Extensive compressor reviews and FAQ

ART Tube PAC: This is a half-rack-width unit, and it operates at both line level and instrument level, balanced and unbalanced. "PAC" stands for "preamp and compressor". Essentially it is an upgraded version of their old Levelar model that I reviewed previously. It has lower noise, the tone is not as dark/muddy, and there is none of the click sound on the attack that I occasionally heard with the Levelar.
There is very little noise, although the highs are "open" enough that any buzz/noise from your signal chain can get amplified noticeably. There is no loss of lows either. Note that during heavy compression the highs can get ducked down, so how the highs sound will depend on how you set and use the unit. The tone overall is warm and smooth, but not an exaggerated tubey effect. Some people have reported good results swapping in different tubes, for either cleaner or fatter sound.
The only attack/release control is a button to switch between "auto" and "fast"; The auto setting works pretty decently, but I found myself using the "fast" mode more often. The ratio control is also limited to a button that switches between "compress" (~2:1) and "limit" (~6:1). The compress mode is better for tonal fattening, and the limit mode is better for a more effect-y dip-and-swell squash action. It's not actually a great peak limiter for slappers; real limiting requires a much higher ratio. The threshold knob and the LED metering are very useful features--using them (along with your ears of course) is the key to getting the best results. The top row of LEDs indicates how strongly your signal is driving the unit, and the bottom row indicates the amount of compression being applied.
Because the PAC is also a mic preamp, it has some mic-related controls. There's a +20dB switch for boosting mics that have super low output; this could also be used to overdrive the input with your instrument, but doing that doesn't sound so good to me. There's a phantom power switch, and a switch for phase reversal. Most guitar/bassists wouldn't need those, but one exception would be an upright bassist who uses both a pickup and a mic at the same time.
The construction is a bit cheap, but not flimsy--it would probably survive if you dropped it. The bypass switch (a button, not a footswitch) is not "true bypass", and it's not really even a bypass at all: your signal is still affected by the gain stage and the level knob. It just switches the compression part of the circuit on and off. The unit has an attached AC power cord--no wall wart, no daisy-chaining. Overall it sounds pretty good, and is a very good value.
Price in USD: $35-$90 used, no longer available new.


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