TRUTH ABOUT “TRUE BYPASS ” (and
some other goodies).
by B. Andrew Barta
Tech 21 USA, Inc.
everyone keeps asking if our pedals are “true bypass.” There’s
been a lot of (successful) hype about it, which has led to the blind
belief that true bypass is the crème de la crème.
After years of researching and evaluating circuit designs, I came
to the conclusion a long time ago that true bypass is not exactly “true.”
The first effect pedals for guitar appeared about 40 years ago. Circuit
designers wanted to enable musicians to easily switch the effect
on and off at the push of a button. So they installed bypass switching.
However, there was a very limited selection of electronics parts
at the time. The only foot-operable switch was actually designed
for use as a power switch in vacuum cleaners and sewing machines.
They were a single-pole configuration like this:
were not exactly high quality parts for audio design, but the engineers
had to make do with what was available. Unfortunately, the early
bypass circuit configurations had a big drawback. When the effect
was in bypass, the input stage of the electronics was still connected
to the guitar’s pickups:
circuits had an input impedance of about 50kOhm to 100kOhm, while
guitar pickups require being connected to circuits of at least
1MOhm (1,000,000-Ohm) to prevent signal degredation. These bypass
circuits effectively “loaded down” the
pickups, causing an audible difference in the sound. Loading of the
pickups reduces high frequencies and volume, causing what is often
called “tone sucking” --a lifeless, muffled
tone. (Note: with active pickups or preamped signals, this effect
is not as noticeable.)
Later, when there was a better choice of switches, engineers started
to upgrade to a more sophisticated method of switching with a double-pole
accomplished was that you were able to prevent the circuit from
loading the pickups in bypass. So, “True Bypass” was
born. This made a considerable audible difference and became so popular
that people started to modify all their old effect boxes to use
is True Bypass Really “True?”
Does true bypass really deliver the best quality signal from guitar
to amplifier? Well, it’s only really true on paper.
employ a double-pole double-throw switch, you will use a switch
which is likely similar in design to the original sewing machine
switch and never intended for use in audio applications. This usually
can be confirmed by looking at the markings on the switch:
the Voltage/Amperage marking is 120V/1A or higher, then you can
be pretty sure that you don’t have a precision device in
These switches have two main problems for audio:
1. There is a noticeable pop when you switch.
2. They have a fairly high capacitance, typically around 20 pF to
100 pF. High capacitance combined with high resistance attenuates
high frequencies, making your sound dull and mushy. Combine this
with multiple patch cables and it puts us back where we started with “tone
sucking” bypass. (It is not as severe as with the single-pole
switch, but it is there nevertheless.) Unfortunately, this problem
is also multiplied when several similar systems are in the signal chain.
(or Buffered) Bypass
In the mid seventies, engineers developed an active circuit to solve
the problems of popping and “tone sucking.” These new
designs employed a high impedance input stage which was achievable
by using new Field Effect Transistor on Integrated Circuit designs.
These high impedance devices matched the input impedance of tube
amplifiers (about 1 MOhm) and therefore did not “load down” the
other added benefits to using active bypass circuits. Active bypass
converts the signal to low impedance making it resistant to “tone
other pedals and poor quality or extra long cables down the signal
path. Designers were able to improve life expectancy over big clunky
switches by using smaller, more resilient parts. Active bypass
gave the option to use a fast cross-fading (about 50 ms) FET circuit,
which eliminates the loud pop associated with the passive true
bypass circuit. As a bonus, designers were able to easily add an
LED indicator into this circuit. For passive bypass design, this
addition would have required the use of a triple-pole
double-throw switch, which was scarce and expensive at the time.
In fact, the only drawback of the active bypass system was that if
your battery died, then you lost your bypass signal, too. It was
a small price to pay for all the other benefits, so this circuit
was quickly adopted by most major effect manufacturers. The exceptions
are reissue, vintage or vintage-like pedals. Some wah pedals are still
made with a single-pole switch.
be noted that not all active bypass circuits are created equal.
Some are good and some are not. The circuit still has to be designed
properly, have the correct impedance and use quality parts.
the Recent Development of Digital Bypass.
This is exclusively used by DSP-based products. With digital bypass,
the signal never actually bypasses the digital processor. The analog
signal from the guitar is still being converted to numbers and then
back to analog, but the processor is told not to manipulate these
numbers. Digital bypass saves money because no extra parts are needed
to switch the bypass signal around the digital processor. All bypass
switching is done inside the digital processor using software. The
sound quality of this bypass largely depends on the quality of the
digital converters used and any band-limiting or anti-aliasing filters
on the inputs and outputs of a given design.
not all DSP products use this shortcut. Some designs use combinations
of the above methods, and others use relays for signal switching.
These systems are not as common as the previous ones, and are more
often used in rack style effect processors. The bypass sound quality
of these systems depends on the quality of the relays used and
the circuit design. Some relays give excellent results, others
have the same capacitance problems associated with passive footswitch
Why Should I
Care About Bypass, Anyway?
Because some designs can noticeably change the sound of your guitar.
You may be using any given effect only 10%-20% of the time, but
your signal is going through each pedal/processor 100% of the time.
So the issue of bypass is surprisingly important.
to decide what is right for you, you will need to listen to the
products available. To properly audition the difference between
these circuits, always test one pedal/processor at a time, using
the same exact setup. This means the same guitar and amp with the
knobs set at the same levels. More than one effect in the chain
could give you false results, depending on the location of the unit
in the signal chain.
in the end, what really matters is that you are happy with the
sound. So use your ears, make your own decisions based on the sound,
and don’t believe
any hype. After all, Jimi did pretty well without “True Bypass.”
1. The bypass circuit in some pedals can be improved by using a double-pull
double-throw switch in a true bypass configuration:
a) Vintage pedals using a single-pole double-throw switch.
b) New or reissue pedals using a single-pole double-throw switch.
other side of the coin, some pedals will not benefit from a true
bypass mod --sonically or mechanically: Boss® and Ibanez® type
can overcome the sonic shortcomings of the true bypass switch by
buffering your guitar’s pickups. This can be as simple as
placing a pedal with a buffered bypass between your guitar and the
pedal with the mechanical bypass.
sure you are supplying enough power to your active bypass pedal.
A dying battery or weak power supply will reduce the amount of headroom.
4. Make sure
you are using quality cables to connect your pedals.