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Foot Volume/Expression

Q.I often hear the term "impedance" in relation to connecting an electric guitar to an amp or effect processor. What does "impedance" mean?


The term "impedance" is often heard when discussing the connections between various electronic devices, especially electric guitars, amps, and effects. Impedance refers to a particular electrical characteristic, the resistance and reactance of a circuit to electrical current. It's used in phrases such as "high impedance" or "low impedance" to describe the input or output properties of an electronic device.

When connecting your guitar, effects, and amp, it's important to match the impedance between output and input to attain the optimal electrical response and get the best possible guitar sound. Though you don't need to become an expert on impedance, it's important to understand a few basic principles when connecting your guitar to amps and effects.

Impedance Matching
Due to the way in which a normal (passive) electric guitar pickup converts sound waves to voltage, its output impedance is high (i.e., a high impedance output). This means that the input of a device to which you connect the guitar's output must be able to accept a high impedance signal. If you connect a guitar to a device with a low impedance type input, you will experience problems such as decreased high-frequency response and decreased volume.

Some guitars have active electronics that include a built-in preamp circuit (if your guitar requires batteries, this is usually an indication that it contains active electronics). Guitars with active electronics usually provide a low impedance output.

In general, here's what you should keep in mind when making connections: The input impedance of the receiving device (i.e., the amp or pedal input) should be equivalent to or higher than the output impedance of the sending device (i.e., the guitar's output).

Impedance of BOSS Compact Pedals
BOSS compact pedals are designed with a high impedance input (to which you connect your guitar) and a low impedance output (which you connect to your amp) in order to preserve the original tone of your guitar and minimize noise problems.

Impedance and External Noise
Impedance is also an important factor in how the sound is affected by external inductive noise (hums and buzzes). In general, lower impedance signals are less likely to be affected by external inductive noise. Since the output from the guitar is usually high impedance, it is easily affected by external electric noise sources. Conversely, the output from an effect processor is low impedance, so it is less likely to gain external electric noise.

With this in mind, it's best to keep the high impedance portion of the signal path (guitar to amp, or guitar to pedal) as short as possible to eliminate the possibility of noise interference. When you place an effect processor - such as a BOSS compact pedal - in between the guitar and amp, you're actually preserving the signal's quality, since it's converted from high to low impedance at the pedal (these benefits remain even if the pedal's effect is bypassed). Once the signal has been converted to low impedance, you can run a relatively long cable length to your amp if necessary.

Note: This high to low impedance conversion is also known as "buffering" the signal.

Another use for impedance conversion comes when you want to connect the output of an electric guitar or bass directly into a line input on a mixer or similar device. By placing a BOSS pedal in line between the instrument and mixer, you convert the guitar's high impedance signal to the low impedance signal the mixer wants to receive. (If you need to convert a signal from unbalanced to balanced as well, you should use a direct box such as the BOSS DI-1).

BOSS Foot Volume Impedance
BOSS manufactures foot volume pedals in both high impedance models (FV50H, FV-500H and FV-300H) and low impedance models (FV-300L, FV-500L and FV-50L). Choose a model based upon the position where the foot volume will be placed in the signal chain.

Note: For tips on choosing the proper foot volume model, refer to the related FAQ: BOSS makes foot volume pedals in both high-impedance and low-impedance models. What model should I use with my guitar setup?


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