Emu XL-7 & MP-7 User's Group

What about this information I've found? I'm no electrician so I don't 
know if this does make any sence regarding the E-mu Command Stations.

\/ \/ \/ \/

S/PDIF-connection (also known as IEC60958) was also originally 
designed to be transformer isolated at the transmitting end. So 
theoretically ground loops should be impossible, as each coaxial S/P-
DIF output should be equipped with an insulating transformer, in 
order to avoid ground loop problems. But in reality the sitation is 
not so good, because in some cases because in some equipments the 
S/PDIF-output are not isolated from the rest of the circuitry. 


Reasons for S/PDIF-problems
In reality many coaxial S/P-DIF inputs and outputs of soundcards and 
such devices lack such transformers. Maybe those products are so cost 
sensitive that the manufactuers have to cut corners in this way. And, 
even if the coaxial S/P-DIF output of an audio component is equipped 
with a transfomer, hat doesn't mean that the output is isolated, 
because in some equipments the ground of the S/PDIF output connector 
(RCA-connector) is still permanetly connected to the same ground as 
all the audio connectors instead of correctly left floating. 

Usually the absense of isolation in S/PDIF-connection is not a 
problem in normal use, but can be a problem among with those audio 
experts who want the best sound quality without humming. Usually the 
noise and hummign problems are the reasons to go to digital audio 
transmission, and it is quite sad that some manufactuers put out 
products which can't usually fulfill their promises in real life 
applications, because of the S/PDIF-interface ground loop problem. 


Solving the problems with S/PDIF
If your sound card equipped with optical S/P-DIF (Toslink) inputs and 
outputs, try to use them instead of coaxial ones. The optical cable 
will mode the digital audio signals but at the same time provides a 
complete galvanic isolation between equipments. So optical interfaces 
are free from humming. 

If you want to use the coaxial output and your equipment with S/PDIF 
output lacks the output isolation transformer on S/PDIF-connection 
you have to make your own extra isolation transformer. 

Elector Electronics magazine issue 7-8/1999 recommend building the 
transformer for S/PDIF isolation in the following way: 

The transformer must have good coupling factor, so the transformer 
core must be a toroidal core made of high permiability material. The 
prototype described in the magazine uses Philips Type TN13/7.5/5-3E25 
core which has permiability rating (yt) of 4500. THe primary and 
secondary windongs consisted of 6 turns of 0.5 mm diameter enamelled 
copper wire laid on opposite sides of toroid. The transformer used in 
this prototype was described to have a bandwidth raged from 50 kHz to 
17 MHz, which is more than adequate for an S/PDIF link. 

The transformer should be fitted directly to the source and the 
receiving end must be protperly terminated for reliable operation. 
The reason for this is that the transformer input and output 
impedances are not exactly 75 ohm.








--- In xl7@yahoogroups.com, Aaron Eppolito <synthesis77@y...> wrote:
> --- Mike-E <d_jumpmaster@y...> wrote:
> > 1) Connecting via S/PDIF:
> > The signal is weak. It's about half the volume of when using 
analog
> 
> See the myriad posts on this subject.  Short answer?  Normalize is 
your
> friend.
>  
> > When using internal on the Audiophile, the signal gets disturbed
> > (clicks and plops). The trick of grounding the S/PDIF output 
didn't
> > fix it. Am I doing something wrong?
> 
> Yes.  As with *ALL* digital systems, there must be one master clock 
or
> else you will get pops.  Since the XL-7 doesn't have a word clock in
> jack, you are forced to use the XL-7's clock as the master.
> 
> > 2) Connecting analog (main or sub):
> > A humming sound is added to the signal. When I close to software 
> > mixer of the Audiophile the humming stops, but still leaves a lot 
of 
> > noise en crackles. Totally not acceptable.
> 
> This probably is a ground loop issue.  Since I can never get rid of
> ground loops either (I'm notoriously bad at solving this problem) 
I'll
> defer to someone else who has knowledge in this area.
> 
> -Aaron
> 
> PS. I hate me some "disturbed plops"...  =)
> 
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