[rwalton]

Hello All,

Though I don't post much here (or anywhere) , I'm often lurking and am a proud owner of two Nirvana amps (55 & 100) which I am very pleased with.  

I recall from reading at Hugh's website, and even in some of his old posts at HD, about the indefinable "tube magic" that tube amps can provide.  However, I don't recall the reason he opted to go for a SS amp  kit vs. a tube amp kit.  I suppose one reason could be that the GK-1 can provide the same "magic" with a SS amp.  So I wonder:

1.  Can the GK-1/AKSA amp really provide the benefit so many have heard with tube amps (I have never actually heard a tube amp setup)?

2.  I realize the answer to #1 is not likely to be a "yes" or "no", but is there some other reason not to consider a tube amp kit?

Just wondering.........

Rick

[JohnR]

It would be tough to get around the inherent cost of good transformers.

Are you thinking about building a tube amp? Go for it, I'd say. Bear in mind there are lots of camps in tube-land, all of whom hate each other

[rwalton]

Hi John,

I'm always thinking about building audio equipment.  The actual construction is another matter altogether!  

Rick

[AKSA]

"...the indefinable "tube magic" that tube amps can provide. However, I don't recall the reason he opted to go for a SS amp kit vs. a tube amp kit. I suppose one reason could be that the GK-1 can provide the same "magic" with a SS amp. So I wonder:

1. Can the GK-1/AKSA amp really provide the benefit so many have heard with tube amps (I have never actually heard a tube amp setup)?"

Hi Rick,

Thanks for your post.  This is an important question, deserves a considered answer.  

A tube amp has rather more tubes than the GK-1, which has basically just one tube in the signal path.

However, this ain't all bad.  Many tubes, each with their sonic flavor dictated by tube, operating point, power supply and coupling caps, adds quite a pot pourri of sonics, and they must be mixed just right, like a good recipe for apple pie, to get the 'right' sound.  (Of course I'm ignoring the very important subjective issues of the 'right' sound, they do differ from person to person).  Consequently, it's much more difficult to get right than a circuit with just one tube, which can be super tweaked to deliver a much 'simpler' but sonically pleasing result.  That's the principle behind the GK-1, where the tube is very carefully set up, and it's power supply even more so, to deliver just that.

A tube power amp has more complicating features, too, which add to the sonics.  They are, principally, the output stage, which includes a very carefully wound transformer, and two very much larger tubes.  I believe that it's here that the 'indefinable' tube magic is added, BUT ONLY ON SOME VERY GOOD DESIGNS.  OTHERS MISS THE BOAT.......

I may be shot down for this, but I'd contend that there are two ways to develop a very good tube amplifier.  One is plain good luck, with judicious choice of all the design parameters and componentry, and the other is sheer hard grind, starting afresh, so to speak, which can take many years to bear fruit.  That is the reason so much tube circuitry is utterly predictable;  it's all been done before, and some circuits work, and some don't.  From an R&D POV, it's better to choose those which work, or risk losing lots of moolah in development........

Now, we add two important considerations to the mix.  A kit amplifier must be light, for shipping purposes.  It must also be relatively robust, so postal staff can indulge a little package football during their lunch break.  Large, highly breakable tubes and heavy, chunky output and power transformers militate against shipping, and then there is the rub.......

Voltage.  A decent tube amp, and I'd choose a push pull of at least 35W, needs at least 550V on the output plates.  This is serious voltage, and is potentially (pun intended!) highly litigious.  One can take a few risks in life, but this sort of voltage is extremely dangerous because it is not so high that it throws you across the room, yet not so low it won't stop the heart.  In fact, around 600V will paralyze, which means that after several seconds you are probably dead at the workbench.  300V will throw you out of the case, 1000V will throw you across the room, but 600V will hold you spell bound until you die.......  These are important considerations for me, the muggins at the other end of the network apologizing to Mrs DIY for the untimely death of her beloved husband.

