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Autocostruire/AudioDigit and Sonic Impact T amp Review

I intially purchased the $30 Sonic T amp just to hear what all the buzz on a few forums and internet review sites was all about. My intial impression of the cheapo plastic boxed, “AAA” battery powered integrated amplifier was one which included a big, wide smile. This is an amplifier that will make you laugh out loud at how well it handles music. I have sold high end audio for several decades and this little amp has many of the qualities that I would expect to get from electronics costing impressive, and out of my reach, dollar amounts. Please, believe me when I say I have willfully sold many separate power amplifiers with four figure price tags which could not better the sound of this amplifier and they certainly had no worse trade-offs than the T amp. This is an amplifier that will keep you up until all hours of the night the first time you plug everything together. (Yes, some of that time will be spent looking for cables to fit the incredibly cheap, plastic speaker connectors and the impossible-to-believe-you’re-using mini plug input; no matter, plan on staying up once you get it all put together.) Unless you have already been fortunate enough to accumulate a system worth more than most people’s automobile, you will hear a sound quality that will surprise and delight you.

Possibly a bit of explanation might be beneficial here. We all know class D amps are justifiably nasty by reputation. Well suited for car audio, cheap boom boxes and subwoofer plate amps, there have not been many class D amps which have excited the audiophile crowd. (Go back into the Stereophile archives for a review of the Channel Island “digital” amplifier which did garner remarkably good comments. It, however, sells for 50 times the T amp’s piddlin’ little asking price.) Class T amplifiers are the product of the Tripath company’s chips. As I hope you all know, “digital” amplifiers are not processing 1’s and 0’s but are conventional analog amplifiers with an other than conventional power supply driving them. The class T flag has been planted by the Tripath company based on the operational characteristics of their designs. They are “digital” but not traditionally so. Details of the differences between class D and class T amplifiers can be found on the Tripath website for anyone wanting further explanation. I encourage everyone to take a look.

With it’s top notch staging and timbre, the kind of neat looking in a Target sort of way T amp impressed me enough that I researched the various reactions to the Tripath chip amplifiers. While there are modifiers who have taken the cost-conscious design of the Sonic Impact T amp to rather surprising levels of (claimed) performance, I decided there was no good reason to modify a $30 amplifier when there were, by all accounts, better sounding Tripath chip amplifiers available to begin with. My ultimate response to the Sonic Impact T amp was one of coolness in portraying music’s emotional impact. It could swing but it was on a rather short tether. It lacks in the lowest octaves; though through my system that isn’t of supreme importance. Somewhere between 40 Hz and 50 Hz most music stops happening (OK, that’s debatable, just go along for now) and I would rather have some fairly decent bass at those frequencies than pay for what it takes to get excellence beneath that point.

An internet purchase from the Italian distibutor (who provided excellent service, I would add) brought a class T kit to my door in less than a week. An afternoon spent assembling the kit and by that evening I was listening to an instant upgrade from the tiny $30 amplifier I had just replaced. Who woulda thunk you could better a $30 amp! Read on.

Once again, let me digress to inform you that the entire “amplifier” that I “built” fits on a board smaller than the hand you would be dealt in a game of Texas Hold’Em. So take “tiny” for what it’s worth. If you are like me and have finally resorted to bifocals, you will have to assemble this amplifier with your specs on the table. The capacitors, proprietary air core inductors and resistors you will be dealing with are also down scaled to suit the short signal paths which benefit this design. Fortunately the manual and the board layout are quite easy to follow. The components are of a generally superior quality to the components used in the T amp and include improved circuitry in both the input and output stages of the amplifier plus what is regarded by many as a better sounding Tripath chip. The Autocostriure amplifier includes a far superior Noble potentiometer which you will fit easily should you wire it as an integrated amplifier; and in any configuration can attribute much of its superior sound quality to the air core inductors included in the design. No matter which Tripath based amplifier you choose, these amps are unusual in every respect and they will have you questioning much of what you have come to accept as audiophile common sense. Where that common sense approach still reigns is when it comes to selecting a power source for the amplifier.

