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DeFrag
Moderator
USA
3409 Posts |
 Posted - 09/05/2008 : 06:57:27
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I couldn't find much info on this & want to know more.
Admittedly, I know less about electronics than I put on even though I minored @Uni.
What can you guys tell me about the need to use +/- voltages.. I mean where are they necessary or applicable?
TIA |
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Dr. Bob
Moderator
Australia
6593 Posts |
Posted - 09/05/2008 : 09:01:07
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Hi DeFrag & Guys
Most op-amps need to be powered from split rails, because of their internal designs.
In most Boss, & other branded pedals that contain Op-amps, this is achieved by 2 resistors of the same value in series, placed across the Positive to Negative side of the battery.
The central join of the resistors, is used as the common or virtual ground reference.
In most case there is also a 10 to 100uf electro cap, from the negative to the the common point.
This is used for stability, & to lower the impedance of the now virtual negative rail.
There are better ways to do this, & some of the later Boss pedals use a transistor as a split rail regulator.
Lots of words, but it's actually easier to show a sample of what I mean.
If I get some time I will take a clipping from a Schematic, to better show you what I was trying to explain.
There are some op-amps that will run on a single supply rail.
This is how it's done on the SD-1, the resistors vary in value 10K and 10K on the DS-1
Regards Dr. Bob |
Edited by - Dr. Bob on 09/05/2008 09:15:02 |
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Laurie
Double Platinum Member
Canada
4854 Posts |
Posted - 09/05/2008 : 15:02:45
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The SD-1 is actually a good example of the problems with the single-sided supply... The virtual ground rail (actually 4.5V) is not "stiff" enough (settle down, the-destructor). The result is that the voltage of the 4.5V rail wanders a little, bleeding the effect through even if it is turned off. The "Laurie mod" is designed to fix that by stiffening the 4.5V rail.
A dual supply like you have shown avoids this completely - the ground rail is actually ground and doesn't move anywhere (not a virtual ground).
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Dual-voltage Power Supply
