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A Closer Look at the New Hex Fuzz Output Expander Module

Our popular Hex Fuzz Amplifier produces a unique hexaphonic distortion sound that is distinctive in any audio mix. This module features control over distortion levels; for most settings the Fuzz output is a square wave with 10Vpp amplitude which can be greater than typical signals from the guitar or other Eurorack modules. While this can be easily adjusted using mixers and cross-faders, we felt it would be handy to offer an expander to provide not only this capability, but tone shaping as well.


Presenting the Hex Fuzz Output Expander module


Overview

The Hex Fuzz Output Expander module is an important add-on for the Hex Fuzz Amplifier, creating a large variety of tones with complete control over the mix of sounds for each of the individual channels.


The module features passive tone control circuitry that consists of low-pass and high-pass filters with cross-fade control, much like the classic fuzz pedals. The Tone controls determine the relative amounts of each filter type. On the rear of the module one can select two different values for each resistor and capacitor in the each of the two filter types, resulting in 16 different possible response curves for each channel.


The tone circuit outputs are fed into an active buffer with variable gain of 0.1x - 2x via the channel Volume controls.


The six EQ’d and volume-adjusted fuzz signals are cross-faded with the corresponding clean guitar inputs (obtained from the Hex Fuzz Amplifier Input Thru connector) for the desired wet/dry balance.


Tone controls - Individual channel potentiometers adjust tone according to switch settings on rear of the module


Volume controls - Individual channel potentiometers adjust fuzz volume from 0.1x to 2x gain (-20dB to +6dB)


Wet/dry controls - Individual channel cross-faders adjust mix between clean guitar input signal and fuzz (or any other effect)
















A100 Bus - Keyed power connection with reverse polarity protection. Red stripe is on the left.


Fuzz Inputs - SynQuaNon Audio Bus input connection for 6 Inputs. While designed for fuzz, any type of hexaphonic effects output may be connected to these inputs.


Dry Inputs - SynQuaNon Audio Bus input connection for 6 dry guitar inputs. Can be any type of audio input to be cross-faded with the processed signals.


Outputs - SynQuaNon Audio Bus output connection for 6 outputs.


Filter curve switch - Selects resistor and capacitor values for each channel’s low-pass and high-pass filter.





 

Connections to Hex Fuzz Amplifier or other SynQuaNon effects modules


Only two SynQuaNon Audio Bus cables are needed to interface the Expander to the Hex Fuzz! This avoids the need for 12 patch cables with unnecessary clutter.


Any other SynQuaNon audio effects module(s) can be connected in a similar manner; for example the 13-pin Input Breakout could supply a dry signal, while the FUZZ IN connector could be interfaced with a Hex VCF output, all without extra patch cables.


Of course any of these Audio Bus connections can be adapter for patch cable use with the handy Hex I/O Expander module, allowing connection to non-SynQuaNon modules!

 

Filter switch settings overview

(see detailed filter charts below)


Making filter adjustments:

The upper dip switch is for channels 1 (switches 1-4) and 2 (switches 5-8), the center dip switch is for channels 3 and 4, while the lower dip switch is for channels 5 and 6. Experiment with different settings for each or for all channels by rotating the corresponding Tone control between minimum and maximum and selecting combinations that create the desired tone.


Examples:

Flat Mids Settings

Mid Hump Settings

























Filter charts


The following filter charts represent the 16 different switch combinations for each channel. These charts are from frequency-domain simulations generated using CircuitLab and are representative of what the actual filter circuit responses are.


The left (y) axis is the filter output signal magnitude in dBV (decibel volts). The horizontal (x) axis represents the frequency range from 20Hz to 20kHz. The simulation calculates the frequency response of the circuit as the cross-fader is rotated from the low-pass filter side to the high-pass filter side.


Chart 1 - Switch settings OFF-OFF-OFF-OFF

With the cross-fader fully counter-clockwise (R=0), the response is a low-pass filter (blue trace) which morphs into a notch response centered around 1200Hz as the potentiometer is moved clockwise.