Subjectives.  I have never been fully satisfied with tube amps.  Yes, they communicate the emotion beautifully, and that's very important, but they lack slam and impact in the bass, which I crave for with my rock 'n roll tracks.  There are tube amps with this sort of performance, but they are rare, and often miss out in other areas, such as refinement.  The ARC amps have marvellous bass, but they seem a little glary to me and certainly run their tubes very hard, necessitating replacement every 18 months or so.  That's expensive!  The Cary 805 (uses an 845) is a beautiful amplifier, but the bass is still a little soft - a customer has one locally biamped with an AKSA 100N on ProAc towers and the combination is stunning.  I know of a stratospheric push pull 845 here in Melbourne - custom built over four years - but have not yet heard it.  I'll keep you posted.  But in terms of cost, Rick, you don't want to know.  This amp (two monoblocks, BTW) needed wheelbarrows of cash to build!

And this brings me to my piece de resistance (a favorite phrase for a follower of Ohm).  I really like hybrids.  Here the possibility of innovation and truly original thinking is almost unlimited, because the two technologies are rarely combined.  We can use tubes alongside SS;  tubes for sonics, and SS for muscle.  This gives us our cake for eating, which is the very reason we wanted cake in the first place.  (Anyone heard Billy Connolly talking about 'cake and eating it too'?  Hilarious, and recommended!)

Lastly, Rick, consider Heathkit.  They produced tube amp kits, some of the best the world has seen, and eventually they went broke.  Why?  I believe shipping weight, loss of interest in tubes with the advent of cheap, linear semiconductors, high R&D costs, and inevitably, inadequate marketing.  Already I'm swimming against the tide, but I don't want to be so different I actually gasp for air.......

Cheers,

Hugh

[U4EA]

Bear in mind there are lots of camps in tube-land, all of whom hate each other

LMAO...no truer words were ever posted.  Especially the oem vintage camps.  Whew...rough crowd.

[Felipe]

Let me just say, this post is the best one yet in this forum.
I really love the way Hugh puts out his thoughts...  

BTW, Hugh.... how is that PUB CD coming along ? If you need help just ask!  No problem in distributing some CD's here over Europe.

Bye

[TG]

Hi Hugh, I'd be interested in your further thoughts on one point:

A tube power amp has more complicating features, too, which add to the sonics. They are, principally, the output stage, which includes a very carefully wound transformer ...

What is your opinion of modern output transformerless valve amps?  I stress modern designs such as Bruce Rozenblit's balanced forward voltage topology or Ralph Karsten's AtmaSpheres - not the old Futterman & circlotron circuits.  Such amps are certainly an esoteric corner of valve amps (which in themselves are an esoteric corner of audio) but it does seem to be a field which has been somewhat ignored.

Leaving aside for the moment the potential downsides which they share with transformer coupled amps (which you have already mentioned) and the aspect of waste heat (which is often wildly exaggerated anyway) what is your opinion of the sound of OTLs?

Cheers
TG

[AKSA]

Hi TG,

I've only ever heard one, which was a Rozenblit design from about ten years back.

It was a fine amplifier and I liked it a lot.  But it lacked bass slam, just like most tube amps.

It was an ethereal sound, not unlike electrostatic speakers, with great accuracy, very twee......

But horrifically expensive to build, particularly in power supply, and using lashes of global negative feedback, which to my mind partly offsets the benefits of using tubes anyway.  Technically, this puts the OTL firmly into the same territory as the conventional crop of SS PP amplifiers using negative feedback, and really comes back to using tubes for the sake of tubes.  Nothing too critical mind, but what for?

Cheers,

Hugh

[TG]

Hi Hugh, you raise some interesting points.

I've only ever heard one, which was a Rozenblit design from about ten years back.  It was a fine amplifier and I liked it a lot. But it lacked bass slam, just like most tube amps.

