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Author Topic: How to interface line-level audio to amps 40 ft away Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-05-2008 03:32 PM                  I want to interface a CP-650 to high-impedance, 10k input, amplifiers located about 40ft away. Not especially interested in active or transformer 10k to 600 ohm balanced cable solutions. Does anyone have experience with the cat5 interface devices listed in the below link? (Note: Link is a pdf page) http://www.calrad.com/download/Audio%20Passive%20Baluns.pdf  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 07-05-2008 04:23 PM                        One possibility is to use the "computer link" as espoused by Crown or maybe QSC. I believe there is also a "digital snake" available through pro audio stores. If level is high enough, you might be able to just "do it" using a conventional balanced line snake as well. I have done so in non-cinema applications. HF rolloff, if present, can well be dealt with during normal EQ. Louis  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-05-2008 04:29 PM                     Phil, I recently used the CAT 5 to VGA devices for a remotely located D-Cinema monitor but can't speak for the audio stuff, I suppose you try it and if it bombs or not. If it does send it back for a refund. The VGA stuff worked pretty good though. I rescued a case of(100)Jensen trannys someone left by the trash a couple of years ago... Would be happy to send you 6 of them if you want to go this route. Will dig em out and see what P/N they are. Mark  |  IP: Logged Richard Fowler Film God Posts: 2392 From: Ft. Lauderdale, FL, USA Registered: Jun 2001 posted 07-05-2008 05:00 PM                     I used the Gefen brand equal for running audio and video for many rentals and visiting road company shows. They work well with the weak point being low quality Cat5 and connection point from those "phone plugs on steroids". I prefer snakes but I have had issues with some poorly contructed or maintained breakout units. + or - to everything  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-05-2008 05:27 PM                     Just because it is high impedance balancing isn't an issue most pro amps have balanced inputs and the cp650 has balanced outputs so I would use some star/quad type cable arrangement  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 07-05-2008 05:46 PM                       quote: Mark Gulbrandsen Would be happy to send you 6 of them He's probably wanting to get it done THIS year...  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-05-2008 05:52 PM                  Yes Gordie, I'm well aware of all that... The amps have ONLY 10k inputs. Pioneer VSX-92TXH. AND, there is NO option for another amp! HA! quote: Tim Reed He's probably wanting to get it done THIS year... Oh Boy! I can't wait to see what our Grand-Poopie-BAH has to say about that...  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 07-05-2008 08:04 PM                     This should not be a problem. I would not bother with the cat5 stuff, BTW the cat5 interfaces are transformers. Good old 8451 should be OK. You could put a 604 ohm resistor (nearest 1% value) across the input of the amp.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-05-2008 10:00 PM                     Oh Phil...connecting professional equipment to consumer crap.... Foget the Cat 5 stuff...as another has pointed out...all you are doing using a transformer to use crappy twisted pair cable. The CP650 is low impedence active balanced out and they have a properly balanced output stage (not just a stupid inverting op amp that would be shorted out if you connected unbalanced). If you have 1V on the output of the CP650 and tie "-" to ground...you still have 1V of output just now unbalanced as the entire signal will be above ground. There will be nothing wrong with the signal coming from the CP650 and it will make it much farther than a mere 45-feet without any help. The problem lies with your consumer A/V receiver. The problems include...unbalanced inputs (not so good for noise immunity)...no good ground reference (note the lack of a third prong on the AC line). The CP650 will ground via the AC input and the signal on its output will travel just fine using the CP650 as the ground reference. The smartest solution is to use a bridging transformers on the inputs of the consumer input (10K - 10K)...this will present a balanced input and isolate the CP650's real ground and the multitude of grounds that the A/V receiver may be receivng (via antennas, cables and what ever else will contaminate the ground system...including the display device). However, you may get lucky in that your grounds will be close enough in potential such that you will be able to connect the CP650 straight up. I would run a ground reference line while