AW: To earth, or not to earth...

[Bob Zimmer]

At 07:46 PM 12/3/97 +1100, you wrote:
>This balanced/unbaslanced thing might be a bit Quixotic...
>after all, there is a hell of a lot of modular stuff out there
>produced over the years and I havn't noticed any of it suffering
>from hum pickup or crosstalk to any degree (OK the switch matrix
>on the ARP2500 does, but that is a different thing). Most of this
>gear has suffers more from IC noise  in my experience...
>Which makes me think that just using commercially tried construction 
>methods and layout might be all that is needed, or worth doing.
>
>paul perry melbourne australia
>

This is my recording background kicking in!

I agree with Paul's comment all this balanced/unbalanced stuff being overkill!

Pro audio gear lives in the balanced world.  But their equipment costs
mega-bucks and requires the utmost in quality and low noise.  Most
recording studios think nothing of spending $100 for a transformer to
balance a line.

To me, balanced lines for microphone level signals is a no-brainer.  Most
consumer gear does not, but most semi-pro gear, and all pro gear does!
Realize also that consumer and some semi-pro gear uses -10dbm signals while
pro gear uses +6dbm levels.

WE ARE SPEAKING ABOUT +5 V SIGNALS!

This is a much hotter level that even pro audio gear!  You have to put some
serious attenuation on that level or you will overload your mixer's
preamps!  Loading that +5 V level into a typical line input which expects a
signal of maybe 100-150 mv or so, requires attenuation (15X attenuation).
This attenuation will also reduce the level of any crosstalk or noise
picked up by the cables to the same degree.

Ground loops are a problem even with pro gear, but it's not an area I know
much about, and therefore will shut up!



  >=== Bob Zimmer -- Phila, PA     bzimmer at voicenet.com ===<
  >===         http://www.voicenet.com/~bzimmer/        ===<
  >=== "Oat-bran noise is more likely to be an issue in ===<
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  >===         Analog Dialogue - Analog Devices         ===<