[sdiy] LM13700 Noise

[Phillip Gallo]

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