backwater Posted July 28, 2009 Share Posted July 28, 2009 Hi Folks, My current project requires me to run a PA link to an adjacent building and I've hit a snag. I'm taking a line-level feed from the desk, running it around 60m to the adjacent building (using a balanced cable) and into a powered speaker. I would like to put a volume control in to the system as the powered speaker will be mounted some 8 feet from the floor (with the built in volume control on the back). Can anyone suggest where I would get a (preferably) active line-level volume control from? An hour or so on google finds me plenty of speaker-level volume controls but not quite what I need. As a fall back I could use something like a Behringer Xenyx 502 as a mini mixer but I would prefer just a single control. Cost would need to be sub £35 as I can buy the Behringer for that. Any ideas? Thanks Andy :P Link to comment Share on other sites More sharing options...
themadhippy Posted July 28, 2009 Share Posted July 28, 2009 All you need is a dual pot perferable log ,one end of the pot track to the line in,other end to ground,center to your speaker input,repeat for the other side.value of pot 10k or 50k should be fine Link to comment Share on other sites More sharing options...
Chris Beesley Posted July 29, 2009 Share Posted July 29, 2009 This may suit your application... http://www.monacor.de/typo3/index.php?id=8...EN&typ=full Link to comment Share on other sites More sharing options...
backwater Posted July 29, 2009 Author Share Posted July 29, 2009 This may suit your application... http://www.monacor.de/typo3/index.php?id=8...EN&typ=full Thanks for that Chris, Gives me one possible solution, Cheers Andy Link to comment Share on other sites More sharing options...
SPTTRIAL Posted July 31, 2009 Share Posted July 31, 2009 I have just the thing for you, a phonic micro1 preamp, brand new, yours for a tenner. Link to comment Share on other sites More sharing options...
cedd Posted July 31, 2009 Share Posted July 31, 2009 It's not active, but this appears to be the simplest unit going; http://cpc.farnell.com/horizon/555-8462/at...able/dp/AV17469 Link to comment Share on other sites More sharing options...
mervaka Posted July 31, 2009 Share Posted July 31, 2009 that attenuator looks perfect. pot in a box. I don't really understand why it needs to be active? Link to comment Share on other sites More sharing options...
bruce Posted July 31, 2009 Share Posted July 31, 2009 I'd agree, no need for active. However, I have just re-read the original post, and note that it says connection to an adjacent building. This may be at a different ground potential. In addition to the advice above re the pot, I would be ensuring that the screen was not connected at one end, that the system was clearly labelled as such, and that an isolating transformer was used. Link to comment Share on other sites More sharing options...
AndyL Posted July 31, 2009 Share Posted July 31, 2009 All you need is a dual pot perferable log ,one end of the pot track to the line in,other end to ground,center to your speaker input,repeat for the other side.value of pot 10k or 50k should be fineIf the source and destination are both balanced and floating and you want them to stay that way you can still use the dual pot. Instead of connecting the 'bottom' of the track to earth as suggested above simply connect the two 'bottom' contacts of the two tracks together, no connection to earth/screen at all from the pot. The two 'tops' are the balanced input, the two 'wipers' are the balanced output. It is important to pay attention to which is the input and which the output since the impedance across the two wipers becomes near enough zero at minimum volume, useful when it is the output, but not good as a load on your source. Maintain screen/ground integrity by connecting pin 1 of the input and output XLR's to each other only. I've built lots like this over the years and jolly handy they have been too for all sorts of uses. Just add a transformer on one end or the other and you have galvanic isolation too. Link to comment Share on other sites More sharing options...
dbuckley Posted July 31, 2009 Share Posted July 31, 2009 "Adjacent building" probably means "seperate equipotential zone with own TN-C-S bond point" so you probably should be thinking "audio isolating transformer" and absolutely no pin 1 connectivity. If you build such a box yourself then the local side of the transformer could quite happily feed a 10K log pot which could then be fed unbalanced for the six feet from the transformer box to the active speaker. A relatively low cost but high quality suitable transformer is the Neutrik NTL1 which can take line level with reasonable bass content; many lessor transformers will saturate. Link to comment Share on other sites More sharing options...
AndyL Posted August 1, 2009 Share Posted August 1, 2009 "Adjacent building" probably means "seperate equipotential zone with own TN-C-S bond point" so you probably should be thinking "audio isolating transformer" and absolutely no pin 1 connectivity.Good point, you don't really want hundreds of amps of earth current rushing down your audio cable shield from one building to the other. :) That would be a bad thing. If it is a balanced line level connection you don't actually need a screened cable, just a twisted pair. The audio isolating transformer is still very important especially since so much modern equipment has electronically balanced inputs and outputs which, unlike transformers, provide no isolation. Without the transformer(s) you can still get current flowing from one equipotential zone to the other via the two signal wires and the electronics in the source and destination devices. Link to comment Share on other sites More sharing options...
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