Hi I made a small headphone amp and powered it using lipo battery.voltage is stepped up to 5v.everything is working with direct supply (ie., while charging battery)but as soon as I unplug the charger ,I am getting high frequency output to amplifier.what could be the reason? Note:this is happening even when battery is fully charged and there is absolutely no noise when battery is charging.

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    \$\begingroup\$ Hello, could you be a bit more specific? If you can create or share a schematic that will be helpful. What is the high frequency? 1kHz, 1GHz? Which amplifier? \$\endgroup\$ – rdtsc Sep 30 '18 at 6:09
  • \$\begingroup\$ Its a mini tda1308 board.I don't have a scope to measure the frequency but its audible through headphones.as I mentioned this noise disappears while battery is charging. \$\endgroup\$ – user196563 Sep 30 '18 at 6:16
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    \$\begingroup\$ Looks like something starts oscillating when you remove the charger. With no scope that is difficult to solve but at a guess I would start with adding a capacitor over the supply pins. \$\endgroup\$ – Oldfart Sep 30 '18 at 6:26
  • \$\begingroup\$ Should I add capacitor after step up for filtering? \$\endgroup\$ – user196563 Sep 30 '18 at 6:28
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    \$\begingroup\$ I schematic would be better but my reasoning is as follows: The charger has a probably a bulk capacitor at its output. This is the component closest to your circuit and thus removing the charger it has a great impact on the functioning of your circuit. Bridging the charge pins with a capacitor of your own is simple and can be done without soldering. If the frequency goes away you have a solution. If not, try to borrow a scope. \$\endgroup\$ – Oldfart Sep 30 '18 at 7:11

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