ODP: [DIY-PCB] Negative / Positive CV input circuit

[Roman Sowa]

For gain-match & constant-input-resistance purists here's my proposition.
I used it as CV inputs for VCO. Uses 2 opamps, but I selected
this one regarding all pros and cons (c'mon, it's only one opamp more).

With this one I can have high resolution in the middle, and the bleedthru
is much lower when in center position (3mVpp at 10kHz 5Vpp input)

this is only 4K file, so...

Roman
	 <<inverter.gif>> 

> -----Oryginalna wiadomość-----
> Od:	Harry Bissell [SMTP:harrybissell at netscape.net]
> Wysłano:	10 maja 1999 06:04
> Do:	DIY-PCB at onelist.com
> DW:	synth-diy at mailhost.bpa.nl
> Temat:	[DIY-PCB] Negative / Positive CV input circuit 
> 
> Harry Bissell writes:
> 
> John: Thanks for the kick in the seat of the pants (gets me off my dead
> ass).
> You're right. But with a slightly different circuit. If you ues the wiper
> as
> the input you are always screwed. The circuit attached will do the trick.
> Make
> all resistors the same value as the pot, except the two feedback and the
> resistor from stage 1 output to stage 2 input. I can't claim the circuit,
> PAiA
> has used this as a "mixer". My spin is to be a positive/negative CV input
> (with multiple stages).
> 
> I didn't like the 100K values (too high for me). The actual input
> impedance
> here is 28.5K with the wiper centered. and 30K at either extreme. Close
> enough
> (for rock and roll).
> 
> If any DIY-PCB folk have comments or questions, please contact me... or
> I'll
> put it in our schematic.... Harry
> 
> 
> JWBarlow at aol.com wrote:
> Hi Harry:
> 
> Thanks for this info! I've been using this as a CV input for VCFs and VCAs
> 
> for a while but I'd not even noticed the gain change due to the fact that
> I 
> have several different module types that are all mixed in my system, so I 
> often have to add gain just to make things compatible. I'm wondering if
> the 
> gain problem might be correctable by choosing different feedback resistors
> in 
> order to compensate for this -- any thoughts here?
> 
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