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Author Topic: How to interface line-level audio to amps 40 ft away John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 07-06-2008 06:09 PM                     Remember that UL-listed devices with 2-prong plugs are frequently better devices than those with 3 prongs. The UL standard for leakage current on 2-prong devices is significantly more strict. It's only when the leakage current exceeds some threshold that manufacturers add the third prong. Phil's constraints seems really weird. He wants to do it on-the-cheap, but doesn't want to use transformers and is considering much more expensive CAT5 transports? Is this for the home screening room, Phil? --jhawk  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-06-2008 08:35 PM                     The point John, is that with consumer grade equipment (or crap) is that they ARE 2 prong devices. Everything that touches their low-side can affect the reference...including a Cinema processor, that will be grounded, 45-feet away. UL is concerned with safety...we are talking about noise immunity over the extended run for an unbalanced input. Steve  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-06-2008 08:57 PM                  Yes jhawk, this is for my home screening room. Let me clarify the issue from my POV: My 1st choice was to "do it right" and use Jensen Transformers and Belden 8451/9451 cables. But: DIN-PC $135 x 6 = $810 ...way too expensive! JT-11P-1 $70 x 6 = $420 ...still too expensive! JT-10KB-D open frame 4:1 xmfr $60 x 6 = $360 Not sure about the open frame thingie...might be the best solution. The Calrad baluns are transformers and would provide ground/hum isolation. The specs look like they have respectable performance and are about $60 pr. But JFC! Almost $400 for the interface? At that point, I may as well do as Brad suggested and buy the QSC amps. Side note: There is a 1.5" steel flex conduit between the locations and a #12AWG insulated common ground wire. In some pile of stuff around this joint I call home, I have 10ea of Jensen-in-a-can input xmfrs 600-ohm to 10k...just don't know where. Oh, and FWIW, Brad is right... I am a cheapass. And BTW: No matter how cute, I've NEVER tipped ANY pizza boy more than $60 on a $18 pizza!  |  IP: Logged John Hawkinson Film God Posts: 2273 From: Cambridge, MA, USA Registered: Feb 2002 posted 07-06-2008 09:24 PM                     I probably should have made a more narrowly-scoped statement. In UL-listed devices, in a 2-prong device (Class II), leakage current is limited 0.75 mA (aka 750 MICRO-amps). For a 3-prong device (Class I), the limit is 5 mA (6x as much). Three-prong devices are frequently those that cannot meet the strict requirements for two-prong devices. So it's a misconception that "three-prong devices are better." Is this directly applicable to the question of "Which crummy unbalanced consumer device is crummiest?" I'm not sure. Yes, everything that affects the low side of the signal can affect the noise floor, but just because there is a third prong does not mean that there is no connection between chassis ground and neutral (yes, there is no direct connection. But noise can run across caps, etc., etc.), or that the ground of an unbalanced signal wire is less noisy. Bill Whitlock (at Jensen) gives a good explanation of this in his talk...it does not seem to be in the notes associated with that talk, alas. (There is some peripheral discussion around page 9 of his Understanding, Finding, & Elminating AV Ground Loops, which is quite a good discusson of grounding-related issues.) ------------------ So Phil: What happens if you Just Do It? Do you actually have a problem? --jhawk  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-06-2008 10:38 PM                     Phil, the BEST "bang-for-the-buck" audio transformers are by RDL. Not necessarily the "best" but when one weighs price and performance...they more than do the job. For your application, there is the TX-1A (which is quite handy for one to lower a +4dBu to -10dBV as it has a trim on it)...the TX-10B is a straight bridging 10K transformer. These are on the "cheap" side of things but are flat 20-20KHz with only a +/- .5dB. THD is less than .05%. In short, they are good. If you want the frequency response down to .1dB 20-20KHz then they have that too with the TX-AFC1F. However, they are going to creep you back up into the Jensen price range again as they are direct competitors. If interested...visit www.rdlnet.com We do sell them so I can speak to their quality. Steve  |  IP: Logged Tim Reed Better Projection Pays Posts: 5246 From: Northampton, PA Registered: Sep 1999 posted 07-06-2008 10:55 PM                       I'll second the RDL suggestion. I've used their "hum-killers" to great satisfaction.  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-07-2008 05:36 PM                  Steve, I totally forgot about RDL's stuff even though I've used their products many times in the past. I will take your suggestion to use the RDL TX-1A. It looks like a good solution at $30 ea. Thanks!  |  IP: Logged Brad Miller Administrator Posts: 17775 From: Plano, TX (36.2 miles NW of Rockwall) Registered: May 99 posted 07-07-2008 07:06 PM                     Told you he was cheap!  |  IP: Logged Phil Hill I love my cootie bug Posts: 7595 From: Hollywood, CA USA Registered: Mar 2000 posted 07-07-2008 07:17 PM                  Hey Grand-Poopie-BAH, NOT cheap but frugal! HA!  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 07-07-2008 08:59 PM                     NO! Parsimonious! That's it.  |  IP: Logged

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