How can I reduce hum & pop from simple amp setup?

Question

I am building a bluetooth speaker and am encountering two issues. Here is my setup so far:

1. When turned on, it gives two very loud POPS before working normally. Is there a simple way of delaying the audio for a few seconds when it is turned on? (other than adding a manual switch)
2. By themselves, each component sound great but when they share power, there is a lot of hum. I've researched and I think I need a "ground loop isolater". Where should this be placed within the circuit for maximum effectiveness? (problem fixed by GLI)

Links: Amp Bluetooth Module

Answer 1

Ah you didn't read the reviews for this amp - it seems that it does cause loud pops at power-up and one user has implemented a switch that disables the speakers but this could be done with a delaying relay circuit fairly simply.

As for the "hum" - if it is "hum" and not degradation of the signal or high frequency whistles (etc.) this is likely caused by your power supply having too much ripple on it. The amp is a class D type and these are notoriously poor at coping with power supply ripple. Power supply ripple will come from a standard transformer/bridge/smoothing capacitor and is inevitable in these configurations - you can try putting a 10,000 uF cap across the supply rails close to the power amp.

Why are class D amps poor at rejecting power ripple - the output transistors are basically used as switches and they alternate rapidly (above audio frequencies) and this means any power supply ripple is superimposed onto the speaker wires. A conventional amp can easily reject ripple because it operates linearly and will only push ripple to the output when driven at very high levels (because the transistors saturate when the ripple causes the power voltage to be cyclically at a minimum).

It could be wiring but it's easy just to put a big capacitor across the 12V power rails first then take it from there if that doesn't solve the problem to an acceptable level.