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It’s over easy bein’ green: GHA’s Liverpool Tube Comp.
If you’ve been around studios for any length of time, you’ve most certainly noticed an old green Altec 436C or two. Y’know the one; Jeep green, big cyclops meter? Typically they are dustily languishing in a rack, radiating “old gear smell,” and waiting for that once in a blue moon when someone wants to “dirty up” a track. “Let’s distort this vocal,” or, “Let’s take this clean guitar track and amp it up.” The gritty old Altec tends to be more like a tone decapitator in that way; used more to color than to compress. Rarely does the green box see use as an every day limiter the likes of an LA-2A or 1176.
But if we “Get Back” in a time machine 5o years, to 1967, we’d see the 436 in a different light. Over in swinging London, The Fab Four had just released “Sgt. Pepper.” As always, The Beatles and Sir George had tracked in that legendary studio on that famous road in London*. The studio, as it turns out, used lots of compressors in the mid-sixties, for many different applications. While the American Fairchild 660 and 670 were their implements of choice, they cost a pile of Pounds, even back then. So the engineers there did something really cool. They bought a less expensive American comp, the Altec 436C, and modified it. The old 436 had been around the sun a few times already by then, being found in radio stations and school PA systems. It was a good-sounding vari-mu circuit, but it had its drawbacks, especially in terms of the attack and release.
So the London studio guys got under the hood and modified it. Their mod made the 436 cleaner, faster and way more useable for the purposes of the studio’s projects. It became more Fairchild-like. (After all, Pink Floyd had just been signed, and they were going to need some useful tools in their sessions). The mod sounded so good they renamed it with its own model number. The rest, as they say, is history.
Having relayed this tale, let’s fast-forward back to 2017, where we find the new Grove Hill “Liverpool” mono vari-mu compressor, which is NEITHER an Altec NOR a Brit-mod. So why did we blow three paragraphs about Beatles compressors? Because this is the story that inspired Brian Cornfield and company to revisit the classic Altec circuit, and not to clone anything, but to design their own enhancements, much the way the Brit engineers did back in the day. The result is a boutique-quality device you’d not hesitate to use on a lead vocal, bass, guitars, or even mix-buss. The price is compressed as well, being significantly under its well-known competitors.
Retro elegance: Liverpool’s front panel w/ big knobs and chickenheads
As Cornfield himself states: “The LIVERPOOL compressor is a distinct and unrivaled product, and NOT a clone of its predecessors. It is a fusion of American and British-modified feedback compressor designs, with modern enhancements that were thoughtfully developed in the spirit of the original Mu tube compressor.”
We chit-chatted with Brian Cornfield recently, and asked him a handful of questions about The Liverpool.
PadGroup: Brian how does your mu circuit work?
BC: The heart of the Liverpool is a 6BC8 dual triode remote cut-off tube for gain reduction (the “Mu” tube). The tube is re-biased by a 6AL5 tube rectified side-chain control voltage, which causes the dual triode tube to smoothly change its amplification.
PadGroup: So you get that desirable soft knee that Vari-Mu limiters are known for?
BC: Correct. The way the Mu tube is re-biased gives the compressor a soft knee curve.
PadGroup: The Liverpool has a simple and elegant feature set with controls that did not exist on the original units, notably “Threshold,” “Attack” time and “Recovery (Release)” time. There’s also a “hold” feature. Can you explain what it does?
BC: Sure. When trying to process the initial attack of an audio track, the slower attack of the compressor may cause an audible downward ducking “thump” to be produced as the triode grabs the signal. The “Hold” control can be used to “prime” the compressor with the required amount of gain reduction and prevent the thump from occurring. So you feed a little of the program signal in to the Liverpool first, let it duck, then select Hold. The gain reduction now sticks where it is. Rewind and start the program again. Once the initial attack of the first note has passed by, the compressor can be switched out of Hold and put back to the desired Recovery setting. The resultant effect is that the instrument is at the exact compressed volume as soon as it plays, no hesitation at all. The result is a punchy, authoritative sound right from the first note.
PadGroup: Would you say that driving the input transformer hard can cause some pleasing harmonic color?
BC: Yes! Many of the users report that they will put the Attack control in the "C" (compressor off) position and adjust the input control to achieve a tube/transformer overdrive that they cant find elsewhere. The unit can adjust from mild overdrive to a square wave of distortion, all controllable to the engineer’s taste.
PadGroup: Where does Liverpool’s mojo come from? Is it the ballistics of the limiting circuit, the tube make-up amp? The transformers? All of the above? What would it sound like if you just ran a signal through it without using any compression?
BC: It’s the whole being greater than the sum of the parts. We find that Liverpool is used by many engineers as a transformer in and out line amp! They will match the gain and just run the audio through it. The sound is very pleasing and more desirable, than running “clean." One of our users even asked if we could make an eight channel box to put in front of his Pro Tools rig!
PadGroup: And the name, Liverpool? An homage to that famous Liverpool band, “A Flock of Seagulls?”
BC: Ha! The Liverpool name is an homage to the British quartet who first discovered that a little compressor from California could be the basis for a significant contribution to the music of the 60's … and today.
June 26, 2017, by Drew Townson
The ears behind the gears, Brian Cornfield with Liverpool
* Due to trademark legalities, we are prohibited from using the name of the London studio or the record label.