v10.1.1 Squawks??

I do have the 540/440/340 combination, but without the Avidyne audio in our panel, but instead a previous G* model that I kept for its 3 NavCom capability.  (In our case NavCom 3 is the marine radio). 

However, the MON output of the standby channel is very useful, especially fed into a audio select input on the panel.  It is fed into the former DME slot, and used generally to monitor 121.5.  It can always be on, nothing gets muted, and using volume controls and buttons, selected as needed, as others have suggested, works well for our purposes.

Tom,

The good news is that the PMA-450 should be a slide-in replacement for the APX-240, so you should not be "out" any of the labor expense for installation.

Like others have said, I manage it with volume settings. I have the standby audio set to a slightly lower level than the active frequency, and I have not observed a need to change it "on the fly" in use. So it is something that I set up once and left alone afterwards. I just turn the standby audio on or off through the PMA-450.

Sometimes I am listening to four things at once, at various volume levels (Comm1, Comm2, Standby, Music).  It is not unmanageable.  You get used to it, like having a conversation is a crowded room.  Not that big a deal.

By the way, my PMA-450 has its own volume adjustments for the switched inputs (including the standby and alerts audio) and the music, so there was a bit of experimentation to get everything the way I wanted, but once set it is quite nice.

David Bunin

n7ifr wrote: Also, where are the PMA450 independent Volume Adjustments for switched inputs?

Let me be more clear. There are separate volume adjustments for the switched inputs and for the music inputs. There is only one volume adjustment for all of the switched inputs at the audio panel in the PMA-450.  Here is how you adjust the volume of the switched inputs:

From the default (main menu) screen, select "Radio" on LSK1 (Line Select Key #1, the top button).
From the Radio menu screen, select "Volumes" on LSK2.
From the Volumes menu, select "Switched Inputs" on LSK1.
Rotate the volume knob to set the level.  The screen will display a value from 1 to 10 and the LED bar on the left side will also indicate the volume level.

Adjustment of the music volume is similar:

From the default (main menu) screen, select "Music" on LSK3.
From the Music menu screen, select "Music Volumes" on LSK1.
Rotate the volume knob to set the level.  The screen will display a value from 1 to 10 and the LED bar on the left side will also indicate the volume level.
NOTE: This is a basic adjustment.  After this volume is set to taste, normal adjustments to the music should be made from the device playing the music.

n7ifr wrote: Explain in more detail how you route and monitor IFD540 Audio Alerts?

In my installation, I have the IFD Comm Monitor wired into Switched Input #1, and I have the Alerts wired into Switched Input #2.   The PMA-450 "Switched Input" volume control applies equally to both of these signals, but the IFD has the capacity to adjust them separately.  (I have something else, a provision for another system, wired to Switched Input #3.)

The PMA-450 remembers which radios are selected when the unit powers down.  So I tend to leave Switched Input #2 (the IFD Alerts audio) selected ON all the time.  The only time I turn it OFF is if I am deliberately conducting a low level flight (aerial survey or such) and I am familiar with the obstacles, where the alerts are a nuisance.  I have the alert volume level set in the IFD so that they are louder than the normal radio volumes.

I select Switched Input #1 (the IFD standby audio) to OFF most of the time.  I turn it ON when I want to hear that frequency.  I have the audio set so that the standby audio is at least slightly less than the volume for the normal radios, but they are close enough that I can mentally tune out either one if I want.

David Bunin