Webcasting Voice Backup

[flyboyscott]

We just did our webcast yesterday for Stake Conference. As audio backup we had someone in our satellite room at the Stake Center with a smartphone capable of conference calling. The satellite room has audio piped into it with a speaker and volume control. At all the other buildings we just had one person call in from each location and added them to the conference call in the satellite equipment room. The phone picked up the audio well from the speaker and all others could hear fine. Our webcast was being received with laptops at the various buildings and they were plugged into the sound system using the crab unit with a mini-jack to the headphone port on the laptop. If the webcast failed all they need do was unplug the audio cable from the computer and plug it into the headphone jack of their phone. Quick and painless. We just kept the conference call going the whole broadcast. Hint: Make sure everyone uses their chargers. We tested and it worked great but thankfully the audio backup was not needed yesterday.

[wxrwxr]

ON the Audio backup solutions for Church broadcasts page instructions are given for using the EJ-10 at both the receiving and transmitting ends. But if the transmitting end is to transmit to more than one building additional instructions are needed. Suppose 3 receiving buildings are to be in the conference. The transmitting end would need three telephone lines and three EJ-10s. But how do you get the audio from the sound system's output into three EJ-10s at the same time?

[rmrichesjr]

The low-cost method is to simply bridge the audio output from the PA system into the multiple EJ-10s with passive cable splitters or equivalent. That will work well if the input impedance of the EJ-10 is much higher than the output impedance from the sound system.

The higher-cost and higher-quality solution is to use an audio distribution amplifier similar to the ones inside the rack. If you're handy at constructing homebrew audio gear, just throw a few op-amps, some Rs and Cs, and a power supply together and it will probably work flawlessly. Otherwise, there are units available commercially that would work.

[russellhltn]

That will work well if the input impedance of the EJ-10 is much higher than the output impedance from the sound system.

This was discussed in this thread, the input impedance is actually quite low. I'd say it's lower then I'd like connect to professional line-level equipment.

I haven't tried it, but if it were me, I'd go find a small speaker amp and use that. A speaker amp would have no problem driving 3 EJ-10s (about 83 ohms). It would also allow you to compensate for the loss in the box.

[Aczlan]

ON the Audio backup solutions for Church broadcasts page instructions are given for using the EJ-10 at both the receiving and transmitting ends. But if the transmitting end is to transmit to more than one building additional instructions are needed. Suppose 3 receiving buildings are to be in the conference. The transmitting end would need three telephone lines and three EJ-10s. But how do you get the audio from the sound system's output into three EJ-10s at the same time?

What we do as backup for the webcast is to use an audio conference bridge as described on the wiki: https://tech.lds.org/wiki/Audio_confere ... nghouse%29

Then we only need one EJ10 in each building and we only tie up one phone line in each building.
Edit: I believe that is also used for High Council and other Stake meetings with far flung participants.

Aaron Z

[rmrichesjr]

This was discussed in this thread, the input impedance is actually quite low. I'd say it's lower then I'd like connect to professional line-level equipment.

I haven't tried it, but if it were me, I'd go find a small speaker amp and use that. A speaker amp would have no problem driving 3 EJ-10s (about 83 ohms). It would also allow you to compensate for the loss in the box.

A small speaker amp would be a good option to consider, but I think I'd want to plan on a suitable attenuator between the speaker amp and the EJ-10 to avoid any possibility of overdriving it (damage to the EJ-10 not very likely but not entirely unthinkable), to attenuate the likely higher-than-line-level noise on the speaker output, and to allow the speaker amp to produce enough output to be well out of the range where crossover distortion would be a problem.

My reading of the referenced thread says the line input impedance of the EJ-8/10 is 4.9k at 1kHz. If that is accurate, bridging three of that load would be 1633 Ohms, which would be entirely reasonable for a good line-level output. The PDF schematic does not state the impedance of the transformer, which could make a big difference.

[russellhltn]

A small speaker amp would be a good option to consider, but I think I'd want to plan on a suitable attenuator between the speaker amp and the EJ-10 to avoid any possibility of overdriving it (damage to the EJ-10 not very likely but not entirely unthinkable), to attenuate the likely higher-than-line-level noise on the speaker output, and to allow the speaker amp to produce enough output to be well out of the range where crossover distortion would be a problem.

Optimal, but I doubt if it's necessary. (I've seen people connect speaker outputs to mic input )

My reading of the referenced thread says the line input impedance of the EJ-8/10 is 4.9k at 1kHz.

That's sounds about right for the line-level inputs on the top of the box, but not the special input on the side that's for feeding the phone line. At best, it's a few hundred ohms.

[russellhltn]

BTW, you might want to read this thread which has a EJ-10 schematic. What you'll see is the "Audio input" has a 100 ohm resistor in series with a 10 ohm resistor to ground. Therefore the impedance has to be somewhere between 100 and 110 ohms. Not exactly "line level friendly".

[Aczlan]

A small speaker amp would be a good option to consider, but I think I'd want to plan on a suitable attenuator between the speaker amp and the EJ-10 to avoid any possibility of overdriving it (damage to the EJ-10 not very likely but not entirely unthinkable), to attenuate the likely higher-than-line-level noise on the speaker output, and to allow the speaker amp to produce enough output to be well out of the range where crossover distortion would be a problem.
My reading of the referenced thread says the line input impedance of the EJ-8/10 is 4.9k at 1kHz. If that is accurate, bridging three of that load would be 1633 Ohms, which would be entirely reasonable for a good line-level output. The PDF schematic does not state the impedance of the transformer, which could make a big difference.

What if one used a headphone amp? You can get one with 1 in to 4 (separately controlled) outputs for $20.
That should take care of the volume differences needed and in my experience, headphone level output just loud enough (or at least the headphone output on my SCM-800 gives a nice level into the EJ-10).

Aaron Z

[russellhltn]

What if one used a headphone amp?

That may work. It probably depends on the amp.