DFPlayer Pro emits a loud pop on power up.

I know this is an old thread, but I recently solved this problem for myself and this page kept coming up when I was still searching for a solution, so thought I'd share in the hopes that it will be useful for other people in my situation.  I'm going to go into a decent amount of detail, because the reasons I did what I did will be important for you to adjust to your own situation.  I'm using a DFR0534 mp3 player module, but the particular module doesn't matter for this solution. Here's my schematic

The basic idea is the speaker starts out disconnected by the relay at U1, and when power is supplied to the circuit there's a small delay before the relay connects the speaker.  The board still outputs the pop, but since the speaker isn't on, you don't hear it.

You'll need to understand the details in order adjust for your situation.  When power is supplied, C1 keeps voltage across it low while it charges.  How long this takes depends on the values of C1 and R1; larger resistance or capacitance means a longer charge time and therefore a longer delay (more details on exactly how this works below).  Voltage across C1 will eventually reach the supply voltage, but before that happens, it will reach the threshold voltage of Q1's gate pin (Q1's pin 2 in the schematic).  Q1 is an n-channel mosfet, and when the required voltage is reached at its gate, it acts like a switch that connects its source and drain pins (1 and 3).  This completes the circuit that includes the anode and cathode (pins 1 and 2) of the relay at U1. U1 then acts like another switch that connects the speaker and turns it on.

It seems like a lot of rigamarole, but I'm relatively new at this and this is the first thing that occurred to me that works (I went through plenty of things that didn't work).  You might need to adjust for your situation, mostly depending on your supply voltage, and how long your delay needs to be.  There's a bit of math that you should understand in order to do this.  The main thing you need to know is that the voltage across a capacitor over time as it charges is given by the equation:

V_c = V_s(1 - e^(-t/tau))

V_c: voltage across the capacitor

V_s: the supply voltage

e: euler's number, a constant

t: time in seconds

tau: the “time constant” for a resistor and capacitor pair. It is equal to R * C, or resistance times capacitance, in ohms and farads

In my case, I have a 3.3V supply voltage and I want a 0.5 second delay.  The gate threshold voltage of my mosfet is 2.4V, so I want to know when voltage across the capacitor reaches 2.4V and switches the mosfet on.  This gives me the equation

2.4 = 3.3(1 - e^(-0.5/tau))

solving for tau gives

tau ~= 0.39

Knowing tau allows me to pick a resistor and a capacitor that give me a result that is close to tau when you multiply them together.  In my case, I picked a 220µF capacitor and a 2000Ω resistor, which gives me

2000 * 0.00022 = 0.44

Doing a bit more math with the same equation above, this slightly higher value for tau gives me a delay of about 0.57 seconds, which is close enough for me.  Hopefully this gives you enough information to figure out how to adjust for your own circuit.

Some notes:

I too am trying to find a solution to stopping this loud pop. I am only using the DFPlayer itself. or else maybe i would say try turning volume all the way down on start up or maybe even turning the amp off? i dont know.

Anyone have any suggestions for stopping the pop?

what if you're not using the TX pin? then, where is the pop coming from?

This loud pop sound has no known solution. I hope dfrobot will add some tips to get rid of this sound in their wiki. 

Could you try to attach a 1k resistor to the TX pin of DFPlayer to see if it works? Usually the working voltage of your mainboard is 5V, but the insid.e working voltage of the DFPlayer is 3.3V