The Valco FX KGB Loop is a utility pedal built for guitar, bass and synthesizer/keyboards. It wraps an FX loop with a wet/dry blend, a boost, and Valco's variable input impedance control around any external pedal you plug into it, so one switch on your board can manage a whole chain. Valco calls it the "Swiss Army Knife" pedal of its KGB line, a name that comes from the series being designed specifically to work with K (keys, synths), G (guitar), and B (bass)1.
How it works: the loop, the blend and the buffer
The external pedal's input connects to the KGB Loop's "LP SEND" jack and its output to the "LP RTN" jack. The LP SEND signal is essentially a buffered dry output: the input signal is unity gain buffered by a low-noise audio-grade OPA1692 op amp, and a second low-noise OPA1692 audio op amp amplifies the blended output1.
Between those two points sits the blend slider, which implements a sigmoid curve cross fader between the dry signal (as fed to the external pedal) and the return signal, built on a dual channel CMOS variable attenuator. That lets you run the external pedal fully wet, fully dry, or anywhere between1.
Two more controls shape the blended signal:
- Polarity Reverse Switch 0/180: reverses the dry audio signal polarity for use with the BLEND function. The 180 setting allows frequency cancellation between DRY and LOOP signals for alternative blended tones1.
- Phase inversion switch: controls a phase inversion circuit at the "LP RTN" input. It does not affect the dry signal to the fader and LP SEND jack, and Valco notes it is especially useful with delay, phase shift and distortion pedals1.
On top of the loop, the pedal offers Boost/Attenuation from -6dB to +24dB, so it can also serve as a clean level stage before or after the looped pedal1.
Modes A and B: how the footswitch works
A "Bypass Mode" switch selects between two operating modes, A and B, which change what the footswitch does1.
| Mode | Footswitch alternates between | Full bypass requires |
|---|---|---|
| A | Full bypass and the complete KGB Loop signal chain, including the external pedal | Just the KGB Loop's own switch |
| B | The external pedal alone, and the external pedal with the KGB Loop features added around it | The external pedal's on/off footswitch |
Mode A is the one Valco highlights for older pedals: it lets you bypass the KGB Loop and the external pedal completely with just the KGB Loop's switch, which the company describes as great for older "tone suck" pedals such as older Fuzz Faces and early Big Muffs. In Mode B, the external pedal keeps control of its own bypass, and the KGB Loop's features sit around it1. If you are pairing it with a fuzz, the fuzz and overdrive pages cover the pedal types this mode is aimed at.
Variable input impedance and the input selector
The input includes a switch to select between instrument and line input levels, and a rotary impedance selector providing six possible input impedances ranging from 10 kilohms to 1 Megohm. Valco describes the impedance control as acting like a tone control, "making your sound warmer at lower settings and brighter and more in your face at higher settings." It is a tone-sculpting tool, and it is only active in "Inst" mode1.
When the "LINE" position is selected, the input impedance is 10 kilohms and the signal level is attenuated to be compatible with up to 4 dBu line input levels, which makes the pedal suitable for keyboards and other line level devices1. The same impedance feature appears across the KGB line, just like in the other pedals in the series1.
The impedance selector only does anything in "Inst" mode. If you are feeding the pedal a line level signal from a keyboard or synth, the selector is fixed at 10 kilohms and the impedance tone-sculpting is out of the picture1.
Power
The KGB Loop can be powered by a conventional 9V center-negative external supply, or by an internal 9V battery. The battery is accessible by rotating the quarter turn latch at the bottom front of the pedal and rotating the top panel away from the bottom1.
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Questions
Is the Valco FX KGB Loop true bypass?
Yes. According to Valco FX's product page, the footswitch provides a true bypass function. The pedal also has a Bypass Mode switch that selects between two operating modes, A and B, which change what the footswitch alternates between when engaged and disengaged. In Mode A the switch takes the whole chain out of the signal path, while in Mode B full bypass is handled by the external pedal's own footswitch.
Does the KGB Loop run on a battery?
It can. The KGB Loop runs on a conventional 9V center-negative external supply or on an internal 9V battery. The battery is accessible by rotating the quarter turn latch at the bottom front of the pedal and rotating the top panel away from the bottom, so you can swap batteries without undoing screws.
What does the variable input impedance do to my tone?
The impedance selector is a rotary control offering six input impedances from 10 kilohms to 1 Megohm, and it works as a tone sculpting control. Valco describes it as making your sound warmer at lower settings and brighter and more in your face at higher settings. It is only active when the input selector is in the Inst position, and it works best with passive instruments.
Can I use the KGB Loop with a bass or keyboard?
Yes. Valco says the KGB Series is designed specifically to work with K (keys, synths), G (guitar), and B (bass), which is where the name comes from. For keyboards and other line level devices, set the input selector to LINE: the input impedance drops to 10 kilohms and the signal level is attenuated to be compatible with up to 4 dBu line input levels.
What is the polarity reverse switch for?
The polarity reverse switch (0/180) reverses the polarity of the dry audio signal for use with the BLEND function. At the 180 setting it allows frequency cancellation between the DRY and LOOP signals, which Valco suggests for alternative blended tones. There is also a separate phase inversion switch at the LP RTN input, useful with delay, phase shift and distortion pedals.
Sources (1)
- Valco FX KGB Loop, Delicious Audio, 2022-12-22