Psuedo-Unbalanced Cable? (Firewire 410 & Event ASP8's)

peritus

peritus

The not fountain head
I'm getting quite a bit of hum from Firewire 410's unbalanced 1/4" TS outputs, through my Event ASP8's (TS to TS).

From what I'm reading, something called a "pseudo-balanced cable" can help me eliminate this problem.


http://www.soundonsound.com/sos/jun99/articles/qa.htm
qafig3.gif



I believe that I need to construct two of the the cables in figure 3 of the article above. Can anyone confirm?


If so, please confirm that the following parts would be sufficient to construct one of these.

Dayton CMX-10K XLR Microphone Cable 10 ft. Black
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=241-344

Neutrik NP2C-B 1/4" Mono Plug Black w/Gold Plug
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=092-107

100 Ohm 1/2W Flameproof Resistor
http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=002-100


Thanks for your help!
 
The 1/2W resistor is much bigger than you need. It could be a bit of a pain to fit inside the plug, but it can be done.

This is usually called "impedance balanced", and it works fine for balanced outputs. In fact a lot of gear is wired like that internally, which has the advantage of extending the shield to the connector shell. For the sake of one resistor and a TRS jack, I can't fathom why manufacturers don't supply impedance balanced outputs . . .
 
mshilarious said:
The 1/2W resistor is much bigger than you need. It could be a bit of a pain to fit inside the plug, but it can be done.

This is usually called "impedance balanced", and it works fine for balanced outputs. In fact a lot of gear is wired like that internally, which has the advantage of extending the shield to the connector shell. For the sake of one resistor and a TRS jack, I can't fathom why manufacturers don't supply impedance balanced outputs . . .
Click to expand...

Agreed...

I just wish P.E. sold 1/8 watt resistors...

Sounds good, though... Thanks
 
I should add that a lot of interference, even 60Hz hum, is misattributed to "ground loops". In fact, there are a lot of household appliances give off rather nasty interference. I can turn dimmer switches on and off that are on different circuits than the studio--indeed, even a different side of the breaker panel, and cause interference in unbalanced lines in my studio. For example, a microphone cannot really have a ground loop because it isn't grounded apart from the cable shield/preamp it is connected to, but boy can they hum if unbalanced.

So it is not simply adding impedance between the the cable shield and chassis for a ground lift, it is also creating a balanced circuit that rejects interference, and kills the hum dead.

I have gone so far as to argue even guitars and amps should be rewired as balanced . . .
 
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