A chromatic pedal tuner will be considered True Bypass when the circuit allows the signal to go directly from the input jack through the switch to the output jack with no connection to the circuitry in the box.
This connection does not degrade the signal output to other pedals or amplifiers. The jacks, wires and switches let only micro-ohm resistance flow inline with the signal which will not affect tone or volume.
This question is often answered by Chromatic Pedal Tuner manufacturers through their clever marketing insinuations. According to http://www.stinkfoot.se/andreas/diy/articles/tuners.htm “Very few actually do produce any tuners with a true bypass arrangement. The only one I have confirmed to be true bypass is the Korg PitchBlack. As for the others... in many cases, I know they aren't, and in others, it hasn't been confirmed to be either way.”
This leads to the Other Question, Which Chromatic Pedal Tuners have True Bypass?
Stinkfoot claims to have checked out most of the Pedal Tuners Brands and found very few with the True Bypass circuitry. Some models are sort of true bypass while other models are not even close. The Korg PitchBlack pedalboard tuner is the only confirmed to be true bypass.
The Peterson Strobostomp is understood to be True Bypass, but it seems to have a 1M resistor in the bypass path that may disqualify this Pedal Tuner. A simple test to confirm if a Pedal Tuner is True Bypass is to plug in the Pedal Tuner. If you can tune your guitar/bass, whether the switch is activated or not, the Pedal Tuner you are testing is not True Bypass.
Remember the definition of True Bypass. The signal must pass straight through the box without going through the circuitry when the effect is bypassed. A failsafe True Bypass can be achieved by wiring a bypass switch inside a separate true bypass box. When this switch is activated, the signal is completely disconnected from the input signal.
When the input to the circuit board is still connected to the signal path and the input impedance of the circuit is loading the signal line, it can cause loss of high frequencies and overall volume. You can test this by connecting the true bypass box to bypass the entire pedal chain so that you have either the straight signal through the bypass box or the buffered signal through the pedal chain. You should be able to hear a difference in sound quality with the bypass box on then off. Let your ears recognize if you need to make adjustment.
The True Bypass Rule is to eliminate the effect of a pedal's input load on the signal when the switch is bypassed. Using a Chromatic Pedal Tuner by itself may not cause any issues, whether it is True Bypass or not. Stacking a series of buffered pedals can lead to signal degradation. To rule out one possible signal underperformance, use a quality cable between the guitar and the pedalboard.
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