Balanced audio networks and impedance matching is a lost art in audio engineering. With the use of servo and transformer-less resistive networks in digital transmission networks, the use of impedance matching and balanced audio feeds is a lost art. When dividing or combining audio on a balanced system remember both (+) and (-) are separate active circuits and require the same but separate loads. That means 10k in the positive lead, 10K in the negative lead and 10k on the output lead. Very few mixers are designed to work exclusively into 600 ohms anymore. In the old days we designed and built impedance matching networks out of resistive equalizing networks and they worked perfectly. From 20Hz to 20KHz within one db; these audio circuits were essentially flat. These days in commercial radio all we worry about is level matching and distortion. Of course, impedance matching would still do the trick. It just takes some knowledge and a little work. Understanding the use of balanced audio and impedance matching will solve all of your problems. Maybe someone here has a suggested article or text on the subject.
You can simply add a simple 1 K resistor network in series with L & R to sum them together and preserve stereo seperation
L-1K
mono-
R-1K/
Paul
Everyone is concerned about audio drop, the way I see it you're not putting any load on L or R (to ground), just summing L&R together with L-1K-mono-1K-R. The mono connection in the middle goes to mono in.
These are the best isolation units I've ever used. No loss in fidelity at all..
Combine the output (L&R) with a 470 Ohm resistor and you'll have both.. Isolation and a good mono signal. I use them all of the time for Stereo systems I build using mono amps being fed with a stereo signal. Amp/Source usually operated from the same battery and this circuit fixes the ground loop issue and give me a good mono input..
Here is a cheap and ghetto way to do this. OK many folks buy a more beefy Android smartphone after a while. I have a few that I really didn’t like because I could not run some of the apps I wanted because of lack of memory.
What you can do on the cheap if you don’t have an extra smartphone is to purchase one of those Android prepaid phones like Straight Talk, Boost, Total Wireless but you don’t need to actually activate it unless you want to put it in a waterproof box and connect it to your AM transmitter sort of like a ghetto version of a Barix box.
Use your Wifi and Download Xiia (the FREE version from the Google Play app store. Now tap Favorites and then tap add new station. Enter your station’s streaming URL into it and save it when done. Vala you have a cheap ghetto Barix box and you’ve saved 100’s of dollars.
Now use a y adapter and if you need a 1/8th inch to RCA adapter for your transmitter those are easily found.
Slowly turn up the volume till it distorts and back off maybe 3-4 notches from FULL volume. Xiia also has an EQ so you can use it too to try and EQ your audio coming into your transmitter without effecting your stream.
Being disabled and having little income I had to find ways to do this hobby while I didn’t break my bank and this has been very effective for me. I can have my computer in a separate room from my TX since I also stream my station.
Good Luck!
I am curious about this myself. I have a stereo balanced XLR out on my mixer that I want to get to mono to the transmitter.
A cheap and easy way to do this would be to build a bridging circuit and from that get a pair of 1000 ohm resistors (one for each leg coming off of the bridging circuit and then merge both left and right channels. It's a clean way to get a stereo circuit summed properly.
Game, can you sketch that circuit and post the image? Not everyone is going to intuitively know what a "bridging circuit" is.
I've been away for a while but I'll try to knock out a diagram over the weekend.
🙂