"If you use any number of stompbox effects, you may have already asked yourself, 'Why does my guitar tone sound dead when it reaches my amp, and what can I do about it?'" says Paul Shedden, president and head of sales at Mission Engineering.
With amplified sound, the story begins with the start of the signal chain: The guitar’s pickups. When, say, the A string is struck, the string vibrations are converted by the pickups into an electrical wave frequency of 440hz. The amplifier increases this signal level through several stages of amplification, until the tiny pickup voltage is increased sufficiently to drive a speaker. But along its journey, higher frequencies are affected by the interaction of the two individual copper wires inside your guitar cable and the way they, in turn, interact with the pickups. During this interaction, higher frequencies are lost in a similar way to running the guitar signal though a "low pass filter"—a type of EQ that just cuts the top frequencies.
The farther the signal travels, the more high frequencies are lost, eventually resulting in dull and lifeless tone. This is where a buffer comes in. A buffer is basically an amplifier that operates at unity gain. Most guitar pedal buffers use an op-amp chip to implement it, but it could be any suitable amplifier circuit. The guitar pickups are only connected to the input of the buffer’s amplifier circuit, but the output signal from the buffer is essentially only connected to the power supply.
In practice, this isolates the buffer’s input signal from anything connected to the output—i.e. your effects pedals. So the normal interaction of the guitar cable with your pickups—which causes the low-pass filter effect and the loss of higher frequencies—is limited to the length of cable between your guitar pickups and the input to the buffer. Most guitarist use a relatively short cable for this, so very little high frequencies are lost over this cable run. The amplifier stage of the buffer works because the input signal modulates the incoming power supply (in our example to equal 440hz) to create the now amplified output signal. This stronger signal now travels the remainder of your chain via the first effect pedal on your board and arrives in much better shape at the amplifier.
So using a buffer first in the signal chain is a good practice for avoiding low-pass-filter effects of the cables. Many modern effects pedals already contain a buffer and are sometimes referred to as having a "buffered bypass." Just make sure you have one of these pedals first, or as early as possible, in your signal chain, or you can use a dedicated buffer pedal.
You can also use a buffer at the end of the signal chain where it can function as a line driver (drives the signal that comes out of the last effect pedal in the chain, onwards to your amp). This is useful if you have very long cables running from the output of your pedalboard to the amplifier. There is not normally any disadvantage to having several buffered pedals in a chain. The main thing is to have a buffer at the beginning and sometimes the end. Adding more in the middle won’t provide any benefit in most cases, but won’t be detrimental either. Modern effects pedals will usually have high input and low output impedances, which means they will all work when connected together.
One exception is the classic Fuzz Face, which was conceived back when interaction with other pedals was not a concern, since few other pedals even existed! The Fuzz Face has a low input impedance that is intended to be connected directly to a pickup. Connecting this fuzz to the output from a buffer can create an impedance mismatch causing the fuzz to sound a little harsh and become less responsive to the controls. The solution is to place a Fuzz Face before the buffer, or use a buffer with a fuzz compatibility option to prevent this problem, such as the Mission Engineering Delta III Tri-Stage Distortion pedal."