[sdiy] Adapting exponential convertor for single supply

[Scott Gravenhorst]

Oren Leavitt <obl64 at ix.netcom.com> wrote:
>I would go with the midpoint derived "ground". It seems to me that would 
>guarantee proper current sourced into the control pin of the LM13600
>
>- O

Also make sure that when you use this circuit, the ground used to reference signals is
the _virtual_ground_ and not the -v supply pin.

Also please understand that a virtual ground is anything but "good".  It is a
technique that is useful in small circuits where almost NO current is either sunk or
sourced from "ground".  It is also susceptible to noise propagation, so do due
diligence in suppression of noise in the part of the circuit that creates to virtual
ground.  An opamp can help to fortify the virtual ground.

My main point here is that I've seen too often an attempt to do a single supply thing
(why? supplies, especially for small stuff are not expensive) resulting in non-working
crap because of the temptation to use the negative side of the single supply as the
ground instead of the virtual ground.  Virtual grounds also introduce variables that
you really don't want to have to chase.  

My opinion on single supply stuff to mimic what dual supplies do - don't.  just don't.

>
>
>On 7/26/17 5:31 PM, Tom Wiltshire wrote:
>> Hi All,
>>
>> What’s the simplest way to adapt this exponential convertor 
>for a single supply (0-9V)? > > http://imgur.com/ZhixiC7 > > 
>Could I use a simple midpoint bias to act as the ground and 
>expect it to work? It feels wrong, although I don’t know why. > 
>Bumping the “grounds” up to a useful level with diodes feels 
>better somehow, more like is done in this schematic: > > 
>https://hackadaycom.files.wordpress.com/2015/09/two_transistors_expo-sch.png 
>> > What would you recommend? > > Thanks, > Tom > > 
>================== > Electric Druid > Synth & Stompbox DIY > 
>================== > > > 
>_______________________________________________ > Synth-diy 
>mailing list > Synth-diy at synth-diy.org > 
>http://synth-diy.org/mailman/listinfo/synth-diy 
>
>_______________________________________________
>Synth-diy mailing list
>Synth-diy at synth-diy.org
>http://synth-diy.org/mailman/listinfo/synth-diy

-- ScottG
________________________________________________________________________
-- Scott Gravenhorst
-- http://scott.joviansynth.com/
-- When the going gets tough, the tough use the command line.
-- Matt 21:22