[sdiy] Panning with LM13700

Matthias Herrmann Matthias.Herrmann at jeppesen.com
Tue Jan 10 10:45:08 CET 2017

Same here.
We adopted the AN120 for 12V operation and used it for a 4U Stereo Mixer (ala Serge).

After some simulations and real life testing we were able to go with just the center trimmer, using 1% resistors. However, we used it with the nice pre-trimmed THAT2180 VCAs.

From: Synth-diy [mailto:synth-diy-bounces at synth-diy.org] On Behalf Of Tom Bugs
Sent: Tuesday, January 10, 2017 10:05 AM
To: synth-diy at synth-diy.org
Subject: Re: [sdiy] Panning with LM13700

Yes, I agree -- THAT notes often need some detailed consideration - they use some absolutely bizarre resistor values.

I actually used the AN120 idea basis with V2164 VCAs - took quite a lot of multisim investigation first and then some physical prototyping afterwards.

On 09/01/2017 21:29, microtonalsynthesis at yahoo.com<mailto: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.


On Sunday, January 1, 2017 6:24 PM, Richie Burnett <rburnett at richieburnett.co.uk><mailto: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.


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 <https://urldefense.proofpoint.com/v2/url?u=http-3A__www.thatcorp.com_datashts_dn120.pdf&d=DgMD-g&c=P3aKjizb3qsxp0SERaL2sw&r=Wo0ERRj3NwEx1MVmRi7Tj3kJss6CkyI0BMe1OujCfok&m=zDrgDUI_B8TYLbrZSvO6ojF6fSU0kZnkFRmtt5rxCkA&s=RUKy4NpD3YapLxB0c-TAwlM740cD6Gu90CN6Ve-p1kc&e=> (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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