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Volume 3, Number 7, September 2005
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Analog Obsession: The LA-610 Compressor
Buy One, Get a Free Mic Preamp!

by Tim Prince
Universal Audio LA-610

An audio compressor has two basic components. One, it's an amplifier with input and output connectors and at least one level control. Two, it has an "automatic gain control" circuit, what I like to call the "little person inside turning the volume up and down." The little guy is "riding gain," trying to keep the volume level smooth and consistent. This very simple overview of a compressor gave birth to the Universal Audio LA-610. Having used the LA-2A for several years and supervised the building and testing of the units here at UA, I've grown to love them. It's not just that warm feeling that happens when I'm smoothing out a vocal for the perfect mix. My admiration for the thing goes deep--that is to say, deep inside the metal can on the back that plugs into a tube socket. This can, what we call the "T4 cell," is the heart and soul of the automatic gain control circuit mentioned above, and the key to the LA-2A sound. Somewhere, some time in the early sixties, James F. Lawrence cobbled together an off-the-shelf night-light and a photo resistor to create the prototype for the first T4 cell. The thing that I find so amazing is that both the night-light and the photocell were being manufactured for simple products that had nothing to do with music, and somehow this guy came up with the idea to use them in an audio compressor circuit. The photocells were used to sense when darkness began and then to switch on lights--like a table lamp in your home. The marriage of these two electronic components serendipitously created the most musically sensitive "little person" to ever ride gain inside a box.

“For many years I chose an LA-2A or an 1176, depending on the tone I wanted. The LA-610 offers another choice, and it’s augmented with pre-compression EQ!”

The LA-610 was a simple idea: Put the T4 cell circuit in the output amp section of our 610 mic preamp. Most of the product cost is in the housing, transformers, tubes, and power supply. A single channel of our 2-610 mic pre is a good value due to our build quantity and manufacturing methods. So adding the T4 circuit and some supporting electronics created an all-tube compressor of the LA-2A style, for a much lower cost. The cost difference between an LA-2A and an LA-610 is due to the high cost of components like transformers that are used in the LA-2A and the intensive hand-built labor required to manufacture an LA-2A. The beauty of the LA-610 is that it rides gain just like an LA-2A or an LA-3A (they all use the same T4 gain control circuit). Though it sounds quite a bit like an LA-2A, it still delivers its own sonic signature. For many years I chose an LA-2A or an 1176, depending on the tone I wanted--not necessarily on how they differ as compressors. The LA-610 offers another choice, and it's augmented with pre-compression EQ!

The LA-610 is great for kick drum. Usually, a kick drum does not need a lot of compression, but using a compressor can tame the big peaks, and add some character and tone to boot. The LA-610 has just the right attack time to let the beater hit come through, then gracefully pull the volume back as the low-end thump happens. The program-dependent nature of the release time works well to keep it all natural. I really like having the EQ right there and can often get everything I want without further EQ. Just use your ears and try extreme settings of high-frequency boost (usually 4.5k for me) and boost or cut of the low frequencies. After finding the desired frequencies with extreme cut and boost values, I'll back them off to low or moderate settings.

I find compressing acoustic or electric bass with the LA-610 is a very similar scenario. The pick or slap of the attack sneaks through, and then a little mild compression really brings the tone forward. Again, a little bit of pre compression EQ yields great results. I do some alt rock sessions and a bit of "progressive Americana." Cello ends up on these projects and it's another instrument that likes the LA-610 compressor, especially if we're tracking pizzicato or plucked parts. Try all the strings--violin, viola, jazz, country, etc.

Speaking of tone and compressors, I sometimes use my Aphex or RNC compressor on "tinny" acoustic guitars. By selecting a very fast attack, it dulls the tone of the guitar and that often works for the mix. This is of course a compromise, as sometimes I lose too much of the dynamics. I tried the LA-610 for this application and had great results. There isn't an attack control to adjust, so I bring the peak reduction knob up until I'm almost always showing gain reduction on the meter (usually -1 to -3 dB), then I might dial in a little EQ--say -1.5 or -3 dB at 7k.

The LA-610 has another attribute that is fun to use. You have a two-stage amplifier that provides a degree of sonic variation through the introduction of harmonic content. Put simply, push the gain and drive the tubes. The LA-610 can be quite transparent and clean if the input is low (or padded) and the gain switch (small knob, upper left of front panel) is set to 0 or lower. In this case, the large level knob will be set at the top end of its range. But if you're looking for something with a little more color, try this: Set the level knob low and put the gain switch at max. Listen to the tone with the compressor off (peak reduction knob at 0). Now turn the level knob up as you turn the gain switch down. Move back and forth in this manner, dirty to clean to dirty. After a while, you will start to get a feel for the sweet spot. It is possible to drive the thing too hard and get unpleasant clipping, so be sure to practice!

There is so much that can be done with this compressor, so it's hard to cut this article off. In closing, I'd like to say that it is an excellent all purpose unit suitable for any instrument. The limitations of the LA-610 mainly concern applications, such has heavily compressed percussion where you may need a faster release time, or any application where you are trying to mold a sound that requires adjustable attack and release times. That being said, please don't hesitate to experiment. The combination of pre-compression EQ, tube-generated harmonic content and the legendary "LA-2A" style gain control produces an extremely versatile and fun tool to use. Oh, and the free mic pre is pretty nice!

P.S. We would love to hear from you, especially any unique applications or instrument scenarios.

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