Symetrix CL-150: This is a one-channel line-level rack comp, sometimes considered to be the "little brother" of the Symetrix 501. The CL-150 is essentially a 501 minus the limiter section. Unfortunately the one I have here arrived not performing as well as the 501's did. One of the risks we take when buying old equipment is that it may not be working quite as well as it should due to the age of the components, and any heavy use, smoke, and other wear and tear over time. It's very common for components to drift out of their optimal range of performance over the years, so whether any one that you find for sale would have issues can depend on whether that unit had a hard life.
The first thing I noticed when testing this one is that it was very noisy, and seemed to be distorting. I opened it up, and saw that there were five opamps in sockets; I happened to have some really nice new high-gain, low-noise opamps (NE5532AN) already, so I swapped those in. Instant huge improvement! The stock opamps had been good quality when they were new, but not anymore. I haven't done any further modding yet, but I suspect a cap job would bring this thing into really excellent territory. The rest of this review will be based on the way this unit sounds and works with only the opamps replaced.
The VCA gain reduction element inside was made by Valley People, and 501's with the Valley VCA are highly coveted. However I think the one I'm looking at right now is not the exact same Valley VCA as the one in the "silver toggle" 501 I had. The action is audibly different as well--but it's good! The action is kind of syrupy and even "chewy", especially at higher ratios. Not in an extreme way like an effect, but playing through it has a sort of fluid "bounce". Quite musical and organic actually. The auto attack/release function works quite well. The ratio control covers a wide range supposedly up to infinity:one, however at that max setting it still does not stop all peaks from getting through. The 501 does a much better job of hard peak limiting.
The noise level is now quite low, and there's no distortion. There is no loss of highs or lows, although the lows don't seem quite as massive as with the 501. The highs are articulate and crisp but they get ducked down noticeably during heavier compression, so I got the best high-frequency results with a fairly high threshold or low ratio. The threshold control has a very wide, useful range.
This model has both balanced and unbalanced inputs and outputs, so it will be compatible with any loop or preamp connection. However it doesn't have any input gain control, so it may not work as well with very low input levels. The bypass control is not "true bypass" but it is very clean and effective. The subtly syrupy/chewy action makes this one a lot of fun to play through (at least if you're a compressor nerd like me). It inspires me to groove.