Warning volume

[Spuds1@dyn]

Through a PS intercom, my radio, intercom, and music are adjustable from barely heard to earsplitting. The EMS warning tone in my aircraft is not loud enough at full volume. My friend has one with an AP74 connected directly to the headphone jack and his is not loud enough either.

Any suggestions? How about a 1 watt amplifier, such as a TDA7052 or LM368?

Thanks

 

[dynonsupport]

There are a couple of commercial products that are designed to mix and amp audio signals for aircraft:

http://wiki.dynonavionics.com/3rd_Party_Accessories_not_supplied_by_Dynon

I'm not an EE myself so I can't comment on the component level amps, but I'll have one of my colleagues chime in.

 

[dynonsupport]

The general issue with the EMS is that it's WAAAY TOOO LOUD, so this is kind of a first. Our install guide recommends a variable resistor in line to reduce the volume. Do you have one of these, or does the EMS go right out to the intercom?

If it goes right out, does it go into the intercom by itself, or does it somehow get shared with other inputs (like hooked in parallel to the radio or music)? Sharing, if not done properly, can significantly mute one output.

Also, are you saying the EMS is too quiet even with all the volumes cranked all the way up? Or is it just an issue where it's quieter than everything else at a given volume, but does get loud enough if you make everything else too loud?

The EMS can put out 16V P-P, which is more than a LM386 could unless you powered it off a bossing power supply in the plane, so that isn't going to get you anywhere.

The output of the AP74 is.... An LM386 run off 12V. However, NONE of the Dynon equipment is meant to drive a headset direct, especially in parallel with the radio. so it's not surprising that it doesn't work well for him.  It is all designed to have an intercom between the equipment and the headset.

 

[Spuds1@dyn]

Yes, we both have the 10K pot for volume control. My audio alert is shared (parallel) with another input to the intercom. I guess I am not sharing properly-how would one share properly?

The PS intercom has a volume which affects all inputs. In other words, the intercom volume set full HI will be too loud, the music too loud, the COM radio too loud. I can turn down the music and COM but the intercom will be too loud. At this setting the EMS warning tone is still not loud enough.

My friends AP 74 output directly into the headphone will be changed into the intercom, but again, how do we share the input correctly?

Thank you for your support. I am huge fan of Dynon products. JIM

 

[dynonsupport]

Well first, if it's too quiet, take the 10K pot out. Even with this turned all the way to loud, it does reduce the volume some.

In order to share properly, you have two options:

Best is to use a mixing device like was mentioned in our earlier post. These use active electronics to add two (or more) audio signals together and can do it without losing any volume.

The easy way is with resistors, but by definition this loses some volume. You want each output to go through a 500 ohm to 1K resistor and then tie all those resistors together at the input to your intercom.

The issue with hooking two outputs together directly is that they fight one another. Imagine your radio wants it's output to be 0V since it's making no noise. It actively drives to 0V. You could consider this to actually be a short to ground.

Then you hook the output of the EMS to this same point. The EMS is now trying to drive against a short to ground. The short isn't "perfect" in that it has some resistance, so the EMS is able to make some noise, but it's a lot quieter than it should be.

Adding a resistor in line with each output increases the resistance so each device can make noise easier, but when it is making noise, it also loses volume through the resistors.

Active mixers get around this by using some amplifiers.

The EMS actually has a 1K resistor inside, so you really only need to put the resistor on the output of the other device.