Print

Please login or register.
1 Hour 1 Day 1 Week 1 Month Forever
Login with username, password and session length

[Roland Storch]

Most professional units with AES/EBU connection use transformers on input and output.

What´s the benefit? Is it only galvanic decoupling or is it also because of the good common mode rejection?

Are there also disadvantages? I mean the transformers have to be really fast and maybe an electronic curcuit can to that faster and better?

[bruno putzeys]

The EBU requires transformers so if you wish to label the equipment AES/EBU you need to have them. AES3 is a bit more intelligent. It does not explicitly tell you what to do but sets forward performance requirements. These can definitely be met without transformers, but not necessarily easily. For instance, AES3 does not require the use of shielded cable (UTP is also acceptable) so common mode requirements are stricter than the -30dB that AES3 itself calls for. It's not easy to design an active high speed driver with really low CM output so there at the very least a CM choke will come in.

For galvanic isolation you do not need a transformer, using sufficiently small coupling caps will do. Clause C.3.5. of AES3-4 acts as a design guideline.

[Larrchild]

What about their effect on timing?
http://recforums.prosoundweb.com/index.php/mv/msg/14324/0/20 8/9858/

[bruno putzeys]

The best way to improve baseline shift generated jitter (other than making equipment insensitive to jitter which of course is really the right way) is to maximise LF extension of the link. For an output transformer this simply means: place any series termination resistors on the secondary side and connect the primary directly to the driver (perhaps with a large series cap to prevent it from shorting the driver during reset). For an input transformer, don't skimp on primary inductance.

Of course, extending the HF response helps equally, except that this may conflict with EMC. LF is the easier way.