[Tabascosauce]

Last Friday the postman brought me a Sonic Impact amp I that bought from the States on ebay.   I have been listening to it for four days now, and feel ready to post my impressions.

My opinions are totally subjective, and expressed without a great understanding of review terminology.

I wired it up in it's stock form.  My speakers are very similar to the Zalytron Aria 5 kits.  The amp drove them very well, and easily filled my room with music to a decent volume.

I tried it as an integrated amp, and then as a power amp with my pre-amp (Metaxas Charisma 11).  It definately sounded better with the pre-amp.

My initial impression (playing Norah Jones and Steve Davis Project CD's) involved my jaw hitting the floor.  I was mightily impressed by the new found clarity.  I was twice as impressed at the fact that this quality of audio could be purchased for the paltry ammount of $60 AUS, delivered to your door step.

I then played my vinyl, and decided that the amp sounded better with a digital source.  It revealed detail in my CD's that the AKSA didn't seem capable of.

My thoughts were that it's time to embrace the new technology.  This stunning piece of audio equipment can be purchased for roughly one fifteenth of the money I have ploughed into my AKSA.

Day four and I was able to put my finger on something that had been bugging me.  In all my listening time with the Sonic Impact, I had never played a CD or LP in it's entirety.  I would listen to the first 2 or 3 tracks, and then feel this compulsion to change the music.  That is a major departure from my usual listening habits.  My conclusion is that the Sonic Impact is fatiguing.

Last night, I switched back to the AKSA, and played a Return To Forever LP in it's entirety.  Suddenly, my listening enjoyment returned.  I was back to feet tapping and finger clicking.

In summary, the Sonic Impact seemed to have more clarity playing redbook, but was not as musical as the AKSA.

I will ultimately mod the SI, but I'm in no rush to do so.  I think I will keep it as an integrated to use as a spare in case my pre-amp or AKSA are down.  I may from time to time listen to it for variety, but I cannot see it replacing my AKSA.

I think digital amps are a matter of taste.  By analogy, the sound is comparable to the new designer drugs like ecstacy.  An initial, amazing chemical rush of excitement followed by fatigue and seratonin depletion.  The AKSA is like a fine, aged red.  Complex in it's flavours, and filling you with a warm, long lasting glow.

[andyr]

Last Friday the postman brought me a Sonic Impact amp I that bought from the States on ebay.   I have been listening to it for four days now, and feel ready to post my impressions.

My opinions are totally subjective, and expressed without a great understanding of review terminology.

I wired it up in it's stock form.  My speakers are very similar to the Zalytron Aria 5 kits.  The amp drove them very well, and easily filled my room with music to a decent volume.

I tried it as an integrated amp, and t ...

Hi Tabascosauce,

(I hope you have that with vodka and tomato sauce!   )

You play vinyl; does your Metaxas Charisma 11 have a phono stage or do you have an external phono stage?  And is your cart MM or MC (if so, Lo or Hi output)?

I ask this bcoz I'd like to get a picture of your system B4 I might be so bold as to make a suggestion (you've already said the pre-amp section of the Sonic Impact amp was bested by your Metaxas).

Regards,

Andy

[DeadFish]

Greetings!
Thanks for your notes about your SI experience (so far).
You didn't mention if your amp was sold to you 'used' or 'as new'.
My own toleration for my SI didn't start getting agreeable until I had at least 150 hours, and more likely, 200 hours plus on it.
Are you using batteries or have a/c adaptor?  
Like yourself, some of my first facination was how you get so *much* sound for so little money, using first the SI and then a TEAC unit(so far.)
Also, the introduction of my tubed Clarinet preamp greatly helped my appreciation for it.
I agree that these amps can be a matter of taste, but the more I listen to them, the more I wonder on what my biases are based on all other gear I ever listened to.  For instance being what I first believed to be 'rolled off' bass, which I am beginning to think of more in terms of precision, as opposed to more 'blurred' or 'sustained' bass notes from tubed or solidstate gear...  As you see, it has me thinking and I am still figuring out how to judge this stuff, wondering if I have to reinterpret how I 'hear', as it were.
Well, anyways, hope it breaks in some more for you.  I've reached a place where I *can* listen to a whole album, but still ready to jump up and listen to something else.  
Regards,
DeadFish

[Tabascosauce]

Hi Tabascosauce,

(I hope you have that with vodka and tomato sauce!   )

You play vinyl; does your Metaxas Charisma 11 have a phono stage or do you have an external phono stage?  And is your cart MM or MC (if so, Lo or Hi output)?

