Extensive compressor reviews and FAQ

Retrospec Squeeze Box: Good news everyone, it's back! The Squeeze Box was discontinued several years ago, and we have heard promises year after year that it would once again be available. Now (mid 2015) it's for real though, with only minor changes from the original. This unit was designed to be similar to the Urei LA2A in a pedal format. It uses two 12AT7 or 12AU7 tubes for gain, and an optical compression element.
Knobs include Output volume, EQ, Ratio, and Threshold. The EQ has an on/off toggle switch so you can take it out of the path completely. Threshold also has a 3-position toggle for selecting different amounts of sensitivity at the input. There's a 4-segment LED meter that indicates the amount of compression.
In addition to the regular 1/4" output to your amp or other pedals, there is a DI output--an XLR jack with output 20 dB lower than the 1/4" one. This is for balanced connection to any recording setup or PA mixer, and it has excellent sound quality. In my older review I had mentioned directly driving a PA power amp, but the current version does not have that much gain.
The first thing I noticed about the new Squeeze Box is how very clean and nearly transparent it sounds. I tested the original one several years ago, and wrote about how super fat and warm it sounded. My best guess at this difference in perception is that the first time around I was so in love with the funky, rubbery quality it can have at extreme settings that I apparently didn't give the pedal as much of a real listen at other settings. Whereas now I have a lot more appreciation for both thoroughness and subtlety. So what I'm finding is that at most of the light to medium settings the action is quite natural and unobtrusive, making it easier to notice that the tone is really clear. This is true across maybe 95% of settings. You might call it warm, in the organic and non-sterile sense, but it's not the sort of warmth that you would hear as a noticeable effect. It will please people who appreciate the fidelity and sound quality of a high-end tube stereo amp. It's possible that trying higher-gain tubes might get you a dirtier sound.
If you want the "hit on the head with a rubber mallet" effect that I described years ago, you will need to turn the ratio knob all the way up, and adjust the Threshold knob and sensitivity toggle until your signal lights up all the LEDs. At this extreme it dips and swells and gets very funky. Also the compression does dip down the highs when you hit it hard, and this contributes to the sense that it sounds fatter or warmer. So one takeaway from this review is that the Squeeze Box may be less of an automatic Jamerson tone machine, but more of a versatile device for getting a range of qualities--from clean and invisible all the way to squarshy and syrupy. I still love that stronger effect.
There is zero loss of low end, and neither cut nor boost in the mids. With the EQ switched off, the highs are very slightly boosted. When you engage the EQ, it can boost the highs just a little bit more, or it can roll them off. The EQ knob has no effect on the mids or lows. I didn't hear any extra noise or coloration with the EQ switched on, at any setting.
One thing I commented on in my older review was that the Squeeze Box was susceptible to picking up ambient electrical noise. This is true of many tube-driven pedal compressors. My work room is very electrically noisy, so it's a good "torture test" for identifying pedals that may not be noisy on their own, but which pick up noise from nearby light fixtures, appliances, computers, and so forth. Interestingly, I do not hear any noise with the new one! Since the housing and internal layout look pretty much the same as the older one, I wonder if the designer came up with a better grounding scheme? At any rate I am very impressed, because this is the one area where I expected to have some possible criticism about the sound or utility of this pedal--I expected to hear some noise. But I don't hear any, beyond the obvious way the make-up gain stage of any compressor can amplify noise already in the signal.
I haven't used a proper LA2A, but I have tested many other opto/tube comps that claim the same premise, so I'll talk about those. I'd put the Squeeze Box squarely among the best of them, but with the caveat that the audible differences among those best ones are not huge.
In most cases, like the Effectrode, the sound quality is similar but it has a much narrower range of action and controls. I'd say the same thing for the Diamond, even though it has no tubes--the sound is very pretty, but it only operates in a particular range, both in terms of your signal level and in how strongly it reacts to that signal. Even in those two cases though, they do not have the headroom of the Squeeze Box, due to the limitations of their power supplies. That will be true for most typically-designed pedals operating on low voltage DC compared to one running on 120V AC. Lower headroom can mean clipping at the input, or it can mean excessive squashing, or a reduction of tonal fullness and power; so even though I'm saying the Diamond and Effectrode may sound "just as good" as the Squeeze Box, they won't sound that good under as wide of a range of signals and settings.
I wish I could compare directly to the Summit TD-50, but it has been several years since I owned that one. Based on my memory and notes however, I feel the Effectrode and the Summit would sound exactly the same (transparent and smooth) at low to moderate compression settings. I complained that the Summit sounded very good but "boring"; while the Squeeze Box can get very interesting and chewy at its higher settings. The Summit doesn't get into that more effect-like range.
The Markbass is an interesting comparison, as it has a much wider range of control than most other pedals, with good headroom in the sense of handling high signal peaks. But it doesn't quite have either the high fidelity of the Squeeze Box at lower settings, nor the intense effect at higher settings. As great as the Markbass sounds, its performance essentially plateaus at a certain point--probably hindered by its power supply.
I spent several hours directly A/B'ing this pedal with the FEA DE-CL, OVNIFX Smoothie, and Origin Cali76 TX. Each of those is a favorite of mine, all excellent; but no pedal is perfect, each also has weaknesses, or at least aspects where another pedal could be "even better". The Squeeze Box's weakness is that it sounds too transparent and non-magical at lower settings, compared to those other three. To be clear it has the highest of audio fidelity, but that isn't necessarily what we expect from a fancy effect box. When set more strongly though, that's when the Squeeze Box gets magical and really throws its weight around. After doing that shootout over a few days, I came away most impressed by the Origin Cali, which sounded equally sweet at all settings, and no matter what I threw at it. But again, the worst thing I'm saying about the Squeeze Box is that it sounds good--just more clean than I remembered. Where the Squeeze box excelled over the others was its wide-ranging control over the input signal strength, making it a valuable tool for getting good results no matter what instrument you bring.
The Demeter, Old World Audio, and most other solid state opto comps that claim the LA2A as inspiration, are generally very nice sounding; but they lack the fidelity, the headroom, the controls, and the range of effect result brought by the Squeeze Box.
The earlier version had a built-in AC cord, but the new one uses a detachable standard IEC cord. It can run at either 120 or 220 volts, with an internal switch. The chassis is quite rugged and cool-looking. It's very large, slightly bigger than the Markbass, but not quite as big as the Origin Cali. The footswitch is not "true bypass"; the footswitch just switches off the compression circuit, so your signal is still running through the other tube gain stages. That means it sounds very good when bypassed, but it's not switched out of the signal path. Since these are back in production, you should be able to get service from Retrospec if you have any issues; just in case though, here is the Squeeze Box schematic.

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