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Part II: KingRex Pre-Amp
The KingRex Pre-Amp shares the same aluminum faceplate, volume knob and chassis dimensions of its siblings. At first glance, that doesn't feel right. It doesn't look like a preamp. Not from the front at least so try the back. IEC AC power receptacle and rocker switch, one set of outputs and two inputs. Back to the front. Am I the only one missing the input selector here? Is it hidden somewhere? I flip to the bottom. Nothing. It's not funny if KingRex forgot to put that in.
As it turned out, the joke was on me. The input select is automatic. What that means is you plug in, say a tuner and CD player. You turn on the tuner and tune to Classical Rock. The KingRex Pre-Amp will play Classical Rock, provided you hook it up to power amp and speakers of course. Now turn on the CD player and spin some Jazz. The KingRex Pre-Amp will play Jazz. Fun, eh? Well, that was news to me. But there's a catch. I didn't mention whether you need to switch off the tuner before switching on the CDP.
The answer is, you'd better. I didn't the first time. Jazz did take over center stage alright but Classical Rock kept knocking on the back door, intermittently yet persistently. Still fun. Just remember these new disciplines: last come, first serve and first in, first out. How is that possible? It's done through a CMOS digital integrated circuit. In our case, it's the Toshiba TC4001B 2-input NOR gate, which is the more advanced type equipped with buffers to improve input/output transmission time. To test its speed, I purposely kept the two inputs on. When one was turned off, the other took over in a blink. A technical note: The NOR gate is an electronic logical gate or digital logic processor that implements the NOR binary operation in logic,
which in this case means, high output is 1 and low output is 0. CMOS NOR gates are available in 2-inputs, 3-inputs and 4-inputs. The American symbol for a 2-input NOR gate looks like this.

The pin assignment diagram of the Toshiba TC4001B shows the quad 2-input configuration:

While I was having fun with the NOR gate, KingRex chief engineer James kindly sent me the circuit path diagram and took me through the rest of the design. The key components include three pairs of Burr-Brown ICs: OPA627 for preamplification, BUF634 for increasing and sustaining higher output current, OPA177 for DC servo. These ICs are long-time favorite discussion topics on DIY forums. The OPA627, a new-generation FET (Difet) op amp, is recognized for its low noise and high speed. James further explained the advantages of the other two: "BUF634 is not only a high-speed op amp current booster, it also improves the compatibility with power amps and loudspeakers. OPA177 makes sure the op amp output is free of DC, avoiding any chances of harming the power amp and the loudspeakers. It also has another advantage. It's not necessary to use extra output coupling capacitors and that improves the sonics a lot."
During the three or four months of run-in and audition, I couldn't help thinking that this compact lightweight preamp actually outperformed a lot of $1,000 preamps especially when mated with the NuForce Reference 9 driving the Dynaudio Facette. I checked the specs sheet: S/N ratio –104.6 dB (A weighted), dynamic range 104.5 dB (A weighted), THD below 0.0047% (20Hz-20KHz), IMD+Noise below 0.006% (A weighted). There's really nothing to cry about. Two things caught my attention though. Voltage gain is a mere 4x (12dB) and power consumption a measly 5 watts. I checked with James: "Our Pre-Amp was designed for T20/T20U and 12dB is adequate. However, we did test it with other power amps. It proved to be good match even with the 200-watt ICEPower and 400-watt UCD. The voltage output of the OPA627 is 12dB but current output is only 45mA. That's why we added the BUF634 to boost the current, capitalizing on the buffer's maximum current capacity of 250 mA. That should improve the power amp's ability to drive the loudspeaker." Though I didn't tell James, I had no problem testifying to this fact, knowing already what it could do with my NuForce and Dynaudio combo.

On the power supply front, the KingRex Pre-Amp is equipped with an 8VA toroidal transformer and a pair of National LM317T voltage regulators, delivering 13V/0.3A DC current to the circuit board. Yes, it's just an 8VA toroidal transformer but it looks bigger. It's all this quite sophisticated preamp circuit needs. Other than passive preamps, this is the greenest preamp I've ever encountered. Sonically, it will also turn every low-budget preamp green with envy - as I'd soon find out.


