Vahlbruch Quantum Compressor Review

The Quantum is pink and sparkly. The folks from Valhbruch of Germany have released a pretty cool little compressor. Dr. Henning Vahlbruch, a German astrophysicist, hand makes all of the pedals in the Vahlbruch Effects lineup. From the BBQ (Buffer, Booster, eQualizer) pedal to the Pipeline Reverb to the Quantum Compressor, Dr. Vahlbruch has a lot to offer.

The Quantum Compressor comes packaged in a very attractive box with form fitting foam on the inside. It has a clean, almost Apple computer feel to it. Very nice. There is a simple overview booklet included with very basic information about the pedal.

The Quantum is an optical circuit and is a pretty interesting design. It is 100% analog and very musical in nature.

There are three controls on the face of the pedal.

The Compression/Sustain dial increases the amount of squash on your signal as you rotate it clockwise. I suspect it is operating both a threshold and ratio control. On the low end it is very subtle, but there. On the high end (more clockwise) it is capable of strong squeeze. Definitely limiter range of performance. No serious dip-and-swell action to be found, even at extreme settings.

The Volume dial is makeup gain to compensate for volume lost due to compression. There is plenty of gain on hand.

The switch located between the two dials allows you to set the compression circuit into serial mode or parallel. In the downward (parallel) position the Quantum allows more of your dry signal through which allows you to feel and hear more dynamics as you play. That's what you would expect from a compressor offering parallel compression. Most compressors with this kind of functionality would have some sort of continuously variable "blend" dial where you rotate a dial to allow more or less dry signal through. Not so here. I was certainly skeptical at first but you know what? It works.

It's as if it reacts to the level of aggression in what you are playing and some how knows to allow more or less dry signal through. It is organic feeling.

With the switch in the upward position, the Quantum acts more like a typical compressor where your entire signal is seemingly compressed equally. It is the more squashy of the two settings. With my 5-string basses I preferred the switch in the Parallel position. With my Fender Stratocaster I preferred the Serial position.

There are three LEDs on the face of the pedal. Just above the footswitch is a white LED that illuminates when the pedal is activated. At the top, between the two dials is a white LED that illuminates when the pedal is in bypass buffer mode. More on that in a minute. Below the Compression/Sustain dial is a white LED that illuminates with varying intensity as you play, indicating the amount of compression taking place.

That compression LED is one of the most dynamic single gain reduction meters LEDs I've every experienced.

Other compressors like the Union Tube & Transistor Lab, Diamond BCP-/Bass Compressor JR, and Origin Effects Cali76 CB have single LEDs for this purpose but none of them react with as much sensitivity as the LED on the Quantum. It illuminates just a bit with slight string motion and much more brightly with more aggressive playing and everywhere in between. Still doesn't replace a full LED array in my book but this is the best execution of a single gain reduction/compression level LED I've experienced.

Internally the "Quantum" can be switched from "true bypass" to "buffered bypass". Inside the pedal enclosure on the circuit board are four dip switches that allow you to set the pedal to operate in buffered bypass mode or true bypass. Used at the beginning of the signal chain the "buffered bypass" mode helps ensure a cleaner tone through long cable runs and effect chains. The white LED between the two dials at the top of the pedal indicates the activated buffer mode as "Bypass Buffer On". Nifty.

The footswitch is interesting. This pedal is equipped with what Valbruch Effects calls their "MagTraB" switching technology. Inside the enclosure above the footswitch is an integrated magnet where the position is measured by a sensor on the circuit board. If the footswitch is moved, such as pushing it downward, the position of the magnet will also change. The sensor measures this change without any mechanical contact to the button and the information is sent via a micro-controller to a gold-plated relay, which then does the actual audio signal switching. In the picture below you can see the black magnet suspended on three poles. The footswitch pin will come close to touching the magnet as it is pressed downward. The footswitch pin never does touch the magnet though. Pretty cool. There is no mechanical connection which should make for a very long lifespan.

The footswitch is one of the most quiet I've encountered.

You can also decide whether you want the pedal to power up in "on" or "bypass" mode. Here's how to set that up.

Step 1: Unplug the power supply cable.

Step 2: Hold down on/off "MagTraB" button.

Step 3: Plug in again the power supply cable.

Step 4: Release on/off "MagTraB"" button.

That's it! The next time the Quantum powers up it will be in the other state.

The Quantum is a unique pedal that seems to strive for simplicity yet offering a pretty robust offering of versatility. I do see it as quite unique in the marketplace.

So how does it sound? Simply put, it is lush and transparent. This is not some sort of "magical tone altering device.” No, it is all about transparency and politely smoothing your tone. It does what a good compressor should. It helps even out dynamics, is capable of delivering a high amount of sustain, can be used to regulate aggressive playing and volume peaks, and just makes your playing sound better.

It reminds me of the Keeley Bassist/Keeley Compressor Pro in terms of feel and performance. It sounds good. It doesn't color your tone. It helps keep things in check.

I did not notice much in the way of low or high roll-off though it isn't going to make your low end stronger. The Quantum is not going to make your tone substantially bigger. It will tighten up your low end and control it. The Quantum compressor is working in the background to make everything rounder and smoother. The compression circuit is very quiet at all but the more extreme settings.

It is great at adding sustain.

The sparkle paint looks great. The Quantum Compressor seems like a high quality device and I am pleasantly surprised by it. It's a great little compressor.

Input jacks are on the sides and 9-volt power input is located at the top of the pedal.


• Quiet

• Looks cool

• Interesting functional set

• Very nice compression/gain reduction single LED

• Transparent and sounds great


• Those looking for a "bigger" tone will be let down

• Possibly price

• Not the most versatile

Retail price: $218

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Reviews by Chris Tromp 

Bassist and Marketing Guru

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