audio signal on cat5 - Page 1
Forum section: electronics / projects

author: jk96
author_rank: Newbie
timestamp: November 07, 2013, 08:46:41 pm
content: I have 40 audio power amplifier in a campus i need to feed same audio to all amplifiers from MIC or CD Player .the distance between each amp 20 to 30 meters. Can i use CAT5 cable to transmit audio using DRV134 and INA134 at amplifiers side.any suggestions or ideas appreciated.

author: walshms
author_rank: Regular Contributor
timestamp: November 07, 2013, 09:06:08 pm
content: Probably not going to work over 1000 meters... if you read the data sheet, things fall off considerably after only 150 meters. They also recommend a shielded Belden cable.If you design a few repeaters and configure it in a star topology, you might get away with it if you keep all of the run lengths down, but don't expect high quality sound at the other end.

author: dannyf
author_rank: Super Contributor
timestamp: November 07, 2013, 09:11:25 pm
content: QuoteYes, you can.

author: tszaboo
author_rank: Super Contributor
timestamp: November 07, 2013, 09:12:32 pm
content: In theory, you can. It is possible, Cat5 is just 8 pieces of copper. However. You have to take care of the ground loops. Different electrical outlets can be on different phases. Also, even in static configuration, the system might work, it might take one lightning hundreds of meters away to kill it. We are talking about 1Km cable. Capacitive loading will be a problem. There might be even reflections.It is possible, but I think it needs more consideration than soldering the datasheet example it on breadboard and good to go.

author: jk96
author_rank: Newbie
timestamp: November 07, 2013, 09:23:30 pm
content: Thanks for all replysI dont need to play high quality music.I need to feed MIC speech or recorded speech.can i expect a average quality sound using CAT5 cable 1 DRV134 & 40 INA134.

author: walshms
author_rank: Regular Contributor
timestamp: November 07, 2013, 09:25:56 pm
content: Quote from: NANDBlog on November 07, 2013, 09:12:32 pmWhat he said. Capacitance will kill you on this. Even if you made every drop a repeater, the signal quality at the other end will probably be useless without some signal conditioning.Best bet is to made a call to TI and see what they say.

author: ddavidebor
author_rank: Super Contributor
timestamp: November 07, 2013, 09:28:25 pm
content: Use some typeof digital conversion

author: walshms
author_rank: Regular Contributor
timestamp: November 07, 2013, 09:33:29 pm
content: Much better idea.

author: jk96
author_rank: Newbie
timestamp: November 07, 2013, 09:37:36 pm
content: any ideas on digital control audios.

author: walshms
author_rank: Regular Contributor
timestamp: November 07, 2013, 09:42:15 pm
content: Offhand, no, but you might consider doing something like using an ADC to make the signal digital, then use RS485 to distribute it, and a DAC at each drop to convert it back.Just watch your unit loading on the 485 layer and be sure that you use or design in repeaters as needed.Either way, you're going to have to do some testing to see what works.

author: tszaboo
author_rank: Super Contributor
timestamp: November 07, 2013, 09:45:20 pm
content: Send AES3, that can go up to 1Km. I have no idea if it is multidrop or not. If the cost of cabling is an issue, than use some other physical layer like RS485 to send SPDIF through, with repeaters. Read this:http://www.maximintegrated.com/app-notes/index.mvp/id/3884

author: HackedFridgeMagnet
author_rank: Super Contributor
timestamp: November 07, 2013, 10:04:04 pm
content: Often Audio Line transformers are used in these distributed Audio situations. You could consider stepping up the voltage for long runs and use CatV for the short runs or after a step down on a long run.Also you have 4 pairs in each cable so you can run part of any star configuration within the same cable and branch it out at the last moment.And drive each pair with a separate driver.Transformers also solve alotof the headache of ground loops and don't actually sound too bad. Its normally the siren cone driver that sounds bad.

author: David_AVD
author_rank: Super Contributor
timestamp: November 07, 2013, 11:50:02 pm
content: I agree. Pushing the audio around at 100V (70V in USA) line level and dropping it back down (via a transformer) at each amplifier is a sensible way to go.

author: calexanian
author_rank: Super Contributor
timestamp: November 08, 2013, 12:18:02 am
content: I agree as well, however you do not need to go up to 100 volt line. BTW 75 and 24 volt line are more common. If you are not too concerned about freq response I would use some of those Xicon cheapy audio matching trnasformers from Mouser on both ends and you will most likely be good. those things are good for about 100hz to 10k, good enough for casual listening and if you drive them with a low impedance rock solid voltage source that can compensate for the low X of L on the low end you can extend that low freq response down a bit. Or drive at 12 volts ac average audio level right onto the catV and use those 1.5K to 600 ohm transformers at the other end. they are a couple bucks a piece. My two cents.

