I think when I made the original post it was late & I was tired!! I work in broadcasting and use the 111C coils often in long analog audio runs for remote broadcasts. I do agree that transformers would be better than active balanced devices.
The active devices are easier to deal with for short audio runs in a production room or control room when you have to interface with something that is consumer grade un-balanced. But for the long runs I definately agree that 111C coils are the best option. ------ Original Message ------ Received: Sat, 27 Feb 2010 01:24:49 PM PST From: "Oz, in DFW" <li...@ozindfw.net> To: Repeater-Builder@yahoogroups.com Subject: Re: [Repeater-Builder] LOOONG audio runs > I vigorously second Jeff's recommendation. This is an application where > iron is still the right answer. > > Make sure you use twisted pair. Station wire like that use to wire > houses is often not twisted. Ethernet cable is good and has a high twist > pitch - better for this application. > > Repeat coils are the classic answer. Here's a hint about what you are > looking for if you don't already know: > > http://users.snip.net/~mrbibbs/gearpix/Western_Electric_Repeat_Coils_4040.jpg > http://users.snip.net/~mrbibbs/gearpix/Western_Electric_Repeat_Coils_4042.jpg > http://oldphoneguy.net/Coils1.jpg > > Jensen's stuff is really nice, but you'd be paying a premium price for > performance you can't use. > > If you can't find an old set of repeat coils, most small audio > transformers with reasonable turns ratios will do the job fine. > Reasonable in this case is probably less than 4 or 5:1, though 1:1 would > be best. > > I'm not sure where you are, but if you can't find anything easily, the > coupling transformers out of **OLD** modems (1200 Baud or less) are > likely suspects. > > On 2/27/2010 10:32 AM, Jeff DePolo wrote: > > > > > > > > > > I'd definately go balanced, but I'd use transformers rather than active > > balanced devices. Decent transformers (even audiofile-grade Jensens) would > > still cost less than Henry matchboxes (or anyone else's active converters > > most likely), and be more reliable. Back in the old days, Western Electric > > 111C "repeating coils" were supplied by the telco for program audio lines. > > Look around broadcast transmitter sites and old studios, you'll probably > > find a few nailed up to the telco backboard that the LEC no longer has an > > interest in maintaining ownership of... > > > > The common mode rejection of Henry matchboxes isn't all that great, I've > > tested them. > > > > If you can, keep the audio level high on the sending side (I think 111C's > > were good up to close to a watt at 600 ohms!), and pad it down on the far > > side's secondary as necessary to maximize S/N. > > > > --- Jeff WN3A > > > -- > mailto:o...@ozindfw.net > Rich Osman N1OZ > POB 93167 > Southlake, TX 76092 (Near DFW Airport) > > > > > > >
