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OnkartGromt Grompressor Review

There is really nothing like the Grompressor on the market. Note: this is a review of the latest version of the Grompressor.

First of all, it is an all digital device. It is designed especially for bass players. It has both LED metering for gain reduction and an OLED screen that shows specifics including the compression curve as you adjust compression. Do you use multiple instruments or wish you could have one setting for finger style and another for slap? No sweat for the Grompressor which allows you to save up to three presets.

OnkartGromt pedals are handmade in Norway.

Per the website OnkartGromt is a combination of two words; Onkart and Gromt. This is dialect from the western part of Norway and means “Something” + “Good”.

The pedal catalog ranges from the Grompressor compressor to GromBass distortion/drive effect to the FunkyFellow filter. All products are catered to bass players.

The Grompressor comes packaged in a wooden carton with laser engraved detail on two sides and top. Real nice presentation that creates a stellar first impression. The user manual is also quite comprehensive.

Let's have a look at the controls of the Grompressor.

The Level dial is there to add volume — Like a makeup gain function as you add more compression.

The Threshold dial is there to increase or decrease the point at which signals trigger compression. You will see your precise adjustments on the OLED screen. As you raise or lower threshold, the curve on the OLED screen adjusts accordingly.

The Attack dial allows you to control the timing of how much of the initial impact or transient gets passed the compressor without getting squished. Rotating clockwise slows the attack. The range is 1ms to 200ms.

The Release dial gives you the ability to control the timing in which the compression releases. The time range is 20ms to 2 seconds which is a real wide range. Very useful effect here.

Below the Level dial is a switch labeled Ratio which allows you to control how much compression you are going to apply to a signal that goes over your threshold. The range is wide from 1:1 to 20:1 which makes for a fantastic limiter effect.

The switch below the Release dial is the preset switch which allows you to cycle through all three presets. You can also use the right foot switch to cycle through the presets on the fly.

OK, that's only the beginning.

Press down the Menu dial and a whole slew of additional functionality is opened up. You can cycle through the following functions:

  • Blend Control

  • Input Gain for both the left channel and right channel (more on that later)

  • Side Chain function

To adjust these parameters you turn that Menu dial when on each function. Click the Menu dial and you move to the next page (next function). To exit the Menu, you step through the pages until you reach the standard view or load a preset by the toggle switch. This sounds more complicated than it is. You can save a preset at any time by pushing the "Save" function which is the Attack dial. Your setting will be saved to the currently selected present. Use the preset toggle switch to move to the next preset, create your desired settings, and then save. Pretty cool.

Having multiple presets allows you to have significantly different or just slightly different compression settings.

I love it for switching between finger style, a more squishy finger style, and then more of a limiter for slap.

Holding down the right foot switch will auto cycle through the presets. It works, but in practice it is not as easy to quickly flip through the presets as it might seem. Doable, but takes some practice. The preset LED above the right foot switch illuminates a different color to reference each preset.

  • Preset one: Green LED

  • Preset two: White LED

  • Preset three: Yellow LED

Let's talk about the Blend control, which is access in the Menu.

You can blend as much or as little of your dry signal with your compressed signal as you'd like. You will see precisely the mix on the OLED screen. For example, if you want exactly 40% wet and 60% dry, you dial in exactly those percentages which you will see on the screen. Nifty! No more wondering just how much of your dry signal is really in the path. Hey, I'm all for using your ear (and really, your ear knows best), but you have to admit seeing your precise settings on the screen is pretty compelling.

On the top of the compressor are four input/output jacks. There is a of jacks for left in and left out (mono) and then right in and right out. Using both allows you to run the compressor in stereo.

In the Menu you have the ability to set different input gain levels for each set of inputs. The range is 0 to +12db. This is a lot of gain on tap and could be useful if the side chain

function (more on that later) is used with an external source. Why? Because the level of the sidechain input can be adjusted without affecting the signal from the instrument.

Another reason to adjust the input would be to compensate for low output instruments (or reduce the signal from higher output instruments). Additionally, there is a switch on the left side of the enclosure that activates a -10db pad. With all of this functionality there is no reason to worry about clipping or distortion.

The Sidechain function can be activated by entering the menu. A Sidechain is functionality that references a compressors ability to analyze a different signal path rather than your instrument to set the amount of compression. One scenario would be to use a bass drum. Historically, the Grompressor offers several ways to utilize the sidechain function.

  • Off: The instrument analyzes the raw input signal and uses this to determine the amount of compression

  • Internal -40hz: The compression is determined by the input signal, but high pass filtered at 40hz. This setting is great to allow your lowest frequencies to go unnoticed by the compressor, thereby leaving more low end intact.

  • External input: Compression is determined by analyzing the other input

  • External input -40z: Compression is determined by analyzing the other input, but high pass filtered at 40hz.

If you play a 5-string bass, the internal -40hz sidechain function is killer. If you like a tight, compressed signal then just leave the sidechain off. But if you want a big low end, set the sidechain to the internal -40hz setting.

The reason I said historically, is because over the last few months Oyvind, the maker of OnkartGromt pedals, and I have been conversing and testing what has become a new firmware version that adds a few significant new features that I think we are both proud of.

The first of which is extended sidechain functionality that allows you to adjust the frequency of the sidechain from off all the way to 300 hz and precise increments across that entire range. Very cool! Talk about enhanced ability to dial in your low end response. This is it. Similar to what Darkglass offers with the Hyper Luminal but with the Grompressor you don't need any computer software to make the adjustments. It is all accessed via the onboard Menu system.