Yes, the perennial bugbear of valves - great voltage amplifying devices but as for providing current  
If the Rozenblits you heard were built 10 years ago they must have been either his first 6AS7 design published in Glass Audio or a very early "T8" design using 6C33C-B valves.  Both amps had inherent problems - the more recent "T8" using EL509 valves and "T16" using 6C19pi valves are much more mature.

It was an ethereal sound, not unlike electrostatic speakers, with great accuracy, very twee......

Good call - exactly how I'd describe them

But horrifically expensive to build, particularly in power supply, and using lashes of global negative feedback, which to my mind partly offsets the benefits of using tubes anyway.

Hmmm, don't know if I'd say horrifically expensive - a pair of 25W "T8"s cost me about Aust$2,500 to scratch build - mind you, as a commercial kit they are WAY more expensive, and that was the original point of this thread - if I was trying to sell such amps I'd be asking around $6,000 a pair.  The negative feedback is a pain to be sure, they just won't work without it.  The T8 has about 40dB of gain and 20dB of feedback - whoa Nelly!  

Technically, this puts the OTL firmly into the same territory as the conventional crop of SS PP amplifiers using negative feedback, and really comes back to using tubes for the sake of tubes. Nothing too critical mind, but what for?

A fair point - I guess the only comment I'd make is that they still sound at least equivalent to, if not better than, any similarly priced SS amp I've heard.
Hmm, I guess in the final analysis that's the main reason the've never taken off in a big way - not enough inherent superiority to the approach to make them more than an interesting experiment for enthusiasts looking for something a bit left of centre (like me  )

Thanks for your comments, much appreciated
cheers
TG

[Al Garay]

I highly recommend you listen to a newer version of the Transcendent Sound OTL T8 or T16 amplifiers.

As much as I like my AKSA 100 watt monoblocks and the way they drive my very inefficient Ellis 1801 speakers (85db), I was captivated by the sound from my friends T8 stereo amp driving his 1801 speakers.  It was not lacking in bass which surprised me for a 25Watt/ch amp. That was one of my lessons for not relying on specifications.

My point is if you are looking for a tube amp kit, you should strongly consider Transcendent Sound.
http://www.transcendentsound.com/index.htm

Al

[ginger]

G'day from Oz,
I went the valve amp path some years ago constructing a EL84 Ultra-Linear Push Pull Amp straight out of the Morgan Jones "Valve Amplifiers" book. Over 18 months the design was finessed along Hughs philisophical road of make a change, listen, if its better leave it in, if its not take it out. Major changes were to Zero Feedback and Current Source Biased Output Tubes, Ultrafast Rectifiers, Polypropylene Power Supply and Coupling Caps and OSCON Cathode Bypass Caps (Better even than Blackgates) on the Output Valves.

About this time I built a 100W AKSA which if you read my feedback on Hughs Webpages you will see that I thought was the best Solid State Amp I'd ever used but did'nt quite match the finessed to the ultimate little valve amp I was using. I tried a few mods of my own to the AKSA including the Nivarna Kit which I recommend you use as STANDARD (large improvement). I also tried emitter degeneration on the input diff amp and came to the conclusion that very small amounts of emitter degeneration helped but more than about 10% definitely did'nt. From all this I concluded that a Power Amp needs some 2nd and some 3rd Harmonic Distortion in the right balance for that warmth and emotion. (Emitter degeneration reduces third harmonic distortion).

This has been bought home to me graphically in recent times. I splashed out major bucks for a 845 based Single Ended Triode Power Amp. The Audiophile Mags all say these are the "ultimate". Their distortion spectrum is almost pure 2nd harmonic and No 3rd or higher harmonic distortions.
Guess what - Yes it has lovely imaging and detail BUT it doesn't have the warmth and emotion of either the AKSA or the little EL84 Ultralinear Push Pull.

So treat claims that valve amps are the ultimate with a grain of salt and listen BEFORE you pay out big bucks.

My preferences run
1) EL84 Ultralinear Push Pull Valve Amp
2) 100W Nivarna kitted AKSA
3) 845 Single Ended Triode Valve Amp.  