I ask this bcoz I'd like to get a picture of your system B4 I might be so bold as to make a suggestion (you've already said the pre-amp section of the Sonic Impact amp was bested by your Metaxas).

Regards,

Andy

My preamp has no phono stage, so  I use a Musical Fidelity X-LPS.  My cartridge is an AT440ml and my turntable is a Thorens TD160 Super.

The amp is new, and I have been using batteries.  I accept it hasn't had any burning in.  It's just not my cup of tea!!  One of the few advantages to getting older is to be able to display your prejudices in public and get away with it!!

[JoshK]

My experience with digital amps (switching amps), SS amps and tube amps is they all have their pluses and minuses.  Typically the cheap digital amps need a lot of tweaking and modding to sound agreable on a long term basis and the initial "hey man listen to me!" sound grows tiring.  The Aspen amp I heard on the US tour does a whole lot well while retaining a musical and agreeable nature.

I think now adays with the current technologies available making a decent amp is easy, making a great amp is an art.  Whatever the technology, the devil is still in the details, the technology just has its own strengths/weaknesses/quirks to deal with.  I think the real plus with digital amps is the low starting cost from which to work, but even with the low cost the ultimate product depends on the love you put into it.

[skrivis]

The AKSA equipment seems to be fairly conventional with a lot of attention paid to the details. (I'm only going by what I've been told and what I read on the web site.)

Enough people have spent enough time with the "standard" designs that designers have a pretty good idea of where the limitations, strong points, and gotchas are, as well as where improvements give the best value for money.

The Class D amps aren't quite worked out yet. Maybe they're as good or better and maybe not. They do pretty well on the standard tests, but what about the areas where they get into trouble?

Will they actually deliver the kind of day in and day out power that they claim? Will they do as well or better than a straight linear design?

I'm reminded of the Carver amps that were once popular, and of some other fads in amp design. Is Class D just another fad? Certainly some of the advertising makes them sound like the greatest thing since sliced bread, and that makes me suspicious right there.

For now I think I'll stick with linear amps, and the AKSA amps look like good examples of the breed. (Although I wonder how much they've been "de-tuned" to allow for construction by DIYers.)

[miklorsmith]

Interesting observations.  I wouldn't write off the breed yet though.  A few moderators:

There are several types of switching amplifiers.  PS Audio, NuForce, IcePower, and Tripath are just a few;

The Tripath chips are universally understood to need much break-in, where the sample amp had none;

The SI only hints at the potential within.  Professional care and feeding releases something very different; and

System-matching is crucial to maximize the 6 watts.

This is surely not a comprehensive list.  The main point is that the cited breadth and depth of experience is insufficient to write off an entire philosophy of design.  Is Class D "the ultimate"?  Only time will tell.  I can say that properly massaged and matched, the 6-watt Tripath experience is giving me the best sound I've ever heard.

[skrivis]

Interesting observations.  I wouldn't write off the breed yet though.  A few moderators:

There are several types of switching amplifiers.  PS Audio, NuForce, IcePower, and Tripath are just a few;

They're all basically doing the same thing though.

I've heard an ARC amp and a Bel Canto. Both sounded rather "hard" to me. It was the kind of thing I'd assume would produce lots of listening fatigue.

The Tripath chips are universally understood to need much break-in, where the sample amp had none;

Why would a piece of electronics require breaking-in? It's not like a mechanical system like a speaker.

System-matching is crucial to maximize the 6 watts.

To me, 6 watts limits its use to headphones, and I would only evaluate it with such a load.

I really wasn't thinking of the SI so much as other Class D amps vs. the AKSO amps.

I guess the SI is cheap enough that you can afford to experiment with it, but I'd rather start with something with a bit more power that will properly drive a real load.

Of the info I've seen on Class D amps, ColdAmp looks the most rational. I think they've covered most of the bases there...

[miklorsmith]

They're all doing the same thing the way that all tube amps are doing the same thing or all heavy SS amps are.  Why they require break-in is beyond me.  It could be placebo, but everything I've read (and experienced) supports break-in of the chips.

