[sdiy] Panning with LM13700

Tom Wiltshire tom at electricdruid.net
Tue Jan 10 01:33:54 CET 2017


Hi Laurie,

Thanks for the reply. Yes, I have looked at the Serge equal power panner, but I'd discarded it for the following reasons:

1) I don't understand it fully. The schematic is spread across three modules (CGS102A, CGS102B, CGS108) plus a mixer board to plug them all into, which makes it somewhat difficult to get a grip on. The CGS108 Serge Gain Cell is a proprietary design for which we aren't given a schematic. I don't want to tread on illustrious toes, so I'm not interested in trying to find a schematic if people don't wish me to know. The parts remind me of the discrete OTA Jürgen Haible designed for his discrete SSM2040 filter, which would make sense.
2) All those parts! Isn't there a simpler way?! Ok, I accept that the image on Ken's site is a dual version, but nonetheless - it's not straightforward:

	http://www.cgs.synth.net/modules/pic/photo_cgs101v10_upap.jpg

The THAT Corp solution is similarly involved.

Currently the easiest way (by far) is to do as Richie suggested and generate the required pan law (*any* required pan law, or even the user's favourite law) with a uP and a DAC, fed to a pair of your VCAs of choice. It's a pity since I'd hoped for an analog solution to avoid the default "throw a micro at it" answer, but in this case, it really does seem like the sensible way. 

Thanks,
Tom



On 9 Jan 2017, at 22:13, Laurie <elby_designs at ozemail.com.au> wrote:

> Have you looked at the Serge Equal Power Panner?
> Go to my site or Ken Stones CGS site and look at CGS102.
> PCB and Component Kits available to DIY it
> 
> Best Regards
> Laurie Biddulph
> Mobile: +61 0400 257 645
> Phone.: +61 02 4340 0938
> Web...: www.elby-designs.com
> Skype.: widgetoz
> 
> Elby Designs
> 9 Follan Close
> Kariong
> NSW 2250
> Australia
> 
> ABN: 70 022 727 605
> 
> Happy New Year
> 
> 
> On 10/01/2017 8:29 AM, microtonalsynthesis at yahoo.com wrote:
>> Like many app notes, the THAT AN120 is something of a DIY project in itself.
>> 
>> The control voltage inputs are reversed. U1 should use EC+ pin 2 and U2 should use EC- pin 3.
>> 
>> The breakpoint generator is very sensitive to offsets and the circuit as given has unequal volumes for left and right sides. Adjustment of all resistors going to -15V is needed. I estimate about 130.5K for the 133K. Of course, if you adapt this circuit to 12V supplies then you need to adjust some more.
>> 
>> John
>> 
>> 
>> On Sunday, January 1, 2017 6:24 PM, Richie Burnett <rburnett at richieburnett.co.uk> wrote:
>> 
>> 
>> You could always generate the two VCA control signals with the appropriate pan law using a micro... Low cost pic with dual output PWM perhaps? Pre-calculated values in lookup table on a low end micro, or use  quadratic fit approximation if you're already using a dspic.
>> 
>> -Richie,
>> 
>> Sent from my Xperia SP on O2
>> 
>> ---- Tom Wiltshire wrote ----
>> 
>> >That's a fairly involved circuit, but I don't think I've ever seen an analog panner with a switch to select different pan laws. Very impressive!
>> >
>> >I'll have a look over it and see if I couldn't use the gist of it in a simpler way.
>> >
>> >On 1 Jan 2017, at 20:14, Tom Bugs <admin at bugbrand.co.uk <mailto:admin at bugbrand.co.uk>> wrote:
>> >
>> >> Not LM13700 based, but the details within the THAT app note here may be some use:: http://www.thatcorp.com/datashts/dn120.pdf (VCAs in pan pot apps)
>> >>
>> >>
>> 
>> >>>>> -----Ursprüngliche Nachricht-----
>> >>>>> Von: Synth-diy [mailto:synth-diy-bounces at synth-diy.org <mailto:synth-diy-bounces at synth-diy.org>] Im Auftrag von Tom
>> >>>>> Wiltshire
>> >>>>> Gesendet: Sonntag, 1. Januar 2017 18:07
>> >>>>> An: Synth-diy at synth-diy.org <mailto:Synth-diy at synth-diy.org>
>> >>>>> Betreff: [sdiy] Panning with LM13700
>> >>>>>
>> >>>>> Hi All,
>> >>>>>
>> >>>>> Happy New Year to everyone! Here's hoping you all have a great year with
>> >>>>> many (completed) synth projects.
>> >>>>>
>> >>>>> I've got  quick question - what's the best way to do equal power panning (-
>> >>>>> 3dB in the centre) with the LM13700? I'm assuming that such a thing has
>> >>>>> been done already, so it's seems silly to reinvent the wheel, but I can't
>> >>>>> find anything that isn't a simple linear crossfade (which is ok for
>> >>>>> crossfading, but not so good for panning).
>> >>>>>
>> >>>>> Any tips/pointers appreciated.
>> >>>>>
>> >>>>> Thanks,
>> >>>>> Tom
>> 
>> 
>> 
>> 
>> 
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