[sdiy] Bending a Sum

[Tom Bugs]

Cheers Tom.

I've only really had a bit of a play in LTSpice (which I'm not fluent 
in!) partly because I'm mainly away from my workshop at the moment.
Interestingly, I did think maybe transistors could somehow be used..
I arrived at something simple with a PNP that gave quite a similar 
shape, but was between 0V and about -0.7 (instead of +5V to 0V) and, 
without adding further opamp buffers, it didn't seem like I could shift 
it up and scale it.
Ha, I'm probably being overly stingey - but I have a basic proto I'm 
playing with (which has the posted simple summer) which has a very tight 
PCB so I'm loathe to rip it all up if there's a simple solution not too 
far away. [reason for change - exponential response isn't ideal...]

Maybe I'll sketch the PNP idea and see if that gives any further ideas.

Ta,Tom


On 18/11/2013 17:12, Tom Wiltshire wrote:
> Hi Tom,
>
> If the blue line was the other way up, it'd be a soft-knee compression curve, or a soft distortion. Perhaps you could experiment with some of the typical soft distortion circuits, and then invert the output to get their output to apparently clip heading towards zero volts instead of towards 5V. Alternatively use the soft clipping on the negative half of the waveform and then shift it up I suppose.
>
> I've only tried straightening out the 2164 in software myself, so these ideas are untested.
>
> HTH,
> Tom
>
> On 18 Nov 2013, at 13:29, Tom Bugs <admin at bugbrand.co.uk> wrote:
>
>> Just wondered if anyone may have a brainwave on this little problem...
>>
>> It is around the area of linearizing the response of an SSM2164 - but, at the moment (blah blah) I wanted to see if I can achieve a rough linearization WITHOUT using the well documented Irwin EDM technique.
>>
>> http://bugbrand.co.uk/images/SumBend.jpg
>>
>> I just have a simple opamp sum stage to generate 5V to 0V from a 0V to 10V control - that's the green line.
>> The standard linearization technique achieves the blue line.
>> How could I bend green to blue without too much extra complexity and, crucially, without using another 2164 cell?
>>
>> Thanks!Tom
>>
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