6 watts drives my Druids easily and cleanly to at least 105 db playing Metallica.  In fact, the sound is bigger and less compressed than anything I've heard since my 500 wpc college system at volume.  But, the sweetness is at quieter volumes than that.  When the teleporter is perfected, I'll buzz you over to show you what I mean.

[andyr]

The AKSA equipment seems to be fairly conventional with a lot of attention paid to the details. (I'm only going by what I've been told and what I read on the web site.)

....

For now I think I'll stick with linear amps, and the AKSA amps look like good examples of the breed. (Although I wonder how much they've been "de-tuned" to allow for construction by DIYers.) ...

Hi skrivis,

Yes, you could say "the AKSA equipment is fairly conventional" but Hugh HAS spent a lot of time on details ... and even more time on "voicing" - ie. components and circuit sections which turn a "conventional" circuit into an emotionally-involving amplifier.

As to whether it's been "de-tuned" to allow for construction by DIYers ... c'mon, man, if you've been perusing this Forum you'll realise that:

a) Hugh is aiming squarely at the DIY market (and thank god for that, I say!), and

b) everyone who has bought an AKSA kit has been able to build it ... albeit some needed more help from Hugh (always given!) along the way.

Go for it!  I don't think you'll regret it.

Regards,

Andy

[AKSA]

Switching Amps are an interesting development, but they are not new.  Clive Sinclair did one in the sixties - you might remember the British Entrepreneur who created the Z80 computer, one of the first, and then bankrupted his company with his vision of the electric car.

I do not follow the technology in great detail, but there are presently issues with the sonics related to switching artefacts.  These spikes penetrate the output filter (which is usually second order) and add a false detail along with a measure of fatigue to the listening session.   This is well understood.  In all instances the way around this is to increase switching speeds to blindingly fast intervals, and thus reduce the switching artefacts to better than 80dB below even with a second order filter.

A secondary cause of problems is the feedback loop and the modulator.  The FB loop is essentially analog, not dissimilar to a conventional linear amp.  The modulator in most instances has low input impedance, which needs to be driven from a buffer, typically a quality opamp.  If you think these things are more analog than digital, you'd be right.....

Finally, a big design limitation is the drive of the output switches, which are always mosfets.  The higher the switching speeds, the greater the drive current needed to switch the mosfet on and off.   These are quite beefy mosfets, with gate capacitance measured in the hundreds of pF, so at 400KHz you need big currents to charge and discharge them quickly.  This is definitely a limiting factor in this technology at present and it is analogous to the grid drive on a large triode.  You don't stir gates/grids, you shake them, to corrupt the immortal words of 007.........

However, there are upsides which bear further investigation.  One is the digitisation of the feedback signals.  This suggests zero phase disturbance passband performance, turning the amp into a band limited amplifier, say for woofer, midrange and tweeter, without use of a conventional crossover.  This certainly has great prospects and Ben and I are looking into it.  The other upside is wonderful impulse response, which makes these amps ideal for special effects sounds in Home Theater.

In the interim, we don't believe that the current crop of switching amplifiers is yet mature for high end, at least, not to the same extent as efficient Class AB linear amps.  Not yet, anyway.

Cheers,

Hugh

[Grumpy_Git]

"the amp into a band limited amplifier, say for woofer, midrange and tweeter"

Do i hear the whisper, nay subsonic rumble of the word: sub-woofer?

Nick  

[rabbitz]

The T-Amp (T-Rex) is an amazing device dishing out bags of detail. Even after full run in the bass still was a bit lean, but for the price not complaining. Still it can't convey the emotion of music and the presentation can't compete with my GC or AKSA.

Only low power but can drive hard providing you use a decent wall wart. It's now used with DIY computer speakers suitably named Raptors which only have an SPL of 85dB but used nearfield so enough to blow your head off.

The AKSA is still the pride and joy and believe me, I've tried to find better at a reasonal price....... not that I don't believe you Hugh. Been fun trying all the different types of amps and confirming the AKSA is still the King. Now what to do with these other amps.... hmmmm.... one to the workshop, one to the dunny......

[miklorsmith]

These spikes penetrate the output filter (which is usually second order) and add a false detail along with a measure of fatigue to the listening session.

Alright, this is your circle and I'm not trying to be a bugger.  However this "fatigue" label being cast on all switching amplifiers is misplaced.  I don't have the technical nor scientific expertise to debate theory.  I do have 20 years of end-user experience.

