frequent noise from basic TDA2822 audio amplifier I built

[Willen]

I just turned ON the PC (played nothing) and connected USB plug to power the amp and plugged audio plug showly. When tip was inserted, speed of "tadat tadat tadat" was little slow like twice in a second then inserted fully the plug and got the frequent noise thrice in a second. Measured the voltage with noise and it was around 4.6V. With no noise (audio unplugged) the voltage was near 5V like 4.9V.

Another measurement was plugged USB to PC and audio to cellphone and playing music. Voltage was same like 4.6V but as I said before, no noises were there.

Now if AG's predict is true then what could I do as an experiment to solve the problem? It has been interesting to me more than my need!

 

[audioguru]

USB is supposed to have a regulated 5V that does not drop 0.3V when loaded a little. Your multimeter cannot measure quick voltage changes caused by the "tadat tadat tadat" so the voltage probably dropped much lower. I think the voltage powering the headphones amplifier in the pc is also dropping and is being amplified by your TDA2822M amplifier and is going around in circles.

Your schematic shows C5 as a 100uF power supply filter. Try removing it to see if the problem becomes worse then try increasing it to 1000uF or 2200uF to see if there is an improvement.
The circuit should have a power ground wire and might also have an audio input ground connection. Try disconnecting the audio input ground connection (the shield on the audio input cable) at the input of the amplifier.
Check that the amplifier has a good soldered power ground connection because maybe the connection is poor and the amplifier power ground is only the audio input ground. I hope the amplifier is not on an intermittent solderless breadboard.
Try shorting the audio input ground connection directly to the power ground wire directly at the amplifier to see what happens.

 

[Tony Stewart]

If the noise appears to be a "motor boating" or porpoise-like" pop sound, this instability often comes from a relaxation oscillator effect that may be triggered by high frequency instability. The latter is suppressed by the 4R7+ C loading where you have 10R0. Other variations I have seen of this circuit use 0R or 2R2. The addition of R5 helps to decouple and debug for instability.

**broken link removed**

 

[audioguru]

Hi Tony, I agree with you that the 10 ohm Zobel network resistors should be 4.7 ohms, I wonder why they were changed from the 4.7 shown on the datasheet?
I think ST Micro goofed because the Zobel networks are on the wrong side of the inductive output capacitors. EVERY audio amplifier IC from National Semi has the Zobels connected directly to the output pins of the IC.

Did you notice that he has a much higher power bridged mono amplifier with tonnes of bass and yours is a lower power stereo amplifier with reduced bass below 91Hz into 8 ohms due to its tiny output capacitors?

 

[Willen]

Hi all again,
It's so much frustating!
Feeling like to quit the attempt! I increased supply decouple to 2200uF and noise reduced almost 5% I think. I modified circuit as Tony posted above but got same noise. Noise sounds like it's being ON and OFF so fast.

I used 4.7 ohms series with 0.1uF cap for output zobel network but got nothing changed. I disconnected audio's ground at amp but noise speed increased little more. I changed IC but got same problem! I checked many more connections but got same thing. In each modification it's working very nice with external audio or external power but with same PC as power and audio, it sounds like being ON OFF so fast (noise as I said before).

It troubled me lot, you said lot more possibilities and I did all as you suggested. If theoretically there's no mistake then maybe I made some silly mistakes. If there's some theoretically mistake then If any expert will try same thing as I did then I hope he will add some comments here again. I am feeling not to trouble you all more. Now I am using 5V wallwart SMPS to power the amplifier and playing quality music via PC.

 

[audioguru]

I have a little circuit board that came out of something. I took some resistors and capacitors from it over the years. It has a Samsung KA2209 dual power amplifier that seems to be a copy of the ST micro TDA2822M that you are using.
The Koreans or the Italians made a few mistakes on their schematic. I will let you guess which one is correct.

The circuit board also has a Samsung KA2402 motor speed controller IC for a cassette player.

 

[moty22]

If any expert will try same thing as I did then I hope he will add some comments here again.

Willen,
I accept your logic that if the amp works well with other supply then it is likely that the fault isn't with the amp.
If you look back at post #2 at my first advice to check that there is zero ohm between your audio output to the USB negative. I didn't see any clear comment from you that you did try that.
Let me elaborate: All the computers I've come across use common ground for all inputs and outputs. It is possible that some don't. If in your computer the ground isn't common then you can have strange problems because your link between the 2 ground points transfers the noise to the input. Some computers have current sense resistors on the common side of the output and that can cause your problem too. You wont notice this when you use the USB or headphones.
The easy way to check is with a DMM while your amp is unplugged. When I say zero ohm I mean not more than 0.1 ohm measured by a DMM.
If you find that the resistance is not zero you will have to add to your circuit an isolating audio transformer, the primary connected to the headphone output and the secondary to the input of your amp. You can try this solution even if you find zero resistance between the commons.

What that works against you the most is that you need a voltage gain of one and this amp gives you 40, it means that your signal to noise ratio is reduced by 40 if the noise comes from the supply.
Maybe audioguru can suggest a replacement amp with adjustable gain. You have to check what audioguru tells you; he is not a real guru and I think that he doesn't even have a beard and a big belly like a proper guru should have.

 

[Tony Stewart]

There must be some wild oscillations when using same USB as Audio source... Decoupling with a choke will test that theory. But good audio needs low impedance power source and USB source impedance is not particularily low like 80 mOhm for a dampening factor of 100 on 8 OHm. I wonder if changing speaker impedance or using two 8 in series helps.

 

[Willen]

There must be some wild oscillations when using same USB as Audio source...

Hi, it's not same USB as audio source. I am using USB for power and 3.5mm output of same PC as audio source. As Moty said I will measure resistance/continuity between USB -ve and audio -ve of the PC and will post reply again. I think 3.5mm headphone output is also little high impedance output.

 

[audioguru]

I betcha if you use a 3.5mm splitter so that the PC headphones output can feed your amplifier PLUS feed headphones then the headphones will also produce the "tadat tadat tadat" sound when the amplifier does. Can you try it?

 

[chemelec]

It Sounds like you have "GROUND LOOPS".

 

[audioguru]

In my post #22 I asked to remove the audio ground from the amplifier so that the USB power ground was the only ground and then no ground loop. It made little difference.
It seems to be when the amplifier draws current from the USB it causes the audio from the headphones jack to make a sound that is amplified which causes the amp to draw current that causes the sound from the headphones jack that causes the amp to ....

 

[Tony Stewart]

Hi, it's not same USB as audio source. I am using USB for power and 3.5mm output of same PC as audio source. As Moty said I will measure resistance/continuity between USB -ve and audio -ve of the PC and will post reply again. I think 3.5mm headphone output is also little high impedance output.

Yes I understood that part for the signal , but rather sharing the same return path . Although not a typical ground loop, any path, where there is negative feedback, ground shift and a hysteresis effect such as from instability oscillations when limiting take the linear amp out of linearity range and causes hysteresis.

What you end up with is a version of a simple relaxation oscillator with delayed negative feedback and hysteresis or a porpoising effect or pop-pop-....due to the RC time constants involved.

Example

https://www.falstad.com/circuit/#$+...+2.3384026197294445+0.09353610478917779+1+-1