Hi, i have a little question about pops in audio amplifier....this is the datasheet of AB amplifier
and this is my circuit:
TPA6203A1 in single ended configuration (Figure 30 of datasheet)
I have problems when amplifier is switched off with shutdown pin: i hear pop noise. This problem is not present when amplifier is switched on with the same pin. I've read that this problem is caused by a different discharge time of input capacitor, but (if so) i shoud have the same effect at switch on...or not? have no idea how can i resove it: obtain the same input impedance it' s very difficult, so i'm looking for an alternative solution. Any idea? Thanks
According to the data sheet, logic-induced start-up conditions are controlled by the biasing network, which also attenuates initial signal throughput. The biasing network apparently cannot control external current flow when shutting down. Hence no turn-on glitche.
How even 50mV (fig8 and 9 of the separate app note SLOA142 )could be generated across an 8R voice coil by 'unbalanced' currents passing solely through biasing resistors of ~47K is a real mystery. You'd need an 'unbalance' of 300V somewhere. Basic common sense suggests that imbalances occuring at the input must still be actively buffered or forced independently by the PA, if they are to have any effect at all, during turn-off.
I'm a little curious about the use of R7 and R8 (~47K from fig6 of the appnote SLOA142). They should have little effect on current flow, compared to the actual pop-transducing 8R load that is connected. I wonder if anyone has actually independently applied this 'cure' with the success that is recorded in the app note?
I have other problems with this app note. The waveforms (fig4 and fig5) show a transient on Vin- that has no origin, unless the input source DAC is being flogged to zero simultaneously. This does not occur in any of the other plots and is unexplained in the text. The time scales of problematic waveforms (fig4 and 5) are also incoherent either with those of the solution (fig7 is tx20) or with any of the other figures provided.
In all cases, the differential input and output voltages are the waveforms that should have been plotted, as these are what can produce audible effects and can be related to any accompanying single-ended traces.
You might consider fooling with a resistor across the inputs after the coupling capacitors. This may reduce the input impedance, but it will also address bleeding imbalances more directly.
I've had to arrange the physical muting of differentially driven transducers that WERE on 300V rails and to rebias them with independent DC levels, sub-audibly, in their quiescent state (with a reversible sequence, naturally). Why they couldn't do a simple shut-down here, quietly, is beyond me.