I would like to know the difference between different types of Grounds like Power-GND vs Pre-GND. Are all the grounds not same? Cant we connect the device to any one of these grounds?
In my application I have a low frequency audio amplifier called "TA8229K" which has 15 pins.
On this picture, on this diagram there is written that only 3 ,5 and 7 pins might be connected to Power-GND.
1) At first which one is the Power-GND? Is it a negative direction of 9v battery?
I think that 4 and 8 Pins might be connected to positive direction of 9v battery (Where is written VCC).
Am I right?
Also There is written that 14 and 15 pins might be connected to Pre-GND1 and Pre-GND2.
2) which one is the Pre-GND1 and Pre-GND2? Is it a negative direction coming from low frequency audio device?
Also there are other pins like 9, 10, 13 which are connected to some kind of GND on diagram, but there is no written which one is!
3) Where should I connect those 9, 10, 13 pins?
4) Where should I connect first pin (1 pin)? What does it mean N.C. ?
Best Answer
Most likely the power amp ground has significantly more current on it than the preamp so they provide separate pins so that you can run separate ground wires back to a single point at the power supply next to the power supply filter capacitor(s). Otherwise, if you just connect the two grounds together at the IC, the inductance and resistance of the one ground wire (albeit small) will cause non-zero voltages which will be reflected on the preamp ground. Meaning you could get increased noise or possibly instability or some other equally bad result.
Grounding issues are the most common cause of noise and hum in audio circuits. The solution in virtually all cases is to have separate ground wires running back to a point where ground currents are no longer present (b/c they have been absorbed by filter capacitors).
For example, if you have analog signals and digital signals in the same circuit, it is absolutely vital that you have separate grounds. If you don't, you will get digital noise in your analog signals.
Another example is shields of pro-audio cables which are (supposed to be) connected to the chassis (at least from the driver end of the cable / receiver end should not be connected at all). Then the chassis is connected to the power supply ground origin (meaning at the filter caps).