Product Review -

Product Review - White Audio Labs B-80 Monoblock Amplifiers - November, 1995 (Replaced by LLano A-50s, 1997)

By John E. Johnson, Jr.

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White Audio Labs B-80 Monoblock Amplifiers; MOSFET output device, 80 watts rms amplifier: 0 - 15 watts Class A, 16 - 80 watts Class A/B; input impedance 47 k Ohm (balanced and unbalanced); output impedance approximately 0.1 Ohm; THD less than 0.1%; Supply capacitance 44,000 mfd; supply rating 0.5 kVA; size 4"H x 7"W x 11"D; weight 10 pounds each; $1,295/pair available January 1, 1996; White Audio Labs, 1001 Slaton Road, Lubbock, Texas 79404, Phone (806)-748-0270 Fax (806)-748-0593. Note: As of January 1, 1997, the B-80s will be called the A-50s, and will be sold factory-direct for $995/pair. The A-50s have two pairs of output devices per channel, instead of one. White Audio Labs is now The Llano Design Group, 4804 84th Street, Lubbock, Texas 79424; Phone 806-794-4879.

When our equipment wrangler unpacked the B-80s, we were surprised at how small they were. If you are into the modular look, these fellows will do it for you. Designing with a U channel chassis, plus tight packing of the innards, allows the B-80s to fit just about anywhere, at least in places with adequate ventilation. The first 15 watts are class A, with the remainder of their 80 watts rms output (each monoblock) in class A/B. So, they run pretty hot. Our measurements indicate 117 degrees F. once they are stabilized (digital probe thermometer placed against the hot spot, which is the right rear portion of the chassis). They are designed to meet specs at 120 degrees, so this appears to be on the mark.

Each amp uses one pair of Hitachi MOSFETs in a push-pull configuration. These are relatively new devices which have a lower output impedance (0.1 Ohm) and higher current capability relative to older MOSFETs. The toroidal transformer (0.5 kVA) and 47,000 mfd capacitance make for a well structured power supply. One of the units had a mechanical noise that was quite audible from across the room, which is a result of the toroidal transformer vibrating (toroidals are notorious for being mechanically noisy). This can be remedied by opening the top and tightening the transformer down.

These amps are built solidly. The chassis is thick and does not rattle, as evidenced by my sore knuckles. The front has an on/off toggle and a blue LED for power-on indication. On the rear are balanced XLR and unbalanced RCA input jacks, and one set of 5 way binding posts. Overall, it is a very nice package and easy to handle.

We tested the B-80s with an Audio Electronic Supply AE-1 tube preamp, Nordost Red Dawn interconnects and speaker cables, Nordost Blue Heaven speaker cables, AudioQuest Argent speaker cables, Velodyne DF-661 speakers, and Monitor Audio Studio 20 SE speakers. An Audio Control SA-3050A Real Time Spectrum Analyzer with calibrated microphone was used for the measurements.

Right off the bat, we realized the B-80s were crystal clear at the top end. So we paired them with the AE-1 tube preamp, which mellows things out a bit (CDs have a notorious edginess about them when all the components in a system are crisp in their performance). To my ears, there was no harshness. However, Jeanne Fairbrook, who has very good high frequency hearing, felt that the sound was a bit too precise . . . too "sharp" (Telemann trumpet concertos), as both the Velodynes and Montitor Audios are capable of reproducing very fine detail. This could be due to the class A biasing which makes the amps very fast (100 volts/microsec). (Another advantage of class A in push-pull is a reduction in crossover distortion as the signal passes from one side of the amplifier to the other.) So, we fine tuned the system by using the Nordost Blue Heaven speaker cables and the AudioQuest Argent speaker cables, both of which tend to smooth out the high end compared to the Nordost Red Dawn. The Blue Heaven was slightly brighter than the Argent, so you have a range of choices here. This combination satisfied everyone, and the resulting sound was beautifully clean. Sibilants were as close to perfect as can be obtained in hi-fi reproduction. Natalie Cole has a great voice for testing accuracy, and she came through like a Bob White (a bird with a beautiful song) on an Arkansas summer morning.

The output of the B-80s is sufficient to drive most speakers to relatively high levels. Using the Velodyne DF-661s (sensitivity 88dB/W/M) and a tail kickin' CD (Steve Winwood's "Roll With It"), we measured 90 -98 dB before noticeable distortion (microphone placed midway between the two speakers, and about 4 feet out). At 102 dB output, the highs were harsh and bass mushy, so the 98 dB setting (about 11 o'clock on the AE-1 volume control) is the limit. This was at a frequency spread (music power spectrum from this particular CD) of 63 Hz - 10 kHz for the majority of the signal, and decreasing amounts of energy on either side of this range (responses obtained at 25 Hz as well as 20 kHz). The outputs of the B-80s are direct coupled, meaning that the drain of each MOSFET is connected directly to the output. The manufacturer states a DC to 100 kHz frequency response, in part due to the direct coupling. Although such frequency response of an amplifier may be measured on an oscilloscope with bursts of sine waves, we feel a real world test with cables and speakers and music (measuring the power spectrum) give the true picture of response. From our listening tests, the B-80s provide a smooth response in a typical music power spectrum, with no audible dips or bumps. The highs are clear, the mid-range neutral, and the bass is deep. What is also important here (with direct coupling) is that you have to be careful about any DC offset voltage being transmitted by the preamplifier, which can damage speakers when amplified by the B-80s.

When used with high resolution speakers, the B-80s are capable of remarkable sound. In particular, we noticed that stringed instruments in symphonic pieces were astonishing. Thus, these amps will make apparent any high frequency problems upstream or down. They need a good front end and fine speakers to make them sing. A careful choice of cables is also important. It will be very interesting when Super Density CDs finally make their debut. I am convinced that the current 44.1 kHz sampling rate CD is the last weak link in the high end audio chain to be strengthened (kind of ironic, no?). The quality of amplifiers and speakers is terrific these days. Tube amps are having a renaissance, and although based on original designs from many years ago, the modern equipment can take advantage of higher quality parts. For the next generation of CDs, a higher sampling rate - probably 96 kHz, along with 20 bit word length - should obviate having to fine tune edgy high frequency signals from CDs that are being passed through superb hi-fi systems with the accuracy that they are supposed to do. Since I was critical of the CD signal in this review, I refrained from mentioning the brand of CD player we used. Although I feel it is the CDs which are the cause of observed sharpness here, I did not want anyone to think I was criticizing the component which was playing them.

The White Audio B-80s will make a fine addition to any hi-fi system. Plenty of power for most speakers, and finely detailed sound. $1,295/pair is a good price for this class of performance. Go for it!

John E. Johnson, Jr.
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