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  • Warm Audio WA-47 Multipattern Tube Condenser Mic

    By Phil O'Keefe |

    Warm Audio WA-47 Multipattern Tube Condenser Mic

    Is this new mic destined to become the volksmikrophon of the project studio universe?


    by Phil O'Keefe




    When it comes to microphones, there are few that can lay claim to as much legendary notoriety as the Neumann U47. It was Neumann's first post-war mic, it was the first mic with a pattern select switch, and its condenser mic technology provided a huge improvement over the standard ribbon microphones of the day in terms of detail and high frequency response; this resulted in significant changes in the recording and broadcast industries, with the state of the art U47 becoming the new industry standard for vocal recording. And boy, has it been used on a ton of recordings - from Sinatra to Ella, the Beach Boys to The Beatles, it's one of the "big five" legendary vocal microphones. It's also been used to record tons of other instruments too. But the U47 (and its close sibling, the U48) has a dark side - replacement tubes are next to impossible to obtain. This has been an issue since the late 1950s and resulted in Neumann discontinuing U47 production, and led to the stratospheric rise in prices for vintage U47s and tubes for them, with mics going for five figure prices, and even a replacement tube for one selling for thousands of dollars - if you can find one. Enter Warm Audio, a company that has built their reputation on mass-producing high-quality reproductions of some of the most coveted vintage studio gear at real-word prices. One of their latest projects is a microphone inspired by the famous U47, which they've named the Warm Audio WA-47. Let's take a close look at one and see how similar it is to the mic that inspired it, and in what ways it's different.





    What You Need To Know

    • The Warm Audio WA-47 is a large diaphragm, multipattern tube microphone that was inspired by the vintage U47. Visually it looks quite similar. The microphone itself measures 254 mm long and it's 63 mm in diameter at the widest point of the head basket, so its considerable size is very similar to the "long body" version of the original mic. 
    • The metal body is finished in a matte gray, while the head basket and grille are chromed. A round WA logo badge is located at the front of the mic, while on the back the Warm Audio and AMI brand names are printed. Unlike the original U47 (which has a pattern select switch on the bottom chromed area of the head basket), there are no switches anywhere on the WA-47 itself.




    • The WA-47 comes with an external power supply, which it needs in order to operate. It can be set for either 115V or 220V operation. An IEC power cable is included. 
    • You'll find a power switch and blue jewel lamp on one end of the power supply, and a 9-position rotary switch on the other end. This is used for setting the desired polar pattern. No need to wait for a WA-48 - unlike the original '47 (which offers cardioid and omnidirectional patterns), or the closely-related U48 (which has cardioid and figure-8), the WA-47 offers not only cardioid, omni and figure-8 polar patterns, but also three intermediary steps between omni and cardioid, and another three in between cardioid and figure-8, giving it excellent pattern adjustability.
    • In addition to a regular XLR output cable, tube mics need a dedicated multi-pin cable to connect the mic to the power supply. Warm Audio didn't skimp here - the WA-47 comes with a high-end Swiss-made Gotham Audio GAC-7 7-pin cable with Zwee connectors. The Gotham GAC-7 cable is a bit on the short side at five meters (16.5'), but not ridiculously so, and it's nice to see such a nice, high-end cable included.
    • There are four main elements to the classic U47 that most experts feel contribute to the majority of its sonic character - the head grille shape, size and screens, the condenser capsule, the tube, and the output transformer. Let's look at how Warm Audio has addressed each of these areas.
    • The physical size, shape, and internal cubic volume of the head basket on the WA-47 is very similar to the mic that inspired it, with a three-layer mesh consisting of thicker outer and inner mesh with a finer mesh sandwiched in between.






    • The U47 used two different capsules over its lifetime - the M7 and the K47. The original M7 used PVC membranes for the diaphragms that hardened over time and suffered a loss in low frequency response. The K47 uses Mylar instead, and doesn't suffer from that issue. Sonically both the M7 and K47 style capsules have their fans, but both are equally capable of great sound. Checking out the interior of the Warm Audio WA-47 reveals an Australian-built recreation of a K47 capsule. It carries the Warm Audio model number WA-47-B-80V.




