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Positive Feedback ISSUE46
T-20 integrated amplifier, preamplifier, and psu
as reviewed by John Hoffman
The mid 1960's saw the introduction of Atom Ant, who was a crime fighting superhero of diminutive proportions. This force of nature battled his archenemies Ferocious Flea or Professor Von Gimmick, and performed astounding feats of strength. Actually, the ant is one of God's most powerful creatures, capable of lifting five times its own body weight. If this display of strength were not enough, the ant can top this by dragging twenty five times its weight. The KingRex product line is the sonic equivalent of the mighty ant; capable of feats of musical reproduction that defy its modest proportions and price.
Obad Imports is the North American distributor for the KingRex products. The company concentrates on sourcing products that have a reputation for high quality sound, yet can be afforded by the audio enthusiast on a stringent audio budget. Within a few days after holding a phone conversation with Sacha Kuettel, a box of KingRex products was delivered to my doorstep. Sacha shipped a T-20 integrated amplifier, a PSU outboard power supply for the T-20, and the KingRex preamp. In short order, these pieces were unboxed and breaking in. The components underwent three hundred hours of playing time before any critical listening sessions began.
The KingRex components are housed in a chassis that measures 7.25" wide by 5.25"deep and 2" tall. The finish is a matte black, which is offset by a blue LED power light, and nickel finish volume knob. A 6mm aluminum faceplate adds to the simple, yet attractive appearance of these pieces. The use of the same enclosure for several products allows the factory an economy of scale, which contributes to the attractive price of the KingRex products. All three components displayed excellent fit and finish, which is not often found on products that are economically priced. Lets be honest, many audiophiles have interconnects and speaker wire that cost more than all three pieces combined.
The KingRex T20 is a $269 integrated amplifier that produces 20 wpc into 4 ohms. At the heart of the amplifier is the Tripath TA2020-20 power module, which can be found in several highly praised chip amplifiers. In order to obtain the best performance from the amplifier, careful consideration must be used when selecting a set of speakers. The T20 would be a wonderful partner for high efficiency single driver speakers, although there is enough power to allow the use of other types of designs. In my mind, the optimum speaker for this amplifier would have a simple crossover, a stable impedance curve, and a minimum efficiency of 88dB. While this does not mean the T20 would not work with a speaker that has characteristics that fall outside of these parameters, I would expect the amplifier to perform at its best with a speaker that presents a benign load.
The stock power supply for the T20 amplifier is a switching unit, which is known to have a higher noise floor than more sophisticated power supply designs. The KingRex PSU is an outboard linear power supply that provides the amplifier large amounts of current during dynamic passages of music. The topology of the power supply provides 11,000uF to the AC input stage of the amplifier, and 14,100uF to the DC output stage. The KingRex power supply also contains an AC line filter, which deals with power grid anomalies that can degrade the music. The PSU power supply is designed with tried and true engineering principals, and effectively deals with the limitations of the stock power supply. For an investment of $189, the linear power supply will provide a sonic improvement that justifies the additional expenditure.
The KingRex preamplifier is the most expensive component of the three, with a price tag of $379. The pre-amplifier circuit is deceptively sophisticated, and the design team should be acknowledged for their efforts. The circuit uses 3 pairs of Burr Brown OPA627, which is a recently developed FET op amp known for high speed and low noise levels. A Burr Brown BUF634 op amp is used as a current booster, which increases current gain in the circuit. The power supply uses an 8VA torodial transformer, and a pair of National LM317 voltage regulators. The KingRex pre-amplifier has a secret weapon, which is an input buffering circuit built from discrete components. The Diamond Buffering Circuit is responsible for matching incoming audio signal, and ensuring an optimal match to the input stages of the pre-amp circuit. The KingRex pre-amp is not a bare bones unit, and proves that high-end performance does not automatically equate to a high-dollar price tag.
The KingRex products were installed in my system in a three-step process. First the T-20 integrated amplifier took the place of a Jeff Rowland Consummate preamplifier and Model 5 amplifier. The next step saw the pairing up of the PSU power supply with the integrated amplifier. The final configuration adds the KingRex preamplifier to the system. A pair of Mordaunt Short Performance 880 loudspeakers is the speakers this amplifier was asked to drive. The 880's are a three-way full range speaker with a pair of eight-inch bass drivers. The speaker's efficiency is 90dB and a nominal 6-ohm load. The speaker essentially meets all the requirements I have outlined for a synergistic match for the amplifier; which includes a moderate 6dB per octave slope on the midrange and treble drivers. The bass response of the speaker extends to 28Hz, and has a reputation of requiring a high-powered amplifier to bring out its full potential. The Jeff Rowland Model 5 is a 150-wpc behemoth, and sets the standard in which the performance of the KingRex amplifier will be measured against.
