> >Mike Keitz <PICLIST@MITVMA.MIT.EDU> wrote:
> >
> >> It appears that two major complications crop up in practical
> >> application:
> >>
> >> Matching two attenuators for stereo use.
> >
> >    Or FOUR attenuators, if you're building a balanced preamp.
>
> Wouldn't you want to use balanced attenuators (something like the Pi
> or
> Tee networks, but between the two lines rather than one line to
> ground)
> in that case?  Such an attenuator won't attenuate (unwanted) common
> mode
> signals, but (a) there shouldn't be any in the first place and (b)
> they
> should be highly rejected at the far end.  Using two seperate
> attenuators
> which were inevitably mismatched would turn common mode signals into
> differential ones, exactly what you're trying to avoid by using a
> balanced circuit.
>
I'd have thought this as well.

> >
> >        1.  It's hard to "adjust the attenuators until they are
> >            matched" if they have fixed one-dB (or so) steps.
> >            Adding a set of fractional-dB "adjustment" dividers might
> >            solve this problem in some circuits.
>
> Right, but it should be possible to build attenuators with large fixed
> steps more precisely than small steps because there are fewer
> resistors,
> so more expensive and precise resistors could be used.  I was thinking
> mainly of designs with potentiometers turned by motors or of the one
> with
> "coarse" and "fine" digital pots.
>
FWIW, the concensus amongst those who have done more experimenting than
I in this area is that the preferred law of 'perceived volume' is (going
from loudest) down at a fairly slow rate, then this rate increasing as
the volume is reduced. So they may start with a 1.5db/step rate at the
top, then increase to a 2.5db/step, and onto a 4db/step for the quieter
levels. Personally, this puzzles me a little, but there you go.

Also BTW, I'm not considering having a balance control in at all ;-)

        Thanks
        jon N