    • The WA-47-B-80V capsule appears to be very well made and it has all the features you'd expect to find in a K47-style capsule - it uses a single backplate with the distinctive K47 hole pattern, and six micron NOS Mylar (PET film) gold sputtered center-terminated dual diaphragms.
    • The metal-bodied VF14 tube used in the original U47 and U48 was made from 1946 until 1957, and Neumann was given first crack at every VF14 tube Telefunken made - those that met their requirements for frequency response, low noise, low grid current, low microphonics and low distortion were stamped with an M (for Mikrofon) and used in their U47 and U48 microphones. According to those in the know, less than one in every three VF14 tubes were up to the task of being used in a mic, and the rest were set back to Telefunken and used in consumer radios. Those rejected tubes either won't work at all in a mic, or if they do, the mic won't sound right. There simply aren't any stockpiles of usable VF14M tubes left.
    • Because of the lack of new VF14M tubes, everyone who has ever wanted to build a U47 style mic has faced the question of what tube to use in its place. Even as early as the late 1950s the supply of suitable tubes was starting to dry up. Neumann's replacement was the Nuvistor, which was nearly universally disliked. Others have used various different tubes in the '47-style mics, including EF12, EF14, EF80 / EF800, EF86, EF732, EF814k, 407A and 408A and various tubes in the 12AX7 family - 12AX7, 12AT7, 6072. etc.
    • The Warm Audio WA-47 uses a JJ Electronic Slovak-built 5751 twin triode tube. This is somewhat similar to a ruggedized 12AX7 with a lower gain factor (70 instead of 100). The 5751 tube is designed to run with either a 6.3 or 12.6 volt heater voltage and a maximum DC plate voltage of 330V.




    • The VF14M used a 105V DC B+ voltage, and it was under-heated in the U47, with the tube filament running at around 35V instead of the 55V the tube was designed for. Of course, the 5751 is a completely different tube, so this is one area where necessity demands a different approach to the design than what the original used.
    • Warm Audio seems to have taken the approach of using a quiet and relatively neutral sounding tube to replace the unobtainable originals. This lets them put more of the focus on letting the sound of the capsule and transformer shine through. Considering their dual goals of trying to emulate the sound of a classic mic and trying to keep the price affordable, coupled with the unavailability of the original tubes, this seems like a reasonable approach to this reviewer.
    • It's not that the 5751 doesn't add to the sound of the mic - in fact, I suspect it contributes significantly (along with the output transformer) to the WA-47's very appealing subtle distortion, which kicks in gradually as the sound source you're miking up gets progressively louder. It's not a heavy distortion, but a subtle growl and grit that really adds character when things get hot and heavy.
    • The overall build quality of the WA-47 is very good, and for the most part, so are the parts that have been selected. The WA-47 uses 1% tolerance metal film resistors. The capacitors are WIMA, Solen French, and polystyrene.




    • The transformer used in a microphone can have a big impact on the sound. The original U47 used a BV8 transformer. Warm Audio is using a high-end Tab-Funkenwerk (AMI) USA-built output transformer. It's marked as a WA Ollie Special - most probably as a tribute to the late Oliver Archut from AMI, who was one of the world's foremost experts on German-built vintage audio equipment.




    • While the WA Ollie Special is in impressive piece of iron from a very well-regarded company, I don't suspect it's identical to a BV8 in all respects. The tube feeding it is different, with different specifications, so the transformer's specifications would have to be at least somewhat different to accommodate that.




    • As far as accessories, the WA-47 comes with everything you need, including the power supply, the 7-pin cable, a shock mount (with two extra elastic bands and an adapter for European mic stands), and a wooden storage box for the microphone itself.




    • About the only thing you don't get is a camera style case, but considering the package price, it's not an unreasonable omission. The cardboard box the WA-47 comes in has foam cutouts for everything and will serve just fine as a place to store the mic, power supply, and accessories when they are not in use. 
    • The sound of original U47's varies quite a bit due to their age and varying condition. Whether or not they've been modified for a different tube, and whether or not they've been professionally restored and reconditioned can also have an influence. This makes trying to match the "sound of a U47" tricky since they can vary so much. Still, an unmodified U47 in decent operating condition will usually have a warm, silky and detailed sound with a bit of a peak at around 3-4 kHz, as well as a second one in the 8-10 kHz region. These are not too drastic - about 3 to 5 dB or so, but they add to the definition and clarity, and help vocals to cut through. Additionally, they will have gobs of proximity effect in the 100 Hz region when you get in close.
    • The WA-47 has a very similar sonic signature. Its output is fairly hot, so it doesn't require a ton of gain from your mic preamp. You'll want to use a preamp with an input impedance of 2 k ohms or higher though. The off-axis sound is fairly neutral by large diaphragm mic standards. The WA-47 has a detailed sounding midrange. The highs are not excessively bright like many low-cost condenser mics, but it's not overly dark or muffled sounding either. Going off of my memory of the U47's I've used (and not side by side comparisons) there is not quite as much of the upper end lift as a real U47, and the WA-47 isn't quite as "big" sounding. It's warm and full, but not quite as much so as a really good U47, and there's not quite as much size when it comes to the proximity effect boost. It gets bigger, but not as much as a real '47 does…but considering the price and the different tubes, it's remarkable how close they got it to the overall vibe of the original.
    • One area where the WA-47 surpasses the original is in noise; with a 11 dBA self noise spec and a 82 dBA signal to noise ratio, it's much quieter than any U47 that I've ever heard.




