Audio buffers placement

[badoumba]

Hi guys,

Could anyone explain where we need an op-amp audio buffer in a circuit with multiple stages? Each guitar pedal effect has an input buffer, but what about if I design a pedal with these two effects in one? It is indeed two effects (only what they are doing in the spectrum makes them different) but there is a continuity in the signal anyway, so it is not clear for me where to place them.

Thanks!

 

[JonSnell Electronic]

It is all about impedance matching, (low impedance will drive equal or higher impedance loads). It gives current gain, nothing else.
So, most manufacturers try and cater for unusual loads by buffering the output.

 

[DF96]

You put a buffer everywhere you need a high impedance load or a low impedance source and the basic circuit does not automatically provide this. You will know where these are necessary as it is part of circuit design to know what impedances you are dealing with. If you take a piece of someone else's circuit then you will need to reverse engineer it to determine the impedance and decide whether it needs a buffer.

 

[badoumba]

Still learning the basics as you can see.

Ok, so these stages are not only found before or after our pedal circuit but might exist inside too, and the design requirements dictates for the addition of such stage.

I found this page which some pretty common ones I guess:
Basic Buffers

Thanks both of you.

 

[badoumba]

What is the purpose of this R3 of 10K in the input buffer?
ElectroSmash - MXR Phase 90 Analysis.

Thx

 

[KSTR]

R3 is a protection (current limiting) resistor for the +input pin of the OpAmp.