pulling the cable (not one of the shields...let them do their jobs of noise immunity) of 18awg or bigger so you may bond the A/V receiver to the CP650 to ensure they are at the same ground point. If you get hums (video or audio), the transformers are the solution that WILL allow a very stable and good performing system. Again, the Cat 5 solution is a bad one that will not do anything more than what good transformers will do and actually will likely do worse. But first, you can try a straight connection...and then fix it from there, if you find you need to. Steve  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 07-05-2008 11:19 PM                     Phil, for that room you could probably get away with a pair of 4 channel DCA amps from QSC. (I say that assuming you will use "consumer" speakers with a passive crossover built in.) BTW, yes the baluns will work, but the man with the cheese is absolutely correct...just run good quality shielded cable and don't jack with the balun crap. The end result will be better...and cheaper. I wouldn't run out and buy any of the DCA amps just yet. You won't be needing them until about the time QSC changes their amp line and can then get them at a discount!  |  IP: Logged Louis Bornwasser Film God Posts: 4441 From: prospect ky usa Registered: Mar 2005 posted 07-06-2008 06:45 AM                        Amplifying on Steve's post: Run an extension cord to power the amps and use the same outlet as the cp650. This will eliminate multiple ground reference points in the building. Louis  |  IP: Logged Jack Ondracek Film God Posts: 2348 From: Port Orchard, WA, USA Registered: Oct 2002 posted 07-06-2008 07:31 AM                        Just tossing an aside in here... Phil started his question out by eliminating most options, then focusing in on what he probably was really asking in the first place... how to hook his amplifiers up with Cat-5. When Paul Allen's Cinerama was remodeled, they installed a new sound system over the original. Much of the old 'booth-to-stage' wiring was kept, and they maintained separation between the day-to-day sound system and the Cinerama electronics. The new setup links the booth to the rack rooms with Cat-5, and the channels are multiplexed, not merely transformer balanced. Don't remember the brand of equipment they used, and it's now something like 15 year-old technology, but I've never heard anyone mention problems with it. I suppose you'd have to study the internal latency of that kind of equipment, especially with the analog sound. The digital stuff you could adjust out with the delay settings. The other question would be how prepared you'd be if something went wrong with the link equipment. Seems a lot of technical overhead, just to replace good-old shielded pair.  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-06-2008 07:52 AM                     Jack, don't confuse any old Cat-5 solution. It is likely that if they were doing DSP processing and extended runs, they were running "Cobranet". That is something entirely different. It is a relatively old standard and very stable. BUT you are not running analog audio on it. You are running propritary digital audio and quite a few channels at that. Since Cobranet is a standard, of sorts, you will find multiple vendors that support it. In the Cinema industry, QSC is using it for their "Basis" systems. Since it is a standard, you can even mix and match manufacturers boxes at each end to suit your needs. Again, you are really doing a A/D conversion at one end and an D/A at the other. Generally speaking, people using Cobranet are doing more complex things than just sending analog audio a mere 45-feet. One thing about Cobranet...it is pretty darn reliable and you can get quite a few channels moving about over very small cable (or fiber). Steve  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 07-06-2008 04:33 PM                     I didn't suggest the Cobranet option to Phil since he is a cheapass (except to the pizza delivery boy) and I knew he wouldn't want to throw down the extra money. I have been playing more and more with QSC's BASIS system and I am liking it more and more over a conventional CP650/amplifier setup. The setup and calibration possibilities are far beyond what you will find in the processor.  |  IP: Logged Bruce Hansen Jedi Master Film Handler Posts: 847 From: Stone Mountain, GA, USA Registered: Dec 1999 posted 07-06-2008 05:05 PM                     Does that piece of "consumer crap" (thank you Steve) even have a ground pin on it's power cord? If not, you may not have ground loop problems. Of course, you could always cut off the ground pin, but that is not the "safe" way to do it. BTW, if you check the link Phil provided, these cat5 interfaces are the passive ones that are just transformers.  |  IP: Logged

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