As a standalone component the KingRex T-20 has several positive attributes. The tonal balance of the amplifier is excellent, although the extreme ranges suffer from a degree of attenuation. On the song "Justice" by Slaid Cleaves [Life's Other Side; Broken White Records BW 1457] the T-20 gets the essence of the music correct, although there are a few areas in which the amplifier is clearly compromised. The amplifier is remarkably smooth with an absence of grain or harshness to the sound. In my mind, tonal balance, especially in the midrange area, is the litmus test for a component. This inexpensive amplifier actually mimics the midrange performance of the Jeff Rowland gear that was recently removed from the system. Cleaves vocals are neatly reproduced, and instruments have the proper texture. When all things are considered, the sound quality of a $269 amplifier is quite remarkable, and will amply fulfill the needs of the hobbyist working on the slimmest budget.
A large portion of the sonic deficiencies of the T-20 integrated amplifier can be directly tied to the switching power supply. Bass notes did not extend as deep as the Mordaunt Short speakers are capable of. Dynamic passages suffered from compression, and this also led a slight hardening of the music. One could argue that the 880's are too much speaker for this amplifier to drive, although it also can be said that a high quality speaker will highlight the shortcomings of an amplifier. Adding the PSU produced improvements that one would expect from a linear power supply. Bass notes were fleshed out, and gained prominence within the recording. The kick drum became energized, and the character became far more realistic. There are several dynamic passages within the song, which were improved by the use of the outboard power supply. As the music increased in intensity, the T-20 amplifier remained smooth and unflustered until it ran out of power. The improvement in sound quality easily justifies the additional expense of adding the outboard power supply to the T-20 amplifier.
The KingRex preamplifier is a bit of an enigma. After all, why would an integrated amplifier need a preamp? Once the music starts to play, questions like this simply become irrelevant. While the preamplifier adds another level of gain, I believe the Diamond Buffer Circuit is primarily responsible for the improvements in sound quality. The Kukama DAC I use has selectable output voltage, and can be set for either 2 or 4-volt output. Switching the DAC to the higher output voltage does not result in an improvement in sound, so it stands to reason that an increase in signal gain is not the contributing factor. Input impedance buffering is not a topic that gets widely discussed in this hobby. Conventional reason is that the output impedance of a source should be lower than the input impedance of the amplifier, and the rule of thumb is a 1:10 ratio. With the buffering circuit in the preamplifier, impedance matching becomes a non-issue. Virtually every aspect of the music improved once the KingRex preamplifier is combined with the two other components. Replaying "Justice" clearly shows the benefits of adding the preamplifier, and these were not subtle improvements. Low-level detail retrieval is improved, and the contrast between instruments becomes easier to hear. The micro-dynamic presentation of the music improves, and the contrast between instruments is heightened. The soundstage snaps into focus, and performers are clearly delineated. Finally, high frequency extension is significantly increased, to the point where the T-20 could now be mistaken for a different amplifier. Ambient information in the song is easier to discern, and the decay of notes have a natural feel to them. The KingRex preamplifier completes the transformation of the humble T-20 amplifier, and the end result is an authentic high performance amplifier with an affordable price tag.
While the KingRex stack cannot approach the power output of the Jeff Rowland electronics, it does come remarkably close in terms of musical reproduction. The Consummate and Model 5 are now considered classic audio pieces, however good sound never goes out of style. The KingRex components have the gracefulness and ease of presentation that are the hallmark traits of the Rowland gear. While the extra power adds a dimension to the music that the smaller amplifier cannot recreate, the KingRex components are really not all that far behind. I spent one evening listening to Michael "Hawkeye" Herman who is a wonderful blues artist that happens to perform at a local folk music festival. I have heard Hawkeye live on a number of occasions, and have found his discs to be extremely well recorded. On "Rocket to Chicago" [Everyday Living Topaz CD-0100] Hermann features a National guitar, which has a unique sound. The National is a precursor to an electric guitar has a metallic tone, and impressive levels of volume. The KingRex electronics allows the music to flow smoothly, and adds very little of its own character to the music. The music takes on a velvety character, and I detect a slight loss of inner detail. Other than these two points, there are no significant issues that I can fault this plucky little amplifier for. After spending an evening listening to Hawkeye Herman, I would be hard pressed to explain the necessity of spending more than the eight hundred and some odd dollars that this combination sells for.
While the villains that Atom Ant vanquished existed only in the world of television, KingRex is championing the cause of high quality sound for audiophiles from all walks of life. Even for those with the slimmest of budgets, the T-20 integrated amplifier offers above average sound quality. For those with a few more dollars in their audio kitty, the PSU linear power supply is a cost effective upgrade that deals with a couple of limitations brought about by the switching power supply. The KingRex preamp is the real show stealer, and anyone who appreciates high quality electronics is going to recognize the merits of this trio of components. The only caveat I have is being sure to use speakers that are moderately efficient, and have an amplifier friendly impedance curve. I suspect the most discerning of audiophiles would be amazed at the performance of these pieces. The KingRex electronics are one of those rare audio finds that make music accessible to everyone, not just those with deep pockets. John Hoffman