Re: [LAU] OT: unbalanced to balanced

On Tue, Sep 08, 2009 at 04:55:48PM -0500, Josh Lawrence wrote:
> I've extracted a little mono amp out of a pair of computer speakers
> that I would like to use as a general practice/noise amp. It
> currently has a balanced 1/8" input. The wires going to the input
> are: black, white, and a braid of wires (I'm assuming shield?). I'd
> like to cut this 1/8" plug off and add a 1/4" female jack so I can
> plug stuff into it. But where do I solder the wires to? (i.e., black
> to tip, white to sleeve, that kind of thing) I have access to stereo
> and mono 1/4" jacks.

For a stereo 6.5mm plug, the two insulated wires are to be soldered to
the tip and ring respectively, and the braid should be twisted together
and soldered to the sleeve.

Assuming the amplifier has two input channels for left and right ... the
polarity of those insulated wires depends on which speaker you want to
be the left one, and which you want to be the right one. The colour
coding used in the device might not match a standard, but you can check
by injecting a signal and listening to which speaker emits it. My
favourite signal for this is loop hum, using a finger.

For a mono 6.5mm plug, the two insulated wires should be soldered
together to the tip, and the brain twisted together and soldered to the
sleeve. This will deliver the mono audio signal to both inputs of the
amplifier.

It's odd that you say it is a "mono amp", but I guess you might mean a
monolithic amplifier module.

If you can put a photo up somewhere then I could confirm or refute your
suspicions about it. ;-)

> PS - I've read that the proper way to do this is to use an audio
> transformer, but that's WAY overkill for this project, I just want
> sound to come out, nothing audiophile or anything like that.

There are many transformers that will work for this, but the best is one
that has a 1:1 winding ratio, assuming you are using signals of
comparable electrical amplitudes. It's not an audiophile thing, but
rather a way to prevent hum caused by loops.

You might not need this, especially for practice amps.

-- 
James Cameron
http://quozl.linux.org.au/
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