CP 120 Power-amp layout Question

[etxycvkb]

Thanks to Saint Gillis for posting his crush pro 120 schematic. ORANGE
Can someone help me understand how the second op-amp is set up, is it acting as a differential amplifier? To have two outputs, why don't they just duplicate the first IC and have the same signal just going into both instead of linking the output of the first into the input of the second? Thanks guys

 

[saint gillis]

It acts in bridged mode.
It's basically the same circuit as the one in page 22 of the TDA7294 datasheet

The first amplifier is connected to one side of the speaker
The second amplifier is phase-inverted and is connected to the other side of the speaker
> double power

Check : Bridged and paralleled amplifiers - Wikipedia

 

[etxycvkb]

Thank you, Saint Gillis. I did a deep dive into class ab amps to learn more. Unfortunately, Im struggling to troubleshoot my problem.

I have determined that the mute pins do not have a sufficient voltage. I measured the following volts at the following junctions. I assumed the Cap (C66) was leaking, so I took it out of the circuit, but none of the voltages changed. Any Ideas what could be causing this low voltage? Could the TDA chip itself be leaking current through pin 9? I cant think of what else it could be. Thanks everyone

 

[etxycvkb]

I fixed my issue. I replaced the IC5. I think It was pulling down the voltage on both pin 9's causing the mute to activate. I swapped the chip and its working now.

 

[saint gillis]

Good job, and good to hear, congrats !