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How to Use a Guitar Buffer Pedal

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.

graph_showing_100pF_and_625_loading — Comparison of 100pF and 625pF capacitive loading on a 6KΩ single coil guitar 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 moulded 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.

dearmond_volume_pedal_320px — A buffer placed before this DeArmond volume pedal is the perfect cure for tone sucking.

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 often have crummy 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 too high output impedance, is also a problem with certain effect pedals too. Even when the pedal is engaged the buffer circuitry may not be able to adequately drive the load that cables or other pedals present. A buffer can be used after these types of pedals to prevent tone loss.

Now, this brings us round to that perennial debate guitarists and sound engineers forever keep coming back to—buffered verses true bypass pedals: which is best? Well, the short answer is neither. Both approaches are compromises in one way or another. A buffer stage will always affect tone. Even a well designed buffer made with top grade components, such as the Effectrode ‘Glass-A‘ will introduce a small amount of noise or hiss into the signal—it’s physics (Johnson–Nyquist noise in engineer-speak), every amplifier does, and a buffer is technically a unity gain amplifier. You may not be able to hear it with just one pedal, however noise becomes increasingly apparent as more pedals are added to the signal chain as shown below.

Buffered effects pedals in series — Noise, distortion and tone colouration becomes increasingly more apparent when more buffered effects pedals are added to a signal chain.

And a well designed buffer is the best-case scenario. In reality there are many effects pedals out there with below par buffers that are not only excessively noisy, but introduce unwelcome artefacts and unpleasant sounding distortions, such as crossover distortion and slew-induced distortion, and also curtail the bottom and upper frequency response causing loss of oomph and sparkle, in short, “tone suck”.

But true bypass effects also have their shortcomings. The disadvantage here is one of accumulated contact resistance and capacitance of the footswitches and jack connections when many pedals are connected in series. As more pedals are added to the chain the tone becomes duller as the capacitance of all those footswitch contacts in parallel adds up.

True bypass effects pedals in series — High frequency tone loss becomes increasingly more apparent when more true bypass effects pedals are added to a signal chain.

But there is a simple fix for this: place one buffer at the beginning of the chain. This way you’re getting all the advantages of true bypass (no added noise and distortion) and none of its disadvantages (tone loss due to accumulated parallel capacitance and resistance). A single buffer at the beginning of the chain is the optimum engineering solution for best possible guitar tone.

True bypass effects pedals with input buffer — Placing a buffer prior to true bypass effects pedals solves the high frequency tone loss problem.

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-wah pedal squealing uncontrollably. Placing a buffer before these problem pedals will ensure they always see a low impedance and prevent self-oscillation.

So, in summary, use a buffer in the following situations:

To drive long guitar cables.
To prevent loading caused by older effects pedals with low input impedance.
As a first buffer stage to drive a chain of true bypass pedals.

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 on-board pre-amplifier. 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 as described above. 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.

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How to Use a Guitar Buffer Pedal