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A little off-topic, but perhaps one of you could help. My transmitter is fed with a single audio cable (mono). My mixer and everything else is stereo because we stream. Thus, in order to preserve both left and right channels, I need a y-adapter going to the transmitter.
Problem: every time I use the y-adapter, from the “tape out” or even the “output 2” from my equalizer, it makes everything coming out of the mixer MONO. When I unplug it, it’s back to STEREO.
So, even though that’s the only wire going to the transmitter, when it’s plugged in, my stream and studio monitors automatically become MONO.
It automatically sums the left and right channel on everything… I just want it to sum the output to the transmitter.
What’s the easiest way around this?
Greg_E
Total posts : 0The best way would probably be to get an audio DA (distribution amp) with isolated outputs. That way you could (in theory) ru one set of outputs into a dead short and not effect the other outputs. I haven’t found a passive device that I like yet, but maybe someone will come up with something.
12vman
Total posts : 0An isolation transformer like one used in car stereo applications for ground loop issues would work. When you combine the lines after the transformer, They won’t be shorted togather at the source..
Greg_E
Total posts : 0I tried that with some Altec audio transformers, no luck at all. It did not provide the amount of isolation that I needed. I forget the model number of those transformers, but they are the expensive model 600:600 ohm and 20-20K reponse.
radio8z
Total posts : 0The transformers won’t work because they pass the audio signals in both directions.
You might try this which worked for me. It depends on the output impedance of your source being low impedance (hundreds of ohms) and the input impedance of your load being high impedance (47 k or so). Connect a 47 k resistor in series with the center conductor of the L channel, and another 47 k resistor in series with the center conductor of the R channel. Connect the other ends of the resistors together and connect this junction to the center conductor of the load (your transmitter audio input). Connect all the grounds (outer shells of the plugs) together. If it works then you can get some RCA panel mount jacks, wire the resistors to them, mount them in an Altoids tin and you will be good to go.
There will be a little cross mixing but I doubt you will hear it.
Another way involves an operational amplifier summing circuit but this requires dual power supplies and is much harder to build. If available, the distribution amp. suggestion of Greg’s probably would work.
Neil
Greg_E
Total posts : 0The resistors will work if you increase the value to more than 50K, probably around 100K. I tried this for another mixer I had to make, and the audio level was far too low for me to use. Even at 10K the signal was too low. Now maybe your transmitter has enough gain in the audio section to make up for the loss. If it does, then you will be all set. At any rate it’s ridiculously cheap to test. There are also other active devices that you can buy, but I’m not sure of the cost. Check Whirlwind or Benchmark to see what they might have for active (or passive) summing devices.
If you decide to build and active device, there are many good op-amps that can be powered with a single ended power supply. And if you are dealing with unbalanced audio, then the cost should be pretty low.
radio8z
Total posts : 0Greg,
How do you know the resistors will work if you increase them to 100 k which implies that the 47k won’t? Since you don’t know, as neither do I, the input and output impedances in his system it appears that we both are making educated guesses and I suppose we can honestly differ in our opinions.
My advice is to try it. Adjust from there if it doesn’t work. The 47 k resistors, if they work, will result in less attenuation than the higher resistance components.
True, the loss in signal will have to be recovered with the transmitter gain. This may or may not work but it is worth a try. By the way, this resistor mixer is very similar to that used in the SSTRAN AM transmitter where it works just fine.
Regarding the single supply op-amps, I assume, perhaps incorrectly, that your are thinking of the Norton amps which I have found can cause problems unless the audio signal is properly DC biased which really complicates the design. Perhaps that is a topic for another time.
Neil
Greg_E
Total posts : 0With the smaller value resistors, you still get that little bit of audio going back the other way. I remember trying somewhere around the 47K, so 50 is indeed just a guess. And really so is 100K. In theory 10K should do the job, but hasn’t worked for me. I would start higher and work down to lower than start the other way around.
As far as the op-amps, many are just as happy running single ended supplies as dual, the key is to have the differential voltage with the operating range. If the range is 12 volts, it doesn’t care if you have +6 and -6 or a full +12 to ground. Some of the older designs did want to have the audio biased to a DC level, but many of the newer designs don’t really care. In other words you can use gorilla engineering to get the job done. It may not be pretty, but it works.
kk7cw
Total posts : 0To convert Stereo to mono, a 10K resistor in the high side (+) of both left and right feeding a 10 K resistor high side (+) of an unbalanced mono audio feed will only drop the audio level by 6db.
If your mixer has 0dbu audio output or better, you should have enough audio to modulate the transmitter.
If your transmitter uses balanced audio, you will need to build the same network for the low side of the line output.
Also, many mixers have balanced audio ouputs. That means you will also have to convert the balanced output will need to be converted to unbalanced inorder to properly interface the mixer with the unbalanced audio input of the transmitter.
