[sdiy] LM13700 Noise

[Cooper Sloan]

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-
> guest/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
> >>>
> >>> _______________________________________________
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> >>
> >
> > --
> > --Tim Ressel
> > Circuit Abbey
> > timr at circuitabbey.com
> >
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