AMR 350 audio panel question

[FORANE]

I have a Collins AMR 350 audio panel, SL40 com 1 and Garmin 430 com 2.

When the AMR 350 toggle switches for com 1 and 2 are both set in the headset position, the volume on the Garmin 430 (com 2) is low. When I move the toggle switch for com 1 to off, the Garmin 430 volume immediately increases to an appropriate level. If I set the Garmin 430 com volume to maximum, with both com 1 and com 2 set to headset on the AMR 350, the volume heard in the headset is loud enough to hear well (though nowhere near as loud as it should be).

I replaced the AMR 350 thinking it was bad. The new AMR 350 does the exact same thing as the old AMR 350.

Anyone have any ideas why this is?

 

[BobTurner]

I do not know for certain, but this sounds like the old ARC switch panels which did not properly isolate the two inputs, but instead just tied them together. The relatively low impedance (looking back into the SL40) can drag down the 430's signal.
Fix 1: get a decent switch panel
Fix 2: put a 600 ohm resistor in series with the SL40 input. This will make the problem better, but not perfect. You will have to turn up the SL40 volume.