How to Use a Guitar Buffer Pedal
by Phil Taylor
What is a Buffer?
Technically a buffer is a unity gain (0dB) amplifier circuit with a high input impedance and low output impedance. In practice buffer pedals are used to prevent high frequency ‘roll-off’ and preserve the brightness of a guitar when connecting it to long cables or effects pedals with lower impedance input stages.
Where to Use a Buffer
Ideally a passive electric guitar magnetic pickup should ‘see’ a 1MΩ resistive load with a capacitance of just a few tens of picofarads in parallel with it. This load is the input impedance of a typical vintage Fender tube amp. If you’re using a good quality instrument cable (such as Evidence Audio or Death Valley Cable Company) of less than 15’ between your guitar and tube amp then you almost certainly do not require a buffer – there will be no significant degradation of tone. However, if the load resistance connected to your guitar pickup is lower than this or the capacitance creeps up into the hundreds of picofarads range then attenuation of higher frequencies will occur. Subjectively this causes loss of brightness or ‘sparkle’ making the guitar tone dull and lifeless. The graph below compares the effects of 100pF and 625pF capacitive loads on a typical single coil pickup.
Guitar cable capacitance can present itself as an adverse load if the cable is very long or poor quality. This is especially a problem with cheaper cables with plastic molded jack plugs, which often exhibit high capacitance. This becomes an even greater problem with longer cables. Even the highest quality cable and connector has some degree of capacitance, however placing a buffer between the guitar and cable will negate its effect to restore brightness significantly improving clarity and definition.
As well as cable loading there are effect pedals that present an adverse load to your guitar. Examples include the Binson Echorec, which – although a beautiful sounding delay machine – has a very low input impedance of 47KΩ. Another vintage effect with low input impedance is the Uni-Vibe at 68KΩ. There are also some older effect pedals that keep their input circuitry connected, even when the bypass switch is pressed, and using several of these pedals in series will result in a cumulative lowering of input impedance. With these kinds of effect pedals, again placing the buffer before them will prevent loading and revitalise tone.
Passive volume or expression pedals are often guilty of tone sucking too. Even a volume pedal fitted with a relatively high resistance potentiometer of 1MΩ can diminish the sparkle and clarity of a Fender ‘Tele’ or ‘Strat’ as the single pickup in the guitar is ‘seeing’ the load resistance of the volume pedal and the amplifier’s input stage in parallel. The cure for this is to place a buffer between the guitar and volume pedal. Incidentally, another point worth noting is that passive volume pedals have very poor drive capability, so it’s good practice to place a second buffer after the volume pedal effectively transforming it into an active volume pedal.
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.
Where Not to Use a Buffer
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.