Poor output drive capability, or to put it another way high output impedance, is also a problem with certain effect pedals too. Even when the pedal is engaged the buffer circuitry cannot adequately drive the load that cables or other pedals present so a buffer can be used after these types of pedals to prevent tone loss.
One final scenario where a buffer is useful is with certain effects that are prone to self-oscillation. These include some wahs, fuzzes and the Effectrode Phaseomatic tube phaser. If these pedals see a high input impedance or open circuit they begin to ‘chirp’ or squeal uncontrollably generating sounds independently of the guitar input signal. In some cases this might be desirable, for instance if you’re trying to create 1950s sci-fi effects with the Phaseomatic, however if you’re in a live situation you, your audience and especially your sound engineer won’t appreciate hearing a wah pedal squealing uncontrollably. Placing a buffer before these problem pedals will ensure they always see a low impedance and prevent self-oscillation.
There are situations where a buffer is of no benefit and can even be detrimental to tone. For instance if your guitar is fitted with active pickups or an onboard preamplifier. These devices already have buffer circuitry in them so placing another buffer after them is redundant – it won’t have any effect.
This is the also case with some effect pedals – they already have excellent buffer circuitry built in. For example the Effectrode Fire Bottle tube boost pedal has a high impedance input and low impedance output. Placing a buffer before or after it will serve no purpose other than to introduce a small amount of noise into the signal chain. This introduced noise isn’t severe with just one buffer, however can add up to become significant with many pedals/buffers in series. As a rule of thumb, keep the signal path as short as possible – use effect pedals and tone tools judiciously.
Finally, buffer placement is as much an art as a science. Fuzz boxes are proof of this! Placing a buffer before fuzz can really screw up their tone. Generally fuzzes such as the Effectrode Mercury tube fuzz pedal like to ‘see’ a naked guitar pickup. This is because the pickup interacts with the fuzz to form part of the circuit. The character and how the fuzz pedal reacts will change depending on playing dynamics and where the guitar controls are set. A buffer can destroy this beautiful relationship.