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  • Warm Audio WA-2A Leveling Amplifier

    By Phil O'Keefe |

    Warm Audio WA-2A Leveling Amplifier

    Holy superlatives Batman - this optical tube compressor-limiter is an awesome deal!


    by Phil O'Keefe





    When you get right down to it, there are only a handful of compressor/limiters that are truly legendary. Modern classics like the Manley Variable Mu and the Empirical Labs Distressor would certainly qualify, as would expensive vintage models like the UREI/Universal Audio 1176, Neve 2254 and of course the Fairchild 660 and 670. But any list of classic compressors would be glaringly incomplete without the Teletronix® LA-2A. Originally designed for broadcast use by a USC trained electrical engineer named Jim Lawrence, the LA-2A (and its predecessors the LA-1 and LA-2) uses an electro-luminescent panel and light dependent resistor combination called a T4 or "photocell" for gain reduction, and this is a big part of what gives them their unique sound. These tube leveling amplifiers were made in Southern California by Jim's company (Teletronix) in the late 1950s through the mid 1960s. The Teletronix brand was later purchased by Bill Putnam Sr. at Studio Electronics (later UREI), who made them until 1969. They've been put back into production a few times since, and Universal Audio makes a Teletronix branded LA-2A reissue today. Several other companies also make compressors based more or less on this classic design. Warm Audio, who are already well-known for their amazingly affordable, great-sounding takes on some other vintage hardware classics have now released a new product that they call the WA-2A - a name that leaves little doubt as to where its influences come from. How similar is it to the classic design, and most importantly, does it offer up the legendary '2A sound?


    warm-audio-wa-2a-fabbc383.jpg.186ff980aebd3ff5e86d0610a00eb77c.jpgWhat You Need To Know

    • The Warm Audio WA-2A is their take on the classic LA-2A Leveling Amplifier. Like the model that inspired it, the WA-2A is an all-tube, electro-optical compressor-limiter or "leveling amplifier."


    • The Warm Audio WA-2A is housed in a two-space high rack mount enclosure measuring 19" W x 3.5" H x  7" D and weighing in at 12 pounds. For maximum opto-cell life Warm Audio strongly recommends leaving one empty rack space above the WA-2A to facilitate proper ventilation and cooling.


    • Warm Audio stuck with the original fully discrete, all-tube circuit. As with the originals, the controls are simple. The compression ratio is fixed outside of a simple Compress / Limit switch, and there is no way to adjust the attack or release time.


    • The attack time is fixed at 10ms although it varies somewhat with frequency, while the release time is program-dependent, and will change depending on the level and nature of the audio signal. It typically is in the 0.06 second range for 50% release, and can take from 0.5 to 5 seconds to release fully.


    • Its program-dependent nature makes the WA-2A not only super-easy to set up, but also very forgiving and very "musical" sounding. Like the original, this is an exceptionally smooth, silky and sweet sounding compressor.


    • The WA-2A has two main knobs on the front panel - Peak Reduction and Gain - that control most of the action. Peak Reduction controls the amount of compression (you can think of it as a Threshold control) and Gain sets the amount of make-up gain. There is 40dB of gain available.


    • A large backlit VU meter in the center of the WA-2A's front panel allows you to keep track of the amount of Gain Reduction.


    • A third rotary switch on the far right of the front panel (just above the Power toggle switch) serves as a Meter Select switch and allows you to also display the output level at your choice of the standard +4dB or at +10dB, which can make it easier to see what's going on when processing louder signals.  


    • The rear panel of the WA-2A is equally sparse. The WA-2A has an internal power supply, and uses a standard IEC power cable and connector. It can be switched for 115V / 60Hz AC or 230V / 50Hz operation.


    • Although the IEC connector is fully grounded, an old-school grounding lug is also included.


    • Balanced Inputs and Outputs are provided on both 1/4" TRS and XLR jacks. You can also use the 1/4" I/O unbalanced if you need to, but you should only use one input or output at once.


    • A Meter Adjust knob allows you to calibrate your meter. Turn on the unit, let it warm up a bit, unplug everything else except the power cable and turn the Gain and Peak Reduction knobs all the way down, then adjust this knob until the needle sits at 0 on the meter.


    • A Pre-Emphasis knob adjusts how the unit responds to incoming audio. It isn't a tone control and it doesn't change the sound of the compression itself, but rather adjusts which frequencies it is most sensitive to and reacts to.


    • With Pre-Emphasis set to the marked "Standard" setting, the unit's compression response is full-bandwidth, but as you turn it the other direction, it responds more to higher frequency peaks and less so to low frequency ones.   


    • A Stereo Link function is also provided, and requires a user-supplied 2' (or less) 1/4" TRS cable to connect the two WA-2A's together. Instructions for calibrating two WA-2A units for stereo operation are included in the manual.


    • The heart of a '2A type compressor is the T4  electro-opto attenuator unit that combines the electro-luminescent panel and photocells. Warm Audio picked a very good one in the form of the highly respected American-made Kenetek T4B.


    • The transformers are also a crucial element that impart their own color to the classic '2A sound, and Warm Audio didn't skimp here either. The WA-2A uses high-quality USA-made large-core input and output transformers from CineMag.


    • The tubes and T4B can be accessed by removing the vented top cover, which requires pulling a total of ten screws.


    • Once inside, you'll find that the WA-2A is built with high-quality, full-sized through-hole components mounted on printed circuit boards with nice beefy traces - no tricky to modify or repair surface mount construction here!




