150 mA in USB 3.0. A device may draw a maximum of 5 unit loads (500 mA) from a port in USB 2.0; 6 (900 mA) in USB 3.0."

Perhaps there is an oscillation in the amp or somehow it wants to draw too much power from the port.
That might cause (as you suggested) the 'motorboating'.

Can the OP connect the amp to a USB 3 port? Is it stable?

Does the OP have a meter to see what current the amp is pulling?

 

[Willen]

Hi all,

As I listed comdition before, power supply of USB is very fine and enough for the amplifier I made because if I used USB 2.0 power supply but audio from my cell phone, it sounds very good. If I used external power supply and laptop audio then again it sounds very good. BUT if I used USB supply and laptop audio then it starts tadat tadat tadat. When I just put a tip of 3.5mm in a headphone socket of laptop (not fully inserted, just 'tip' only) it starts 0.5Hz sound like oscillations.

I will measure consumed current and will EDIT the post after few minutes.

 

[flat5]

Please measure current with no audio and with laptop audio connected but with zero level audio.

 

[audioguru]

If the amplifier plays "tadat, tadat, tadat" when its audio is connected, playing or not, then of course its current will be bouncing all over the place. Instead of measuring the USB current, it would be better to measure the USB voltage that is probably also bouncing all over the place when it should be steady and regulated. If the USB voltage is not bouncing then the audio or its ground is bouncing.
The amplifier's input plug has a tip, (left input), ring (right input) and sleeve (ground). It seems that if the left input of the amplifier is connected to the ground or the audio output of the laptop headphones output jack then the problem occurs.

I suspect that the USB +5V is poorly regulated and also powers the headphones output amplifier. When the TDA2822M amplifier draws current to play the headphones signal then the USB +5V collapses a little which also causes the headphones output DC voltage to change. Or the ground voltage to change.

 

[flat5]

Yes. Measuring the voltage (also) will provide useful information. I missed that.

 

[Tony Stewart]

Pls define " frequently twice or thrice in a second" for "tadat"

To me .... this sounds like the Cell Phone RF getting into your high impedance imbalanced input and RF AM detected as the cell phone base station sync pattern. The amp cannot amplify the GHz signal but as diodes it can detect the microwave's carrier and amplifies the amplitude modulation.


Classic interference pattern !

Add RF cap across input or output and add ferrite sleeve around cable.

 

[audioguru]

To me .... this sounds like the Cell Phone RF getting into your high impedance imbalanced input.

I also mentioned the cell phone in my post #5 and the OP said in post #6 that it still happens with the cell phone turned off.

 

[Tony Stewart]

I missed that, Perhaps his [OFF] button only disables Rx and not Tx Sync.
But it still sounds like a cell phone until a better description comes forth.

THe real test is move phone next to wires for loudest effect then outside room.

 

[Willen]

I am very familier with cellphone RF noise. 100% sure that It's not a froblem I am getting. OK I will measure and post again.