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TDA7297 and TDA2822M with the same supply

Question asked by almeida.daniel on Dec 24, 2012
Latest reply on Jan 9, 2013 by almeida.daniel
Good afternoon,
I've mounted 2 amplifiers using the same power supply using 3 breadboards, one is for a TDA7297 power amplifier which is running perfectly with some changes to the specified circuit, like 470nF input capacitors instead of 220nF, and 100nF capacitors between pins 3 and ground and pin 13 and ground, 100uF standby/mute capacitor, two 470uF rail capacitors instead of only one, a 10kohm potenciometer at the inputs.
The second breadboard is used for a 15V/4A regulator LM338T based, the power ground pin and the signal ground pins are both connected to the 2*470uF supply filtering, and the signal from the audio source is connected to the same path as signal ground and so the potenciometers.
In the third breadboard I've a TDA2822M headphone amplifier, when this amplifier is running alone with TDA7297 with the potentiometer at the cut position the sound is very good, but if I turn the volume up at the TDA7297's potentiometer the sound coming from the headphones become distorted, both amplifiers share the same audio source but the signal ground reference is only connected to TDA7297, the TDA2822M also have a potentiometer of the same type but it's connected to the TDA2822M ground path, for TDA2822M is used a L7806 linear regulator. The power supply itself is unregulated and as 45VA.
Can anyone help me solving this problem?
Thank you very much for your atention,
Best regards,
Daniel Almeida