[sdiy] Balanced/unbalanced inputs?

[media.nai at rcn.com]

At 8:30 PM -0500 03/11/02, DTK wrote:
>
>> To use an unbalanced line into a balanced input, you
>> could try attaching the unbalanced line to one of the
>> balanced lines, and ground the other side. This may
>> work, but there's a problem: balanced inputs tend to
>> be higher levels (+4 dBv) than the unbalanced ones
>> (-10dBv).

So turn up the gain :)

>> Or you could go to Radio Shack and buy a
>> unbalanced-to-balanced adapter for about $20.

That's usually unnecessary.  If impedance matching or ground loops become
an issue, Markertek sells a variety of transformer adapters.

>So If my instruments have unbalanced output, I can't use them with a mixer
>that has balanced inputs unless I 1) modify the cable or 2) buy an adapter?

No, you can plug an unbalanced TS cable into a balanced TRS line input and
it should work fine.  I do it all the time.  Obviously, you need an adapter
in order to go from 1/4" to XLR -- the jack won't fit :)  Then again,
Neutrik now makes 3-conductor jacks that can accept both 1/4" and XLR.

I'd check out to Rane's website.  They used to have this nice wiring chart
you could print up.  You might also want to check out the ProCo and Mackie
websites -- I've seen wiring charts from them too.

>How can I tell what type of output my instruments have? I assume
>they're all unbalanced, but I don't know how to check. It's not it the
>>manuals...

It should be in the manuals!!  It also should be written on the chassis
next to the jacks.  XLR is almost always balanced.  Most musical
instruments with 1/4" jacks are unbalanced.  Balanced 1/4" jacks have an
extra click when you insert a plug.  If you use short runs of quality cable
in a decent environment, none of this should be an issue.

You want to go from a lower output impedance to a higher input impedance.
I've never seen a line input that didn't have a higher impedance than a
line output, including the outputs of consumer gear and electronic musical
instruments.  The only way you can get into real trouble is if you try to
run a line output into a the low impedance input of a mic pre, but such
inputs are never 1/4".