PanPot design

I am trying to come up with an 'Orban' style panpot for use in a mixer.

The panpot should feed 10K mix resistors going into an active mix amp.

3db's down in the center position.

Sine/Cosine response.

Minimal loss through the panpot.

I am having trouble finding the appropriate values for the feed resistors and the potentiometer.

Any help would be more than welcome.

Thanks.

Full design data can be found in:

Orban, Robert

Notes on Panpots

Journal of the AES, Volume 19 Number 11 pp. 935-939; December 1971

Available from www.aes.org

I built a spreadsheet once (aiming for sin/cos) which plotted the response ov various options, if you plugged in different values for the pot, the reed resistors and the load impedance from the wiper onwards.

Using a linear pot, you can't get all that close, but if you accept either a variance in summed signal level (change in apparent volume across the sweep of the control) or angular inaccuracy (more steady level across the sweep range, but uneven angular response: eg. a tentency to spend a lot of time at the center then suddenly accelerate in apparent posisition towards the edge) then you can get closer. Closer, but not sin/cos.

Here's as close as I got:


Keith

LRRec:
Hopefully, attached is a schematic diagram showing a channel strip I designed around '95 or so. Pay no attention to the missing caps around the fader and level pots...that's another object lesson for me. However in the lower section is shown the active pan circuit that was certainly "lifted" from somewhere. I believe this circuit covers all but the sin/cos required attributes you posted.

http://groupdiy.twin-x.com/displayimage.php?album=lastup&cat=0&pos=0
http://groupdiy.twin-x.com/albums/userpics/10067/mix_channel_sch.pdf

Hope this helps,
Peace - Out

Douglas Self has som info on the subject; http://www.dself.dsl.pipex.com/ampins/mixer/mixerdes.htm#5

You can find the schematic for his unusual but working "NIC" circuit at www.soundcraft.com:

http://www.soundcraft.com./download.asp?filename=pdf/user_guides/8000/8000_spares_kit_diagrams.pdf

(at the bottom of page 18)

Thanks to everyone who replied. The information has been very helpful. I downloaded the Orban article and also found an interesting AES paper by Richard C. Cabot entitled Precision Pan Pots. It gives detailed equations and tables for stepped panpots.

The Cabot paper is also very good, albeit incredibly dry :wink:

Here's a "worked" example of a stepped pan
(actually, part of an ambisonic decoder):

schematic (PDF)