After trying various options and settling on a 12VDC Sealed Lead Acid battery for power (with a floating charger for simplicity) and placing all the guts of the amp, connectors, switches, cabling and battery into a case, the “power supply” of this integrated amplifier is equivalent in size to a few dozen (no, make the several hundred) of the actual amplifier boards. That should easily qualify it for some type of audiophile “Guts of the Year” award.

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My particular unit was wired as an integrated amplifier with a soft start power switch and a capacitor across the battery supply to give a bit more oomph to the sound. After listening for about a week to get used to the Autocostruire’s sound, I pulled the Zobel network out of the board, upgraded the input caps and removed the diode protection circuit. This is all well laid out in Autocostruire’s instruction manual and amounts to the “audiophile” version of their amplifier. If you so desire, you can also remove the potentiometer from the board and replace it with a pair of jumpers which would then turn the unit into a straight power amplifier and satisfy those of you who have assembled your own stepped ladder type volume controls. Otherwise the included pot performs the duties of a passive pre amp and cable choices, along with system set up, should be made accordingly.

This particular amplifier, and my original $30 T amp, are rather low powered devices with a max output of about 7 watts into a nominal eight Ohm load. While neither amp would be said to shine on my fifteen Ohm LS3/5a’s, when I dug out a more efficient pair of KEF bookshelfs with a solid eight Ohm load the sound was comparable to some very pricey systems I’ve sold and heard. The staging is very wide and portrays exceptional depth. A bit laid back in my room the Autocostruire gave a close mic’d vocalist the up front sound I assume they wanted when they OK’d the mix. Pianos existed outside my left side window (I wondered what the neighbors would think) while drums and guitar were pushing out the right hand wall to have more room to swing (I assume they’ll come out of the closet when they’re good and ready). The front wall simply wasn’t there any longer as the BIG drum thwack from the Telarc “Fanfare for a Common Man” came from the guest bedroom. Fortunately, I had the house to myself other than Buck, my Cocker Spaniel. He seems to like the way the Telarc drum makes the floor tickle his tummy, even with the whole seven watts of the Autocostruire.

Timbre of instruments and vocals was exceptional, as was the focus on each performer’s space and those spaces where they weren’t. This was even more impressive given the low cost of the KEF’s I was using. (Cheap, good sounding speakers are some of my favorite audio toys. I can’t afford anything that has much more than a single capacitor on the tweeter for a “crossover”. Rather than “cheap and dirty” the best of this speaker type will be “inexpensive and remarkably clean”.) Within the SPL limits of this system the images were rock solid and never varied with frequency or volume. I have no hesitation in suggesting Mr. Wilson’s infamous demonstration of a loudspeaker’s dominance within a system’s heirarchy would be blown into so much flotsam with this little system I was listening through. Not counting the source player (a Denon 2900), I had less than $400 invested in this system. Honestly, I didn’t want to hook up my $105 Sony SACD player for fear of just laughing myself to death.

Unlike the original three saw-buck T amp, this Italian “dolci” was musically involving and all but totally satisfying in the areas I consider important. Enough so that I was up several nights in a row listening to music of all sorts that hadn’t been played in years. Stereo and mono, analog and digital, direct-to-disc and must-have-been-recorded-through-a-cheap-answering-machine stuff all did what I expected of them. They sounded intriguing. Old friends that had lingered in the stacks for too long were pulled out for a dance around the room.

Any explanation of the Tripath chip amp’s strengths has to involve their bargain basement deep noise floor. Particularly when driven by a battery supply these “digital” amps are virtually dead quiet. This is the type of quiet you get from solid state amplifiers of legends. Seldom experienced in a normal lifetime and passed down as vocal history from audiophile to audiophile, this is a silence that startles you as if you had just walked into the back of the cathedral during the Mafia Don’s funeral. “Black” is not an apt description because this level of silence allows the ambient clues of the recording venue to transform your room into a different space with each new selection from your record library.

