I have recently built a 25w tda2050 based amplifier. After double checking all routes and pcb connections, the amp fired up flawlessly the first time. Its clean channel is great, without any hums or hisses. However as I continued using, i noticed that the on/off popping sounds were somewhat much more than tolerable and it may not be safe for the speaker even. The pops are loud and when turning off the amp, after the initial loud pop, 2-3 secs later a silent crackling, tearing sound comes off the speaker too!
I tried to do a we search but I could not find some confirmed reliable basic practical information. Theres supposedly a circuit to prevent this pop in audio amps but best solutions are the simple ones so I would really appriciate if you can point me in the right direction
My build is TDA2050 datasheet with a 10uF nonpolar feedback capacitor instead of the 22uF shown at datasheet. Rest is pretty much the same. It does nto have any hum, hiss or oscillation. It runs pretty smooth and quiet only problem is this popping at turn on/off. For power suplly, I use a 35A bridge rectifier, a 15-0-15 tranny and 4700uF filter caps with one additional 100nF ceramic between the +vcc and -vee capacitor tabs. My star ground is right between the power suplly caps and tda2050 (about 2 inches away from both). My star has a direct connection to mains earth and chasis ground goes directly to mains earth as well. My preamp is a marshall mg15 with a suplly of +-15V zener diodes with 220uF and 100nF caps connected with 680R resistors to power suplly. At around 1w output, my measured dc voltages are +-14.9V at preamp and +21.5V, -21.7V (cheap tranny
) at powersuplly. This pretty much sums it up as far as I can remember.
There are 3 main things I am concerned about that may cause this pop
- I read some claims that popping is mainly due to arching at on/off switch. Some people suggest a small mains cap at power switch. Can this work? If yes, what type of cap and how to connect it?
- Some guy talked about DC balance. I'm not sure if he meant +21.5V, -21.7V suplly difference or the 22k non inverting to ground dc resistance and 22k inverting to ground (by speaker). Something about DC offset at output. Are these values critical? I used +%5 varying carbon resistors at poweramp. Shall I measure components induvidially and put 2 22k that are pretty much identical down to less than %1 so these 2 22ks are matched?
- I also have a valve amp and theres absulately no audible pop at on/off. It has a kind of slow start (preamp suplly has some 5k resistor + a series choke) Can the timings of preamp and power amp turn on cause this pop? If yes, then shall I delay the preamp, or the power amp by installing some series resistors? I assume the 680R resistors have that purpose but they dont seem to be enough.
Thanks for your help