What I'm getting from my rig currently is organic and natural and completely devoid of artificial etch or detail.  It is clear and defined too.  Many users of smaller switching amps agree.

This is no knock on AKSA at all, as I have no experience with them.

[EchiDna]

Alright, this is your circle and I'm not trying to be a bugger.  However this "fatigue" label being cast on all switching amplifiers is misplaced.  I don't have the technical nor scientific expertise to debate theory.  I do have 20 years of end-user experience.

What I'm getting from my rig currently is organic and natural and completely devoid of artificial etch or detail.  It is clear and defined too.  Many users of smaller switching amps agree.

This is no knock on AKSA at all, as I have no experience with them.

I think you answered your own comment there miklorsmith
until you have heard an AKSA, the comparison is null and void...
I've heard (and/or owned) hotrodded GC, seriously modded T-amps and teac digital amps. The sound of the modded T-Amp is very nice, but it has it's restrictions - you have to use high efficiency speakers or be restricted to near feild listening (like your desk - the function I use my own GC in). This is not the playground of the AKSA, flea amps, low powered tube amps and headphone setups are the competition for each other, not AKSA...

But when you move up the scale and talk about high powered digital amps like ICEpower, Hypex and their bretheren - they are very analytical (read clinical, detailed or 'high resolving power' depending on who writes the comment) and to my ears- fatiguing. Perhaps it is the sound I am used to, but IMHO it is a direct result of the type of sound that we the listener prefers to hear!

analytical type - digital is pretty damn good
relaxed without being overly 'warm' - the AKSA sound great
seriously laid back  - tube power is your only choice

YMMV etc etc
IMHO only

[Tinker]

Thought I might add my 2c on a few points.

Is class-D a fad?
  IMHO. No. As Hugh points out the concept is old, and commercial units have been available for nearly 20 years.
A huge drawcard for class-D is that it can, in theory, achieve 100% efficiency and in practice realises substanitally over 90%. This means that for boom boxes, car stereos,  flat-screen, and PC based systems high output can be achieved with very low power and very low heat. In most cases the heatsink can be smaller than the active device itself!

I spend a bit of time perusing the new chips on offer by manufacturers, and have noticed not only a plethora of new circuits for class-D but also a growing number of integrated audio chips (eg format decoders, tuners, signal processors etc) which contain necessary technology to interface directly with class-D technology.

What this suggests to me is that the future of domestic mass market audio will be class-D because it is cheap, powerful, efficient, low-heat (great for 5.1/7.1) and to be somewhat cynical, having looked into DIY class-D - hard to mod and virtually impossible to build, creating a ready market for replacements and upgrades. Class-D is likely to be THE domestic amp.

Whether class-D will attain the dizziest heights of audiophile nirvana is a whole other issue. Given the variance in taste I doubt that any technology will eclipse others quickly in the taste stakes. How many folk own a low-wattage class-A amp when these have been out of mass market favour for decades?

A final point - development of class-D:
Let me talk in vague terms. Hugh has already discussed a significant stumbling block of better class-D: the non-negligable currents required to turn on the output device and output device switching times. The rise time of these devices is typically of the order of dozens of nanoseconds and needs to be very fast (a few nanoseconds) to make meaningful use of higher modulation rates. For MOSFETs we are talking AMPS of juice just to turn them on!

Consider that many of the best class-D have (idle) modulation rates ranging from 400-1000kHz.
Consider that SACD, which has varying degrees of acceptablity to listeners, is based on the same concept: 1 bit modulated at 2.8MHz.


Cheers,
   Ben.

[jules]

Ben,

this might seem a silly question, but is 100% efficiency particulaly useful or desirable?

The full sound of an orchestra cannot fit into even the largest listening room not only because of the volume but also because the vast amount of information simply becomes a soup from which the human ear is unable to extract anything more than a sample. Even the problems of room acoustics are insignificant compared with just accommodating directly radiated sound. Of course if we turn the volume knob down to acceptable listening levels we are effectively removing a large percentage of the original [100% efficient] signal down to maybe 20 or 30% at best. Presumably, what will go first will be the subtle quieter sounds that are the essence of many musical instruments while what will be left is the louder primary note. With a woodwind instrument the sound that comes out of the bell would remain while the sounds that come off reeds, out of key holes and off the body of the instrument would be lost. With stringed instruments the story would be similar.

