[sdiy] Using both OTAs in 13700 as one OTA

[Simon Brouwer]

Hi Mattias,
 
I mean the circuit like this:
http://www.bernacomp.com/elec/lockbox/lockbox_vca2.gif
 
 
So, no.
 
Best regards
Simon
 

> Op 10 februari 2016 om 12:31 schreef Mattias Rickardsson <mr at analogue.org>:
>
>
> Simon,
>
> what about the temperature dependencies in the transistor case?
> Is that control circuit more sensitive for temperature variations?
>
> /mr
>
>
> On 10 February 2016 at 09:08, Simon Brouwer <simon.o at brousant.nl> wrote:
> > Yes it was.
> >
> > However, this circuit still uses one opamp, a resistor and at least two
> > diodes.
> > The more straightforward approach adds two resistors, and replaces one diode
> > by a
> > transistor.
> > So this doesn't add much in complexity and cost, and you can control both
> > halves of an LM13700 independently.
> >
> > Best regards
> > Simon
> >
> >
> >> Op 9 februari 2016 om 20:20 schreef Mattias Rickardsson <mr at analogue.org>:
> >
> >>
> >>
> >> Aha!
> >> It *was* a beautiful trick. :-)
> >>
> >> http://electronotes.netfirms.com/AN399.pdf
> >>
> >> /mr
> >>
> >>
> >> On 8 February 2016 at 19:09, Ian Fritz <ijfritz at comcast.net> wrote:
> >> > The reference to the original Jung article is JAES, 23, 1975. This
> >> > method
> >> > was widely used in EN projects. I looked at using this method with the
> >> > LM13700 to aid people who want to build off of these projects, but who
> >> > can't
> >> > obtain the CA3080. It's also an easy way to improve S/N by 3dB, as
> >> > pointed
> >> > out by Serge T. in his EN article from when the chip was new.
> >> >
> >> > I couldn't wade through Aaron's article either. It sounded like negating
> >> > then subtracting? Isn't that the same as adding?
> >> >
> >> > Ian
> >> >
> >> >
> >> >
> >> > On 2/8/2016 2:41 AM, Mattias Rickardsson wrote:
> >> >>
> >> >> On 4 February 2016 at 05:52, <ijfritz at comcast.net> wrote:
> >> >>>
> >> >>> Good grief! Just connect them directly in parallel. An example,
> >> >>> complete
> >> >>> with the W. Jung trick:
> >> >>>
> >> >>>
> >> >>> http://electro-music.com/forum/viewtopic.php?highlight=jung+ota&t=50884
> >> >>
> >> >>
> >> >> What does it do? What is the "trick"?
> >> >> I feel like one of the answers in that thread:
> >> >> "I hadn't heard of this trick before, is there an article somewhere
> >> >> that explains the benefit of drawing bias current from V-? I feel like
> >> >> there's something obvious that I'm missing."
> >> >>
> >> >> I spontaneously found Aaron's idea potentially better than nothing,
> >> >> but I haven't plunged into it.
> >> >>
> >> >> /mr
> >> >>
> >> >
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