[sdiy] Equal power law

[blacet at blacet.com]

There is this from various National Semi sources:
http://www.next.gr/uploads/135-8988.png

The math is there and this is a -3dB curve. Works well and you can leave
out the 1 uF caps.


> 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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>
>
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