ADK CLA-1: This is another fairly high-end half-rack unit in the vein of the Summit TLA-50 and Safesound P1. It is an opto design more or less based on the Urei LA3A, aiming for an old-school "character" compression with the added feature that you can swap in different opamp modules for different tonal qualities.
At first I was a little disappointed by this unit because the front panel controls are minimal and poorly marked (there are no numbers indicating dB, ratio, mSec, anything), and it seemed a bit noisy. But the more I worked with it, the more I have fallen for its fantastic tone and action. You have to learn its quirks, and you have to set it "by ear" rather than by principle, so it is not for beginners. But once you have dived in and spent some time learning how to work with it, the tonal results can be awesome- lively, punchy, "3D", funky, warm, syrupy, and surprisingly articulate. There is no loss of highs or lows. Even in spite of its quirks and slightly elevated noise floor, I keep reaching over to switch it on, because it just makes everything sound so good. The noise level is about the same as with the Summit TLA-50, but the ADK's compression and tone is far more "interesting" and fat.
At this point I have only used the stock ADK opamp (their "DOPA-1") and an API 2520; the API has a slightly lower noise floor and a slightly darker sound. I also bought a John Hardy 990C, which ADK had claimed was compatible, but for some reason it is not working in this unit. I have tried to get answers from ADK, but they are a bit spacey. When I called to ask questions about the CLA, the company owner answered the phone, but told me he had no idea how it worked, that his design team came up with it, and he didn't even know what information was or wasn't in the owner's manual (and incidentally the manual says almost nothing useful). I'm still trying to resolve the issue with the Hardy opamp, and I have to admit it's frustrating... but again, this compressor just sounds so good that I can't be too mad about the other bumps in the road. Update: a reader with the same problem got in touch with the actual designer of the ADK, Jon Erickson at Helsing Audio, and Erickson says the ADK can be modified with one extra capacitor to work with the Hardy opamp. This is good news for users who have the luxury of sending their ADK off for modification.
It has a switchable "bass pass" function where the compression is only triggered by frequencies above 150 Hz, which keeps the highs from being "swallowed" by the more intense compression that would normally result from peaks in the stronger low frequencies. They advertise this as being especially good for bass instruments, but you have to decide whether your goal is to limit the low end peaks or to let them through. Both methods are useful. The external appearance of this unit is not quite representative of the high price point, but the interior construction, layout, and components are excellent. The VU meter actually seems honest, for a needle-type meter, and it has the neat feature that the light in the meter dims when the unit is bypassed. The bypass is a hardwire true bypass. It only has balanced XLR in/outputs. I really like this unit, it has become one of my favorites for its tone magic. I recently described to a friend as "the most delicious compressor I've ever heard".
Price in USD: new $900, used $500, if my memory serves. It seems that they are no longer available new, and I haven't seen any used ones around at any price, for the last couple years.