[ShinOBIWAN]

WOW!

I had the chance to hear a UcD700AD today in a mates system and it totally blew me away. We also took the opportunity to do a direct AB with my AKSA 55N+ that I'd brought with me and to show him what a real amp sounds like - more on that later.

He uses a PC as the source with lossless audio and a highend RME fireface 800 convertor - pretty much the same as I'm running except digital filters for the crossover on my DIY speakers. He has Nordost Reddawn speaker cabling with Chord balanced XLR interconnects(used with the UcD700AD) and Scorpion Canare/Belden RCA interconnects for unbalanced operation(used with the AKSA). His left and right speakers are modified Reference3a Veena.

We connected both the amps up directly to the DAC's on the RME Fireface 800 and this enabled us to do a direct AB comparison right there in the software on the PC by simply setting up and thereafter clicking one of the presets that either used the AKSA or the UcD700. The AKSA was connected using unbalanced interconnects and the UcD was on balanced XLR's. The RME uses servo balanced outputs so the appropriate line level was automatically selected. We also matched the levels of each very closely as there were clear differences in overall volume - no suprise. Overall the UcD needed bringing down a fair amount to match the quieter AKSA. All interconnect cables used were high quality though we did use different brands on each amp unfortunately because of the balanced vs. unbalanced situation. We did have to swap the speaker cables from one amp to the next though but this took only a few second with banana plugs and yes we did it with the amp left on Sorry!

After just casually listening to each amp for around a half hour we set about doing a direct comparison. All listening was done at a true to life type listening level or the point where it sounds about as loud as the real thing would.

First up was Vivaldi - The Four Season (Chesky Records). I love this disc and there are some real tests of imaging, nuance, flow and atmostphere in a few of the tracks. I've listened to this many times and I've heard it on bad systems, average systems and superb systems. You know when your listening to a superb system because you completely and utterly forget about everything, the music just takes over and fills the room in a completely natural manner. Both the AKSA and, much to my dismay, the class-D UcD achieved this, it was the little details that were different and ultimately made the difference.

Overall tonality between the amps was very similar ie. completely natural. But the big thing that I really noticed was the bass, and to a slightly lesser extent, the difference in imaging and specifically focus and depth.
The AKSA sounded great but I just couldn't help realising that every time we switched over to the UcD the imaging got that bit more sharper and more realistic, I really like the way the it moved sounds behind the speakers - something the AKSA did attempt but it just wasn't as definite or clearly defined, its a difficult thing to describe but when you hear this effect its a wonderful thing to behold and especially with superb recordings like this Chesky one.
The biggest difference for me though was in the bass and its here where the AKSA got shown up. The UcD was tight and effortless and the AKSA was a bit blurred and didn't really sound as though it had quite the same grip. Or put another way, the definition of the deeper tones and the colour of the room wasn't as 'right' on the AKSA.

After this we moved on to some Andreas Vollenweider and Craig Armstrong. It was a pretty similar story and in the end I preferred the UcD though the AKSA was still very strong.

Drawing things to a close, we put a few of the 'test' scenes on from the Matrix, Starwars movies and other big SFX movies. Again the UcD was clearly the better performer, its transient abilities are nothing short of a revelation.

After a great day of just listening and comparing I'm now wondering what the hell is going on. My lovely AKSA 55N+ was convincing beat by a class-D amp! After bulling the AKSA up so much to my mate over the last few weeks, I've got to say that I was rather embarrased because of my over confidence.

I'm going to be selling the AKSA but thought I'd ask if there was anything obvious that I should check that could be causing the performance to be slightly off - or maybe the UcD is just the better amp?

I've got at least 300 hours on the AKSA and I left it playing music for a whole week into a dummy load of 8ohm on a fairly loud setting. Thats about 150hrs and because is rigged up to the digibox, PC and projector its in use very often and this has been the case for around 3 weeks now, so its probably more like 400hrs actually.

I've checked the bias again and its as per Hughs intructions.

[AKSA]

Hi Shinobiwan,

Interesting post;  you are comparing a 55W amplifier to a 400W amplifier, in fact the UcD700 might even be 700W!!   Is it fair to expect the same performance, particularly on highly dynamic material?

When you highlight what you see as faults in the AKSA in this forum, and you say you will sell it because it no longer reaches your standard, you are unnecessarily undervalueing your original choice, and you might reconsider what the AKSA really does do well before you sell it!

Here's my comments on the matter.

