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Author Topic: Wiring up a stereo cell Matthew Taylor Expert Film Handler Posts: 186 From: Essex, UK Registered: Mar 2004 posted 05-15-2004 03:58 PM                     I am attempting to wire up a stereo cell into my portable projector. At the moment it is mono and has an XLR connector to hook it up to the amps. I would like, if possible, to still use that XLR connector and the 2 core+shield cable that I have. The problem is if I do that, I will have to use the shield as a 'common' and the two conductors in my cable as the Left and Right signals. This will leave me without a shield to connect at the pre-amp end. Would this cause hum?  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 05-15-2004 07:32 PM                       Using the shield as the solar cell common will almost certanly add hum and noise to the signal. You should switch to a 4 pin XLR.  |  IP: Logged John Anastasio Master Film Handler Posts: 325 From: Trenton, NJ, USA Registered: Sep 2000 posted 05-15-2004 08:18 PM                        Sam's right....it's going to hum like crazy. XLR-4's are readily available from any electronics or A/V supplier. 4-conductor shielded cable can be found at any home improvement warehouse for about 30p per foot.  |  IP: Logged Frank Angel Film God Posts: 5305 From: Brooklyn NY USA Registered: Dec 1999 posted 05-15-2004 09:29 PM                        Or go the other route -- come out of the soundhead with two standard 3 pin XLRs and use two standard, shielded single pair audio cables to the processor. That's what we've done in all our theatres. Mark you cables clearly.  |  IP: Logged Michael Schaffer "Where is the Boardwalk Hotel?" Posts: 4143 From: Boston, MA Registered: Apr 2002 posted 05-16-2004 01:25 AM                        Correct me if I am wrong, but don`t have most solar cells unbalanced outputs anyway with just L/R/G? I had this problem recently when installing a reverse scan reader - there were only three connections available on the sound head even though a 2-pair shielded cable went from there to the processor. The L and R of the solar cell was connected to L+/R+, the solar G was coneected to L-/R- tied together, the shield was connected only at the processor`s G. There was no noticeable hum, but it didn`t work out for the reverse scan reader. Since the cable din`t reach to the soundhead terminals, and I didn`t want to splice them inside the projector, I ended up pulling all new wiring to the processor.  |  IP: Logged Peter Hall Master Film Handler Posts: 314 From: London, UK Registered: Dec 2000 posted 05-16-2004 10:09 AM                        We always use 5 pin XLRs, retaining the pin config for mono, eg 1 screen (n/c at projector) 2 L+ 3 L- (common with 5 R- if wiring to a cell) 4 R+ 5 R-. This way if you ever upgrade to a basement reader which continues the screen straight to the preamp all wiring is in place. We'd rather install SRD heads however at the moment we are having delays getting hold of the best SRD readers on the market - thus we have the time to participate in forums like this ! I guess they are worth the wait !! (Subtle nudge Mr C !!)  |  IP: Logged Sam D. Chavez Film God Posts: 2153 From: Martinez, CA USA Registered: Aug 2003 posted 05-16-2004 11:35 AM                       Peter, I also only have time for these forums because I'm juggling which of 150 orders to fill first. Judt kidding! I agree the 5 pin approach is better for future upgrades.  |  IP: Logged Demetris Thoupis Phenomenal Film Handler Posts: 1240 From: Aradippou, Larnaca, Cyprus Registered: Apr 2001 posted 05-17-2004 01:23 AM                     Why bother with all the technical connections Use Connecting BLOCKS!!!!!! Or even better some scotch tape and don't even bother to solder it. That will give you a perfect FULL Humming sound!! D  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-23-2005 02:16 PM                     Michael they are balanced in the sense that the common of the cell (black wire) isn't ground referenced So L+ is balanced in respect to the common black wire and R+ is balanced to the common black wire of the cell  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 02-23-2005 02:36 PM                     If I saw an XLR connection on a piece of equipment I would assume that it is a balanced output. (Or input, as the case may be.) Since a plain solar cell is not balanced, if you plugged it into a sound system that was expecting a balanced input, you would get all kinds of noise and just plain crappy sound to boot. My sound board (at work) doesn't really care if the inputs are balanced. It's better if they are but the system will work at a minimal level. Just make damn sure you keep the polarity straight! Pin #2 is HOT in an XLR connector. Pin #3 is the SHIELD. Don't get those wires crossed! Some sound systems have "phantom power" That means there is 48 volts going through the line. (Used to power condenser mics, etc.) Wire the thing up the wrong way and you could turn your equipment into quite an efficient smoke generator! I would build a small preamp with balanced outputs which has two 3-pin XLR connectors and embed that in the projector. If there's only room for one XLR I'd make it a 4-pin then solder up a "Y" adaptor that ended up with two 3-pin XLRs. If you are not going to make the outputs balanced I would not use XLR connector(s). Make it a 1/4 inch stereo phono plug or something. That way people won't acidentally connect things up the wrong way.  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-23-2005 07:04 PM                     Randy said "Since a plain solar cell is not balanced, if you plugged it into a sound system that was expecting a balanced input, you would get all kinds of noise and just plain crappy sound to boot." I would like to know who says a solar cell isn't balanced and how is it ground referneced since the silicon ship is mounted on an insulator there is no signal that is ground referenced  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 02-23-2005 07:38 PM                     It may not have a reference to ground but the black wire is common between the two cells. You don't have common mode rejection between the "hot" and "cold" wires because the signal isn't equal and opposite. Do you? I thought that was the main reason for using balanced lines. Is it not?  |  IP: Logged Scott Norwood Film God Posts: 8146 From: Boston, MA. USA (1774.21 miles northeast of Dallas) Registered: Jun 99 posted 02-23-2005 08:16 PM                        By "connecting blocks," do you mean "terminal strips"? If so, what's wrong with using them? The Dolby manual indicates that this is how one should connect the cell to the shielded cable that runs to the processor. Soldered connections (with heat-shrink tubing) seem to be more popular, but I'm unclear as to what is wrong with terminal strips (if anything).  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 02-23-2005 08:45 PM                     Actually it is it also has a very high CMR which is why it has to be connected to the preamp in a balanced fashion  |  IP: Logged Randy Stankey Film God Posts: 6539 From: Erie, Pennsylvania Registered: Jun 99 posted 02-23-2005 09:41 PM                     So, assuming it isn't otherwise grounded, a solar cell is a naturally balanced system? I'll have to remember that!  |  IP: Logged

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