[sdiy] Panning with LM13700

Dave Manley dlmanley at sonic.net
Thu Jan 12 19:58:37 CET 2017

Is there a separate diode breakpoint circuit for the left and right channels?  Is that the cause of the mismatch?

If so, can you use one circuit for the left and then derive the right from that?


On January 9, 2017 8:17:05 PM PST, microtonalsynthesis at yahoo.com wrote:
>I think you are on the right track with the microcontroller version.
>I've been simulating the THAT AN120, which is just a simple diode
>breakpoint generator. But the amplitudes never match up for the given
>circuit, with differences of 50% or greater depending on the setting
>and the left or right channel. In reality I think this circuit will
>need multiple trimmers to get everything right. Considering it is
>modifying CVs that go into an exponential control circuit, just small
>errors can be significant.
>On Monday, January 9, 2017 7:34 PM, Tom Wiltshire
><tom at electricdruid.net> wrote:
> 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
>    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. 
>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
>>> 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
>>> >
>>> >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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