[sdiy] Equal power law

[Neil Johnson]

Well, you can use op-amps as VCAs if you are that way inclined.  But
it's a bit of a kludge...

Neil

On 11 February 2016 at 20:18, Mattias Rickardsson <mr at analogue.org> wrote:
> But poor Rutger wanted something *without* VCAs. :-)
>
> I just browsed through Douglas Self's small signal book without finding
> anything that was enough spot on to advice about.
>
> /mr
>
> Den 11 feb. 2016 9:13 em skrev "Matthias Herrmann"
> <matthias.herrmann at fonik.de>:
>>
>> it is the one we used as basis for a stereo mixer module
>> http://www.thatcorp.com/datashts/dn120.pdf
>>
>> cheers,
>> matthias
>>
>>
>> > -----Ursprüngliche Nachricht-----
>> > Von: Synth-diy [mailto:synth-diy-bounces at dropmix.xs4all.nl] Im Auftrag
>> > von
>> > Neil Johnson
>> > Gesendet: Donnerstag, 11. Februar 2016 20:15
>> > An: Rutger Vlek
>> > Cc: Synth DIY
>> > Betreff: Re: [sdiy] Equal power law
>> >
>> > Hi Rutger,
>> >
>> > > Inspired by the lin/exp/log thread, I've been wondering about
>> > implementation of other curves, most specifically those used for equal
>> > power law and BBC panning law (center at -3dB or center at -4.5dB).
>> > >
>> > > Are there simple ways to approximate these curves in analog domain
>> > > (e.g.
>> > without using a VCA). I've been playing in Spice with an approximation
>> > of
>> > the curve using a simple opamp circuit with back-to-back zeners. The
>> > zeners
>> > already have a rather 'soft knee', but I'd like to know if there are
>> > ways
>> > to get the shape even closer to what's needed for an equal power law
>> > curve.
>> >
>> > There's a THAT app note where they use diode function generators to
>> > approximate the sin/cos curves for panning VCAs.
>> > Don't remember the number at the moment but there aren't that many
>> > THAT app notes.
>> >
>> > Neil
>> > --
>> > http://www.njohnson.co.uk
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