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Science Forum Index » Electronics Forum » Ground loops by design in AES/EBU interconnects?
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| Author |
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| David Gravereaux |
 Posted: Fri Apr 20, 2007 2:48 pm |
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Guest
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The AES3 standard (AES-2id-2006) for AES/EBU digital transmission of 2-ch audio
states in section 7.1.1.3 that the cable is supposed to be grounded at both ends
(aka a ground loop).
Yet the standard also says that the transmitter and receiver are based on the
RS-422 hardware UART.
According to documents about RS-422 hardware
<http://www.bb-elec.com/tech_articles/rs422_485_app_note/transient_protection.asp#ground>,
ground is only a reference for the single-ended signals and not to be made common
between end-points. Also, shield of the cable is lifted at the modem side
<http://www.interfacebus.com/Design_Connector_EIA530.html>.
The electronics themselves can only handle a common-mode voltage between -5V and
+12V. And best isolation is achieved with opto-couplers (LED->opto transistor).
The AES standard does mention the use of transformers, but digital (ie. 1 and 0
levels of a carrier) doesn't need an "analogous" coupling.
Bill Whitlock of Jensen Transformers @ the SF AES show last October did mention in
his talk the importance of attention to ground loops in data hook-ups. So how is
AES/EBU different than RS-422, aside from half-duplex?
Hmmmm... Is it possible the AES standard is not exclaiming the best manner of
realization? It certainly is worth asking about.
--
"I propose we leave math to the machines and go play outside."
--- Calvin |
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