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This is my first post and I have a million questions. I hope some kind souls out there will not mind my noobness and be able to guide me any way they can.

Firstly, I have a headphone amplifier circuit that runs off 9v using the TDA2822M chip. The amp works fine as a mono amp (yes i know class D no good for headphones) but that is all i need for my purposes. My question is in regards to the nasty 'thump' I get when I switch on the amp. Is there some kind of capacitor/resistor combination that I can use on the input voltage that powers the circuit on slow enough to minimise the thump in the earphones?

Secondly, I have redesigned and enclosed a digital wireless transmitter/receiver, connected it to a headphone amp and built myself a nice little cheap digital earphone beltpack system. My issue is with the digital noise that is part of the circuit. I also have a great deal of noise when nothing is connected to the transmitter input. I know this probably sounds a bit vague but unless I post pictures and describe in great detail the whole setup (which I can do) it may or may not help with the issue. I have powered the transmitter circuit with a linear regulated 5v power supply. I have used a 10k 1:1 transformer on the audio input. I am suspecting its a shielding issue somewhere. Any advice or questions for clarification will be much appreciated. Please let me know any specifics you might require to be able to answer this question. I know there's probably so many variables and I am not experienced enough to know where to start more than what 'google' has suggested. Kind regards..

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  • \$\begingroup\$ Regarding TDA2822 "thump", it is not something which can easily be avoided without adding extra circuitry. Different component values might get you a different "thump" but a "thump" nonetheless. In mode fancy amplifiers the headphone jack is only connected a few seconds after power on so the amplifiers have had time to settle (that causes the thump). \$\endgroup\$ – Bimpelrekkie Jun 20 '17 at 5:56
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    \$\begingroup\$ I'm curious why you think a Class D amplifier is 'no good' for headphones. \$\endgroup\$ – replete Jun 20 '17 at 5:58
  • \$\begingroup\$ You will have to give a proper description of what you did (components used) with the wireless gadget including links to datasheets. The noise might simply be a property of the chosen components. \$\endgroup\$ – Bimpelrekkie Jun 20 '17 at 5:58
  • \$\begingroup\$ @replete Most class D amps have outputs like a bridge amplifier, meaning none of the signals to the speaker is ground. In case of a stereo setup, you cannot share the ground line which is how almost all headphones are wired. I do believe though that you could still use a class D stereo amp with headphones. By using only use one of the two outputs and adding an AC coupling capacitor. Similar to standard analog power amps. Not every class D amp might like this though. \$\endgroup\$ – Bimpelrekkie Jun 20 '17 at 6:04
  • \$\begingroup\$ I can draw some schematics and take some pictures asap. The digital transmitter/receiver is proprietary technology so there will be no info online for it. I am more than happy to add some components to the voltage before it hits the headphone amp. I read somewhere that a cap in series will slow the initial voltage to the amp but I've looked everywhere and cant find the exact values neccessary. Capacitor values are still something I need to learn about. @Bimpelrekkie, you are correct about the class D amp thing. I've looked for a decent workaround but looks like its far too complicated \$\endgroup\$ – Damien Jun 20 '17 at 7:13
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I am not familiar with your exact situation, but it seems to be related to the fact that one side of your headphone is grounded, while the amplifier output floats at some potential different from ground.

Therefore, consider using an output transformer to isolate the DC floating voltage of the amplifier from the grounded output circuit.

If you really want to educate and empower yourself, consider building your own transformer. It is not as hard as the big boyz make it sound.

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I am not familiar with your exact situation, but it seems to be related to the fact that one side of your headphone is grounded, while the amplifier output floats at some potential different from ground.

Therefore, consider using an output transformer to isolate the DC floating voltage of the amplifier from the grounded output circuit.

If you really want to educate and empower yourself, consider building your own transformer. It is not as hard as the big boyz make it sound.

Back in the day, we used vacuum tube amplifiers. They used high voltage. It was possible to save money on a transformer by wiring the headphone between the vacuum tube and the high voltage supply. As a California board-registered EE, there are some forms of death that are professionally embarrassing for us, so do as I teach you, not as I did when I was young and smart.

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