In just about any digital audio system there are demands for 110Ω to 75Ω and 75Ω to 110Ω impedance conversion. In fact there are many applications for the Graham-Patten AES to AES3id and AES3id to AES digital audio impedance converters. This is a tool to keep on hand, to be instantly available when a need arises.

Figure 1 : DATS-10: The DATS-10 accepts AES balanced digital audio at 110Ω (5 to 7 V) and outputs AES3id unbalanced 75Ω (1V).		Figure 2 : DATS-21: The DATS-21 accepts AES3id unbalanced digital audio at 75Ω and outputs balanced 110Ω AES.

Graham-Patten Systems make the highest quality audio impedance converters on the market today. I’ve heard people say, “So what? It’s only a simple balun impedance converting transformer.”

Okay, but the design of the transformer is critical to maintaining balance, impedance, and bandwidth. Failure or poor performance in any of these parameters will without doubt cause poor performance through the digital audio path, especially where multiple impedance conversion has been necessary through a longer than normal or tortuous signal path.

We should also remember that when converting from 110/75Ω we have AES in at 2-7Vpp and AES3id out at 1Vpp. It is essential that the proper attenuation be built into the converter to ensure that there is no over voltage at the output of the device. This allows us to use normal video 75Ω distribution techniques and equipment for the distribution of digital audio signals.

So what’s so clever about the Graham-Patten DATS converters? Simply put, it’s the size of the units, and the critical design of the balun transformer. The Graham-Patten DATS are the only converters built using standard XLR shells mated with standard, high quality BNC connectors. I should also have mentioned that they are rugged, too! The balun transformer is designed to meet very precise parameters for this specific application.

In order to help keep installations neat and tidy, we also offer the Graham-Patten DATS panels. These are 19” rack mount panels to which up to eight DATS of any gender can be mounted or even inter-mixed on custom jobs. We also added a cable tie bar at the back of the panel. However, what is slick is that the panel itself is punched out of FR4 material – thus it is insulated from ground ensuring that ground is carried through the DATS converters only.

Figure 3 : DATS Panel

Following is more information from the DATS Converters datasheet:

Cable Length and Connectors

Our tests and experience demonstrate that 100 meters of commonly used twisted pair cable is too long for error-free transmission of AES signals. Use of a pair of DATS Converters results in an error-free transmission distance of at least 1000 feet using Belden 8279 cable. Low-cost, RG-59U cables are acceptable, and for short transmission paths, smaller, higher loss cables are sufficient.

Figure 4: Typical application of DATS converters

DATS Solve Crosstalk and Radiation Problems

Technical concerns arise when digital audio is distributed around a facility that has been designed to work with baseband audio in the 20Hz to 20KHz region. The AES digital audio standard, while more than adequate in its codes and formats, is characterized by inferior electrical parameters. The AES standard calls for a balanced signal using the same wiring and distribution methods as baseband audio. A problem occurs when an approximately 3 MHz signal is passed through twisted pair cabling and unshielded jacks. Crosstalk and radiation at significant levels result. Hence, the length of cable run is limited.

Some analog output drivers and input stages have marginal external high frequency signal rejection. They are also prone to generating intermodulation products caused by digital signal crosstalking into the analog audio band. Passive normalization of the digital audio signal into a common format so it can be treated like a video signal using standard 75Ω equipment alleviates this problem. Graham-Patten DATS converters effect such a passive normalization by converting the AES signal to an unbalanced, 1 Vpp, 75Ω signal. This signal can be passed through ordinary video distribution amplifiers, jackfields and cabling. Both channels of the signal can be routed via a single level path of a video routing switcher. The signal is unaffected by dc restorers or sync tip clamps; however, hard back porch clamps may distort the signal.

You can see technical specifications on the product datasheet at www.gpsys.com/products/accessories.htm