The point here is that for that warmth and emotion and a listening experience to make you grin from ear to ear or leak tears you need some 2nd and  some 3rd harmonic distortions and they need to be in the right balance.

This is why top end transitor amps with distortion figures of 0.001% and less sound cold, sterile and boring.

Its also the reason why the AKSA sounds so good - check the schematic, particularly the front end diff amp - No current mirror loads, no current source biasing or any of that fancy stuff which gives you vanishingly small distortion figures but kill the emotion of the amp stone dead.

If you do a maths treatment of the AKSA you can show that the amp gain formulae contains an expression for the gm of the input diff amp on the top line. AS input signal voltages increase either side of 0 volts the gm of the diff amp rolls off - what does this mean sonically? It means that you get a lovely "Valve Like" soft compression.

Conclusion - the AKSA is more "Valve Like" than many of the top end valve amps, its a lot less expensive and its zero maintenance which is something that NO valve amp can claim.

Any Valve Amp to out perform the AKSA (and they do certainly exist) is going to be damn expensive.

Cheers,
Ian Miller
Senior Electronic Design Engineer
Adelaide, South Australia

[AKSA]

Hi Ginger,

Thanks for your insightful post!  I read it with great interest.  I felt some satisfaction that you vindicate my stand on harmonic spectrum, the correct ratio of H2 and H3.  The difference between reproduced sound and fulfilling music lies in this obscure area, I am convinced.

Almost ten years ago I set out on a crusade to make SS sound a little like tubes.  I was convinced that with hard work and a lot of listening - and little distraction from complex, expensive measurement regimes - I might just be able to bring something new to this fascinating artform.

It wasn't that I thumbed my nose at the establishment on this, but I certainly had something to prove to myself, and loved both technologies, so it was a pleasure.  I tried heaps of degeneration, scads of current sources, litters of current mirrors, and all the other techniques of modern audio design, and slowly came to see that none of them were particularly musical.  Sharp, detailed, lots of impact, positively surgical, but unfulfilling.  This took it all back to first principles, the basic Bailey/Citation 12 topology, and pushed my thinking towards Nelson Pass, and Kevin O'Connor, whose writings and general approach I admire.  I built the original Zen, and it was marvellous, then I moved on to the Aspen Glass Harmony, which is a very different topology (inspired originally by the Zen) with an octal front end, giving impact and slam with all the refinement of the best Zens.  Then the challenge was on to do this with Class AB push pull circuitry for its efficiency;  I deplore wasted energy, something which will hit a chord with those who have just been through the recent traumatic power outage in NE USA.  We are reaching a point in western society where our dependence on energy is beginning to create very severe social issues, quite aside from the disparity in wealth between the First and the Third Worlds.  Failure of our huge, complex, energy-centred infrastructures will bring draconian consequences, and we'd be wise to minimize our energy consumption wherever possible.  This is not to criticize NP, incidentally, who continues to build audio works of art......!

Ginger, what sort of 845 did you buy/build?  I have some experience with this technology, for some time I held a Cary 805 (owned by a friend and now owner of an AKSA 100) as a reference.  Can you tell us a little about the tube lineup, voltages, and transformers/caps in use?  In a tube amp, since direct coupling is more difficult, the capacitors become VERY important as their choice determines sonics.

