From wikipedia:
Typically a current buffer amplifier is used to transfer a current from a first circuit, having a low output impedance level, to a second circuit with a high input impedance level. The interposed buffer amplifier prevents the second circuit from loading the first circuit unacceptably and interfering with its desired operation. In the ideal current buffer in the diagram, the input resistance is zero, the output resistance infinite (impedance of an ideal current source is infinite). Again, other properties of the ideal buffer are: perfect linearity, regardless of signal amplitudes; and instant output response, regardless of the speed of the input signal.
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From Pete Cornish:
The true-bypass function can create dreadful problems with a system that uses many pedals. Take for instance a 20' guitar cable linked to 10 pedals (Julia has 8), each linked by a short cable and then onto the amp by a 25' cable. If all pedals have true bypass and are off then the total cable length hanging on the guitar output will be over 50'. This will cause a huge loss of tone and signal level particularly if the guitar uses low output singles or medium output humbuckers and high impedence. The amp volume is then turned up, and the treble control increased to compensate for the losses.
The inherent background noise now increases by the amount of gain and treble increase, and is usually, in my experience, too bad for serious work. If one of the pedals is now switched on, then its high input impedance and usually low output impedance will buffer all the output cables from the guitar, and the signal level will rise due to the removal of some of the load on the pickups.
Consider the change to approx 22 ft of cable. But the treble will rise and the tone and volume will not be as before. If that pedal was say a chorus or delay, devices typically set to unity gain, then your overall signal level and tone will vary each time an effect is added. This is not a very good idea.
My system, which I devised in the early 70s, is to feed the guitar into a fixed high impedance load that is identical to the amp input, then distrubute the signal to the vaiour effects by low-impedance buffered feeds. This gives a constant signal level and tonal characteristics which do not change at all when effects are added.
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From me:
Now the Cornish system can be very expensive to implement, however it does have its merits. Running buffers at the beginning of the chain will adversely affect stuff like fuzz faces, germanium transistor fuzzes, and germanium transistor rangemaster circuits, which is exactly what I've got at the beginning of the chain. Then comes the Dano Cool Cat TOD. Everything up through here is true bypass, including my Peterson Strobe tuner.
This I run into an Ibanez Tubescreamer, which is my buffer that tightens up the signal before going onto anything else beyond it. This goes into a true bypass Little Big Muff Pi, into a true-bypass Micro Q-tron, then into an always on MXR M-108 EQ (this has no bypass. It is always on, even if you bypass the graphic part of the circuit), then into the amp.
I find this gives the benefits of running my germanium fuzzes, a buffer to tighten the signal, and then onto some other effects that I use before the amp. I have no horrid signal degradation with my single coils. They are still as bright and glassy as ever.
I don't need the bright switches turned on. I don't need a noise gate, even when I dime the gain on the Grail, which I've only done once just to see what it would do. Same chain.
So the effect of a buffer in the chain is to effectively shorten the cable run to that of between the buffer and the amp, rather than have it be the entire run. Buffers are there for a reason.
And if you look at these photos.....
1) I don't think Dave Navarro (RHCP) is particularly worried about this board sucking his tone:
Nor is Satch:
And Les Paul wasn't too concerned either:
And now for the ridiculous from John Frusciante: