[sdiy] LM13700 Noise

[Quincas Moreira]

Tim, Vinicius Brazil designed our Overfolder, which is also "a wavefolder
with a ridiculous amount of gain" made with Lm13700s.  It is kind of noisy
in some settings, so I'm not sure looking at this helps, but here are the
schematics:

https://synthdiyguy.wixsite.com/vbmodulardiy

And a demo video

https://www.youtube.com/watch?v=Jen7IQr5DJU


I have these for sale if anyone is interested by the way. Both built and
kit form, and the kits are on their way to Modular Addict, Thonk and
Synthcube

Cheers!

Q

On Thu, Jul 6, 2017 at 4:18 PM, Phillip Gallo <philgallo at gmail.com> wrote:

> Yes.
> I have run two sections in parallel.
> Less uncorrelated noise, twice the thump.
>
> Differential works well.
>
>
> On Thu, Jul 6, 2017 at 1:32 PM, Cooper Sloan <mistercooper at gmail.com>
> wrote:
>
>> I asked about this once before and no response, so maybe a stupid idea...
>> has anyone ever tried stacking these for reduced uncorrelated noise? Not
>> saying it would be worth it...
>>
>> http://www.linear.com/solutions/5657
>>
>> On Thu, Jul 6, 2017 at 12:09 PM, Tom Wiltshire <tom at electricdruid.net>
>> wrote:
>>
>>> Isn't the problem there the "ridiculous amount of gain" rather than the
>>> unsurprising amount of noise? I think you may be looking in the wrong place
>>> ;)
>>>
>>> Would there be a way to reduce the thresholds for the wave folder
>>> circuit so you can get a similar amount of folding without so much gain
>>> required? Or pass the signal through two stages of folding or something
>>> instead to get a similarly complex effect?
>>>
>>> I don't think there's a sweet spot on the 13700 that will suddenly make
>>> everything ok. Sure, you can abuse it, but as long as you're using it
>>> right, it is what it. Fine-tuning isn't going to change the fundamentals of
>>> the device at all. More control current gives more control feedthrough.
>>> That might be ok if your control signal doesn't change fast, but it'll
>>> thump worse if you're feeding it envelopes (for example).
>>>
>>> HTH,
>>> Tom
>>>
>>> On 6 Jul 2017, at 19:05, Tim Ressel <timr at circuitabbey.com> wrote:
>>>
>>> > Thanks for all the info, but I am concerned about broadband noise. I'm
>>> already using the lin diodes.
>>> >
>>> > I am making a wave folder that has a ridiculous amount of gain on the
>>> back end, and the VCAs are making too much noise for my customer. I'm
>>> trying to minimize the noise through optimizing the LM13700 circuit if
>>> possible. The alternative is to switch to a linearized 2164 VCA, but I am
>>> trying to avoid the redesign.
>>> >
>>> > I'd like to know if there is a 'sweet spot' on the 13700. Less input,
>>> more control current, or vice-versa. that kind of thing.
>>> >
>>> > --timbo
>>> >
>>> >
>>> > On 7/6/2017 5:33 AM, Tom Wiltshire wrote:
>>> >> There's a great paper on minimising *distortion* in the LM13700:
>>> >>
>>> >> http://www.openmusiclabs.com/2015/10/my-summer-vacation-by-g
>>> uest/trackback/index.html
>>> >>
>>> >> It covers noise in passing, but you might learn something useful.
>>> >>
>>> >> In short, I'd agree with Richie. Maximise the signal level, accept
>>> some distortion (just call it "warm analog character") and be sure to use a
>>> decent op-amp I-to-V convertor on the output not just a resistor to ground.
>>> >>
>>> >> HTH,
>>> >> Tom
>>> >>
>>> >> ==================
>>> >>        Electric Druid
>>> >> Synth & Stompbox DIY
>>> >> ==================
>>> >>
>>> >>
>>> >>
>>> >>
>>> >> On 6 Jul 2017, at 12:51, Tim Ressel <timr at circuitabbey.com> wrote:
>>> >>
>>> >>> Hi,
>>> >>>
>>> >>> Does anyone know how to minimize noise in an LM13700 design? I've
>>> been playing with the balance between input level, control current, and
>>> output I/V conversion gain trying to minimize noise but with limited
>>> success. The datasheet doesn't seem to cover this.
>>> >>>
>>> >>> Thanks!
>>> >>>
>>> >>> --
>>> >>> --Tim Ressel
>>> >>> Circuit Abbey
>>> >>> timr at circuitabbey.com
>>> >>>
>>> >>> _______________________________________________
>>> >>> Synth-diy mailing list
>>> >>> Synth-diy at synth-diy.org
>>> >>> http://synth-diy.org/mailman/listinfo/synth-diy
>>> >>
>>> >
>>> > --
>>> > --Tim Ressel
>>> > Circuit Abbey
>>> > timr at circuitabbey.com
>>> >
>>> > _______________________________________________
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-- 
Quincas Moreira
Test Pilot at VBrazil Modular
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