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How to Avoid Unwanted Noise in Eurorack Single-string Guitar Processing

Updated: Mar 1, 2022


The Eurorack modular ecosystem is ideal for single-string guitar processing due to the large variety of modules available, allowing for essentially an infinite number of effects combinations.


The majority of Eurorack modular systems today are dedicated to synthesis, sequencing, and percussion applications, to name a few. All modules in such applications are processing signals at full Eurorack levels, namely 10Vpp or higher. Modular synthesizer noise originates from mainly two sources:

  • Switching power supplies

  • Digital modules

Both of these sources are of even greater importance when processing guitar signals; in addition, there's a third source of noise to deal with:

  • The first stage of amplification from low-level string signals to Eurorack levels

 

In this section we will take a closer look at each source:


Switching Power Supplies


The most popular power supplies for Eurorack modular systems are either a 15-18V AC-DC switching adapter coupled with a power distribution board (busboard) that generates +12V, -12V, +5V

or built-in AC-powered closed frame triple output power supplies with passive power distribution boards.


In both cases, a significant amount of power supply ripple (80-120mV) and noise is present, even though some power distribution boards employ modest filtering.

In modules with amplification stages the switching noise is manifested as a high-pitched whine that gets worse with increasing circuit gain.


Digital Modules

Modules that contain microcontrollers or microprocessors can inject clock noise back into the busboard ground planes and spread noise throughout the modular system unless care is taken by the designers to apply proper filtering. This can be mitigated by employing separate power supplies for digital modules, as well as power distribution boards with low-impedance ground paths (note that the latter cannot mitigate switching power supply whine).


High Gain Modules

At around 30-40dB of amplification (which is the range required to amplify guitar string signals to Eurorack modular levels) even the slightest amount of noise in a guitar signal becomes an obvious nuisance. Depending on noise-prevention techniques utilized in the guitar the noise can be a 50-60Hz hum, massive amounts of hiss, or even radio station reception! The entire ground path from modular power supply through the amplifier module and cable to the guitar pickups plays a critical role in suppressing guitar noise.

 

Recommendations in Order of Effectiveness


  • Use linear power supplies for lowest possible ripple & noise; the good ones are typically around 1mV RMS. I recommend Acopian Gold Box 51212T Triple Output supplies as the best you can buy.

Other good options include the Konstant Lab ZDROJ

and L-1 PSU.


  • Use power distribution boards that are designed to have the lowest possible ground impedance. My recommendation is the Genus Modu LIBB.



Don't forget the Guitar!


  • Use a single-point "star" grounding system inside the guitar with the largest AWG wire possible

  • Shield any active electronics using the copper foil method, including the inside of the pickguard

  • Use multiple conductors in the guitar cable for ground connection; do not rely on the shield as the only ground - it is there to shield the conductors and does not have a low enough impedance.

For more details on our noise studies, please see the following thread on VGuitar Forums.

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You mentioned that bringing a pickup signal up to eurorack levels will bring the noise floor up to where you can hear it, but there is yet ANOTHER area which can makes any supply or other digital noise MUCH more apparent. If you take you nice clean eurorack guitar signal & route it through any 'traditional' guitar overload/distortion/gain stages, that will also brings the noise floor up yet again. If these noise sources are not eliminated, then this wonderfully processed guitar signal will probably need to be gated (probably with a VCA controlled by an EF). Additionally, if you are not very careful, these drastic gain stages may showcase certain types of board layout design problems where the traces themselves have unintentionally incorporated…

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Peter Knoot
Peter Knoot
Sep 30, 2022
Replying to

Fuzz is certainly an example of what you mention. The good news is that if one starts with clean Eurorack level guitar signals takes a little less gain than with guitar pedals (not much less). For example our Hex Fuzz maximum gain is 34dB, while the 7-Channel Amplifier/Attenuator (used as preamp) goes up to 40dB. Every dB helps! 😁

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The best thing I've done for noise across my entire studio = Equitech balanced power. I did it 20 years ago, bit more pricey today, but the drop in noise was just amazing - had one of those moments where I turned everything up with no signal to hear noise, didn't hear noise, forgot everything was at max volume and almost blew my speakers/ears when I did play some sounds... https://equitech.com

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Peter Knoot
Peter Knoot
Mar 01, 2022
Replying to

The older Doepfer supplies were linear; now unfortunately they've gone to switched power - fine for most modular applications.

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