It's only natural that I tried it first with the T20U bi-amped powered by two PSUs. Source was the Philips DVP-9000S. Speakers were Loth-X BS-1 in D'Appolito array as usual. Immediately I noticed that the somehow lackluster Sutherland/Bonynge home recording suddenly transformed into a well-proportioned three-dimensional live recording with optimal separation between the vocal and the piano, which sat further back. The Menotti ballet Sebastian also evidenced leapfrog improvements. This rather analog-sounding recording always gave me the illusion of listening to open reel tape. Indeed, I could pick up the tape hissing in the background. Earlier on, with the T20U alone and one pair of speakers, it was confined to small-scale home audio parameters yet scoring high on most sonic attributes. Now with the Preamp and two T20U bi-amping four speakers, its real potential was unleashed. Every sonic attribute was augmented to a new level. Scale and dimension were elevated to concert hall presence, musicality to connoisseur grade. The only thing I could criticize was the bottom octave.
So I took the trouble of moving the Klipsch Synergy F2 down to remedy the situation. My diagnosis proved correct. The amps could reach the bottom octave without the slightest sign of stress or fatigue. The F2 synergized perfectly with this KingRex pre/power combo and the whole shebang was so close to a tube experience. If the F2 is indeed made for tube amps, then the KingRex combo is made to emulate tube amps. Unrestrained valve bloom released freely in the air. Musicality lingered on and on yet layering and definition were not compromised. Klipsch has been so good at doing that since the La Scala and the
Synergy F2 follows suit. And KingRex jived with it all so naturally. Instead of opening up the volume pot of the T20Us now acting as power amps to full throttle, I kept them at 3 o'clock to maintain the Tripath chip working at the lowest THD+N possible. With the 95.5dB sensitive Klipsch, the volume knob of the preamp only needed 10 o'clock. (Both T20U and Pre-Amp feature a 50Kohm pot.) That's proof that the 12dB gain of the Pre-Amp is just right.

I threw in another CD, Roby Lakatos and his ensemble's yellow label debut recording Lakatos [DGG 475 879-2]. Hungarian Gypsy passion filled up the room. High and low vibrations of the strings riding on the resonance of soundboards big and small, curved and square, they all radiated through the musicians' body heat. I secretly noted down: "Who needs tube amps?" Not if you heard the kind of rhythmic pulse and forefront transients of strumming fingernails on acoustic guitar, deftly wooden hammers flying across the cimbalom and lightning-fast pizzicato fingertips on the violins that all added up to the heart-throbbing reality I just witnessed. If I may say so, there's one advantage of this KingRex combo over your entry-level tube pre/power combo, which almost certainly will cost more: the KingRex is more capable of adding verisimilitude to every musical plot and with more attention to inner details.
Undoubtedly, high-sensitivity tube-friendly speakers like the Klipsch provided a comfort zone for the little innocent KingRex Pre-Amp. My evil mind then lined up some dangerous liaisons to ruin its fidelity. Now standing in place of my F2 was another 'F', the amp-humiliating Facette by Dynaudio. Since this seducer is not bi-wirable, the T20U had to remain single and vulnerable. 84dB sensitivity and 4-ohm nominal impedance are merely on paper. Deep down, the Facette is even less forgiving, rationing out the bottom octave only as it pleases. And that's exactly what happened to the KingRex. With the Pre-Amp's volume knob at 12 o'clock, sound pressure level was adequate but the midrange to upper bass warmth and resolution were penalized, layering and soundstage were compressed. No, this wasn't a speaker for the KingRex T20U. But how about the Pre-Amp with the NuForce?

If Facette is the ferocious black stallion, the NuForce Reference 9 SE is the John Solomon Rarey. Most of the time I have the NuForce teamed up with the Audio Zone Pre T-1 TVC and enjoy the crystal clear transparent sound images. I seldom need to flick the 6dB gain switch and the NuForce is not merely whispering into the Facette. Matching it with the 12dB gain KingRex Pre-Amp apparently increased drive. The Facette became dynamically more potent, carving out a well-defined lower register on the double bass and the piano in the Lakatos CD. The Audio Zone Pre T-1 helps the NuForce/Facette team to remain neutral, analytical and rational. The KingRex Pre-Amp goaded them to become more emotional and organic. The other preamp I like to use occasionally in this setup when I really need more SPL and valve bloom (for Mahler Symphonies and Richard Strauss tone poems for instance) is the Dared SL-2000A, which has a high 26dB of gain. With the KingRex Pre-Amp I got about the same warmth and valve bloom with perhaps a bit more natural decay. But the soundstage was definitely wider and that's so much better for Mahler. When I dialed up the volume to 12 o'clock, the sound pressure felt like a body massage yet musicality was still impeccably well mannered.

How could an op-amp-based preamp sound so much like a valve preamp? Wasn't that too good to be true for a $360 budget item? James helped clear the clouds and provided the explanation. The secret weapon of the KingRex Pre-Amp is a plug-in PCB called a Diamond Buffer, a dual-mono buffer that gets its pet name from 4 -- or now more commonly practiced 6 -- transistors forming a rhombus shape on the circuit diagram (not the actual PCB). One of the pioneers of the diamond buffer was Marantz whose proprietary HDAM (Hyper Dynamic Amplifier Module) was first introduced in 1992 with the release of the PM99SE integrated amp. Since then HDAMs have been implemented in virtually every high-end Marantz audio product from amps (even phono stage) to SACD/CD players. My second reference SACD player is a Marantz SA8260 and equipped with HDAMs. HDAM is a compact and shielded module that utilizes surface-mount and multi-layer circuitry [below].

