OnkartGromt / Grombass V2 / Effect For Sale

Grombass v2 is an analog overdrive/distortion effect for bass guitar.

It has a microcontroller inside that controls the gainstages. This is Arduino(TM) compatible. The code is open source.

It is named after the tractor the designers dad had at his farm when he was a kid; “Grombasen”.

It has three modes of distortion.

-Germanium diodes gives you a mild distortion in the background

-LED diodes has the highest sound level and gives more low end

-Silicon is a more modern tone adding more mid-range fuzz

The Grombass has 2 outputs; one distortion and one clean. This way you can either use it as a clean boost or a distortion. The Boost functionallity will work on both outputs.

The distortion in the Grombass is inspired of one gain-stage of the BigMuff. This gives a combination of the clean signal and the distorted, leaving the lowest frequencies intact through the effect.

It is also input for an expression pedal. This will increase the gain and reduce the output level at the same time. Giving you the same level, but with more fuzz. All analog sound.


The power input is quite unique. You can use 7-20V  DC (positive or negative center) or 7-18V AC. Min current is 200mA.

Inside there is a isolated DC/DC converter that supplies the analog end of the effect with +/- 9V. This gives a headroom of 18V. And the best thing of all? It is isolated from the digital part of the box. So you don’t get any nasty digital noise in the signal chain.

And you do NOT need an isolated power supply for this one.

The code is open and can be modified by the owner by connecting an USB cable. The two analog gain stages are controlled by an Arduino Nano v3 compatible card. The code can be found at Github

Onkart Gromt, Norway  

Contact name:
Oyvind Mjanger
Onkart Gromtar
Bass effects for farmers and likeminded
Opening hours:
By Appointment


Welcome to OnkartGromt! We are proud designers and makers of durable and solid effects for bass guitar.

We sell a series of effects, but it is also possible to get a custom build.

Take a look at our products and see why so many musicians are prefering OnkartGromt effects.

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