Chart 2 - Switch settings ON-OFF-OFF-OFF

With the cross-fader fully counter-clockwise (R=0), the response is a low-pass filter with higher cutoff frequency (blue trace) which morphs into a flatter mid-frequency response as the potentiometer is moved clockwise.


Chart 3 - Switch settings OFF-ON-OFF-OFF

With the cross-fader fully counter-clockwise (R=0), the response is a almost flat (blue trace) which morphs into a notch response centered around 1200Hz as the potentiometer is moved clockwise.


Chart 4 - Switch settings OFF-OFF-ON-OFF

With the cross-fader fully counter-clockwise (R=0), the response is now a high-pass filter (blue trace) which morphs into a band-pass response centered around 800Hz as the potentiometer is moved clockwise.


Chart 5 - Switch settings OFF-OFF-OFF-ON

With the cross-fader fully counter-clockwise (R=0), the response is a low-pass filter (blue trace) which morphs into a notch response centered around 800Hz as the potentiometer is moved clockwise. This is the typical curve for a 1973 Ram's Head Big Muff Pi.


Chart 6 - Switch settings ON-OFF-ON-OFF


With the cross-fader fully counter-clockwise (R=0), the response is almost flat (blue trace) which morphs into a band-pass response centered around 1000Hz as the potentiometer is moved clockwise.


Chart 7 - Switch settings OFF-OFF-ON-OFF

With the cross-fader fully counter-clockwise (R=0), the response is now a high-pass filter (blue trace) which morphs into a resonant high-pass response centered around 1200Hz as the potentiometer is moved clockwise.


Chart 8 - Switch settings ON-OFF-ON-ON

With the cross-fader fully counter-clockwise (R=0), the response is now a low-pass filter (blue trace) which morphs into a resonant low-pass response centered around 800Hz as the potentiometer is moved clockwise.


Chart 9 - Switch settings OFF-ON-ON-OFF

With the cross-fader fully counter-clockwise (R=0), the response is now a high-pass filter (blue trace) which morphs into a mid hump response centered around 1400Hz as the potentiometer is moved clockwise.


Chart 10 - Switch settings OFF-ON-OFF-ON

With the cross-fader fully counter-clockwise (R=0), the response is now a low-pass filter (blue trace) which morphs into a notch response centered around 1200Hz as the potentiometer is moved clockwise. This is the typical curve for a 1975 Ram's Head Big Muff Pi.


Chart 11 - Switch settings OFF-ON-ON-ON

With the cross-fader fully counter-clockwise (R=0), the response is now a high-pass filter (blue trace) which morphs into a mild notch response centered around 600Hz as the potentiometer is moved clockwise.


Chart 12 - Switch settings OFF-OFF-ON-ON

With the cross-fader fully counter-clockwise (R=0), the response is now a low-pass filter (blue trace) which morphs into a symmetrical notch response centered around 600Hz as the potentiometer is moved clockwise.


Chart 13 - Switch settings ON-ON-OFF-OFF

With the cross-fader fully counter-clockwise (R=0), the response is now a low-pass filter (blue trace) which morphs into a notch response centered around 1000Hz as the potentiometer is moved clockwise.


Chart 15 - Switch settings ON-ON-OFF-ON

With the cross-fader fully counter-clockwise (R=0), the response is now a low-pass filter (blue trace) which morphs into a notch response centered around 1500Hz as the potentiometer is moved clockwise. This is the typical curve for a Triangle, Civil War, or Russian Big Muff Pi.


Chart 16 - Switch settings ON-ON-ON-ON

With the cross-fader fully counter-clockwise (R=0), the response is now a low-pass filter (blue trace) which morphs into a mild resonance low-pass response centered around 800Hz as the potentiometer is moved clockwise.

 

Final comments


This expander was designed to be an inexpensive add-on for existing SynQuaNon modules, hence the absence of voltage-controlled parameters. Next in our pipeline is the Hex XFADE, which features 6 voltage-controlled cross-faders, as well as a Master voltage-controlled cross-fade. It is DC-coupled and can handle both audio and CV signals. It will be introduced in 2023.














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