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DIY Stompboxes => Building your own stompbox => Topic started by: Oliver on February 27, 2004, 11:57:02 AM

Title: Biasing Network on OPAmp Circuits like TubeScreamer....
Post by: Oliver on February 27, 2004, 11:57:02 AM
Hi,

comparing some Overdrive Schematics with OP Amps. noticing,
that the Voodoo Lab Overdrive (old Version - 2Knob) dont using
a 4.5 Volt Biasing Network like  TS - SD-1 and so on.

Did someone tried to remove the BIAS Network and what will happen, if
you do that to a TS Circuit.... I know it sounds barmy, but i always question for everything i think about (just like a child?)

Thanks for some answeres

bye
Oliver
Title: Biasing Network on OPAmp Circuits like TubeScreamer....
Post by: spongebob on February 27, 2004, 12:24:19 PM
This one?
http://www.geocities.com/CollegePark/Library/1355/voodoolabOD.gif

There are two 47K resistors (right in the middle) that form a voltage divider to create 4.5V, the non-inverting input is connected to it through the 470k resistor.

If you run your opamp on battery power you will always need some kind of biasing, otherwise the input signal would sit right at the bottom of the opamp's operating range. The bias voltage "elevates" the signal so it swings around 4.5 volt. At least that's how I think it works...
Title: Biasing Network on OPAmp Circuits like TubeScreamer....
Post by: Oliver on February 27, 2004, 12:39:07 PM
Quote from: spongebobThis one?
http://www.geocities.com/CollegePark/Library/1355/voodoolabOD.gif

There are two 47K resistors (right in the middle) that form a voltage divider to create 4.5V, the non-inverting input is connected to it through the 470k resistor.

If you run your opamp on battery power you will always need some kind of biasing, otherwise the input signal would sit right at the bottom of the opamp's operating range. The bias voltage "elevates" the signal so it swings around 4.5 volt. At least that's how I think it works...

ahhhha - OK - thats the same kind in green, as we would say here  :D

Thans !!

bye
Oliver