Home » Recording Resources » Featured Reviews » NOVEMBER 2018: Softube Tube-Tech CL 1B Mk II Plug-in CL 1B Mk II Plug-in and Lydkraft Tube-Tech CL 1B

Classic hardware, compared to a wonderfully faithful software emulation


Review by Paul Vnuk Jr.

The Tube-Tech CL 1A, a hand-wired all-tube optical compressor, was released in 1987. It was followed in 1991 by the CL 1B, which used circuit boards in place of the point-to-point hand wiring, but with zero compromise in quality. The CL 1B is still in production today; it’s gone on to become Tube-Tech’s best selling product, and is widely considered a modern classic in its own right, having been in steady production for 27 years.

In 2007, Softube modeled the CL 1B for the now-defunct TC Electronic PowerCore DSP engine system and for Pro Tools TDM hardware. A native standalone version followed, which we reviewed in March 2010. Softube has also crafted software models of Tube-Tech’s PE 1C and ME 1B passive (Pultec-style) equalizers. The three models were combined together into the Tube-Tech Classic Channel.

Fast forward to 2018, and Softube has just updated all three of the Tube-Tech models to Mk II status in the Tube-Tech Mk II Complete Collection. The new versions offer improved graphics and use the latest advances in analog circuit modeling.

This gives us a great reason to put the new Mk II version of the CL 1B plug-in through its paces, and as a bonus, thanks to the US Tube-Tech distributor TransAudio Group, we also got our hands on a current production hardware CL 1B for direct comparisons. This should be fun!


The Tube-Tech CL 1B: a big blue modern classic

The CL 1B is an all-tube optical compressor. As such, comparisons to the Teletronix LA-2A, which went back into production again at Universal Audio in 1999, are inevitable and justified. The CL 1B definitely nods toward the basic design and function of the LA-2A, but ads additional features like dual-bus sidechaining, attack, release and ratio controls.

The CL 1B is a 3-rackspace 19″ unit dressed in Tube-Tech blue with five large black variable knobs for Output Gain (Off to +30 dB), Ratio (continuously variable from 2:1 to 10:1), Threshold (Off to –40 dB), Attack (continuously variable from 0.5 to 300 milliseconds), and Release (continuously variable from 0.05 to 10 seconds).

There are three large stepped switches for the selection of fixed or manual Attack and Release or a unique hybrid of both, selecting one of the two sidechain buses, and lastly a control for switching the large amber backlit VU meter between Input, Output, or Gain Reduction. There is also an on/off switch and a separate bypass control.

The unit is a single channel mono device with balanced XLR I/O in the back as well as 1/4” TRS connections for the two sidechain bus options. Note that each jack will require a TRS Y-cable for breakout/interconnect.

The optical gain-reduction element of the CL 1B comes just after an input transformer. As mentioned, this is an all-tube design; the only semiconductor op amps are found in the output bus section. After gain reduction is a tube-based push-pull amplifier followed by an output transformer. 

Some specs: frequency response @ –3 dB: 5 Hz to 25 kHz, noise < –75 dBU @ 30 dB gain, CMRR > 60 dB @ 10 kHz, and input impedance: 600Ω


CL 1B sound and use

While LA-2A inspired, the CL 1B is not an LA-2A clone and never was. They can perform similarly depending on how they are set, but sonically the CL 1B is much more modern—especially in its sound, which is sharper and cleaner. Even when pushed, it saturates much differently than an LA-2A.

When the CL 1B is set to around a 3:1 compression ratio to compare to the LA-2A, with the attack and release matched ballistically on each unit’s meters, I would characterize the LA-2A as having a bit more of a dusty “tube” tone, while also being gently spongier in its ballistic feel. The CL 1B, meanwhile, is more ballistically hard-edged, for lack of a better descriptive. This descriptive only applies when comparing these two opto compressor units side by side; the CL 1B is not as hard-edged as a FET compressor, for instance.

For an additional comparison, again at a 3:1 setting, the CL 1B not too far off in sound and feel from the Vari-Mu (tube) compressor in the Manley VOXBOX (reviewed February 2017), meaning the CL 1B has a very hi-fi sheen. I say “around” when setting the CL 1B to a 3:1 ratio, because all settings on the CL 1B are a best guess/feel thing. There are no notches, lines, dots or numbers to guide you… which functionally suits me fine.

The CL 1B offers a very broad range of sound shaping capabilities, not only with its sidechain but also thanks to its unique fixed/manual/bit-of-both attack and release. In fixed mode it functions as a vintage-style compressor with predetermined settings of 1 msec attack and 50 msec release. Most of the time I leave it in this mode, as I like the “limitation” of a compressor doing what it does and asserting its will as it keeps me from having to get too tweaky. 

I also like the flexibility of having fully adjustable attack and release to suit a track’s needs; when that’s the case, the manual mode is right there and waiting for me. Fixed/manual mode, which I also like a lot, is a combination of the two; combining a faster fixed attack with a variable release that lets go quickly and automatically based on the initial sonic peak, and then continues to further release beyond that based the release knob’s position.

