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KingRex T20 integrated amplifier

Unleashed! Budget High-End monster sinks its teeth deep into the music!

[KingRex T20 amplifier]
[Italian version]

Product: KingRex T20 Amplifier & PSU
Manufacturer: KingRex - Taiwan
Approximate price: $399
Test samples: Loaned from manufacturer
Reviewer: John May - TNT UK
Review period: April-August 2007

I have a bit of a weakness for budget Hi-Fi. There's something 'pure' about their design - which can often be of benefit in terms of sound quality. Some of the more expensive amps get so carried away with superfluous facilities, or complex 'clever' circuit designs, or inch thick casing which would take an anti-tank missile to dent, that something gets lost along the way - their raison-d'etre if you will. Simpler and cheaper designs do not have the luxury of such 'over design' - they need to 'get to the point' without any preamble if they are to make a mark in today's marketplace. Recently the budget amp sector has never been quite so exciting, due - in no small part - to a certain minimalist, yet expensive design - the 47 Labs Gaincard. Whilst my opinions on its pricing remain unprintable, its superb performance from just two op-amps and a carefully considered minimum of additional parts is not in any doubt. It didn't take long before a group of tenacious and resourceful bunch of DIYers had reverse engineered 47 labs cunning little design - the cult of the Gainclones had begun, spear-headed by such seminal figures as Peter Daniel with his Audiosector kits, and so forth. High-end sound at a budget price was now within reach of those willing and able to wield a soldering iron and follow a few simple instructions (and having built two Gainclones myself I can testify to the simplicity of the design, and the impressiveness of the performance).

Whilst the DIY community were falling over themselves to get the best out of National Semiconductors 'Overture' series of op-amps, into the fray quietly stepped the now cult Sonic Impact T-Amp, for as little as $19! This little wonder made the fuss surrounding the Gainclones seem like a murmur at a Quaker meeting, helped in no small part by Lucio Cadeddu's seminal review on this very website. As with the Gainclone phenomena, the Sonic Impact's performance was centered around a chip, in this case the TA2024 Class-T from Tripath. Once the dust had settled, a cottage industry sprung into being based around modding these marvels of the digital age: Vinnie with his awesome Clari-T, and the Sonic Impact modding site from Michael Mardis helped the audiophile world sit up and take very seriously the sound the tiny TA2024 based designs were capable of. The one complaint leveled at the T-amp is its somewhat diminutive power output of around 6 watts. High sensitivity speakers are the order of the day to really get the best from such a low powered design. Fortunately Tripath offer several higher powered alternatives, one of the most popular being the TA2020 chip, offering as it does the same levels of fidelity as the TA2024, but with a more useable 13 or so watts of high quality power on tap (20+ watts actually... albeit with a THD level which suddenly peaks to around 10%!). Well regarded designs in the DIY arena to use this chip include the Autocostruire TA2020 design, and the much loved 'Charlize' from DIY Paradise.

Into the fray strides the handsome T20 amplifer and partnering PSU, from newcomers KingRex. While no strangers to the world of electronics - a quick glance at their website shows a variety of products from PDA batteries to memory modules for PCs and so on - the T20 and PSU mark their first foray into the crazy world of audio. And what a grand entrance...


[KingRex T20 amplifier - inside view]

Both the T20 amplifier and partnering PSU are housed in the same handsome black satin finished enclosures, measuring 180mm x 138mm x 45mm. The front panels are brushed aluminium, and are 6mm thick. The T20 has a well finished metal volume knob in the center of its fascia, and a rather over-zealous blue LED to the right. The PSU merely contains the LED at the front, AC power in at the rear, and a DC out socket and on/off toggle switch. The T20s rear also has the toggle switch, a DC in jack, a pair of simple 4mm speaker inputs, and one pair of gold plated phono sockets. In all senses this is a minimalist pairing.
Not that this is a bad thing - the simple designs often have a habit of capturing some 'magic' which eludes the more complicated designs, even if this is at the expense of extra power, a flawless measured performance and so on - witness the cult which surrounds 300B Single Ended Triode valve amplifiers to name just one such design. It should be added at this point that the PSU is an extra item - the T20 comes with a standard 'wall-wart' type PSU. However I think the PSU should be viewed as an essential part of the package, rather than something to buy at a later date. I'll mention more about this in the proceeding paragraphs.