author: trackman44
author_rank: Regular Contributor
timestamp: November 08, 2013, 12:48:44 am
content: How about 40 Raspberry pies in each amp box. Program each one of them to receive streaming audio and output them through the audio jack? You'll also need to get 40 RJ45 connectors wired to the CAT5 cable. I know, It's a crazy idea and would probably break your budget, but I posted it here as a possible solution.WillP.S. One more Raspberry pie and RJ45 connector as the host and input to the MIC.

author: nctnico
author_rank: Super Contributor
timestamp: November 08, 2013, 01:17:06 am
content: Quote from: HackedFridgeMagnet on November 07, 2013, 10:04:04 pmI agree. I'd use transformers to connect the audio into the twisted pairs. Plain (cheap!) telephone transformers will do just fine; I've used lots of them for all kinds of analog communication equipment. No need to go digital.

author: NiHaoMike
author_rank: Super Contributor
timestamp: November 08, 2013, 03:06:11 am
content: Quote from: walshms on November 07, 2013, 09:25:56 pmIt's a transmission line. Terminate it properly and it will not appear capacitive.Twisted pair has been used to carry telephone signals for many decades. It can be made to work very well. Transformer coupling is an obvious solution to the ground loop issue, but a differential amplifier (plus transient protection) also works. Just make sure there's a path to ground at one point (most likely the sender side) so charge cannot build up. Use a common stereo amplifier (connected as BTL) to drive the line at a relatively high voltage (a few tens of volts peak, maybe using a matching transformer) in order to keep the SNR up.

author: David_AVD
author_rank: Super Contributor
timestamp: November 08, 2013, 04:50:09 am
content: Quote from: calexanian on November 08, 2013, 12:18:02 amI've never heard of 75V and 24V audio line levels, only 100V, 70V and 50V in PA applications.

author: Zero999
author_rank: Super Contributor
timestamp: November 08, 2013, 01:54:40 pm
content: Quote from: NANDBlog on November 07, 2013, 09:12:32 pmImpedance matching will solve that.

author: tszaboo
author_rank: Super Contributor
timestamp: November 08, 2013, 05:54:36 pm
content: Quote from: Hero999 on November 08, 2013, 01:54:40 pmAs I said "it needs more consideration". The Impedance is 100 Ohm for UTP, I dont think that you can just drive it with anything simple for 100V if you terminate it.

author: macboy
author_rank: Super Contributor
timestamp: November 08, 2013, 06:26:44 pm
content: Quote from: jk96 on November 07, 2013, 09:23:30 pmYou will be much better off with 40 DRV134, not 1. One will not be able to drive the capacitance of 40 parallel pairs of cable. The load is much too high.Also with long lengths of cable, don't forget that they act as antennae. So use ferrites on each end, and consider some type of TVS devices to help dissipate any spikes causes by lighting or high powered equipment switching on/off.

author: calexanian
author_rank: Super Contributor
timestamp: November 09, 2013, 01:36:29 am
content: Quote from: David_AVD on November 08, 2013, 04:50:09 amMy rusty brain again. 70 volt. 25 volt came about to get you under the 40.2 V peak or 30VRMS UL listing threshold. Technically you would need an electrician to install a 70 or 100 volt system. I bodged my numbers. I have noticed people getting very upset with me for not being precise.. Kinda takes all the fun out of this.

author: techm
author_rank: Newbie
timestamp: December 06, 2013, 02:50:45 pm
content: I have run audio successfully through Cat5 with minimal losses. The trick is to convert the unbalanced audio signal to balanced (i.e. three wire, like a microphone). The extra wire cancels out noise quite effectively. When I did this I was able to run sound 100ft using Cat5 and it sounded fine.What I did was buy (gasp) an unbalanced to balanced converter (it's a passive converter and bi directional, probably just a transformer, i'll have to find it and pop it open) which can be picked up from any pro audio shop. I then punched the wires into a RJ45 modular jack. Make a twin of the jack at the other end and another converter to convert it back to unbalanced.Distributing it is more difficult. What you will also need is a balanced line driver/distribution amplifier with 40 outputs so you get equal and full signal to all of your amplifiers. I remember looking into this a while ago and to buy them is expensive, but to build is just a matter of wiring up a bunch of opamps. I don't have the schematics handy, sorry. Then you will just need a passive converter at each of your amps. I've seen balanced line driver ICs out there as well - above is mentioned the DRV134.good luck!

author: dfmischler
author_rank: Frequent Contributor
timestamp: December 06, 2013, 03:52:19 pm
content: Is this a homework problem? Or does it have to be useful?If this was the only wire on campus then all these ideas are better than mine. But here I would just piggyback on the existing campus ethernet and useSIP for pagingwith the existing VOIP phone system. That also means people could call an extension for paging over the whole campus, or other extensions for parts of the campus.http://www.voipsupply.com/paging