I have designed and built the project below.

enter image description here

Open the image on new window or imgur will not let you scale it up and you will not see the components.

This is a 4 channel stereo switch. You press the button and select channels 1, 2, 3 and 4 in sequence. The channel you choose is sent to the TEA2025 and amplified.

This is almost working well but I have two problems: when I increase the volume beyond a certain point the audio starts to fail, like it is being interrupted and when that happens the LM337 from the power supply starts to heat fast.

The input comes from 12 VDC external adapter. This power supply creates a virtual ground (-6 VDC, 0 , +6 VDC). The LM337 is responsible for the negative voltage.

I have asked this on reddit and someone there answered this:

Strangely enough, the LM337 actually provides the positive voltage. As the load between the +6v rail and virtual earth increases, the virtual earth will try to move towards the +rail. Only current through the LM337 can drag it back again. A fairly simple fix is to add a power resistor from earth to -ive rail. Enough, say, to balance out the current drawn by the output IC at half power. That will mean that the 317 will get a little hotter on low volume and the 337 will get a little cooler on full volume.

I am not sure if I know how to calculate this resistor and btw is there a way to make a symmetrical power supply from an external 12VDC adapter input without this problem or making this virtual ground ground be at 0V always?


1 Answer 1


Yes, the LM337 takes the positive loads.

enter image description here

You should not have the amplifier running on +5/0V, it should run on +5/-5.

  • \$\begingroup\$ that is what I was suspecting. I will modify it now. Thanks \$\endgroup\$
    – Duck
    Apr 3, 2018 at 22:48
  • \$\begingroup\$ The change did solve the problem but created another one... :)... now the LM337 is cool, the sound is not chopping but the hum and buzz is louder than the music... going back to the drawing board... \$\endgroup\$
    – Duck
    Apr 3, 2018 at 23:11

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