Taking off the covers of each component reveals a well layed out, extremely neat and well constructed set of circuit boards. I couldn't find any cause for complaint here. The component quality of both is sensible and chosen for reliability and longevity, rather than some 'flavor of the month' over-hyped & over-priced boutique brand. Interestingly whilst the general consensus on DIY forums seems to be that surface mount components are the best for Tripath based designs, KingRex eschew this for through-hole components. When quizzed about this they told me they could detect no audible difference between using through-hole or SMT - fair enough. An added bonus to owners with a tweaky disposition (and I fall very much under that category) is that upgrading certain key components should be a relatively easy task, but more on this later.

[KingRex T20 amplifier]

The T20 more or less follows the components values recommended by Tripath in their application notes, with just a few deviations of note. The reservoir capacitors are 2200uF items, which is considerably more than the mere 180uF suggested by Tripath. At the every least this extra juice should ensure a more robust delivery, or so the theory goes... Of particular note is the heatsink attached to the TA2020 chip. This is a very nice addition, and shows the attention to detail KingRex have lavished on this design. Most DIY cousins using the TA2020 appear to forego the heatsink, and it is true that the chip appears to be pretty stable without it. However better safe than sorry as the saying goes. The heatsink also offers another advantage in that it acts to damp out any vibrations running through the chip from outside. While the subject of whether or not microphony can affect the sound from op-amps is a bit of a subjective one at present - and I firmly believe that 'bad-vibes' can muddy the sound slightly - the heatsink still offers a reassuringly solid surface upon which to mount the Tripath chip. To some the simple 4mm speaker sockets may appear woefully lacking. Certainly they do not look as visually impressive as - for example - the monsters attached to some Musical Fidelity behemoths. However the key to these designs is simplicity. Why ensure short signal paths and purity of sound and then have this compromised by having the delicate signal force its way through some huge chunk of gold or silver-plated brass? The less in the way of the signal the better. It's of interest to note that 47 Labs feels the same way with their Gaincard amplifier. Another nice touch which shows the attention to detail lavished on this design from KingRex is the near-direct connection of the phono and 4mm speaker sockets to the circuit board - just a few mm worth of wire connects one to the other. Again - simplicity is the key. The less in the way of the signal the better. In addition the four (very) short pieces of wire which connect the speaker outputs to the circuit board each contain what appears to be a ferrite bead. It's well-known that the Tripath chips can put out a great deal of RFI, and the use of these beads lessens the chance of the connections acting as RFI 'antennae' and muddying the sound. In fact Tripath themselves - in their application notes for the TA2020 chip - mention using ferrite beads. Again full marks for attention to detail from KingRex.

From my own experiences building several TA2020 based amps, I would say the PSU is fundamental to the performance of these Class-T designs (and - indeed - any amplifier design for that matter). There are those that swear by battery power (the offerings from Red Wine Audio spring most readily to mind), those that insist a decent SMPS is the only way to go (Nick Whetstone of this very site swears by the Skynet 8080 SMPS), and those that aren't happy until they have a bank of caps and a transformer that could probably power a small country! KingRex tow the line of sensibility again and go for a regulated power supply. This is a ground up design rather than some re-badged off the shelf job, and it shows. Despite the diminutive size of the 13 volt PSU, it is quite a weighty affair, due mainly to the custom designed toroidal 48VA transformer. The original sample I was sent had a two way mains input - no earth - but later production items are now earthed. This may be cause for concern for those with sources that are also earthed. I didn't have any problems with the later earthed model, but it may be something to bear in mind.

