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A couple of questions about op amp distortion

Started by chromesphere, January 27, 2014, 11:35:39 PM

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chromesphere

Hey guys,

Occasionally I get the urge to like...you know...do some learnin'.  At the moment I'm looking at some basic op-amp circuits and I have 2 things I'm not totally sure about.  Lets use the Dist+ as an example:
(http://www.freeinfosociety.com/electronics/schematics/audio/pictures/mxrdistp.gif)

1) For biasing the positive input of the distortion plus there are the 1meg resistors coming from +9v.  I would have assumed that we'd want the positive input of the opamp to sit at +4.5v?  As far as my knowledge of voltage dividers go, +4.5v should be a the middle junction of those 2 (3) 1 meg resistors.  Wouldn't the point where the positive input is actually connected to be closer to ground?

2) The low pass filter on the feedback loop of the dist+ (the distortion pot) is connected to ground.  I have seen some circuits (the love pedal for example) connect this to the +4.5v point of the voltage divider as I described in the last point.  Is there a reason for this?  Is it effectively achieving the same thing? (your guitar signal sitting at a +4.5v bias point).

Hope this isn't too complicated a question(s) to be asking, thanks for any help!
Paul
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