You can envision the smokey shafts of light glowing faintly onstage and the dimmly lit audience members crowded around the tiny tables of the jazz club as the band strikes the first few notes of what will be an memorable evening. Ever wonder what the Village Vanguard sounded like when Evans, LaFaro and Motain spent the weekend? The Italian class T amp will bring the club into your room. No kidding! The ice in the Manhattan glasses clinks differently than in the Old Fashion glasses and the various conversations ebb and flow from side to side and front to back. You are looking for a waiter to top off your drink. There he is over against the bar talking to three of his friends. Don’t bother him, the music is about to begin. The famous interplay of talent which Evans cultivated is as well served as I can imagine without truly being there. LaFaro’s bass has a suitable degree of wood in its construct and Motain’s cymbals the sound of stick on real metal. Evans remains, as always, hunched over the keyboard of his piano pulling emotion from the inner workings of the soundboard.

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The same sort of uber-realistic ambience is heard from any well recorded disc you have on your shelves. How about some Kriesel from 1925? Basie from ’45? Casals from ’65? New Orleans tribute album from 2005? Time and space travel are here and not at all expensive. If your preference is for the “I am now there” approach to audio, these amps will brighten your room, your heart and your bank account.

For some reason all the Tripath based amplifiers, and there are several to choose from, require a long burn in time. My little Italian charmer remained as my amplification of choice for several weeks. In that time I ran an Audible Illusions tube based pre amp into the class T amp and got a modest improvement in quality despite adding the slightest bit of noise to the signal (or at least so I assume, even NOS tubes have to produce noise; right?).

The Italian based company has a few new designs coming along which include an integrated amplifier with a tube based line stage all on one board. This is not an advertisment, just some information for anyone curious enough to look.

Eventually, I went back to my McIntosh tube amplifiers (6L6 outputs) and my AI pre amp (NOS 6DJ8’s). I cannot, in all honesty, tell you the chip amp offered better or even equal sound to this combination in some important areas. The AI/McIntosh sound presents a more realistically sized image of performers in front of me. Both T amps bisect the vocalist at the chest and slightly flatten the performer against the backdrop of the studio in comparison to my tubed gear. There is a touch too much top light and not enough from the rear 45’s to make the performer fully “pop” into a three dimensional being with the T amps. Take this as a very slight criticism of the T amp’s performance. When compared against most of the solid state designs that the Average Joe can afford, these amps paint with vivid colors and tight control. More than likely your solid state boat anchor cannot do this as well as the T amps. The lowest octaves are given more weight with the 65 Lb. Mac tube amps and dynamics have a more natural bloom at the beginning of a note (we are talking McIntosh and tubes, after all). The T amps probably win when comparing small detail retrieval, though I’ve personally found detail retrieval for the sake of detail retrieval to be over valued in too many cases. Vocal and instrumental timbre is believable (though different enough to be noticeable) through either the tubes or the “digital” system. The Italian amp, and most especially the Sonic Impact amplifier, are somewhat dry and slightly in need of some air before they are consumed. The tubes are pleased to provide a burst of fruit flavors and an 300 year old cask type of “oakey” finish.

The Italian class T amp is neither bright nor lightweight. It is a well made espresso that any barista would be proud to present. The only bitterness to be found in its enticing but by no means guargantuan seven watts is when you over heat the pot; in other words, if the amplifier is asked to perform beyond its physical limitations. Treating this amplifier as you would a SET tube amp would be the wisest idea when it comes to speaker selection. Using a few of the various pairs of speakers I have on hand, I felt the more sensitive the speaker, and therefore the more headroom you allow the amplifier, the more musical magic you will hear from the six or seven watts available to you. The most efficient speaker I have on hand are the KEF’s at 90dB and it is an easy load to boot. If you have a speaker with another six dB or so of sensitivity, you really should give these ridiculously inexpensive amplifiers a listen. (The Autocostruire is avaialable as a fully assembled amplifier if you don’t have a fifteen watt soldering iron in the house.) They are educational even if you go back to your pile o’ iron rig and they are cheap enough (and of more than sufficient quality) that you can keep one of these around for the office (or take a battery powered unit out on the deck with a pair of monitors and an Ipod) or for a spare amp if/when your big boy toy needs to go in for service. These amplifiers are not perfect. What is? But you will spend dearly to get anything that is better and I would guess you will be left scratching your head at what you thought had to be true.

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