Like the amp, parts quality falls into the tried & tested 'sensible quality' category, with Nippon Chemicon capacitors, close tolerance metal film resistors, low noise Schottky diodes amongst the key parts used. As far as capacitance is concerned the T20 PSU features five 2200uF capacitors on the AC side of the circuit, with 3 x 4700uF bolstering the DC stage. Such a design offers a steady supply of DC to the T20 amp, one which shouldn't - in theory - wilt under demanding musical material. However, the proof of the pudding is in the eating so they say - now it's time for the main course!


I started listening to the KingRex with its supplied 'starter' PSU, the source was my Naim CDI CD player. Right away I was greeted by a very 'clean' sounding presentation to the music. This suited classical music in particular, but anything a little more up tempo seemed too well mannered. Rock music didn't fare too well for example and seemed to sound very 'transistory' sounding and 'flat'. Fortunately having had a lot of experience with the TA2020 chip I knew that they benefit from a period of 'burning in' before sounding its best. I left music playing through the T20 for 24 hours before attempting another serious listening session.

What a difference a day makes! The sound had warmed up considerably and lost its clinical edge. Music sounded more involving to listen to, less 'take it or leave it folks'. Mercury's seminal Living Presence CD of Stravinsky's Firebird suite sounded superb. There was a very fine texture to the performance - strings had a particularly finely etched tone. One could clearly hear the character of the instruments being played, rather than it sounding like some synthesized MIDI version of the same. Dynamic ability was fairly good, though it didn't really pin me to the back of my chair like it should do on this piece. Suspecting the bog standard PSU was undoubtedly making its presence known, I switched to a Skynet 8080 SMPS module, with an Elna Cerafine 10,000uf stiffener cap added at the DC output for extra va va voom! Ahhhhh this was more like it. The same quality of tone and character as before, but with vastly improved dynamic ability which had the hairs on the back of my neck standing to attention on some of the more dramatic moments on this track. Moving over to some Rock and Dance music revealed a more confident and dynamic performer than had previously been the case with the standard PSU. Spinning some Alice Cooper in the shape of 'Women of Mass Distraction' from Dirty Diamonds on the Naim CDI had me banging my head like a total rock addled mentalist, playing air guitar to an imaginary audience in my bedroom (girlfriend reads this and exits stage left!). Still, there was something missing from the brew. Some feeling that the T20 was still being kept from displaying its true potential. This feeling persisted no matter what I played through the T20. At this point I was beginning to yearn for a little more excitement & involvement from the music - especially with Rock - which I was used to from my Audiosector Gainclone.

Enter the KingRex PSU for the T20. Some upgrades take time to create a positive impression, others you don't realize have made much of an improvement, until you take them out of your system and you get withdrawal symptoms. Thankfully the PSU is a no-brainer. The improvement wrought by changing from the Skynet 8080 to the PSU was profound. All the usual clichés apply here: there was more of everything; bass went deeper, soundstaging & depth was improved, greater delicacy & clarity and so forth. Most importantly musical involvement was now on a par with my Gainclone. Alice Cooper was now free to strut his leather-clad musical stuff unhindered by any lack of uF! Dynamic ability was now also up there with my Audiosector Gainclone, as was musical involvement, coupled with the neutral tonal colouring of the T20. Subjectively I'd have to say if I had to live with either the T20 or the Gainclone it would be a close-run thing, but I'd favor the T20 with PSU - however those with low sensitivity speakers might be better off with a higher powered alternative. My Mission M72s are an 89db 8-Ohm load and the T20 seemed to have plenty of power on tap.

One of the reasons the TA2020 has been such a success with DIYers and audiophiles is its almost valve-like delivery. When called for, music has all the smoothness and delicacy one could wish for, but without any apparent draw backs. Indeed, the T20 reminded me several times of my own restored pair of Quad II amplifiers, but with a little more ooomph and speaker driving ability. Think a well implemented Quad II using premium film/foil coupling capacitors and you're pretty close to how the T20/PSU combination sounds - no mean feat, especially for the price.

