Michael Klein Audio Design Compton Advanced VCA Compressor

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From Michael Klein:

Compton is the result of a long collaboration between Kyle Rasmussen of Vitriol and myself. Kyle asked if we could do a compressor designed with metal in mind, which requires A LOT of care and consideration with this type of effect.

After a number of failures and a lot of thought, I decided to try the THAT4305 dynamics processor I’ve used in my Ball Gag gate forever. THAT Corp has a wealth of information available in their technical documents and engineering support, both of which came in clutch. That being said, this is no copy of a datasheet, and an embarrassing amount of work went into its design.

The result is an incredibly low-noise and frequency transparent compressor that’s so versatile it’s replacing some boosts on my board. I’ve started to use it as an always-on pedal, which makes playing easier, adds note clarity in complex chords, and makes fast passages sound clearer. It has many of the advantages of running an overdrive, with better compression control, lower noise, and no change in tone. I’ve been somewhat shocked at how much I like it in the place of a traditional boost for amps I inherently like their tone.

Compton also features selectable settings, and a switchable clean blend. Both features can be controlled with external TRS switching.

Top Row Controls

CLEAN BLEND – This control adds your unaltered dry tone back into the compressed signal via a lossless mixing circuit. This is only engaged when the Blend LED (blue) is lit, which can be done via the Blend footswitch or through an external TRS switcher (explained later)

At minimum, the output will be 100% the output of the compressor. At maximum, there is no contribution of the compressor circuit and therefore the output is completely unaffected.

THRESHOLD – Threshold sets the signal level at which the compressor starts to do it’s job. In other words, this control tells the compressor WHEN to work.

At minimum, the threshold is lowest and therefore will engage compression at lower signal levels. At maximum, the threshold is highest and therefore will require higher signal levels to activate the compression circuit.

To help simplify setting this control, the indicator LED for the BYPASS footswitch is bicolor, with each color indicating if the pedal is compressing or if it is allowing signal through without actively compressing. RED = compressing, GREEN = not compressing.

Simple!

COMPRESSION – Even for the unfamiliar, this control is very intuitive. Compared to the threshold control, Compression sets how much the signal is turned down when it exceeds the strength as set by the threshold. Comparatively, this control tells the compressor HOW HARD to work.

At minimum settings, the compressor does not limit the signal strength. As Compression is increased, the compressor works harder and more aggressively limits (“turns down”) the signal once exceeding the threshold.

For those in tune with compressors, this control works as a “ratio” control. At minimum Compression setting, the ratio is 1:1. At maximum Compression setting, the ratio is ∞:1.

Not too bad, right?

GAIN – This control serves as an output level compensation, partially to address any possible loss in signal strength from the pedal doing its job...but also to allow the player to use this to boost the input of his or her amplifier.

There’s no need to overthink this – you can treat it like the volume control for the pedal.

At minimum, there is approximately -15dB in gain, at maximum there is approximately +15dB in gain. Note, though, that is interactive with any signal strength reduction from the compression circuit.

Bottom Row Controls

THRESHOLD - as above

COMPRESSION - as above

GAIN - as previously described

Note – the bottom row controls are only active when the A/B LED indicator (yellow) is lit. These controls can be engaged via the A/B footswitch or through an external TRS switcher.

Switching and Feature Utilization

As mentioned, you can engage the Clean Blend control, or the bottom row of compressor controls with their corresponding footswitch OR through the use of an external TRS switcher.

Footswitch use: 

• Blend – pressing turns the Clean Blend control on (lit blue) or off (unlit)
• A/B – pressing engages the top Threshold, Compression, Gain controls (led unlit) or bottom row (lit yellow)

External TRS switcher:

Connect a 1⁄4” TRS cable into the EXT jack. A/B is assigned to tip, and BLEND is assigned to sleeve. Set your external switcher to connect tip to ground/sleeve to engage the bottom row of controls. Set your external switcher to connect ring to ground/sleeve to engage the clean blend.

Even when using an external TRS switcher, the LEDS will still function as normal to help verify what the hell is going on.

Approaching your first dialing session

Start with the controls set as below:

• Clean Blend: minimum
• Threshold: maximum
• Compression: 12:00 o'clock
• Gain: 2:00 o'clock

First, use the Blend footswitch to disengage the clean blend (blue LED off).

Second, use the A/B footswitch to activate the top row of controls (yellow LED off)

Third, engage the pedal using the Bypass footswitch. The red/green LED will turn on.

Fourth, begin to play while watching the behavior of the red/green LED. Remember that when this is green, the compressor isn’t doing anything.

Next, begin to turn down the Threshold control, and continue to play guitar. Continue to watch the LED indicator. As you turn it down, you’ll start to notice it will switch to red. When it switches to red, the guitar output is exceeding the current threshold setting, and the pedal is starting to compress the signal.

At this point, you can arbitrarily set the Threshold guitar at a level that where the pedal is actively compressing the signal. Now, turn the Compression control to maximum, and hear/feel how dramatically the dynamics are reduced. Turn Compression to minimum, and hear/feel it as though the pedal isn’t on. Now, begin to fine tune your desired compression amount while playing...making note of how things feel under your hands just as much as how they sound.

Also, make note of the interaction between Threshold (WHEN to compress) and Compression (HOW HARD to compress).

Lastly, use Gain to adjust the output level to the amount you desire.

Feel free to compare what your playing feels/sounds like with Compton on/off at this point, and continue to tweak! Cool, huh?

Once you have a setting you’re liking, you can now engage the Blend footswitch (blue LED lit) to engage the Clean Blend control. Begin to increase this control, and you’ll start to notice more of the pick attack artifacts and “roughness” of the guitar start to come through more and more. This isn’t a bad thing, and is a VERY welcome addition under different settings!

Power Requirements

Jack - power jack is the industry standard 2.1mm “Boss style” center negative

USE 9VDC ONLY! Use of higher input voltage will damage the Compton pedal

Current draw = 110mA (minimum 150mA power supply recommended)