[sdiy] Linear input on expo...confused

[Rutger Vlek]

Hi Roman,

Thanks for the reply! As the list doesn't deal with attachment, I'll send the schematic to you privately. The expo is indeed modified in more ways than replacing the NPN with a PNP pair. The reference current is coming from the negative supply indeed. And I have removed the HF trimmer section and input scaling. The CV input section does have a 1K tempco.

Best,

Rutger



On 9 sep 2014, at 13:04, Roman Sowa wrote:

> You said "a bit", while you have to mirror everything and not only replace NPN/PNP. For example the current setting resistor should go now to negative supply.
> Hard to tell anything without your changed schematics.
> 
> Roman
> 
> W dniu 2014-09-09 12:13, Rutger Vlek pisze:
>> Hi all,
>> 
>> I have a fairly standard expo converter here, quite similar to this
>> one
>> (https://plus.google.com/107231411209962227230/posts/C8iVtXKzvet?pid=5628330677174689314&oid=103342596752795218521).
>> However, I needed a current source, rather than a sink. So I changed
>> the circuit a bit and replaced the NPN pair with PNPs. Besides the
>> expo input, I'd like to have a linear input as well, but this is
>> where I'm stuck. I was expecting the principle to be the same as in
>> the current sink expo example from the link, where a resistor to the
>> inverting input of the opamp does the trick. But in my case it
>> doesn't... Any ideas why?
>> 
>> Rutger _______________________________________________ Synth-diy
>> mailing list Synth-diy at dropmix.xs4all.nl
>> http://dropmix.xs4all.nl/mailman/listinfo/synth-diy
>> 
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