It's like comparing a motorcycle engine to a big block Chevrolet V8!!  They can't possible be the same, and if you are to compare them at all, it should be at a power level which does not in any way disadvantage the smaller amp.  Even then, the larger amp will ALWAYS sound more dynamic.   I can assure you that a 400W AKSA would sound incredibly powerful too and astonish with its dynamics.  That's just the physics of it!
But no such beast exists, sadly.  

First, you need to know the impedance curve of the (modified) speakers.  If they drop below 4R appreciably, then the AKSA is at a huge disadvantage and I would suggest the test is invalidated anyway, because it was not designed for low impedance loads.

Second, you need to compare them at volumes the AKSA handles with ease, preferably on nominally 8R speakers in a smallish room.

Thirdly, you need to play a variety of music, particularly soft acoustic music, to tease out the real differences, which are chiefly in refinement.  Anything with pop or high impact content will advantage the larger amp for obvious reasons, but the quiet, acoustic stuff will advantage the smaller amp.

I actually own a UcD180, and have done for two years.  I have compared it to my AKSA 55N+ many times, and so have others, and the consensus would appear to be very different to your observations.  I bought it precisely so I could compare it, and give others that opportunity too.  I took pains to ensure it ran from the same high quality power supply as the AKSA.  I can tell you that in three areas, the UcD is very good;  Bass, Imaging, and Dynamics.  In all other areas, it's bested by the AKSA, which tops it for lack of fatigue, 'natural' sound, and relaxing, lifelike presentation.

For Home Theatre applications, where special effects and high impact is de rigeur, I do recommend the switching amps.  In this role they are superb, and in short order they will come to dominate the market.  But in the high end areas where audiophiles listen for emotional engagement and lack of fatigue, the analog technology is still superior by a wide margin.  I expect this will change, but not for a while yet.

Cheers,

Hugh

[ShinOBIWAN]

Sorry Hugh my post wasn't intended to place the AKSA in a bad light but merely highlight the differences I heard between the two amplifiers.

After reading back what I've wrote I realise now that I should have perhaps emailed this to you rather than posing it on a public forum since it creates the wrong impression. In no way is the AKSA 55N+ inferior to anything I've heard its in that upper echelon that just sounds a little bit different to the rest. I'm guessing I have a preference for the more visceral sound of the UcD but to be honest I didn't feel it was grainy or edgy at all which most of the higher power amps I've heard display to some degree. In many ways it sounded much like the 55N+ but 'sharper', sorry I'm not explaining the differences very well.

Its just stuck me that we didn't actually listen to any real vocal based music; it was all ensembles, orchestral or piano solo's. We did watch movies but that's not a real test of amplifier quality and I agree that the amp with the more guts generally sounds more impressive.

Also as I understand it after doing a little research, the UcD180 is an older design and the new UcD700 is a further refinement of a technology that's still relatively new. It sounds like I'm trying to sell you the UcD700 that's not the case though and I'm just pointing out that what I heard wasn't indicative of your own comments.

I should also point out that the AKSA 55N+ cost roughly half the cost of the UcD700 with matched PSU's. So that may put things in perspective again as slightly better for double the cost is definitely diminishing returns territory.

Also I used the AKSA 55N+ with non standard PSU's:

http://www.bmm-electronics.com/Product.asp?Product_ID=3310

It uses two of those in dual mono configuration. Maybe this has caused a different signature to the AKSA 55N+ you know?

[ShinOBIWAN]

Its also worth mentioning that his room is average in size. About 11ft x 16ft would be my estimate.

BTW Hugh, I still haven't listened to the AKSA yet with my own designs since they require 6 of them. You do remember I was using ESP P101's with them and found out it was a little too edgy for the ATC's which have a studio monitor heritage and hence accuracy. Perhaps the Hypex would be too much as well? I'm really not sure whether to order the other 2 x 55N+ and 2 x 100N if I would prefer the Hypex.

[AKSA]

Hi ShinoBIWAN,

Many thanks for your response;  no problem at all, we just need to be sure to compare apples and apples.

I think the BMM power supply is very good, and a very good choice for the AKSA.  I thank you for showing it to me!

The visceral sound you like is what attracts people to the big AKSA, the 100W version.  I suspect I should roll out a 200W AKSA;  this would have more grunt than a pig farm!  As a general rule, almost everyone likes the visceral sound on rock 'n roll, heavy metal, and movies.  Even a big orchestra sounds better if the amp has plenty of power.  But for jazz, vocals and chamber pieces, the smaller amp is quite sufficient, depending a bit on speakers and room sizes.

I think you are dead right about the improved refinement of the big UcD over the original 180.  They are improving in leaps and bounds, but the ultimate improvements will only show when the switching speeds are a little higher, around 1MHz.

