Input buffers

Buffers are devices that are interposed between a signal source and the downstream circuit. The most common ones do not provide a voltage amplification but operate impedance matching. This prevents from signal losses of level and the bandwith.
They are technically very useful but little known, and sometimes badly regarded by vintage electronics purists under the pretext that historical circuits do not have any of them — and that Japanese equipment is stuffed with.

Guitar Poppa could not stay indifferent to this electronico-aesthetic quarrel…

Basic properties of impedance buffers

Their first property is to have a high input impedance
They take a very low current on the source, which cannot provide much anyway.
This preserve the level of the incoming signal, and all its harmonics and transients.

Their second property is to have a low output impedance
They are generous. They can output greedy circuits like some old stompboxes, all tone controls, low impedance mike inputs.
They also are able to manage lengths of good or poor cables without losses.

Principles of the input common buffer

input buffers

The buffered input of the stombox is high impedance
• The stompox is permently high impedance, and never sucks any source you plug in.
• The guitars are glad to keep all their level, their clarity and dynamic.

The buffer provides a low impedance signal to all devices in the pedal
• The effect circuit works to its full capacity.
• The bypassed signal is pure and mighty.


The main functional advantages will be found in output connectivity :

Any signal coming out of the stompbox is low impedance.
• In bypass mode : the buffer provides the output signal.
• in effect mode : A good effect circuit is to have a low impedance output.

Each pedal is able to drive the downstream devices.
• Losses in connections, even several meters long and leaky, are minimalized.
• The signal imposes its spectrum and dynamics : it is no longer darkened and dulled.

Input buffered pedals eliminate chaining problems.
• There are no more problems of compatibility and connecting order. .
• Each stompbox works as an adapter at the advantage of those downstream.
• In particular: True bypass pedals which are connected downstream a buffered pedal will work better and with less noise.

buffers - likeyouface basic

Input buffer of a basic LikeYourFace, using one BC549b transistor.

Traditionnal critics

Numerous purist fans of vintage equipment often express criticism about buffering, which focuses on two axis:
• On the one hand the fear of losing some almost magical sounds, some “mojos”.
• On the other hand the discomfort of feeling controls that respond differently.

“The input buffer changes the sonic character”

A buffered effect circuit receives a clean signal, less prone to the hazards, but also to the “good defects” of the sound chain. Many of us knows that some sound chains with separately questionable links can give an inimitable color and grain. We must admit that the sound’s mystery often holds of these combinations which however appear doubtful on diagrams. Now we must also admit that such configurations are little varied, and a bit uncertain.

We are then faced with an alternative:
• On the one hand a distinctive and affective sound, a bit always the same, which is based on a rudimentary technology, and accepts the losses and noise that come along with.
• On the other hand a less uncompromising tone, but as far not uneducated, which can keep close to historical sounds, but more developable, and especially reliable.

“Volume setting of the guitar is shifted”

The buffer pumps much less on the guitar than an ordinary circuit, and makes us feel a higher level. The usually very sensitive shift of the guitar volume knob widens. Overdrive or distortion come faster and with more presence. The Fuzz Face’s clean up  effect when turning down the volume is still active, but seems less contrasted … We must act more widely the button.
Nothing has changed, but everything is changed, or the reverse…

“Tone controls do not have the same effect”

The tone control seems to have more effect, especially in low positions and maximum volume. The resonances due to the interaction between the low pass  capacitor and the pickup inductance are growing in the lower medium. The overall impression is of more darkening settings.

A dilemma can then install: is it a fault inherent to the buffer, or is it that it reveals that the traditional 47nF tone capacitor is oversized most of the time, and that a 27nF or 33nF would be more musical ?

I respect those critical arguments against the buffers

These arguments are both very subjective and understandable.
Can it necessarily mean that a stompbox works badly when buffered ?
The buffers restore sound properties that were often lost in impedance mismatch or leaky cables. Therefore, we have to master a wider range of settings, which upsets some of our guitaristic habits: one can have the impression of losing some fetishes sensations. This is the story of the favorite rag of a little child that passed to the washing machine: it takes time to restore its smell …

Nevertheless, the buffers, if they bother some habits, bring a technical strength and a sonic width that are worth exploring.

Guitar Poppa’s stompboxes : with or without buffer ?

My pedals are designed to be both close to their elders and more flexible in their connectivity with other pedals, less focused on a single sound or a single routing.

I chose to work on the principle of the input buffer, because I believe in the advantages of low impedance connections, and because my effects circuits are designed to undertake without sonic acidity the nervousness  that the buffer brings…

• My pedals requiring a vintage tone have a low pass filter at 5500Hz.
This filter rounds off any acidity coming in a circuit that is too modernly built.
•  I use mostly old op-amps like JRC4558 or even the old 741, which don’t try to overshine.

There is one case where input buffers are not welcome

This is the case of treble boosters like the Range Master…
Their complex response to the microphones and adjustment of the potentiometer paradoxically comes from the impedance mismatch between the microphones and the input stage. This denier must remain unbuffered to obtain a clear and flexible sound, variously colored, never sadly stiff.

Go and see : 
True Bypass

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