System components:
ESP32
3v relay
Pam8406 Mini Amplifier Boards
GE Univeral remote
I have designed and installed a system to, in part, switch between wired headphones and surround sound using an IR universal remote. Its all working great except often, when we are on headphones and switch to surround sound (or back) we get a loud 'pop' which is irritating. Is there any way to reduce or eliminate the 'pop'? (It can also happen, for example, when we navigate between thumbnails on YouTube)
Here is how the system works:
I altered the headphone jack receiver on my AVR to allow me to electronically 'remove/insert' the jack. I then ran the cable around the baseboard to our 'TV watching chairs' where I have installed " Pam8406 Mini Amplifier Boards" on each chair. Which along with amplifying, also makes for a convenient way to individually adjust volume.
So when I hit the button on the remote (which toggles) the selection, the relay is "energized/de-energized" which, in effect, switches between headphones and sound system.
Any advice/suggestions?
A pop is caused when there is a sudden change in the DC level of an audio signal.
So it is more about your hardware setup than software.
The trick is to find out where this DC offset is coming from and take steps to eliminate it, by doing things like biasing your audio signal so that no sudden DC change occurs.
There could be "floating" DC on one if the inputs or outputs. Assuming these are line-level signals, try adding a resistor between the PAM input and ground (10k - 100K) and/or at the other inputs & outputs.
Otherwise they may just be "normal glitches" in the digital audio when you switch between stereo & surround, and you can also get a click if you switch in the middle of a "wave". Probably the only solution to that is to temporarily mute while switching, possibly with a short (a few-milliseconds) fade-out and fade-int.
The Pam8406 has bridge-mode outputs,
meaning the outputs have half the supply voltage on them.
That's not a problem if you connect a speaker to both outputs (DC is cancelled),
But if you connect (asymetric) headphones to one output, then the DC component will flow through the headphones. That will pop, and eventually fry the cans.
You must use a suitable series capacitor if you connect headphones to one output of the PAM.
A coupla images showing the project.
Thanks to all who have responded. Just so you know... once you get past the basics, I am a lightweight when it comes to electronics.
I see on the first image you have tied the two speaker negatives together.
Can't do that, because speaker negative is not ground.
You effectively have shorted out the left and right outputs of the amplifier.
As I tried to explain before, the four outputs terminals of this amplifier are all outputs.
Leo..
OK, I just learned something(I think). But I am also confused. So if I understand you correctly, I really need to have 4 wires going to each headset? (L+ L- & R+ R-) but how do I do that. I just took an old headset apart and it looks the the jack receiver has just 3 connection points (TRS). Of course, I am using a TRS jack into the headset.
Also, are you saying this is related to my 'POP'?
Connect ground of the headphones to ground of the board.
The easy place is power negative.
Connect a 220uF cap between Left(+) output and Left channel (tip) of the headphones.
Connect a 220uF cap between Right(+) output and Right channel of the headphones.
The (-) outputs are not used for headphones, only for speakers.
The positive side of the cap towards the amplifier.
Leo..
Bingo! I modified the first (of the 3) amps and the pop is there but almost imperceptible when I toggle between headphones and surround. More than acceptable. However, there is still an unacceptably loud POP when the amp is turn on/off. We never turn the amps off at the amp itself (so the volume level stays put) as I use ESPNOW from the ESP32 at the AVR, which uses a 'current sensor' on the AVR power cord, to the ESP32 close to the amps which actually controls power to the amps. In this way the amps are powered on/off in concert with the TV.
As shown in the image below I use a mosfet to control the power to the amps. Could I incorporate a capacitor here to deal with this 'POP'? If so, how would I do that?
Thanks again Wawa for the fix. Really appreciate that effort.
(Solved) While I was never able to eliminate the 'pop' when turning the TV on/off using the Pam8406 amplifiers I did stumble across a solution that works. I purchased (under $10) a blucoil 4-Channel Headphone Amplifier just to try something different. Since I wanted to retain the convenience of individual volume controls mounted on the arms of our chairs, I removed the controls from the body of the blucoil, spliced in USB extensions and mounted them where the PAM8406 unit were originally mounted. While this resulting in simpler wiring to each chair (originally, 3 cables [audio input/output and power], to a single 4-wire cable) the main purpose was to see if this solution would eliminate ALL 'pops'. It did. Of course... I don't know why!