Knowing the output impedance of the mixer is key to being transmitter friendly audio. If the output is 600 ohms, then a 10K ohm input will cause the audio output to act like the audio level has been elevated. It involves the loading of the output amp of the mixer. Impedance matching of both devices will allow for better quality audio.
My AM transmitter is 600 ohm balanced audio input. The Mackie mixer has a 1K balanced audio out impedance. So, the resistive network above has served my purposes.
Marshall Johnson, Sr.
Senior Pastor, President
Rhema Christian Fellowship, Inc.Rhema Radio – The Word In Worship
AM 1660 – FM 93.5
http://www.rhemaradio.org
Greg_E
Total posts : 0But are you using that same output to also feed a stereo device and keep proper stereo separation? That’s where I’ve had the issues. When I spilt the signal to another stereo device, and to the mono summing network, then the stereo path suffers.
If keeping a stereo signal is not important then you can use around 100 to 120 ohm resistors to make the network, this will keep the signal level approximatly at the correct level.
For active devices, I just looked for a couple things and found this:
http://www.opamplabs.com/va14sum6.htm
http://www.opamplabs.com/4s4x10.htmI’m not sure if the second one will do the job, but if it does the price is right.
radio8z
Total posts : 0To the original poster, you have received many suggestions here. Don’t get too wrapped up in the technology. Just try what looks reasonable and see if it works. I would like to know if our suggestions were helpful.
Neil
scwis
Total posts : 0
Great point Neil.I’ve used this circuit (adapted from THIS ARTICLE) to combine stereo output into a mono input with a passive circuit.
I have also used resistors of lower Ohm values for inputs and outputs lower than line level.
1/8th watt resistors seem to work OK at low audio power levels
The circuit seems to work equally well as a splitter or a combiner.
Experimental broadcasting for a better tomorrow!
Greg_E
Total posts : 0I tried something similar in my Kluge Box that combines 3 1/8 inch stereo sources to a single stereo source for use with BSI’s Simian automation. It might have been the sound card I used, but the level got so low that I had to change to a lower value. I think I ended up with something around 250 ohms as a good compromise between level and what should be proper engineering. I tried something similar with a stereo to mono where the stereo side still needed to feed a stereo device. This didn’t work so well because the stereo side lost a lot of separation.
For stereo to mono where you are not trying to protect the stereo side for other devices, these types of passive devices work really well, especially considering the price.
radio8z
Total posts : 0The reason you want to use a high resistance in the network is that the stereo separation depends on low source impedance and high mixing impedance to keep the source channels separated. There will always be some mixing with these resistive networks and it becomes a matter of experimentation or calculation to tradeoff the signal attenuation in the mono channel against the loss of stereo separation in the stereo channels. Higher mixing resistance equals more separation but less mono signal. A quick off the cuff calculation shows that with 100 ohm source Z and 47 K mixing and mono load resistances the stereo cross channel mixing will be below -57 dB. This also shows that the attenuation of each stereo channel signal into a mono load of 47 k will yield a loss of 9.5 dB for each channel but since the two channels add in the mono circuit the overall loss is 3.5 dB. This can easily be compensated if the mono circuit has reasonable gain.
This does not apply to a 600 ohm balanced system in which case a new set of calculations would be needed and it is my guess, without having done the calculations, that if the input and output Zs are 600 ohms, the mixing vs. mono signal loss will be unacceptable.
My experience is that using a sound card and 47 k mixing resistors in a single ended low output Z, high input Z system works adequately. Your results may vary.
Neil
Greg_E
Total posts : 0Maybe that’s my problem. Everything I do is balanced audio, though very little is actually terminated into 600 ohms. The trend is to leave it unterminated which gives better headroom, better high frequency response, and lower power consumption. Most devices are now some sort of active buffered high impedance inputs and active balanced outputs.
kk7cw
Total posts : 0Balanced 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.
Paul Bilek
Total posts : 0You 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
Paul Bilek
Total posts : 0Everyone 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.
12vman
Total posts : 0These 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..
Thelegacy
Total posts : 0Here 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.
Would this work? https://www.sweetwater.com/store/detail/YXF119–hosa-yxf119-6-inch?mrkgcl=28&mrkgadid=3274408774&rkg_id=0&product_id=YXF119&campaigntype=shopping&campaign=aaShopping%20-%20Core%20-%20Accessories&adgroup=Accessories%20-%20Cables&placement=google&adpos=1o2&creative=249895767051&device=c&matchtype=&network=g&gclid=Cj0KCQjwqPDaBRC6ARIsACAf4hCc6XbO21-THkrQjlyA-_98lDoGpkJLOjkG8l4yy9tSOF7l_2QaOeIaAn1cEALw_wcB
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.
🙂
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