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Author Topic: Bi-Amp Stage Speakers Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-23-2006 10:30 AM                     Mark odd you liked the internal crossover in the cp500 as I don't think it had CD horn correction in it (I may be mistaken) I don't like the use of premade cables as I find racks tend to be messy with them  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-23-2006 11:10 AM                     Yea, had great luck with the 500's internal 683 card in the installs I used it in. Although its more primitave than todays x-overs it does offer all the necessary adjustments one needs to correctly align things. It definately has CD compensation and LF delay. Both delay and x-over freq make use of several factory presets or are also user configurable. For what it is and when it was designed its actually quite a versitle card. Of course todays stuff if far more flexible. The toher nice feature if the 683 is that the card also sounds good. I look foreword to trying the 650's interanl card since it offers for the most part the full gamut of adjustments needed. DB cables come in many differnt lengths and can be easily made up to a specific length if needed. Neatness is easily possible with some pre-planning and use of the typical cable trays. Also the flexibility and durability that these cables afford is also very adaptable to slide out equipment. Mark  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-23-2006 11:19 AM                     If you are referring to QSC's method of connecting, then they are indeed HD connectors...they put 15 pins where a typical 9 pin DB connector would fit. There are standard DB15 connectors but those are not typcially used in Cinema. I found the CP500 internal crossover to be wanting and it did not incorporate any screen loss or CD horn compensation. As for HD15 cables...have you done any capacitance tests...you have high-level and low-level cables in the same jacket...very bad idea. As for using discrete crossovers...yes they do introduce extra cabling but I feel I get substantially better control and performance with them to justify the extra cabling. With crossovers at the amps, then the cabling is very much mimimalized. The XC series of crossovers for QSC are flexible enough for many situations. We always make our own cables, regardless of connector on the ends. For this sort of rack, we would use a 6-snake cable like Belden's 1409R to come off of the CP650 and feed the amps. The cables can be premade out of the rack and installed quickly with user removable connectors (XLR or DB25) so that goes quick too.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-23-2006 11:56 AM                     Steve, Actually way back when I worked in television we were concerned alot with excessive capacitance in the cabling at the station.... especially when we constructed the stations new location. But in analog television we were dealing with some pretty high frequencies over some hundreds of foot long runs and at those higher frequenbcies any rolloff did matter and capacitance also affected chroma system phase. Fortunately the line amps (op-amps generally operating in class a ) in todays cinema audio equipment are on the norm extremely well designed and capable of driving extremely low impedances with abnormally large amounts of capacitance. They generally don't suffer any audio range roll off of any sort until get into large amounts of capacitance in long cabling as might happen with back stage located power amps. Indeed todays buffers and line amps are pretty much blind to any normal amounts of it. Unless your using 6 to 8 racks for sound systems and piling in the cable the amount of capacitance in any of the cabling that any of us are using in typical sound racks is so low as to not even matter...the amount we deal with might cause some roll off in freqs above 100 to 250 khz, and thats not necessarily a bad thing. Even Belden 8451, a popular cable, is pretty low... in the mid 30's per foot if I remember correcty and some of the better cables in production today are even less than that. Back about 1977 it was partly a capacitance issue that caused many major broadcasters to switch to Gepco Wire away from Belden when they began upgrading or building new studio facilities. NBC, ABC, and PBS were three of the biggies that switched. There are some Belden cables that are VERY old designs and were fine in the old B&W tv and mono sound days but that today are very unstutable for much of anything. All in all cable capacitance in the normal single rack sound system is irrelevant. BTW, I just checked and 1409R measures at 39 pf per foot... thats a tad bit more than 8451 at 34 pf per foot. If you are really worried about capacitance as you claim you are then you might want to take a look at Gepco's equivelent of 8451 since it is a mere 28pf per foot... Their snakes are also 28pf between conductors, way better than 1409R checks. I've been using their wire for the most part for hard wired racks since I've been in this buisness. For general wire types Gepco's products are almost always far superior to Beldens products. And this from the spec sheet of the LF155 an older obsolete op amp design...... "New output stage allows use of large capacitive loads (5,000 pF) without stability problems" This