In message <007d01c134b7$882a0800$0100a8c0@piii500a>, Jim
<jvpoll@DALLAS.NET> writes
>A couple of questions:
>
>1) What exactly is a 'direct box' (I have never heard
>   of one - but I have heard of "impedance matching
>   transformers")?

It's commonly used in the music field, for example connecting guitars
directly to the PA system.

>2) What would the source be that you be converting
>   from 20,000 Ohms (plus) to the range of 150 to
>   600 Ohms? Would this be say, studio/musical gear?

Yes, almost always, either studio or live performance.

>There might be other ways of 'driving' a low impedance load
>(like 150 Ohms) other than through the use of a transformer,
>such using an op-amp (or two). If the transformer is to
>provide some amount of common-mode isolation even this can be
>accomplished to degree using op-amps.

That's not the main point, it's isolation to prevent earth loops, a
large problem for live performance (I spent a number of years building
and operating PA for some friends in a local rock band).
--

Nigel.

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        | Nigel Goodwin   | Internet : nigelg@lpilsley.co.uk           |
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