Ok, so all music doesn't have the volume of information contained in it that orchestral music does but 100% reproduction of a rock concert that was originally launched into the ether by a few thousand watts of amplification is even less able to be faithfully fitted into your living room [without destroying your house] while at the other end of the scale musicians usually suggest that the sound of a single grand piano is too loud for smaller rooms and specifically designed for larger halls. A human voice, a paino, a trumpet or any one of a number of instruments can challenge smaller spaces on their own and would probably call for the volume knob if you happened to be able to achieve 100% reproduction in your listening room.

So my point here in relation to the debate on switching amps is that one way or another we are only going to listen to a sample of an original performance that could be as low as 20%. What we get to choose is whether this sample is clinically excised by a digital system or strategically chosen by a combination of the ear and skilled adjustment of circuit design in the many places where it is possible to make choices.

For all the above reasons I'm sure the AKSA amps will not be seriously challenged by class D amps  even if they do  achieve the 100% true reproduction mark. Amp design becomes a very different matter if it is considered as a selection process whereby the designer chooses what representative  elements are going to be selected out of a whole to give a sample [maybe 30%] containing the essence of the original.

Echidna,

I don't know if I'm being excessively cynical here but I suspect some people buy amps that impress them on the showroom floor partly because they don't listen to music for long sessions [which could become fatiguing] and maybe even because they would like to impress others in the same way.

jules

[Tinker]

Ben,

this might seem a silly question, but is 100% efficiency particulaly useful or desirable?

Hi Jules,
    It's not a silly question at all, but does require some qualification. In this context efficiency refers to how much of the power drawn by the amp is turned into sound. The analysis applies to all amplifiers of the same class regardless of their maximum wattage. This does not relate to the actual SPL, but the watts comsumed. My point was that 100% efficiency is highly desirable to mass quantity manufacturers because it hugely reduces the cost of the power supply and hugely reduces the cost of the heatsink. Power transformers and caps are not just expensive, they are also bulky, meaning a bigger case, meaning more money.

As far as turning up the wick, class-D is still highly efficient (usually > 85% at low volumes) which A/B and B are not. So yet another class-D plus is that they opearte equibly over wide demands.

My cynical conclusion from the above is that regardless of how good they sound, class-D will become domestic de rigeur because they are super-bang-for-the-buck in terms of watts.

You correctly identify the main point of my previous post. This argument is of little interest to us. Efficiency is a silly question when it comes to sound quality*.  On this forum we are talking to the elite. The relatively small group of individuals who are passionate about the sound and know their gear intimately. We don't care so much about efficiency as emotion, imaging, slam etc.

 My corollary is that ultra-sweet class-A and class A/Bs like AKSAs will still occupy a solid niche in the audiophile market as they do now, and the nameless amps inside 95% of the rest of the domestic gear will become class-D instead of A/B or (ugh) B. How many people with a name-brand integrated hi-fis know what class it is?


Cheers,
  Ben.

* Before the gentle listener writes in, sometimes efficiency is an issue. I know someone who built a 1000W class-A mosfet amp. It needed a 30kg fan-forced heatsink to stop it blowing up.

[jules]

ah yes well Ben, I clearly misunderstood your comment on 100% efficiency as being related to the signal in/ sound out, reproductive qualities of these amps and not the power efficiency.

I quite see your point about efficiency in relation to HT systems although I tend to go against the flow of opinion that sees HT as somehow a social family friendly concept. To me this looks like just another way to bunker down in fortress home rather than dare to face the wilds of the Movie Theatre [or live music in another sense] and the sweating masses.

jules

[Tinker]

I quite see your point about efficiency in relation to HT systems although I tend to go against the flow of opinion that sees HT as somehow a social family friendly concept. To me this looks like just another way to bunker down in fortress home rather than dare to face the wilds of the Movie Theatre [or live music in another sense] and the sweating masses.

jules

I'm on the same page as you with that one, Jules.

For the record, I am highly interested in 3-D sound but believe that most of the extant "surround sound" concepts have significant technical flaws as well as social ones. I own an AKSA 55 and a 38W class-A behemoth achieving about 20% efficiency (well short of the 50% theoretical maximum) with 5%THD at full output.

Ben.