[sdiy] basic electronics question - voltage divider

[Jim Bob]

I'm making a basic mixer w/ a tl072.  Each input will have a pot.  I want to take two of the inputs and normalize them to +7 and -7v so that I can shift the mixed signal up or down.
Basically, Im trying to do what Ken has done w/ his mixer
http://www.cgs.synth.net/modules/mixer.html
   
  Thanks again

Scott Gravenhorst <music.maker at gte.net> wrote:
  The +/- version is basically the same as the single ended version, the
negative is just a copy of the positive side. The main problem with a
voltage divider delivering is that the load contributes to the resistance
one of the resistors (usually the one connected to ground). The more
current the load can draw, the lower the voltage will be because the
load's resistance makes that portion of the divider lower. 

A load that varies it's resistance will produce a varying output voltage. 

We need to know what you will use the +/-7 volts for. 

If you will be powering some circuit with +/-7V, then you would be far
better off with two additional regulators to reduce the 15 volts to 7. 

If the divider is "stiff" enough (this means that the resistors are the
correct ratio, but low enough resistance that the load has only
negligible effect on the output voltage) it can be used as a "poor"
voltage reference.

Jim Bob wrote:
>I'm trying to get + and - 7 volts from +/- 15. Im guessing I need 
>a voltage divider. I did a quick google search, and found basic 
>explinations of them, and even problems where they give you the 
>resistor values and u need to figure out the voltage at the 
>output. I haven't found anything that tells me how to figure out 
>what resistor values I need if I know what output I need. I also 
>dont know if anything would be different for a +/- circuit vs a + 
>circuit. I obviously have no electronics background, but Im 
>learning fast! I'd appreciate it if anyone could enlighten me as 
>to how this is done. 
> 
> thank you,
> Scott
> 
> 
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