Camera CCU Interfacing to Clear-Com Party-Line
There are some rules one must consider as "cast in concrete" when interfacing cameras to Clear-Com Party-Line that make answering questions and assisting customers easier. (Some of this information is generic about interfacing in general and applies to things other that cameras and to Matrix also.)
It frequently helps to explain some of these rules to the customer, (even if they are technical types)With almost no exceptions, using the Camera "4-wire" connector will provide the best interface to a Clear-Com partyline system. We always recommend and insist that customers purchase Cameras CCU units with a 4wire port or include the 4wire option.
1. RULE: Every intercom circuit starts out as a 4-wire circuit (i.e. headset earphone/microphone; or separate microphone/loudspeaker). (Note: In “carbon mic” circuits, one side of the headset earphone and microphone are connected together to become a “3-wire” connection, but for practical purposes it is treated as a 4-wire circuit.)
2. RULE: The basis of every 2-wire party-line intercom system involves a conversion of the intrinsic 4-wire circuit into a 2-wire circuit and then back to 4-wire again. The circuit or device that accomplishes this is a 2-to-4 wire conversion called a "hybrid".
3. The basis of Clear-Com party-line communication is an active hybrid circuit invented by Charlie Butten, that we call our “line driver” circuit.This hybrid presents a high impedance to the 2-wire party-line, which must be terminated with 200 ohms (the channel “termination”).(The same is true for RTS. The RTS equivalent circuit is called the “bi-lateral current source” or “bi-lat” for short.) .
4. The primary purpose of the hybrid is to block the 4-wire “send” signal from looping back into the same 4-wire “receive” portion of the circuit. This blocking is called the “null”.
5. In interfaces, this null must be adjusted or “balanced” to achieve the desired amount of “blocking”. How effective a null can be obtained is dependent on the impedance characteristics of the 2-wire party-line.
6. The simplest two channel party-line intercom station must have at least two 2-to-4 wire hybrids (one for each channel).
7. RULE: Every time communication goes through a 2-to-4 wire conversion (hybrid) the signal is degraded somewhat. The more hybrid conversions a signal goes through, the more the signal is degraded. Therefore, in any intercom system, the fewer hybrids a signal must go through, the less the signal will be degraded.
8. BIG RULE:
The best way to interface a camera intercom is, without exception
, to access the intercom circuit as a 4-wire circuit, and then use one of our 2-to-4 wire interfaces to convert to our 2-wire party-line. Like the EF-701M or IF4W4 unit 9. The 2-to-4 wire hybrids that are part of most cameras that are used to create a 2-wire party-line are very poor compared to Clear-Com’s line driver hybrid. Even if the camera manufacturer says they have a Clear-Com or RTS plug-in compatible party-line connection, it rarely is truly plug-in compatible.
10. The best answer for camera interfacing is to order the camera with a 4-wire intercom connection. Most higher-end cameras provide this as standard or offer it as an option. This is always
the best way to interface to the camera intercom. A 4-wire connection is frequently not available on lower cost cameras.
11. RULE: If a 4-wire connection to the camera intercom is not available, almost always the next best choice is to interface to the headset connection on the camera CCU/DCU. (Remember rule #1, the headset connection must
be a 3 or 4-wire circuit.)
12. The IF4W4 (IF4-B) Interface was specifically designed to correctly interface to the CCU/DCU headset connector of almost any manufacturer. It will correctly match the levels of both carbon or dynamic headset connector. It uses superior circuitry than the AC-10 and will obtain a better null, at less cost. (The IF4W4 was specifically designed to provide a good interface to the headset connector on the Sony M-3 CCU – see below.)