While most optical compressors get quickly relegated to vocals and bass duties, these added controls on the CL 1B make it quite adept at pretty much any source you throw at it. I was pleased at its performance on acoustic instruments, modern synths, and drums—from snare (a personal favorite) to overheads. The CL 1B is highly favored for its use on hip-hop and hard rock vocals, where it offers a ton of punch and control and sounds nice and aggressive if pushed.

Just tickled a dB or two, it is also great on program material. I tested the hardware on some folded-down mono mixes (as I only had the one) and really liked the results. Note Tube-Tech does make a stereo unit, the CL 2A… and this is a perfect segue to talk about Softube’s new CL 1B Mk II, since it functions in mono or stereo!


Softube Tube-Tech CL 1B Mk II

The CL 1B Mk II plug-in is available for Windows 7+ (64-bit) in VST, VST3, or AAX (Pro Tools 10.3.7, 11.0.2 or higher), and for Mac OS X/macOS 10.9+, all of the above plus AU. You will need both a Softube/Gobbler account and an iLok account, although a physical iLok key (generation 2 or 3) is not vital—you can authorize one computer’s hard drive to use the plug-in and skip the dongle if you prefer.

Everything I’ve described above and experienced in the hardware is 100% applicable to the new plug-in. As with the original Mk I plug-in, every knob, switch, and meter is an exact replica of the hardware. On the new version, the GUI is more photorealistic and almost three times bigger in size than that of the original (which is shown in the screenshot later in this article and is included with the new version). I used the new plug-in with a Slate Raven controller, and the larger GUI and knobs make for a very satisfying faux-tactile experience.

In the plug-in, there is one functional limitation compared to the hardware: the sidechain only offers one output or bus choice. However, it can function like the hardware if your DAW supports external sidechaining. 

There are also two added functions available only in the software version. First, there’s an internal lowcut-style sidechain with settings of 80 or 220 Hz; this allows signals below those frequencies to pass through the detection circuit without clamping down. Second, there’s a wet/dry mix control, allowing for “in the box” parallel compression techniques. Both of these features, along with the fact that the Softube CL 1B Mk II can be launched as a stereo plug-in, make it very well suited to bus work.


Mk II vs. Mk I… and Mk II vs. the real deal

Like most plug-ins, regardless of how well they are modeled sonically, the biggest differences are in the accuracy of the controls—not functionally, but in the literal positions of the dials, which can of course affect ballistics and tone. For side by side comparisons, I started by setting all three units with a test tone.

I compared both plug-ins to the hardware on everything from individual instruments to a dedicated mono mix/recording of two singers and an acoustic guitar around one mic in a figure-8 pattern (the Josephson C725, reviewed October 2018). I found overall that the neutral, hi-fi top end of both plug-ins were close to the hardware. The exception is that the hardware has a touch more headroom and air prior to breakup.

Where the Mk II clearly improves over the original plug-in is in the thickened depth of its lows and general dimensional fullness. I also found the CL 1B Mk II more tonally laid-back and less obvious than the Mk I. That is a statement that is hard to describe other than to say that the Mk II seats itself in a mix like the hardware, and can be more or less indistinguishable on multiple sources in a dense mix.

Nevertheless, the hardware still has a definite edge over the software when used on elements in a sparse mix; the difference is quite audible. While we’ve all read plug-in vs. hardware reviews that state that “the hardware has a 5–10% analog something”, it really holds true here. The CL 1B hardware does have more dimensional weight, with its top end boasting a hi-fi opulence and airy soundstage that is just beautiful. The plug-in gets close, but that real analog-tube goodness is undeniable.

I suspect that part of this is that, as mentioned above, the the hardware has greater headroom, which gives it a broader ballistic range. Also, of course, when pushed it can reach analog saturation levels that the plug-in simply can’t. It’s awesome to use the CL 1B on the front end and track through it, especially when needing to control vocals or bass on the way into your DAW. All this to say—there’s a definite sonic reason why the CL 1B is as revered as it is and why it’s a fixture in so many studios.

Having said that, Softube really did a stellar job with this emulation. If the hardware is out of your budget for now, there is no way to get closer than Softube has with the CL 1B Mk II.



Looking back at my 2010 CL 1B Mk I review, I found the original to be quite analog-ish and—at the time—one of the best-upper echelon plug-ins on the market to accomplish that illusion in the box. How awesome is it, then, that the new Mk II CL 1B is even more so!

Plug-in modeling has grown significantly in 15 years, and the CL 1B Mk II takes full advantage of these modeling advances. The Softube CL 1B Mk II retains its status in the cream of the crop of today’s best analog modeled plug-ins. I will also say that it takes the throne as Softube’s single best analog-modeled compressor, especially considering how well it holds its own in a dense mix alongside the gorgeous sound of the original hardware… which remains, with good reason, one of the best optical compressors in history and a hard processor to beat at any price.


Prices: Softube CL 1B Mk II, $299.99; Tube-Tech CL 1B, $3650; Tube-Tech CL 2A, $4350

More from: Softube, softube.com; Tube-Tech, tube-tech.com; dist. by TransAudio Group, transaudiogroup.com

2018 Reviews