Woo’s Newest Creation – The WA7d Fireflies Duo

WA7d Duo Fireflies

A few product cycles ago, Jack Woo of Woo audio introduced a new head amp & USB combo called the WA7 Fireflies ($999). The most recent iteration (identified by the inclusion of a “d” in the name) tacks on a digital optical input that increases its application to optical-exclusive sources like the PS4, Blu Ray/CD players or computer sound cards. Also in the mix is a new separate tube power supply called the WA7tp. The two together retail for $1,598.

The WA7d Fireflies Duo mimics nearly the same external design for each block. A large push power button on the WA7tp replaces the round volume knob on the main unit. As with the original WA7 the real eye candy here is the solid block of clear glass that sits atop each unit. Not really as polarizing as one might think, the demo unit on display at this year’s AXPONA show got consistent remarks and compliments on its design. It seems readily apparent that consumers are hungry for something beyond the black or silver aluminum boxes that categorizes so much of the market in this hobby.  The block itself is not physically connected to the casing, it actually sits on the base surrounding the tubes quite freely. As with all of Jack’s creations, the WA7d is not easily knocked around. The weight of his amplifiers is usually one of the most solid and heavy in its given class. While headphone design craves lightweight solutions, the inverse seems to present an interesting proposition for full size amplifiers. The amp section features a high and low gain setting while the input selector switch designates input from USB, optical or analog RCAs. The back of the “d” retains the same design as the original WA7 except that now the revisable D/A switch selection has been replaced by the optical input, so the WA7d combo unit can no longer act as a external DAC to another amplifier. Given the nature and intended use of this type of unit the output may have qualified as “nice to have” feature but in execution it is hardly a sacrificial tradeoff for most scenarios, especially if you are evaluating this product with the intent of optical connectivity.

While output is limited to single ended headphone connectivity, the WA7d does have an additional mini headphone jack designed specifically for in-ear monitors. This IEM output is borderline miraculous with its appropriated yield. No white (or otherwise) noise was audible at any level through a pair of sensitive JH16s. For a tube amp this is practically unheard of. Background hum and noisy background plague even the most sophisticated full size tube amplifiers at the IEM level. The WA7d mini jack raised the bar even higher with a pleasant, even and manageable sweep in volume that produced a very nice measure around 11 ‘o’clock for normal listening levels. The tubes that rest atop both cubes can be rolled, although a very interesting and definitive sound can be achieved with the stock pair of matched Sovtek 6C45 (WA7d) and Woo Audio selected 12AU7 (WA7tp) that come with the amplifier.

The Sound

The WA7d rounds out a very nice warmer (but not overly-tuby) kind of sound. Mid tone saturation is very complementary, highs and lows are well balanced well in turn. The presence of analog technology is noticeable, but not distracting. Woo is capable of some of the very best implementation of tubes on the personal audio market, and the WA7d is no exception. For the price, the tubes sing and the bells (and whistles) ring. Even more surprising was the bass response from the stock russian tubes. Big bass slam and extension were immediately noticeable with the applicable genres. Rock music emphasized a bass drum punch even bigger than the solid state Oppo HA-1 on hand. Trading tubes can quickly tailor the taste of your tunes to your liking, but those interested in dance and rock may be very pleasantly surprised with the stock tubes Woo offers. The low-end pounce here is really fun and tight, all the more unusual considering the analog technology implemented on order to recreate it. It may be a bit north of neutral right around the bass drum (with stock tubes), but its well done and leaves everything else untouched. Audio trade show songs like Diana Krall struck a fine linear balance and offered a very similar response to all of the other frequency-neutral amplifiers on hand. Those familiar with the Woo sound will find a similar homage to the house sound within the WA7d. Mids are rich and full of life, but not pushed to the point were they feel overly dense. The amplifier lays out a very nice wide stage for instruments to play upon. With vocals anchored clearly in the center, songs like Fever off of the Black Key’s Turn Blue album have a chance to deliver focused instrument sounds from all around, the WA7 in turn creates a wide virtual circle of sonic engagement around your head with a complementary headphone attached. Treble frequencies are a tangible, non-fatiguing presence fit for all genres. The balanced, yet highly detailed upper frequencies should satisfy even the biggest accuracy addicts.

Jack decided to go with a C-Media 6631A USB chip and a TI PCM5102A 32-bit DAC chip for digital connectivity on the WA7d. Internal comparisons to other DACs via the RCA inputs revealed a ruler flat frequency response from the digital section and above par detail retrieval for the price point. While direct evaluations to the much pricier Auralic VEGA ($3,500) were accompanied by some improvement, the Texas Instruments silicone performs very well in the $1k-$1.5 range in terms of both solid musical composure and tonal vibrancy. The overall effect complements the amplifier section well and doesn’t come off as anemic or dry.


Jack keeps pace with his tradition of producing well built, yet elegantly designed pieces of the audio equipment with the WA7d. It fully satisfies the needs of those looking to have rich tube sound, digital translation and controlled headphone amplification without compromising on desktop space. The addition of the WA7tp power supply allows consumers to upgrade the powerful little combo to an arrangement similar to Woo’s top shelf separates gear, for a top shelf piece is exactly what it is. With its striking good looks the dual glass blocks could star as a conversation piece as much as it does as a sonic translator. While looks aren’t everything, attention to detail does matter. Details in sound, details in design, details in construction. The WA7d exudes detail on every level. Stock tubes play nice with frequency balance and have a good punch in the low end. The entire package makes for a very pleasant addition to any tube-lover’s desktop rig.


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