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I have built an audio amplifier using TDA2030. The amplifier works fine with very low noise, the input is given through 3.5mm jack of my phone. Everything works fine until I touch or pick up my metal phone, as I touch my phone the speaker starts giving out a loud noise until I place it back on the table.

Please tell me what is the cause of this noise, and how can I fix/reduce it. TDA2030

Note: C1= 20uF in my circuit

Edit: It's a continuous buzz sound. It is the same type of noise we get when we touch an unplugged 3.5mm jack. I am providing power through a 12V 2Amp rated adapter (which is giving 18V output when not connected to load). I am using long wires to build the circuit. Actually, I used a breadboard to build the circuit and test it.

Many of you are suggesting that it's because of improper grounding. Please explain this because I am not getting your point, I will be happy to learn a new concept. And suggest a method to fix the noise.

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  • \$\begingroup\$ Is your phone connected to the amp in any way? Are you hearing the GSM "dit-dit-dit" noise or something else like mains hum? Is your amplifier grounded? How is the amp powered? Add this info to the question. \$\endgroup\$
    – user16324
    Jun 18, 2020 at 19:06
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    \$\begingroup\$ a loud noise In engineering "noise" means a signal that sounds like "shshsh", a good example is an oldfashioned TV or radio that isn't tuned to any station. The typical signal I would expect when you touch an amplifier is called "hum", it sounds like Bzzzzz, a bit like a bee or other insect. What sound do you get? This amplifier is quite sensitive and you need to pay attention to proper grounding, this site has some tips: sound-au.com/earthing.htm also read this and follow the links mentioned in it: hifisonix.com/ground-loops \$\endgroup\$
    – Bimpelrekkie
    Jun 18, 2020 at 19:40
  • \$\begingroup\$ Its a buzz sound like bees and other insects. It is the same type of noise we get when we touch an unplugged 3.5mm jack. I am providing power through a 12V 2Amp rated adapter (which is giving 18V output when not connected to load). I am using long wires to build the circuit. Actually, I used a breadboard to build the circuit and test it. \$\endgroup\$
    – Vishal
    Jun 19, 2020 at 4:17

2 Answers 2

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If it is a Bzzz or Hmmm and not a Shhhh (thanks to good input from a commenter) I think you have a classical ground loop.

When you touch your phone you form a loop from ground, via your feet to the phone to the amp and back to ground. This large loop captures significant EMI from the mains and other low frequency circuits.

You can confirm that it's not related to the phone by touching the unconnected amp inputs (e.g. at your 3.5mm audio jack when it is not plugged in to the phone). If you touch the ground ring you might hear a soft buzz, and when you touch the tip or middle ring (L/R signals) you'll hear a loud buzz.

To prevent this you have to isolate the amp input from any ground loops. A sub-100Hz decoupler could be all you need. Advanced audio equipment use a opto-coupler right at the input to prevent ground loops.

More: https://www.google.com/search?client=safari&rls=en&q=audio+ground+loop+isolator&ie=UTF-8&oe=UTF-8

This is a classical topic, and there are plenty of good videos and articles.

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    \$\begingroup\$ A ground loop would make sense if both the phone and the amp were on mains adaptors and the grounds would form a loop via protective earth. Note that phone chargers typically do not have PE connected in the wall socket (called safety class II device, here in the EU). But if the phone is running on battery, the only link being the audio cable, then it's not a ground loop. If the OP touches the metal chassis of the phone, and gets a loud SSHHHHH maybe with some pops mixed in, he may be facing RF oscillations. I've heard these happen with the TDA2040. Not enough clues though, in this case. \$\endgroup\$
    – frr
    Jun 18, 2020 at 20:51
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    \$\begingroup\$ In my understanding, a ground loop consists of sections of ground conductors, and the resistance around the loop is low units of ohms to milliohms. If the OP touches the phone (possible) and the amp's reference ground or chassis ground at the same time (unlikely), the electric resistance of that touch would be in kiloOhms. \$\endgroup\$
    – frr
    Jun 18, 2020 at 21:27
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    \$\begingroup\$ I'm curious if something in the output of the amp could radiate electrostatic electricity, that could be picked up by a human touching the phone (comprising a good antenna for some RF band) - and re-introduced into the input of the TDA2030. Hence my theory about feedback-based oscillations. \$\endgroup\$
    – frr
    Jun 18, 2020 at 21:30
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    \$\begingroup\$ I'm afraid that's a matter of PCB layout and mechanical engineering :-/ Would you dare to share some photoes with us? Your PCB layout, your mechanical chassis? Do you actually have an oscilloscope available? Could you maybe add a simple LC filter on the output and maybe input as well? Could you test at a lower power supply voltage? 18V is not much, but the amps are generally slower at lower Vcc = have less gain and less bandwidth, which makes them a little more stable. 100 nF parallel with 100 uF for power blocking doesn't look like much. How about say 2.2 - 10 milliFarad. \$\endgroup\$
    – frr
    Jun 19, 2020 at 14:56
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    \$\begingroup\$ Keep your circuitry shielded. Add low-pass filters = RF blocks at input and output, so that cabling attached to those ports does not function as an antenna, so that the parasitic feedback loop loses gain. The electrostatic coupling is more significant at higher frequencies so that's what you need to suppress. Pay attention to PCB layout. Have one layer mostly filled with GND, make power traces short (no large loops), avoid large loops of cable. This is rather superficial and hypocritical advice, I know :-) \$\endgroup\$
    – frr
    Jun 19, 2020 at 17:14
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Thank you for all the responses. But finally, I find a wonderful video that explains the exact solution to this and other noise-related problems.

https://youtu.be/xbinXh1ZSqk

Edit: The solution in the video is best, I tried it by myself and there is not even a single type of noise in the amplifier.

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