This is not what I’m seeing with the Sonos port, but its line-out in my case is connected to a BT transmitter (to use with headphones). When I manually stop its playing audio source, using the Sonos App for example, or stop it’s line-in audio source, the analog output immediately falls silent and that’s reflected in the Sonos App room/browse tab too. Are you actually stopping the source audio that’s playing on the Port?

Yes I have stopped both ports. I was thinking that perhaps activity in the app might be causing an issue or perhaps it didn’t time out for a long time. Have not figured out what is happening to not have the amp trigger off. Was thinking maybe that is why they have a trigger out of the port. 
 

In one case the port has a line in and in the second case I don’t have a line in but can select the line in from the first port or perhaps select other music. The second port is really used as a volume control for a second zone. 
 

In any case, I am struggling to get the amp to turn off which means it is seeing voltage from one of these two outputs. 

I don’t use its 12v trigger, so can’t say, it maybe a setting on your Amp? See this link for info. on a Rotel Amp (just as an example) - maybe it’s a case that your Amp perhaps has a similar setting?…

https://rotel.com/faq/what-purpose-12-volt-trigger-switch

There is an old thread here on the Ports 12v trigger - perhaps see this link too:

I understand the purpose of the trigger. The amp should turn off based on auto sensing the output of the Sonos. Don’t know what triggers the Sonos Port to stop the output voltage. 

This thread is what made me wonder what triggers the port to stop the audio output voltage.  
 

in the thread it says “When I tested the port, after the music stops playing the 12v trigger turns off exactly 2 minutes later”

I assume it’s the pausing/stopping of the playing audio source, as the Port then goes into standby mode - not sure about the two minute period, but maybe your Amp is not a 12v trigger input, but a 12v output, or a ‘limitation’ of your Amp, that’s just keeping the Port awake? Is there maybe a setting that needs changing on your Amp, perhaps? What happens when the cable connection is removed from the trigger?

I currently do not use the trigger from the port to the amp. There is only 1 trigger input into the amp so having 2 port triggers won’t help unless there is a box that I can combine the two port triggers with and output only a single trigger. I can’t find that type of device. I don’t think I should take a Y splitter and join the two triggers together.  

My hope is that I can figure out the audio output so that the amp works correctly based on the output of the ports with no trigger. 

Perhaps I need to change the Port’s line-in Source Level to 8, 9 or level 10 in the App “Settings/System/tPort Room Name].  I’m not sure if any of this would help differentiate on and off from the output perspective  

The ‘source level’ voltage adjustment will apply and increase/decrease the volume of the line-in input only ...and whilst that might help to wake your Amp etc. It seems your issue is not that, but instead it appears the Amp is not going into standby, which perhaps should happen when your playing audio source (line-in, or built-in Sonos audio sources) are paused/stopped.

To begin with, I would expect you to to be able to see the audio as no longer playing on the Port room in the Sonos App. Check the Port ‘room’ on the the Apps ‘browse tab’ (usually the small graphic equaliser icon stops/disappears). Then after a short period (perhaps 2 minutes) I guess the connected Amp should power off, that’s if it’s 12v trigger is connected to the Port and the Amp software is designed to do that action.. maybe see what it says in the Amp user manual.

Check too that the Port is stopping playback of the audio - I would disconnect the Ports line-in cable and just use the built-in Sonos music services when testing the stopping of the audio playback and just see what happens in that case?

Listen carefully to the amplifier’s output. Is there some sort of constant, low level, low frequency signal?

If you have an expert friend or kid, they could make you a simple combiner for the 12V triggers.

The amp has output lights and they turn off properly. The only thing that doesn’t happen is that the amp doesn’t go into low power mode. 

What happens if you mute the PORT’s?

If I hit mute for each of the PORTs, there is no change.  It looks like there is always power to the analog output of the PORT.  Not enough power to turn the amplifier on so that the output channels are active, but some power so it doesn’t go to low power mode. 

Things will become more difficult to diagnose from here on. Likely you have what is known as a “Ground Loop”. These can become quite a problem in large installations, such as recording studios and radio/TV stations. There are specialized consultants that earn a nice living resolving these large issues.

The “shield” in audio signal cables is a knitted wire mesh that encloses a center conductor carrying the signal. The shield attempts to keep out stray electric fields. The idea is that an electric field will be intercepted by the shield and conducted away from the signal wire inside. This works well as long as the electric field is not too intense. 

You are also familiar with electric generators where a moving magnetic field induces current that can be channeled for lighting and mechanical functions. A magnetic field near our audio signal wire can induce a small current in our signal wire -- but our signal is also a small current. This induced signal can swamp our audio signal. Sorry, but the magnetic field will not be stopped by the shield.

I’m sure that at some point you’ve touched two appliances and received a shock. This is due to the (usually metal) appliance shells being at different potentials and, as you touch both, current flows through your body. Appliances should be “grounded” in attempt to keep all the shells at the same potential and eliminate this shock. Unfortunately, all “grounds” might not be at an equal potential (why? This is where the consultants earn their big money) and you receive a shock anyway.

With respect to electronics, it is common that the outside shield of an audio jack is connected to the equipment shell, which is often connected to the building electric ground. If the grounds are not equal, current will flow in the audio cable’s shield. We call this a “Ground Loop”. Part of the physics is that this current creates a magnetic field. Just as in our power generator, this magnetic field will induce current flow in our audio wire -- competing with the audio signal.

As a diagnostic:

If you don’t have a couple “shorting plugs”, create a pair by cutting into a discarded RCA cable and connecting the central conductor to the shield. Keep the wire short. First insert your shorting plugs into the amplifier inputs (power down before doing this) and verify that the amplifier remains in standby. This eliminates the possibility of a ground loop between PORT and the amplifier.

Next connect PORT as usual and install the shorting plugs into Line-In. If PORT is muted, the amplifier should shut down and stay shut down. Even if you unmute PORT and play its Line-In, its output should be near zero because of the shorting plugs. Other than the wire connection to the amplifier, PORT’s  own power cord, and the shorting plugs, there should be no wire connections to PORT.

If the amplifier-PORT combo goes into standby when shorting plugs are inserted into Line-In, we’ve eliminated the possibility of a ground loop between PORT and the amplifier and need to start casting a larger net for ground loops. We’ve also eliminated the possibility of some low level, stray output from PORT.

You may find that simply reversing and re-inserting a power cord in its socket will create or improve a ground loop. And, you’d need to explore every possible combination of power plug orientation.

I understand what you are after.  I am starting by unplugging (from the power supply) both sonos port.  The result was that the amplifier did go into low power mode.  I then plugged in 1 of the ports and it stayed in low power mode.  When I plugged in the second port, the amplifier came out of low power mode.  I have to wait for 20 minutes to see if it will go back into low power mode.

It appears that it is one of the two ports that make the amplifier stay out of low power mode. That amplifier has no inputs.  It only outputs items from other inputs that it can select. I tried to use the digital output to the amplifier and same issue.