At present the European based Hypex models are rather expensive, particularly here in Australia, and there are not the savings in power supply due to increased efficiency that we expect.  Not yet, anyway.

Again, thanks for your post,

Cheers,

Hugh

[JoshK]

As a general rule, almost everyone likes the visceral sound on rock 'n roll, heavy metal, and movies. Even a big orchestra sounds better if the amp has plenty of power. But for jazz, vocals and chamber pieces, the smaller amp is quite sufficient, depending a bit on speakers and room sizes.

This is a good point Hugh. I am the RNR, heavy metal, big orchestra fan and pretty much gag at jazz, vocal and chamber music.  I like the presentation done by the UcD's, but thought your AKSA 100N+ did a better job at presence and 3D.  I got much better depth presentation, all else being equal when I evaluated the 100N+.  

There is some rock that I like that is real acoustic, blues rooted or vocal that is better on a good analogue amp, but the majority of what I listen to is more entertaining with a more visceral feel.  I hadn't really thought much about how a large amp would give more slam at the same listening volume.  That is food for thought....

Anyway, I just thought I'd put in my $.02 as someone who has listened to your amps but owns UcD amps.  I thought extremely highly of your design but here stateside they are quite a bit more expensive than the UcD amps and the UcD amps were meant as a stopgap.  I have often thought that music preference plays a vital role in what technology and sound one chooses.  It is pretty hard to have it all.

[EchiDna]

Hi ShinOBIWAN... interesting findings!

IMHO - the AKSA's signature sound is more 'natural' to my ears while digital amps (UcD's included) are more 'clinical' or "sharper" as you put it... the difference in clarity of the sound can be intoxicating, and if this is the sound you crave, then digital is for you... I totally agree with Hugh - this type of sound suits movies and special effects down to the ground.

As for reproducing the feel and sound of a live concert... I'm yet to encounter that from a digital amp. I'm also using PC as a source so I've run similar comparisons myself I like the less sharp sound you can get from an AKSA, it's what draws me into the material... I just don't enjoy sitting and listening to clinical sound (so far anyway).

So end result - its a horses for courses thing  

[ShinOBIWAN]

Thanks for your thoughts everyone.

I entirely agree that its largely down to personal preference and musical habits that sways the choice we make in amplification, source and somewould argue, cables. I've already tried Rod's ESP101 design and liked it but it did have a hard edge that was both grainy and fatiguing with my speakers. In warmer systems I expect it would sound very nice.

Another thing is that I haven't listened to the UcD700 nor the AKSA on my intended main speakers. The reason for that is they 3-way actives and therefor need to be tri-amped. I bought the AKSA 55N+ to road test with a view of purchasing another 55N+ and a 100N kit should I like it. I thought that was the case until I listened to the UcD700AD and now I'm just confused again.

I've got a couple of options:

Beg/borrow my friends UcD700AD amp and road test that in a similar fashion to the AKSA. The benefit being that I can listen over a long period in my own listening room at different volumes and with a wider genre of music that I listen to. Whilst doing this I can periodically switch back to the 55N+ for a reality check.

Or

Carry on regardless and ignore the evil thoughts in my head then simply order the 55N+ and 100N from Hugh.

Or

Order a 100N+ to make a slightly more fair comparison to the UcD700AD.  If I like what I hear then I can change my plan and order another 100N+ for the midrange and use the 55N+ on the tweeter.

I'm thinking that since I'm tri-amping 3xUcD700AD's is going to be a wee bit of overkill.

What are your thought's on mixing amps Hugh? What about the UcD700AD on the bottom and AKSA's on the mid and treble? Crossover is at 400hz which is right in the fundamental range of human hearing. I'm guessing any tonality difference would be ruthlessly revealed and the sound would become distracting rather than coherent.

I'm back on the fence once again watching life pass me by

[andyr]

Sorry Hugh my post wasn't intended to place the AKSA in a bad light but merely highlight the differences I heard between the two amplifiers.

After reading back what I've wrote I realise now that I should have perhaps emailed this to you rather than posing it on a public forum since it creates the wrong impression. In no way is the AKSA 55N+ inferior to anything I've heard its in that upper echelon that just sounds a little bit different to the rest. I'm guessing I have a preference for the more visceral  ...

Hi shinOBIWAN,

You say you have an AKSA 55N+ ... and with your next breath, you say: "Also I used the AKSA 55N+ with non standard PSUs:

http://www.bmm-electronics.com/Product.asp?Product_ID=3310".

I clicked on the BMM link you gave but couldn't find a power supply with the ID of 3310.  However, without the Nichicon PS caps which Hugh supplies for the AKSA 'N' or the 'N+' upgrade ... you do not have the bass which an 'AKSA 55N+' has.