Rightly or wrongly, being a reviewer one becomes used to a certain level of performance, at a certain price point. Over the past three months I'd gotten used to the T20/PSU's performance, and thought I had a handle on the performance. It's always a nice surprise to discover that a component is capable of more than you'd previously expected when paired with a different source. I'd recently fished a DPA One Series 2 from the back of my Hi-fi equivalent of Aladdin's cave, primarily for use with my laptop, running Apple Lossless files through a USB to SPDIF link, to the DPA DAC. I cued up a track and was absolutely astounded by how good this combination sounded. The T20 revealed itself to be a highly neutral performer, by sheer virtue of the fact that it clearly revealed the differences between the elder multi-bit TDA1541 based chipset used in the Naim, from the slightly more modern Philips 7350 Bitstream chipset used in the DPA. Chameleon like, the T20 could have been another amplifier entirely such was its change in 'character' from changing sources. The T20 clearly revealed the astounding bass punch from the DPA, as well as a more tonally balanced delivery and less shrill treble performance. So impressed with the sound quality was I that I had one of those increasingly rare occasions where the music didn't stop - I just wanted to hear all my favorite tracks/albums through this combination, and not once did this marriage of technologies disappoint. The T20 successfully keeps all the positive attributes of the successful Sonic Impact TA2024 amp, and supplements this with extra power and more authority, particularly in the lower registers. My current bench mark for amplifier design remains the sublime GB150D kit from Mr Greg Ball, but the little T20/PSU came pretty close at times to its performance. There's a certain 'magic' to the Tripath sound, something that's very difficult to put into words (and I am supposed to be a reviewer - doh!). I think it comes down to the atmosphere of a piece, and the emotion - music just seems to make more sense from the best of these amps. You are aware of being able to hear 'into' a piece of music, of being present at an 'event', rather than some nice sounding but obvious electronic reproduction of an event. It's an addictive and fascinating listen. Not bad for an introductory product from a fledging Hi-Fi company, and one that won't break the bank - very impressive.

Criticisms? Very few actually! Scraping the barrel for minus points, the LED brightness on both the T20 and PSU could do with being dimmed a little. If - as I do - you leave your components on all the time, you'll have trouble getting to sleep with these babies glowing away. I woke up one night convinced I was about to be the victim of a UFO abduction! My only other more serious criticism concerns the lack of inputs available. Most audiophiles have at least two sources connected at any one time i.e. CD/SACD and vinyl. Having to keep swapping cables around is a right pain in the phono! I think at this price point KingRex really should consider more than one input to increase its attractiveness to potential customers. Whilst it can be argued it is a budget amplifier, it is still more expensive than the Trends, and really cries out for an input or two more. Perhaps KingRex could look into producing a matching 'switching box' as an optional extra?

Lastly, this is more of a wish request than a criticism. The basic design of the T20 and PSU is so nice that it really cries out for an alternative casework option. Personally speaking I'd love to see the option of a 'raw' brushed aluminium facia, and polished & lacquered metal casing. This would really make the T20 and PSU stand out from the crowd, and I'm sure would sell well - pretty please KingRex!!!


If you're anything like me barely a nano-second has passed before the urge to improve your system kicks in! Well the good news is that the KingRex T20 can be improved for a low price. It's pretty much accepted wisdom that the input capacitors on the Tripath series of amps are best served by using film/foil types, rather than the cheaper and sonically inferior electrolytic types. From my own DIY excursions I'd concur with this. The T20 currently uses a pair of low cost 2.2uF electrolytic capacitors in its input. These can be usefully upgraded to a pair of film/foil types for improved performance (mainly increased resolution, more clearly defined detailing, and a less grainy presentation). Changing from electrolytics to film/foil types on both my own Autocostruire TA2020 and Amp6 Basic from 41hz both yielded substantial increases in performance, and I see no reason why the T20 should not similarly benefit from such an upgrade. I mentioned this to KingRex and it looks like the newer production versions of T20 will use film/foil caps when current stocks of the existing models are spent.

