[sdiy] Panning (again)

[David G Dixon]

Because 7.07k is the square root of 1/2 times 10k.  The closest resistor in E96 is 6.98k.  Actually, using 11.5k and 16.2k gives a ratio of 0.710, and is as close as one can get to 0.707 in the E96 (1%) series or resistors.
 
The panpot attenuates 7.65dB at the midpoint, and the opamps amplify by 4.65dB, to give 3dB net attenuation at the midpoint (about 71%).
 
For the "compromise" law which is 4.5dB attenuation at the midpoint, one would want a resistor ratio of 2.14, so the 7.07k resistors would be replaced with 21.5k (the closest value in E96), or use 10.7k and 4.99k resistors to get even closer.  Now, the panpot attenuates by 14.5dB at the midpoint, and the opamps amplify by 10dB, to give 4.5dB net attenuation at the midpoint (about 60%).
 
I don't know for sure, but I suspect that if "linearized" 2164 circuits were used in place of the pan pot, the signal bleed because of the wiper contact resistance that Douglas Self worries about could be eliminated, because the VCA could be fully turned off.

  _____  

From: Didier Leplae [mailto:didierleplae at yahoo.com] 
Sent: Tuesday, December 15, 2020 1:36 PM
To: Mattias Rickardsson
Cc: David G Dixon; Synth DIY
Subject: Re: [sdiy] Panning (again)


[CAUTION: Non-UBC Email] 
Out of curiosity, why 7.07k resistors? That seems like such a specific value


On Dec 15, 2020, at 3:27 PM, Mattias Rickardsson <mr at analogue.org> wrote:



 
Douglas Self shows this connection as the first example in the Passive Panpots subchapter of his Small Signal Audio Design book, with the description 
"... has several disadvantages, not least the poor offness when panned hard over, caused by the current flowing through the wiper contact resistance to ground."

The rest is left to the reader, but thanks to separated L/R channels with law-bending resistors, the story ends well. And most of you have already figured out that the next subchapter is even better. ;-)

/mr

Den tis 15 dec. 2020 19:34David G Dixon <dixon at mail.ubc.ca> skrev:



Hey Team,
 
I've been thinking about this panning thing, and I came up with the following very simple pot-based panning circuit:
 

 
The gain responses of this circuit are shown below, and compared with sin and cos responses:
 

 
I believe that I can create a voltage-controlled version of this simple pot panning circuit fairly easily by replacing the pot with a pair of modified Irwin 2164 circuits.  I did this for the Morphing LFO.
 
Would this response suffice as an "equal power" panner?
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<SimplePanner.png>
<PanPlot.png>
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