    • There is no pad or high pass filter on the mic or the power supply, but then again, a vintage U47 doesn't have those features either.
    • The two bands that lock the mic into the shock mount don't grip the microphone quite as firmly as they should, so it has a tendency to slip - which could be disastrous if the mic were to fall to the floor. Thicker rubber inside of the bands would help to keep the mic from slipping.
    • Are you looking for an exact clone of a vintage mic? If so, then this isn't what you're after. It is not identical to a real U47 in all respects (different pattern switching, different tube, transformer value differences, etc.) , but you really can't expect a mic that sells for under $1k to be an exact clone when the original tubes alone sell for several times more than the WA-47 costs. Let me be clear: This isn't a U47, or even a part-for-part clone of one. But while it's not exactly the same thing, when you evaluate this mic on its own merits, it doesn't disappoint.




    What are your expectations? I think it's safe to say that if you're expecting this mic to be a perfect clone of a vintage U47 you're going to be highly disappointed - but I also think that if you're expecting that from a mic that sells for $899 you're really expecting way too much, if for no other reason than the fact that the nearly unobtainable VF14M tubes you need to remain 100% true to the originals now cost several times that much when you can find one for sale. Fortunately, high quality 5751 tubes are still readily available, so if you ever need to re-tube your WA-47, you shouldn't have to pay through the nose to do it.

    I do have a couple of quibbles. I can't really fault Warm Audio for the lack of a pad or high pass filter when the mic that inspired the WA-47 didn't have them either, although both would be nice to have. The lack of a camera case for storage and transport really can't be held against Warm Audio at this price point either - they put their money into the microphone components, which is as it should be… but I do wish the shockmount held the microphone more securely. With the stock unmodified shockmount, I would caution against using a "hanging" orientation for the mic, with the capsule below the body - the potential for a disastrous accidental drop is too great. When it's mounted upright, with the capsule sitting above the body, the WA badge serves as a failsafe and prevents the mic from dropping out of the mount completely, even if it does slip. 

    Neophytes shouldn't buy one of these mics with the expectation that it's going to give then a "U47" - it's not. But it does bear a strong sonic resemblance to those vintage classics, and it does so at a price that's much less than any other '47-inspired mic that I'm aware of. And again, considering the price is 1/16th of what a vintage '47 typically goes for, it's amazing that the Warm Audio WA-47 has a sound that is as similar as it is to those vintage classics. This mic does have a heck of a lot going for it. The nine polar patterns are a step up from the original U47's choice of two, and being able to change patterns remotely (at the power supply) means you can do so without having to get in-between what you're trying to record and the mic to change the setting. It sounds fantastic on vocals, but it's also well-suited for use on a variety of instruments too, and it performed well for me as a drum room mic (I'd love to try a pair on stereo overheads), hand percussion, acoustic guitar, and guitar amps. I didn't have the opportunity to try it on upright bass during my tests, but I suspect it would perform very well there as well. 

    The WA-47 is destined to become the volksmikrophon of the project studio crowd, and it's not just for those who can't afford the real thing… regardless of price, es ist ein wunderbares mikrophon! I suspect we will see it in wide use in professional studios too. I own a lot of microphones, including some that cost considerably more, but I was so impressed with it that I'll be making room for the WA-47 in my collection - I'm purchasing the review unit. If you give one a try, and judge it on its own merits (and don't expect it to be identical to a U47 in every way), I suspect you'll be equally impressed, and just as tempted to get one of your own too. -HC-



    Want to discuss the Warm Audio WA-47 or have questions or comments about this review? Then head over to this thread in the Studio Trenches forum right here on Harmony Central and join the discussion!




    Warm Audio WA-47 Multipattern Tube Condenser Microphone ($899.00 "street")

    Warm Audio's product web page  (includes sound samples)   


    You can purchase the Warm Audio WA-47 Multipattern Tube Condenser Microphone from:


    Guitar Center     

    B&H Photo Video    

    Musician's Friend     

    Full Compass   



    WA-47 Specifications:

    Frequency Response 20 Hz - 20 kHz (no +/- tolerance listed)

    Output impedance 200 ohms

    Signal to Noise Ratio 82 dB A weighted

    Equivalent Noise 10 dBA (IEC 651)

    Rated Load Impedance: Equal to or greater than 2 k ohms

    Maximum SPL: 140 dB (<0.5% THD)

    Dynamic Range: 130 dBA

    Self Noise: 11 dBA










    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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