balanced to unbalanced question

[jstark]

Hey y'all.

Wiring up a Soundtracs Megas that I just picked up.

The manual for my Crown DC-300a shows to wire the input as follows:

I'm really confused as to why you would ever attach the Cold line to the sleeve of the TS...

Are they assuming that you would tie the Cold to the Sleeve at the source, as in Figure 5 of this http://www.rane.com/note110.html document?

(if it helps, the output of the Megas that I'm using is a ground-compensated output...)

Thanks,

David

 

[Rob Flinn]

you attach the cold line to the sleeve of the TS because if you leave the sleeve floating the hot has nothing to reference against.        In a balanced signal the hot & cold are referenced to ecah other & NOT ground.  In an unbalanced line the signal is referenced to ground.

 

[jstark]

Thanks Rob-- yeah, I get that part, I was just confused by the Crown drawing which shows connecting cold without tying it to the shield.

 

[Rob Flinn]

Thanks Rob-- yeah, I get that part, I was just confused by the Crown drawing which shows connecting cold without tying it to the shield.

The shield is grounded at the other end so it still acts as a shield. 

Some balanced outputs aren't happy with the cold side being earthed (i.e tying it to the shield)  as effectively you could be shorting the output of an op amp.

If the signal is transformer out it's not necessary to ground one side of the transformer.

 

[okgb]

You either leave the  [-] or cold line  usually pin 3 , floating  - unconnected or
grounded , as rob mentions specific , somewhat to the send & receive circuitry
a xfmr out can have the neg polarity half grounded easily , opamps may produce
some distortion . Be prepared for either scenario , grounded or floating
probably plenty of info from gear manufacturers on the net

 

[jstark]

thanks for the help, y'all.

Tying cold to the sleeve of the TS (and leaving the shield float) yielded hum-free results.

peace.
david.

 

[JohnRoberts]

The DC300 is an old design and doesn't do well at rejecting noise coming into it's audio ground via a shield connection to another chassis ground. I am not a big fan of floating grounds but as long as all your equipment is using 3 wire line cords you have adequate safety ground paths to protect all the meat puppets in the area. 

JR.

 

[PRR]

> The DC300 is an old design

AND at-the-time "all" balanced outputs were full-floating transformer.

With modern transformerless forced-Balanced, you would drop the "-" lead and take shield to sleeve. That's half-level but half of any forced-Balanced output is plenty to clip the Crown.

Some transformerless outputs semi-float, an attempt to Do The Right Thing with most input types. The best work very well. Some are not the best.

For mos gigs you just try both ways until happy.