13. NOTE: Sony M-3, M-5, M-7 CCU/DCU (and maybe others). One of the most frequently asked questions is how to interface to Sony CCU/DCUs that use the “only-used-by-Sony” miniature 1/8” 4-conductor “tip/ring/ring/sleeve” headset plug. I do not know of anyone who manufactures this plug other than Sony and R-Columbia. It can be obtained from Sony as a replacement cable (with molded plug) for the “DR-100 Video Accessory Headset”. The Sony part number is: 1557-093-00. A replacement cable is also available from R-Columbia (tel: (001)-847-432-7915). Order as: “Sony headset replacement cable”. The R-Columbia cable uses “tinsel” wire which is difficult to solder to. The pinout is VERY unusual "tip/ring/ring/sleeve"tip = headphone hi; next ring (closest to the tip) = headphone low; next ring (closest to the sleeve) = mic hi; sleeve = mic low/shield.
14. NOTE: Many camera CCU/DCUs have the intercom connection on a 3-pin connector, or on three pins of a multi-pin connector (frequently along with the "tally" controls).The pinout is frequently identified as: “common”, “+”, “-“. Many people assume that this indicates a 3-wire intercom circuit, with one pin “send”, one pin “receive”, and one pin “common” to both. This is not true. The “+” & “-“ pins are a 2-wire party-line, with the “common” simply being a shield/ground. There are no known exceptions to this.
15. RULE: It is always
best to interface each camera individually. Trying to combine the 2-wire party-line circuits the CCU/DCU provides into a single party-line and then use an interface to convert the camera party-line to Clear-Com party-line is the least effective way to interface multiple cameras. There are several reasons. -First, the more cameras you connect in parallel, the worse the party-line impedance characteristics become, therefore a good null is difficult, if not impossible, to obtain. -Second, if the impedance characteristics of a single camera are worse than the other cameras (which is not uncommon), the overall party-line impedance characteristics are degraded to the level of the worst camera.-Third, to convert the camera’s 2-wire party-line to Clear-Com’s 2-wire party-line, a 2-to-2 wire converter, like the AC-10 or TW-12 is needed. These units first convert each 2-wire party-line to a 4-wire circuit, and then connects the two 4-wire circuits together. This adds an additional 2-to-4 wire conversion in the signal path which adds further signal degradation (remember rule #7).
16. RULE: Sometimes the interfaced communication from the Clear-Com party-line system can never be any better that the communication from one camera to another, when the camera party-lines are connected together. If a good interface null cannot be obtained, we have no choice but to tell the customer that we cannot do better. A way to prove this is to have the customer connect the cameras CCU/DCU party-lines together and listen to the camera-to-camera communication, and realize that the limitation is in the camera’s internal intercom circuitry. We can do nothing in terms of interfacing that will improve the camera’s internal circuitry. A customer may not like that as they will compare and want the camera intercom to equal the Clear-Com volume and quality, which frequently simply can’t be done. As the cost of a camera goes lower and lower, something must be sacrificed by the reduced cost, and frequently, the quality of the intercom circuitry is one of the things to be lost. It is just a fact of life.
In Summary: interfacing to cameras, especially low cost units, especially when the intercom is not available as a 4-wire circuit, is probably the most difficult party-line interface problem there is. And while we want to do the best we can for customers, we cannot compensate for the intrinsic quality, or rather lack thereof, of the internal camera intercom.
The best way to interface a camera intercom is, without exception
, to access the Camera CCU intercom circuit as a 4-wire circuit, and then use one of our 2-to-4 wire interfaces to convert to a Clear-Com party-line. Like the EF-701M or IF4W4 unit
Note: For Sony Camera and CCU information, here is a good resource:Louis FleflehLouis.Flefleh@am.sony.com
Sony Electronics.Product Application SpecialistProduct Operation Support Center (P.O.S.C.)Voice: 800-883-6817 option 2,5,2Fax: 201-833-5210 Professional Services Website: www.sony.com/professionalservices
for SONY CCU D50, see attached, plus...The information you seek is on page 19 and 22 of this document. On the DB-15, pins 5 and 13 are the lucky winners…corresponding to XLR pins 3 and 1 respectively to the Clear-Com.