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TRUE BY-PASS
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Many pedal effects in commerce, because of economics
and constructive reason, adopt "electronic" by-pass system.
It means that an active powered circuit is able to exclude the effect.
The problem is caused by the limits always present in an active
circuit that could seriously compromise the performances of the
other equipment externally connected: an active by-pass excludes
the effect but not its circuit, with limits and defects.The same
occurs for the devices containing active "buffers".
The best solution consists in TRUEBYPASS, that
is "real by-pass".In this case, the switch function is
supplied by a banal (but very expensive!) bistable piston commutator:
it is easily recognizable for its sturdy metal structure and the
unmistakable noisy mechanical action..."clack".
The use of such type of mechanical commutator removes any doubts
about the transparency
of by-pass: with the use of pure electrical contacts, the effect
is physically disconnected and
the direct connection is restored, like if everything was made with
connection cables.
In order to be sure of the presence of a truebypass
and of the complete absence of active circuits,disconnect the pedal
battery and verify that, on by-pass position, the signal works.
A further try: invert IN with OUT; the signal must work as well.
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OTHER SYSTEMS FOR TRUEBYPASS SWITCHING
- RELAIS are mechanical devices where an electrical input allows the contacts
exchange through an electromagnet.
There are many categories of relais in commerce: as regards the signals
treatment, the ampoule REED type is the one thet guarantees the best results.
- RESISTIVE OPTOCOUPLERS: photo-resistors with cadmium sulphide, that
means components which operate as a normal resistor; they do not influence
the timbre and are piloted through the light of a led diode. The particularity
is that the resistor changes according to the light emitted from the control
led.
Used in an audio context, they guarantee an absolute galvanic separation
of the circuit control.
The resistor value can vary from a minimum of 100 ohm to a maximum of
20 Mohm.
In the MIDI control equipment, where some exchanges are managed at the
same time, in order to obtain a pure and transparent action,
it is advisable to use the RELAIS and, in case of more sophisticated equipment,
such as MIDILOOP or
LS42,
both devices have to be used: REED RELAIS + RESISTIVE OPTOCOUPLERS.
In this way, besides having enormous advantages on commutation quality,
the TRUEBYPASS condition is guaranteed.
In order to be sure of the presence of a real by-pass (truebypass), it
is not possible to reveal the presence of eventual active buffer phases:
if the signal does not work when an active buffer circuit exists, the
power is on, and IN/OUT have been inverted, it is not truebypass.
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