This solution soon morphed into many PCB/discrete component implementations known as diamond buffers and became hot within the DIY community who praised it for dynamic sound reproduction with accurate tonal and image balance. The KingRex Pre-Amp is basically a hybrid design that improves on conventional voltage amplifiers with discrete components and high-performance op amps. The proprietary diamond buffer takes the form of a detachable expansion board that is mounted on top of the lower-deck main board through multi-pin connections. James suggested I report on the difference with and without it. Following his instructions, I removed the diamond buffer, reattached the grounding screw and set the two jumpers in place, leaving the middle pins open.

Here are my audition notes. Without diamond buffer, everything seemed faster and cleaner, with resonance trails dying off sooner. Guitar strumming, violin pizzicato and cymbal crashes had more bite but a harder, blunter kind of bite. The extreme upper highs were missing. The major trade off was less bass, less warmth, less air. The soundstage was set back. Front-to-back layering got compressed. The uppermost treble and lowest bass were truncated, with both ends of the frequency range rolling off too quickly. With diamond buffer, frequency extension and soundstage expanded and three-dimensional instrument placement was accurately plotted. The atmosphere became warm and tube-like. The NuForce and Facette combo was punching out tight and deep bass, oozing out a rich and mellow midrange and weaving silky-smooth highs. Microdynamics and macrodynamics depicted every move of the members of the Lakatos Ensemble. Every detail and every nuance was well preserved. The rapid yet tranquil murmuring dialogue, the high-pitched violin bird song and the building up of the climax in "L'Alouette" were effortlessly rendered. The violin was more yearningly lyrical in "Schindler's List", the cimbalom more nostalgic and rustic.

Part II: Conclusion
There once was a market for inexpensive, compact components popularized by QED and Creek. With Tripath patronage and other electronic advancement like surface-mount technology, this market has seen a renaissance with ever smaller but mightier components flourishing. Among the reborn generation, there seem to be very few preamps and no USB Tripath amps, making KingRex even more outstanding.

Within the first year, this Taiwanese company has developed no less than three audio models, all cleverly conceived and brilliantly executed, each one distinctive in its own right. No other Tripath-based company has demonstrated quite the same level of commitment and dedication. With their preamp, the KingRex team frees itself from the established Tripath frame of mind and ventures into the unknown, with sound quality emulating tube amps. The Pre-Amp is adorned with proven technologies such as its input NOR gate and diamond buffer. When matched with low-power Tripath amps, it helps to improve compatibility with lower-efficiency speakers. When matched with high-power class-D amps, it offers unbelievable value and uncompromised performance. Its possible applications go on and on. On the last few days of auditioning, I even used it to substitute a $2,000+ tube preamp in an all-tube preamp/monoblocks setup and honestly preferred the KingRex for its much quieter background noise, wider tonal spectrum and logical balance of musicality and resolution. I know it might seem unscrupulous on my part to give out second and third Blue Moon Awards to KingRex within just two consecutive reviews. But I could not possibly deny them this well-deserved honor: the T20U for "The tube-sounding USB Tripath amp" and the Pre-Amp for "The best compact preamp embodying value and performance".

Quality of packing: Retail carton box, carton partition, content individually bubble-wrapped, enough protection for such compact, light-weight item. Additional outer carton box with bubble foam filling when shipped through DHL.
Reusability of packing: Can be reused multiple times
Ease of unpacking/repacking: Entirely unproblematic
Condition of component received: Flawless
Completeness of delivery: included generic power cord, AC/DC adapter, DC cord, warranty card - no owner's manual for preamp, one main spare fuse (1A), no on-board spare fuse (3A)
Quality of owner's manual: one page manuals for T20U and PSU are somewhat too simple. Also no standard safety instructions as most manuals would. But then who would read those? No manual for Pre-Amp.
Website comments: Recently updated but now even less useful information. Definitely not up to the same standard of their products.
Warranty: 1 year
Global distribution: Taiwan, Canada, U.S.A., New Zealand, United Kingdom.
Human interactions: Professional and courteous, timely responses to questions, adequate English skills despite being non-native English speakers, forthcoming about technicality and everything, always accompanied with photos and captions.
Other: PSU is now upgraded with IEC receptacle and 48 VA toroidal transformer (from 45 VA).
Pricing: Irresistible.
Application conditions: Without the Pre-Amp, higher efficiency and higher impedance speakers are still my recommendation with T20U.
Final comments & suggestions: I didn't spend too much time tweaking except for the power cord on the Pre-Amp. When using the factory generic power cord, there's a very low noise like tube amp transformer hum when I dial up full volume and stick my ear to the speaker driver. When it is replaced by Unity Audio Link power cord, the noise is reduced to almost inaudible.
KingRex website