    • All of the tubes that the WA-2A comes equipped with are from Tung-Sol. There are four tubes installed on sockets on the WA-2A circuit board. Two 12AX7, one 12BH7 and one 6P1. A user-supplied 6AQ5, 6005 or 6N1N can be used instead of the 6P1 if so desired.


    • There is a fifth tube socket left empty on the circuit board. This is designed to be used with a 6AQ5 tube. Warm Audio decided that due to the difficulty getting these discontinued tubes today in sufficient quality and quantity it wouldn't be possible to include them with every unit. Instead, a 6P1 tube is used instead.


    • The 6P1 tube has the same electronic characteristics as a 6AQ5, but uses a different pin configuration. The 6AQ5's socket is wired in parallel with the 6P1 and is there for those who want to use a user-supplied 6AQ5 to remain 100% true to the original design, although there is no operational or sonic improvement to be gained by doing so.  


    • The Kenetek T4B is also socketed, making replacement easy and allowing you to experiment with other T4 opto-attenuators if you happen to have any sitting around. The WA-2A is compatible with T4A, T4B and T4C opto cells.


    • A printed manual is included and it's a good one, with lots of clearly-written information about not only the unit itself, but tips on how to use it, historical notes, hook-up diagrams and even photo-realistic recall sheets.




    • Unlike the originals, the construction doesn't use turret boards and point to point hand wiring. While this may disappoint purists who are concerned about absolute authenticity, it does save considerably on the amount of time and labor it takes to build the WA-2A, which is reflected in the price.


    • There is no bypass. There wasn't one on the original either, but this is one area where deviating from the original design would have been appreciated by many engineers. The best way to do comparisons is to lower the Peak Reduction knob all the way, although you will need to remember where you had it set, and you'll still hear some coloration from the tubes and transformers when you do.


    • No 6AQ5 tube is included with the WA-2A, but they're not all that difficult to find - at least not yet, and the unit works equally well with the included 6P1.




    There are a few big reasons why the LA-2A has been a studio standard for several decades now, and those important elements are all well represented here in the Warm Audio WA-2A. The control simplicity is the same, and the overall silky tone and gentle sweetness of the program-dependent release hits all the right notes too. So what's the catch? Well, the case is smaller and looks a bit different, and a 6AQ5 tube isn't included, and the build, while very well executed, isn't done in the same way as the lovingly hand-wired originals. But it is still the same classic circuit, albeit with a different layout.


    So how does it sound? Strikingly familiar in its gorgeousness. The WA-2A is a warm, clean and very musical sounding compressor. You can hit it remarkably hard without it distorting or even sounding like it's working hard. It is a knockout on vocals, as well as on bass, both miked up and direct. If that's all it could do it would be more than worth the asking price, but it's wonderful on anything where gentle, smooth compression is desired, with the added benefit of giving whatever you run through it some added low / low-mid beef and color.


    Not only did Warm Audio build a quality product that really gets the classic sound right, but they are selling this tube opto-compressor at a unbelievably low price. What - you're still reading this? What are you waiting for? Scroll down to the Resources section below and click on one of the retailer links and get one for yourself - I'm certainly going to! -HC-




    Warm Audio WA-2A Tube Optical Compressor ($899.00 "street")


    Warm Audio's product web page    



    You can purchase the Warm Audio WA-2A Tube Optical Compressor / Limiter from:




    Musician's Friend    


    B&H Photo   


    Guitar Center    


    If you'd like to discuss the Warm Audio WA-2A or have any questions or comments, please check out this thread in the Studio Trenches forum right here on Harmony Central!





        •    '2A Style, Transformer balanced, high voltage, opto tube compressor

        •    Utilizes premium grade input and output CineMag USA Transformers.

        •    Utilizes USA made Kenetek opto attenuator.

        •    Premium Tung-Sol and Electro-Harmonix tubes. 2x 12ax7, 1x 12bh7, 1x 6aq5

        •    Fully discrete signal path

        •    Socketed to allow for retro-fitting with other opto-cells

        •    Variable Pre-emphasis, allows for compression hipass filtering

        •    Stereo-link capability

        •    XLR and TRS balanced line level inputs - 600 ohms impedance

        •    XLR and TRS balanced line level outputs - 600 ohms impedance

        •    Frequency Response +/- 1 dB, 15 Hz to 20kHz

        •    Gain 40 dB ±1dB

        •    Input Level +16 dB maximum

        •    Output Level +10 dB nominal, +16 dB maximum

        •    Distortion Less than 0.1% THD at ±10 dBm

        •    Noise  = -74dB

        •    Attack Time - 10 milliseconds

        •    Release Time - 0.06 seconds for 50% release

        •    0.5 to 5 seconds for complete release

        •    Meter shows both dB gain reduction and dB output

        •    Power - 115/230 volts (switchable), 50/60 Hz

        •    Dimensions - 19" Rackmount chassis, 2U. 19" x 7" x 3.5"

        •    Weight - 12 lbs










    Phil O'Keefe is a multi-instrumentalist, recording engineer / producer and the Senior Editor of Harmony Central. He has engineered, produced and performed on countless recording sessions in a diverse range of styles, with artists such as Alien Ant Farm, Jules Day, Voodoo Glow Skulls, John McGill, Michael Knott and Alexa's Wish. He is a former featured monthly columnist for EQ magazine, and his articles and product reviews have also appeared in Keyboard, Electronic Musician and Guitar Player magazines.  

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