The next target for improvement is the cheap carbon volume pot. In normal use this is perfectly adequate, but I noticed with very low level listening (i.e. at night) the channel separation is off, with one channel cutting out while the other is still audible - this is classic cheap volume pot performance and NOT a fault of the amp. An Alps Blue or similar would be a useful upgrade here, and one which I intend to investigate in the near future.

Lastly, a quick glance at the Tripath TA2020 datasheet clearly shows that the design is an inverting one. Accordingly, you might like to experiment with reversing the polarity of your speaker cables to see what polarity you prefer. I tried listening with the speaker cables + and - reversed, but found the sound to be a little 'thinner' and less full bodied than the 'standard' setting. However trying reverse polarity again a few days later the sound appeared to be better - perhaps the little KingRex is so revealing it can reveal if a CD has been recorded out of phase? It's all very subjective - as usual experimentation is the order of the day here, and the T20 offers superb value for money offering a fantastic 'out of the box' performance, and an ideal base with which to experiment if desired by the user.


Reviewing the T20 and PSU has been a great deal of fun, and a real ear-opener. For the price the performance really is better than it has any right to be - in fact I'm still using my samples! It's the proverbial giant-killer, deserves to sell well, and gets my highest thumbs up for sonic performance (providing the KingRex PSU is used). That its performance can also be upgraded at a later date by a few simple modifications only increases its value for money. I'd love to try two units in a 'bi-amping' configuration - I'm sure this would yield even greater levels of high fidelity.

Ignore the relatively low price, and go into this with your ears open and I'm sure you'll come out smiling. It's the kind of component that clearly shows improvements & upgrades elsewhere in your system, providing your speakers are sensitive enough to show these improvements. I'm now firmly hooked on the Tripath sound, and look forward to new products from KingRex. There's already a 'super' T20 called the T20U which offers film/foil input capacitors, as well as a USB input and DAC for improving the sound from a PC, as well as a specialized pre-amp soon to hit the production line. So, well done KingRex for such an outstanding debut product - top marks all around! One to audition without any reservations.

I would like to thank Ms. Christine Wu of KingRex for her courteous & prompt replies to my myriad questions over the past four months, patience in waiting for this review, and superb handling of the language barrier! Such helpful and polite customer service is a welcome surprise in this day and age. Lastly, at the time of writing this (September 2007) KingRex have yet to procure a distributor for their products in the UK - any potential distributors should contact KingRex directly.

System Used:

© Copyright 2007 John May - www.tnt-audio.com

A second look (by G. Husband)

This is just a quick 'second-look' at the Kingrex as I was fortunate enough to have a pairing available at the same time as John - I used it exclusively with the large power supply. I've nothing to add from a technical point of view as John seems to have covered this extensively. My one big disagreement being that I thought the black finish extremely classy and much nicer than silver :-)
There was almost a 'baby-Cello' look to the beautifully machined volume control... I also really love the jewel-like quality of tiny hi-fi.
As for sound I am fortunate in having speakers ideally suited to such low-powered beasts in my Loth-x Polaris horns. Once again a budget digital amp working into a very expensive pair of speakers. Like John my initial impressions were rather poor with the amp sounding harsh and thin. As with every Tripath amp I've tried a burn-in rectifies this to a ridiculous extent.
The Kingrex had the misfortune to follow immediately after the much more expensive Lehmann Stamp, and in this case the latter clearly showed more power, weight and warmth, to the point where it sounded quite different to the original 'T-Amp'. The Kingrex on the other hand sounded more like the original on steroids, with the expected huge soundstage width and good depth coupled with superb detail. The downside was that in this combination the Kingrex did sound a bit lean and pushy for my personal taste, it's not an 'easy listen' or pipe-and-slippers amp.
It's not harsh, as in grainy and distorted, in fact the top end is noticeably smooth and extended, it's just that it can be forthright without the warmth or weight to balance it out. This is of course very personal and dependent on partnering equipment but a characteristic nevertheless.
But with care in partnering the Kingrex is, as John has said, a superb budget amp with real hi-fi capabilities, given the price it's also something of a bargain.

© Copyright 2007 Geoff Husband - www.tnt-audio.com

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