DonFromTX

DonFromTX

Well Known Member
My RV12 has a stereo intercom/com system and I have a stereo headset for me. I however have a couple Sigtronic mono headsets I wish to use for passengers. Can I just plug them in and they will work, do I need to rewire the plugs, or can I buy an adapter for this. Tell me what my options are please.
 
I have a Sigtronics SPA-4S in my spam can that has no issues with my Stereo set and my kids mono sets all plugged in together.

I wired all four seats for stereo. The jacks [can be wired] so that when a mono set is plugged in, it simply sends both left and right to the same [tip] on the headset plug [but that cancels out the stereo]. (Mono's only have 2 [contact points e.g. tip and barrel] on the plug, so the left and right [channel] contacts essentially hit the same [contact, the tip]. Stereo plugs have three [contacts] so each of the jack contacts hit a separate [contact].)

In fact, if your stereo headset has the ability to switch to mono, more often than not, they are simply bridging the left channel [tip] and right channel ring on the plug into one so that the mono gets sent to both ear cups.

What is your intercom?
 
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Thanks for that information Jason, exactly what I needed to know! I just did not want to plug them in and blow something.
 
Just plug the mono headphone plug in until it make the first "click". It will be sticking out about 1/4" and look like it's not seated fully. That's OK because the "tip" of a mono headphone plug is the audio "hot" connection, and when partially plugged into a stereo jack that way, the tip of the plug will be making contact with both the "tip" and "ring" contacts of the jack and bridge them together so you'll be able to hear both channels.

If you plug a mono headphone jack all the way into a stereo jack, then the ground "sleeve" of the mono plug will ground out the "ring" contact and completely kill the signal of one of the stereo audio channels.
 
Well Neal, now you have me thinking.

You are right, in a Stereo, the left is sent on the tip, the right is on the ring, and the common ground is the barrel.

Mono is the tip for signal and barrel for ground.

You can buy simple adapters from Radio Shanty to get the tip and ring signals from the intercom jack to then send the tip and ring to the tip only.

Easy fix, however something to loose.

Sigtronics says you can wire the SPA-4S to run mono by simply taking the left and right wires and wiring them to the tip contact in the jack. No brain-er.

Sigtronics states that putting a mono plug in a stereo jack will NOT ruin the sigtronics unit, but MAY result in reduced performance.

When I fly with the family, I am the only one with a Stereo set. The rest are mono. I simply plug them all in and the mono sets get audio in both ears and so do I since all inputs except the Audio in are mono anyway. When I have put a stereo source to play into the system via the audio jack, I distinctly get stereo sound. However, I have not checked to see if what the kids hear is one channel (the left) only in both ears which should be the case.

So it appears that I still get full stereo with no reduction of performance between when I fly solo and when I fly with the whole family.

Again, this may be dependent on the intercom as well. So knowing what your intercom is may change the answer.
 
Some intercoms don't care if you ground out one of the headphone output channels, their output amp circuitry is designed robust enough to handle it without damage. Cheaper intercoms (e.g. the FC 403) might possibly indeed suffer damage, just like some comm radios will fry the transmitter RF final output stage if you ever key the mike with a shorted antenna coax, while others can handle the abuse just fine.

With a mono headset plugged all the way into a stereo intercom's jack, you'll still hear sound out of both earcups since the tip contact is connected to at least one audio channel, but since you're powering two earcups with only half the power you might otherwise have, the volume level might not be as strong as it could be by plugging a mono plug only halfway into a stereo jack, where it will then get the power of both channels fed to it.*


*a caveat: if you're playing stereo music into the intercom connected to a mono headset this way, you might hear some funny phase-cancellations in the music due to the way a lot of stereo music is mixed and processed during the recording, but you'll hear the voice of the other occupants of the aircraft thru the intercom just fine since that's all mono anyway.
 
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