The Grompressor allows you to set the foot switch to buffered bypass or true bypass. There is relay switching internally that will always bypass the signal when powered off. There is much written elsewhere about the attributes of either form of bypass, but know you have the option to have either with the Grompressor. One thing to note though is that the -10db pad (if you choose to activate) is always inserted after the relays. That means that in true bypass mode you will get a 10db louder signal when the pedal is turned off. If you don't use the -10 db pad then there will be no difference.

To set the bypass setting you hold both footswitches down when powering on the unit. You then use either toggle switch to adjust.

Remember the three presets referenced earlier in this review? There are three presets stored by default. The included manual describes each in detail but suffice it to say, each is set quite different ranging from subtle to very squashed. Each represents a great starting point for you to further refine to taste rather than starting from scratch.

I really like default preset one which is called "Bread and Butter. It gives you more attack and "loudness" when playing finger style. Punchy would be another way to say it. Blend is set at 20% dry and 80% wet. Real nice sound and feel.

Preset three is called "Super smashed" and that it is. Squashed and all out sustain.

The second new feature Oyvind implemented as a result of our conversation and testing is an onboard noise gate that helps make the pedal substantially more quiet. Earlier versions of the Grompressor could get a bit noisy — too noisy for me. Maybe not a problem live, but certainly problematic for recording. The thing is, the Grompressor is a fantastic piece of kit and sounds great but the noise floor was just too much. That bug has been squashed and is no longer an issue due to the hardware improvements and adjustable noise gate (activated through the menu system) to compensate for noise in your chain, instrument, or electrical outlets.

The third new feature Oyvind implemented as a result of our conversation and testing is a tilt EQ function. Yes, like the Diamond BCP-1 or Bass Compressor JR, the Becos Stella, JHS Pulp 'N Peel, and others with an EQ dial. The killer difference here is you can select the tilt center point precisely between 250hz and 1250hz with +/- 6db at any point. The Diamond, for example, allows you to select 900hz or 250hz as the center point. With the Grompressor you could select 250 or 900 or 310 or 590 or 1140... you get the idea.

All new Grompressors will come with the newest firmware that includes these significant enhancements.

If you have an older Grompressor, contact Oyvind trough the OnkartGromt website to see if your device is compatible.

These new updates make the Grompressor an even more compelling option. If you've made it this far in the review, no doubt you can see the amount of functionality baked in to a device that is very pedalboard friendly. The fact that it is all digital allows for updates to firmware that bring new functionality and tweaks.

But not of this matters if the compressor is lackluster in performance. No worries on that front. It sounds great and is highly versatile. It could easily be the only compressor you ever need. Prior to the tilt EQ function I would have said the Grompressor was quite transparent overall. Now you can dial in some more low end or accentuate higher frequencies. The Grompressor is capable as a subtle smoothing effect or as a limiter. It is not a highly colored device so don't think of it as a "tone magic" machine. But it is not sterile or boring either. Especially when you factor in the tilt EQ and side chain functionality.

All that said, there is complexity that comes with all of the functionality.

For those that love tinker and tweak, the Grompressor will bring much happiness. For those that see all of this as unnecessary complication, well that's where the three presets come into play.

But it is not for the faint of heart. It isn't for somebody who is afraid to navigate a digital menu system and make adjustments. But once you dial it in, you can save your settings.

It is also important to note that both the 7 LED's for gain reduction and the OLED screen make it very intuitive to understand exactly what the compressor is doing. In that sense, the Grompressor could be the best pedal compressor yet for those really wanting to understand how compression works. You do not need to worry about messing up your pedal either. Play around as much as you want because you can always reset the firmware back to default settings simply by pressing down both foot switches while powering on the device and then selecting reset with the right toggle switch.

As a guitarist and bassist who gravitates to bass, I really like this compressor. It was developed especially for bass players and it shows. Oyvind is also a stand up guy and very open to new ideas. It was a lot of fun to collaborate with him on the functionality additions.

Input/Output jacks are top mounted.

There is a green LED that illuminates when power is supplied to the pedal.

A white LED illuminates above the left foot switch when the pedal is activated.

Both foot switches are the soft switch variety.

Power requirement is 9 volt standard Boss style.

The pedal itself feels quite lightweight but seems to be well made. The enclosure is a lightweight aluminum.

Because of my interest in the Grompressor, I have also been using the OnkartGromt TurboTore which pairs very well with the Grompressor. The TurboTore is a killer parametric EQ pedal for bass. It works real well as a preamp too. A review of the TurboTore is for another time, but it is worth mentioning here that anybody looking for preamp and compressor pair should consider these two devices.

It's a shame OnkartGromt is not more well known. My experience with the Grompressor and TurboTore make me want to try other Onkart pedals.

If you can handle the configuration aspects of the Grompressor, I highly recommend it.


  • Versatility

  • OLED screen

  • LED meter for Gain reduction

  • Presets and the ability to save your own

  • Extendable firmware

  • Side chain functionality

  • Tilt EQ

  • Noise Gate

  • Dry/wet blend

  • Form factor

  • Easy power requirements


  • Complexity

  • All digital may be a turn off for some

  • Ability to cycle through presets on the fly not as easy as you might think

Price: $299 USD


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