I was happy to live with this amp pop (whenever the amp is turned on it pops, so there are pops at the beginning of RX and beeps) but I got some audio adapters so I can plug in headphones and wow is that pop hot. It's a good hard thump on the speaker.
So I'm thinking again that there must be a way to make that not happen (even if the OEM firmware does it too). Is it possible there's garbage data in a buffer when the amp is turned on, so that it's actually just playing that data? Could the amp be turned on just after we start feeding sound into it, so that the level is being held when it's coming up?
If it's really not possible to fix I guess that's what we get, but it seems like it should be possible.
Alternatively, how much power does the amp draw if we leave it on all the time and nothing is being fed into it?
[Can't fix. Hardware problem] The audio amp POP
Re: The audio amp POP
Its a hardware design problem with the way the external speaker is connected.
The audio amp (LM4951) is designed to be connected as push-pull to a speaker, which is how the internal speaker is connected.
However the external speaker connection is only single ended from the VO- output of the amp to ground.
Every time the audio amp is enabled (there a physical pin on the audio amp chip for this), the amp immediately applies the same voltage to both its push pull outputs. So you don't hear anything on the internal speaker as its connected to both outputs
However for an external speaker the VO- from the amplifier is directly connected to the speaker, which causes that loud click.
The only way to prevent this happening is to never turn off the audio amplifier, but that causes other problems, because the reason they turn the amp on and off like this (in all radios, not just the GD-77), is that they pickup supply noise and also general RF noise.
People on this forum have complained a lot about the hiss that happens if the amp is left enabled when there is no audio input.
Also FYI. The firmware can't control the volume or gain of the amp, its totally controlled by the hardware, i.e a pot in series with the amplifier input pin
AFIK the MD-380 has a different design, as I think they have a way send beeps to the speaker even when the volume is turned down.
Also the MD-380 and the Baofeng DM-1801 and the RD-5R use a different audio amp chip, a TDA 2822, however this poses its own problems, as it doesn't have an enable pin, and the whole amp chip is powered on and off via an external FET, which causes a delay in when the amp turns off and results in hisses at the end of beeps on FM.
The audio amp (LM4951) is designed to be connected as push-pull to a speaker, which is how the internal speaker is connected.
However the external speaker connection is only single ended from the VO- output of the amp to ground.
Every time the audio amp is enabled (there a physical pin on the audio amp chip for this), the amp immediately applies the same voltage to both its push pull outputs. So you don't hear anything on the internal speaker as its connected to both outputs
However for an external speaker the VO- from the amplifier is directly connected to the speaker, which causes that loud click.
The only way to prevent this happening is to never turn off the audio amplifier, but that causes other problems, because the reason they turn the amp on and off like this (in all radios, not just the GD-77), is that they pickup supply noise and also general RF noise.
People on this forum have complained a lot about the hiss that happens if the amp is left enabled when there is no audio input.
Also FYI. The firmware can't control the volume or gain of the amp, its totally controlled by the hardware, i.e a pot in series with the amplifier input pin
AFIK the MD-380 has a different design, as I think they have a way send beeps to the speaker even when the volume is turned down.
Also the MD-380 and the Baofeng DM-1801 and the RD-5R use a different audio amp chip, a TDA 2822, however this poses its own problems, as it doesn't have an enable pin, and the whole amp chip is powered on and off via an external FET, which causes a delay in when the amp turns off and results in hisses at the end of beeps on FM.
Re: The audio amp POP
Wow thanks! That was a very detailed explanation of the problem.