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GROWLER - Bass Guitar Enhancer


Sound Clips for the GROWLER are available on the Media page.

Owners manual are available here: Printable (249KB) | e-Manual (339KB)


NOTE: This product has been discontinued.


The FEA Growler was designed as an enhancement pedal to provide a true analog even order harmonic tone to the notes of a bass guitar. This tone is mostly comprised of a generated second harmonic of the fundamental of the input signal. These even order harmonic tones are blended with the original signal to make a rich full tone.

This even order harmonic tone also makes the sub audible or low amplitude notes from a down tuned bass guitar more audible.  Most bass rigs do not efficiently reproduce the fundamental frequencies of the lowest bass notes.  By adding more of the even order harmonics, the amplifier and speakers appear to be louder and more efficient.

How It Works:

The Growler generates a harmonic signal to add to the clean dry signal.  The generated signal by itself has a hollow sound (lacking the fundamental and the higher partials), but when added with the original dry signal a pleasing textured tone is created.  The Growler will not make your bass guitar sound like a regular guitar, because some of the harmonic structure of the bass note exists in the generated signal.

The Growler has a toggle switch that allows the user to add asymmetrical soft clipping to the generator amplifier. This asymmetrical clipping adds more harmonic content to the generated signal. It can be heard as a very soft distortion or fuzz sound.

The Growler has a input level toggle switch that adds a 6dB gain to the input amplifier.  This is useful to allow low output instruments to drive the Growler circuitry harder for better effect of punch and growl.


  • Small footprint - 4 1/2 inches by 3 1/2 inches
  • WET 1, WET 2 and DRY LEVEL controls for mixing the original signal (DRY) with either of the analog harmonic signals (WET).
  • The CH SEL footswitch selects between the WET1 or WET2 harmonic channels when the pedal is active.
  • GEN FILTER switch applies a 12 dB/octave low pass filter before the generator circuit.  Two cutoff frequencies of 250Hz or 1KHz can be selected by this switch.  This switch only affects wet channel two.  Wet channel one has its filter is set to 250Hz all of the time.
  • ASYMM switch adds asymmetrical soft clipping to the harmonic generator amplifier. The ASYMM function will add more harmonic content to the WET1 and WET2 channels.
  • BRIGHT LEVEL is a treble tone control for the generated wet signal on channel two.  Wet channel one is not affected by this control. 
  • ACTIVATE foot switch places the Growler unit in the signal chain or in Direct Bypass mode. In Direct Bypass mode the signal at the input is directly connected to the output and does not pass through any electronics.
  • The Growler has minimal components in the signal paths to maintain the utmost signal quality.   All resistors in the circuit are low noise 1% metal film type. The capacitors used in the dry signal path are tight tolerance, quiet, multi-layer and metallized polyester film type. The operational amplifiers used in the signal path are JFET input, low-noise, low-distortion “hi-fi quality” devices.
  • The compander (compressor/expander) circuit in the Growler utilizes AOI’s (Analog Optical Isolators), also known as light dependent resistors.  This allows the circuit to have only passive components control signal gain to keep noise and distortion to minimum levels.
  • DIRECT OUT output jack for optional use to send the input to another signal processor or amplifier. This is a passive direct connection from the input jack to the dry output jack.
  • TRS INSERT jack for external processing of the generated signal on the WET2 channel. This is a standard TRS insert where the signal is sent out via the Tip and it is returned via the Ring of a TRS plug.
  • The power supplies onboard voltage charge pump allows the circuitry to operate at 18volts (+9 and –9 volt rails) from a single 9-volt battery or DC power adapter of 9 volts. This allows the signal plenty of headroom from active electronic guitars and aggressive playing techniques (i.e. pop and slap).
  • The “switch on” power supply current is less than 1µA (micro amp) on the signal ground at the INPUT jack. This is approximately 45,000 times (-93dB) less than the commonly used method of connecting the battery’s negative terminal to ground via the sleeve of the plug inserted into the INPUT jack. The “switch on” sensing method used in the FEA Growler keeps nearly all of the circuit’s generated white noise and transient currents out of the INPUT stage signal ground. Extreme measures have been taken to keep the power and signal paths as clean as possible.
  • The power and grounds for the signal path circuitry are separated from the compander side-chain power and grounds to protect the audio signal from spurious noise. The power for the signal amplifiers is exceptionally clean, filtered twice for each rail and all filter stages are oversized.


FEA GROWLER Block Diagram


Fundamental signal input -10dBu @ 50Hz with second harmonic @ 100Hz.

WET level set to unity and DRY signal set to minimum.

FFT Graph - Wet Level Max, Dry Level Min

Fundamental signal input -10dBu @ 50Hz.

WET and DRY levels set to unity.

FFT Chart - Wet and Dry Max


  • DRY Signal level:

Adjustable to +3.5dB

  • WET Signal level:

Adjustable to +6.0dB

  • INPUT gain level switch:

Selectable 0dB or +6dB

  • Maximum Input:

13dBu @ 0dB Gain switch setting

  • Maximum Output:


  • Harmonic GEN LP filter:

220Hz or 1KHz of DRY signal

  • Residual Output Noise:

-65dBu from 15Hz-15kHz
(un-weighted) output gains set to maximum. **This is the absolute worst case noise scenario.**

  • Frequency Response:

15Hz – 15KHz @-3dB (100Kohm output load)

  • Input Impedance:

1M ohm

  • Output Impedance:

1K ohm

  • Power adapter
    noise rejection:

40dBu @ 60Hz
>90dBu @ 2KHz

  • Current Consumption:

Approx. 35mA

  • Battery Life:

Approx. 14 hours
(Due to the higher current needed for the generator circuit the use of a power adapter is advised.)

  • Power adapter (not included):

9VDC 2.1mm Barrel Connector with negative center pin

Product Related News:

March 17, 2010 - News:  Press release on Premier Guitar -- FEA Labs Introduces Growler Bass Pedal

March 15, 2010 - News:  Press release on Harmony Central -- FEA Labs Presents: The Growler Pedal


Specifications and design are subject to change without notice.  However, we will make every attempt to keep information on the web site current to the latest product revision.