Why I know this is that I used these Nichicon electrolytics to upgrade the PS of my active crossovers - and got a whole lot more base as a result!  

Regards,

Andy

[AKSA]

Hi ShinOBIWAN,

Thanks for your post.  Good questions!

I think from a purist standpoint it's best to have all identical amps if you can, BUT the audio waveforms are so slow that group delay issues are not evident.  So, you could select amps for the different bands;  top end, something very fast, yet sweet (maybe an AKSA 25N+), for the midrange, something of body and warmth, a 55N+ is fine here, and for the bass something very solid, perhaps even an AKSA 100N (you don't need the N+ in this role), or even a UcD400 if you wanted to save a few pennies.

This would be a relatively economical way to do it, giving a good presentation and the best of both worlds costwise.

The power supply in the AKSA, supplied of course in the kit, is really VERY good, and as Andy says, the bass is better with the N+ version.

In any event, if you want to talk more about this, do email me!

JoshK,

Many thanks for your post.  Yes, horses for courses;  it is significant that the SET guys like 'smoke filled jazzclubs', where ambience and vocals are the principal focus.  Since we are attuned as human beings to the voices of other human beings, the vocals better be right, and the typically machine delivery of digital amps and most SS amps is just not amenable to this environment.  OTOH, hard rock needs POWER, baby, and this is where the big power of monstrous PP output stages is king.

Cheers

Hugh

[lord dubious]

You cannot have it all in audio.  I actually appreciate Hugh's view of audio and think it's really sensible.  Certain technologies lend themselves to certain applications.  All skilled designers must make decisions within the limits of this reality.  I think it would be nice to have a couple of systems that do different things and do those things particularly well.  For now, my AKSA does most things really well.  I cannot see the point of parting with it.  Later, I will probably just get something more or less powerful, perhaps tubed, maybe digital.  As long as it sounds good in its own way, who cares?

[PSP]

I have recently been able to compare the AKSA 55N+ with the 100N+, both driven by the same source (Scott Quick modded Philips 963SA) and the GK-1, same interconnects and speaker cables, and speakers (GR-Research Paradox 3 floorstanders).  Since I am working to build a set of Orions, I have a lot of amps in the basement these days (all AKSA, by the way!).  Switching amps can be accomplished in a minute or so.

Since I have only been comparing the 55N+ and 100N+ amps for a few days I really don't have a lot of audiophile detail to relate, but I can confirm Hugh's comments above on the effect of added power.

I like many kinds of music, but I really like large orchestral works.  I have a large room (L-shaped 41 long, 17 feet wide except for a 23 foot wide alcove at one end, speakers 3 feet from the end of the alcove, 8 ft ceilings, carpet over cement floors), and the Paradox 3s are about 90db efficient).  I have listened to the 55N+ for several years now in this room.  Jazz, vocals, small ensembles have always sounded extremely nice, but large orchestra played at high levels has sometimes sounded a bit congested.  I recently completed the 100N+, put it in my main system for several months of break-in (the 55N+ was moved to the bedroom system and run at least once daily so it could be compared with the 100N+ without worrying about whether the 55N+ was still broken in).  

So far, I have only listened critically to a few large orchestral works.  In quiet passages, I think it would be hard to tell the two amps apart.  Solo violin might be a tad sweeter on the 55N+, but I'm not sure about that yet.  At high volumes, however, there is no contest.  The 100N+ is noticably more dynamic and retains focus and clarity while the 55N+ becomes increasingly conjested during louder passages.

This experience has been a real eye-opener for me regarding the importance of power (and I suppose speaker efficiency too).  I think that for me multi-amp approaches, although they bring cost and complexity, are probably the way to go (if you want to listen in a big room to large works at realistic volumes).  Examples are Jens Thorson's excellent system (  http://j-a-thorsen.homepage.dk/home_gb.html ), andyr's multi-amped Maggies, Tinker's Phoenix, and the Orions.  

Peter

[ShinOBIWAN]

Hugh,

I've arranged for my friend to bring his amp over the next time he drops in. Looking likely for sometime next weekend.

I'll have a thorough listen on music I really enjoy on the AKSA and that I felt highlighted its qualities. I'll be careful to ensure a more moderate listening level too when comparing.

I'll report back with my thoughts and hopefully some of my confusion is cleared up.