National Semiconductor Buffer Amp spec sheet is also iteresting, In particuluar page 12 paragraph 1. Figure 24 on page 13 is quite revealing as to just how much capacitance today's op-amp designs are capable of tolerating. Mark  |  IP: Logged Gordon McLeod Film God Posts: 9532 From: Toronto Ontario Canada Registered: Jun 99 posted 07-24-2006 05:24 PM                     regarding the cp500 crossover card Mark G said "It definately has CD compensation" I checked with Lonny and he says it doesn't have CD correction  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-24-2006 06:43 PM                     You're right! I only installed three of them... musta been thinking about some other Dolby board. I thought there was a suitcase link on the board for screen loss in/out. As I said its a pretty basic but good sounding board. It does have LF delay though. I still have the raw and eq'd files in my R-2 folders... will have to dig em out. Hi Lonny! Mark  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-24-2006 06:45 PM                     Mark, I have nothing against Gepco...it is not WAY better than Belden but typically on par with it. Belden is merely my standard cable but not my only source. FWIW...I don't use 8451...for single cable runs, I use 9451. I can't imagine why anyone would use 8451 when they know of 9451...which wires substantially faster (shield is bonded to the jacket so stripping is very clean), is slightly smaller in OD, and is available in all of the colors. As to the capacitance...I was not referring to the conductor-conductor but with the HD systems of the DCA amps you now have high and low levels of the same signal within the same jacket...that is just plain bad design. Additionally, the HD15 terminals on the DCA amps do NOT have the same gain structure as the XLR or phoenix connector inputs...it is quite easy to clip out a DCM monitor but not clip out the amplifier, despite having the amplifier set to WFO. Sorry, no sale. The CP500 did NOT have CD horn compensation unless you called raising the treble compensating for the CD horn. The best CD horn compensation or screen loss is going to come from a proper filter that is matched to the horn...DSP crossovers will typically do this with ease. However, the QSC XC-1 for the MXa amps did a VERY good job on the JBL 4675...the USL XTA-1 also do well with the JBL 4675...it is what happens when you get a product designed specifically to work with another product. BTW...it is the Cat 517 for the CP50 and the CP200 that has the screen loss compensation switches on the output card. Steve  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-24-2006 06:52 PM                     quote: Steve Guttag Additionally, the HD15 terminals on the DCA amps do NOT have the same gain structure as the XLR or phoenix connector inputs...it is quite easy to clip out a DCM monitor but not clip out the amplifier, despite having the amplifier set to WFO. Agreed on the gain structure of the two. Capacitance is going to be so low as to not even matter. It would be inter-cable coupling that I would worry about and with twisted pair cabling in the better quality cables there just has not been any problems since there is a cancelation effect between the pairs. I admit that with cheapo cables it could be a problem. Have not had the clip problem you talk about... If that is the case then QSC needs to take a look at the problem. Perhaps pad down the amp inputs a little more or install a limiter before the monitors power amp. While you might think these are HD connectors and they may be classified as such by the manufacturers I wouldn't consider anything less than 50 pins any sort of HD connection. I think the major broadcasters would disagree with you that Gepco is on a par with Belden. They switched to it after exhaustive tests that indicated that it was vastly superoir. Mark  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-24-2006 07:09 PM                     Believe it or not...the HD15 is the same type of pinout as the standard DB50. That is, a triple row. The HD15 designation is to distinguish it from the standard DB15 which is a double row connector that is wider. The HD15 is the same profile as the DP9...hence it is higher density. I don't name them but I'm not going to buck the system...if you prefer...call it the VGA connector...not as technically on the mark but it congers up the right picture in most peoples mind. Anyway...I do work with broadcast types a lot...and I tell you...there is a pretty even split on the Gepco versus Belden...like me...while most have a preference mainly for tooling and availability/pricing reasons...either are equally acceptable. I see 1694A and 1695A from Belden more around hear than Gepco's equivalent for HDSDI. Kings crimps seem to be the standard too for BNC though I'm a rebel in that I use AMP...I've just had such success with those Pro-Crimper IIs in so many applications.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-24-2006 11:06 PM                     All I'm saying is that what they call an HD-15 isn't very high density. When you get to 50 pins... yes. I agree with you on the Amp BNC's... I've literally installed thousands of them and never one bad one. We used to get them in boxes of 1000 at the station. Mark  |  IP: Logged

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