Stompboxes : True Bypass

This article is devoted to one of the best known switching system : the True Bypass, which is generaly said to be the best, although it has some not so known limits … We shall see that the big question is that TrueBypass keeps a high impedance bypass routing, which makes this circuit not so efficient as usually said when many pedals are chained.

This introduces to a classical quarrel among guitarists : Pro and cons buffering…
Input buffering will be the subject of a second article.

 General principle of True Bypass

 True Bypass

True Bypass appeared as soon as 1965-1966 with the early english Fuzzboxes.
Nowadays, it is still a reference circuit, often said to be ideal.
• Yet it has competitors, as good and sometimes higher.
• Yet it has its limitations which are easy to understand.

True Bypass is based on a double switching principle :
Two inverters operate symmetrically at the input and at the output.

• The first connects the input signal either to the effect circuit, or towards the bypass.
• The second selects  either the “wet” signal or the “dry” signal and send it to the output.
• This double switching creates two well separate routes: “Effect” and “Bypass”.


True Bypass deserves its name and reputation, because the question of routing was actually well thought out:

• The “effect” routing  is what it is to be : it is studied to have a low output impedance…• The bypass routing is fully independent, so it should transmit a pure “dry” signal.
• If one considers only the switching logic, True Bypass is perfect.

At most, it might be objected that one can do the same with only one inverter and some electronics … But it is a marginal objection. The problems are elsewhere.


True Bypass - High impedance dry routing

Despite the myth of the perfect circuit, True Bypass has a weakness:
It is in the bypass route itself, which is a high impedance passive circuit.

•  The “dry” signal is high impedance because it comes directly from the guitar pickups.
•  True Bypass works well if the bypass path stays short : few chained pedals, short cables.
•  It is not suited to numerous chained stompboxes and long or leaky cables :
• Multiplicated cables, jacks, dual inverters, cause losses all along the “dry” route, increasing from pedal to pedal, which may become heavy…

Solutions and rebounds of the problem

If the question is to get a strong  signal on “dry” mode, then an electronic interface should be used. It would take little on the guitar signal, and provide much to the bypass routing, therefore throughout the pedals chain.

• Technologically, it would be perfect …
• But some musicians say that this changes the sound …
• Interesting quarrel, to be followed in a forthcoming article: “Input Buffers

Go and see : 
Input buffers

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