[AKSA]

Thank you Peter, a most measured and thoughtful analysis and one I agree with categorically!  The differences between the amps are primarily of scale;  it doesn't sound like much, and on acoustic and vocal/jazz it's not really noticeable, but on large scale orchestral - particularly heavy stuff like Berlioz' 'Fantastique' - it is a pivotal difference.  This all makes me think that a 200W AKSA might be the go;  I've done early design work on this, and two adventurous people have built them up (notably Romeo Tiu in Italy who did a marvellous 200W AKSA which he really likes!), but of course this amp is VERY expensive in power supply componentry and I have always felt it would be hard to sell.  Perhaps I'm wrong;  some here might like to comment.

Brad (it is you, ShinOBIWAN, I hope??)

Thanks for your courtesy and quiet acceptance that there is more to the assessment of amps than meets the eye.....  Your 55N+ is a superb amp for smaller scale acoustic, vocal and light orchestra listening, and it was an economical choice.  To truly compare to the PWM amps like the Hypex, you need to have similar power ratings, and the 100W AKSA is much more appropriate.

Incidentally, all the switching amps belong to the rigorous 'straight wire with gain' philosophy, from which AKSA philosophy deviates.  While they are consistently improving all the time, the so-called digital amps cannot match the musicality of the best SS and tube amps, though their imaging and transient response is very good.  There will always be a place for the carefully voiced SS AB/A PP/SE and tube amps, as these amps bring out the emotion in the music, something the 'straight wires with gain' cannot do.  This will only change when the psychoacoustics is better understood, and bears little relationship with the rapid technical advances of the switching amps.  I remember critically listening about two years ago to a Bel Canto Evo II with JM Labs speakers.  The whole rig was about $US80K, an absurd amount of money.  I found it aggressive, over detailed, and it shredded my ears with high energy treble.  There were standouts in the imaging and bass, but the rest was not what I'd term 'musical'.  It's a matter of mindset.......

Cheers,

Hugh

[andyr]

Thank you Peter, a most measured and thoughtful analysis ... This all makes me think that a 200W AKSA might be the go ... some here might like to comment.
 ...

Hi Hugh,

Just confirming I certainly would like to audition a 200w AKSA to see whether it gives me anything more with my Maggie bass panels!  

If it does then ... hang the expense!!  

Regards,

Andy

[ShinOBIWAN]

Thank you Peter, a most measured and thoughtful analysis and one I agree with categorically!  The differences between the amps are primarily of scale;  it doesn't sound like much, and on acoustic and vocal/jazz it's not really noticeable, but on large scale orchestral - particularly heavy stuff like Berlioz' 'Fantastique' - it is a pivotal difference.  This all makes me think that a 200W AKSA might be the go;  I've done early design work on this, and two adventurous people have built them up (notably Romeo  ...

Hugh I'm hurt that you've mistaken me for 'Brad'!

After our thoroughly engaging emails I thought you would have remembered me better. Maybe this will jog your memory:

http://www.bristol-aeroplane.com/

And the sleeve valve aeroplane engine? Or maybe my DIY speakers that we discussed:





Surely you remember now?

[jules]

In response to part of PSP's post I can say that a 55N+ driving higher efficiency speakers is a very imposing combination.

When I first fired up my 55N+ my speakers were a pair of middling quality, lowish efficiency  B&Os. I am now using a pair of MTM phenomenals [PHL and Raven R2 drivers] with around 95 db/metre rating. As I calculate it, 55W into a 95db speaker is more than equivalent to 100W into say 88db efficiency and what looks right on paper also works in reality.

I can assure anyone in doubt, that for large powerful orchestral works the results are hair raising and magnificent. One practical example that particularly impressed me was the reproduction of the string section of an orchestra. A large massed string section playing softly, smoulders with a sort of detailed latent energy that is often lacking in other systems while the same string section at full volume conveys a wonderful sense of strength.

In short the dynamic range of a 55N+ driving medium/high efficiency speakers is totally satisfactory. If I've got any complaint here it's that, with the amp set at a good listening level, I can no longer fall asleep with the system on. Somewhere along the line a forte passage from an orchestra or organ is going to startle me into wakefullness again.

jules

[JoshK]

Shin, those are some of hte coolest looking DIY cabinets I have ever seen!  Good job mate!  I had seen them before on diyaudio.com but not this version I think.

[soitstarts]

ohh yeah... Is that a harlequin paintjob or am I seeing things???

[ShinOBIWAN]

Shin, those are some of hte coolest looking DIY cabinets I have ever seen!  Good job mate!  I had seen them before on diyaudio.com but not this version I think.

Thanks but...

On the 5th of November we have something called Bonefire night here in the UK, you may or may not have heard of it, anway we main use the night as an excuse to spend £££'s on firework and burn a load of old stuff that's no longer any use...

...those cabinets in the photo's went on the fire I know it pained me at the time but the replacements are even better sound wise.