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One day while Carl was adding some compression to a guitar track in his studio, he thought, why hasn’t anyone built a small opto-compressor for guitarists?  An optical compressor performs gain reduction control via a light source into a photo sensitive cell… as the light source gets brighter, the photo sensitive cell sends a signal to reduce dynamic range, or what becomes a compressed signal.  Welcome to the Classic Optical Compressor….an old-school compressor from the days where colouring was an important factor to the sound.  The four controls (from left to right) are the Gain, which controls the ‘pre-glow’ of the optical circuit (the more you turn this up, the fatter the sound); Level, which controls the overall volume of the compressor; Compression, which controls how hard or soft the compression is, and the Attack control which takes the signal from transparent to outright total squeeze.  A short time with this compressor will allow you to find some of those classic guitar sounds which may somehow have escaped you before.  Again, like all the Vintage pedals, the Classic Optical Compressor comes in a solid diecast housing with cool chicken-head knobs, CM colour and graphics and a 9v battery compartment.  Due to the nature of compressors, we highly recommend a regulated power supply (like the CM ProPower) or a large stock of batteries…..

This is what they say

VINTAGE GUITAR (USA) September 2010
The Carl Martin Classic Optical Compressor is designed specifically to give guitarists the type of optical compression used in studios and on bass-guitar tracks for years.
Like the DC-Drive, the Classic Optical Compressor is impressively musical. And it’s capable of being very subtle – it easily dials in very slight compression to even out the overall sounds, which is great for players who want to clean up notes without squashing them. If you’re going for spanking, vintage compression, fear not. It does that, too. Just keep honking on that Attack knob. Chicken-pickers and surf guys, in particular, should sit down with this box and take notice – the Classic Optical Compressor sounds as good as some top-dollar studio components.

Fuzz Magazine (Sweden) November 2011
I’ve always liked compressors, but often encounter compressor pedals that are not versatile enough. One may work and sound great to singlecoil but not at all with humbuckers. One might have a perfect attack, but is a bit too dark in tone. There are more compressors I do not like, than the ones I do like to use.
Typically, compressors are not equipped with more controls than sustain / compression and level. Here are four knobs which is more than most compressors and this requires that you have to understand a little more about what compression is to set it correct.
However, it is not that difficult and well worth it. I started out setting all knobs at 12 o’clock. Then I turned on the knobs according to taste and to my great joy that gave these four knobs a flexibility that is rare in the pedals. With different combinations of Gain and Attack, I got it to work for both single coil and humbuckers.
The gain is valuable because I can tune it so humbuckers don’t get too thick and woolly in the sound, but I can also “fat” a thinner single coil and give it a really funky attack. Level has quite a lot of output so it can be used as a combination of compressor and booster. The CM Classic Optical Compressor is a great and unusual flexible compressor pedal that works both to creatively transform your sound and to adjust the level of the guitar as is often done in the studio.

From Harmony Central
For the price, its fantastic. I have a high end rack optical compressor I was using for my guitar sound, nice sound not so easy to cart around.
So I thought I would try this Opto pedal. To my delight it is every bit as smooth and fat as I was looking for. Thick and smooth is the way I would describe the sound. Great

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