Let me answer your comment about 'damn expensive'.  When a technology becomes mainstream and purely objective, like PCs for example, and production techniques are well understood, it soon becomes cheap.  Ballpoint pens, cheap automobiles, mid-fi systems, CD-R are all good examples.  As soon as subjectivity creeps in - women's fasions, Italian sports cars, interior decorating, architecture, audio - there is a recognition of a certain art, and a market arises to service this plethora of tastes.  Simultaneously a marketing machine swings into action, frequently using 'in-crowd' images and sex-appeal to sell a particular product, and this complicates the image even more.  A glance at the high end ads and a quick read of a Jonathon Scull review in Stereophile clearly reveals this strange development.  This is deadly serious stuff;  creating a viable market.  A great deal of media money is involved to win the hearts and minds of the moneyed audiophile, and those in the trade take this very seriously.  Over the last two decades the objectivity of consumer audio choices has been threatened, and now most of the big names sell on the basis of their audiophile press ads and reviews, particularly in Asia.  In Hong Kong and Singapore, audio, not motor vehicles, is the social cachet.  A good review is fundamental to sales, notwithstanding the fact that many reviews are actually disguised advertising copy.  In this unhappy way the true audiophile has been partly deceived, and we finish up with $US100K plus systems with huge WOW factor but striking listener fatigue.

Incidentally, the best amplifier I believe I ever heard was a modded Mullard EL84 push pull owned by a teacher - an Englishman - in the boarding school of my youth, back in the sixties.  Vinyl, of course!

I am presently auditioning Black Gates in my 55W Nirvana.  All four 100uF caps on each module have been replaced - thank you Phillip! - and while at first I felt it was grainy and metallic, this is now improving by the hour.  The final take I'll give in a week or so, but it's pretty bloody good right now, I can tell you.  My thanks go out to Lou who first raised the use of Black Gates.  Does anyone know where I can buy these beasts in quantity at the LOWEST price (like around a dollar each!).

Thank you again for your post, Ginger.

Cheers,

Hugh

[Seano]

Hugh
Ask the bloke at Soundlabs in Sydney where he gets his Black Gates from. He doesn't sell them but claims to use them in all of the source upgrades he offers. I've done a couple of searches already and have failed to turn up a local dealer/supplier/extortionist for these things. While you are there check out how much he wants for the DACTs. Scarey............but still quite nice.

http://www.soundlabsgroup.com.au/index.htm

Alternatively.........if the Sanyo OS-CON capacitors are as good as Black Gates as Ginger suggests........they are available in Oz from Braemac who have a Melbourne office. Check contact details at www.braemac.com.au

And if you really want to go nuts - and tech specs appeal to you then hit here http://www.secc.co.jp/english/index.html and you can really go to town

Now if anyone can tell me which one/s I need for a 100Nirvana???????

[stvnharr]

Interesting posts on tube amps.   I've been living with tube amps for past several years, Conrad-Johnson and BAT's.   Have listened to others in the fancy salons, but usually preferred the BAT to all of them.
I have just finished my second Aksa 55N.   This one is 2 as I've made mono amps, using black gates, rikens, chimera braid wire, Cardas posts.
I can only compare it to the BAT VK-60 in an A/B comparison.   The BAT is a very highly thought of tube amp and is a superb performer.
That being said, I prefer the little AKSA's.   The low end response is simply phenominal, so tight, so controlled, and so mujch deeper. This is something any tube amp can only dream of, and that the BAT amp cannot match.   And this control seems to reverberate up through the musical spectrum.    I have a BAT tube front end, which likely tends to any midrange ss leanness that may be in the AKSA.
The natural musical sound of music with the AKSA's is a truer rendition than the bloomy, lush tube sound that tube audio lovers find so beguiling, as I myself once did.
Tubes have their place.  Just might not be in an amplifier output stage.

[ginger]

Thanks for the input stvnbarr.

You can see when we start discussing tube amps we are talking about a whole range of topologies and designs.

You have the straight Pentode Push Pull like a lot of the small vintage British Stuff. (BTW one of my favourite Resurrection jobs is a little Rogers Cadet III using ECL86s in straight Pentode Mode Push Pull).
Then the ULtalinear connected Push pull like my favourite little EL84 UL PP.
The Single Ended Triode (SET) which is subjectively slow compared to push pull amps but has fastastic definition and image.

Then there is the BAT VK60 - For info of readers following this thread, this is a topology that looks much like a Output Transformerless (OTL) design. Its raw output impedance is very low (say about 500 Ohms for the sake of the discussion) which is matched to 4 and 8 Ohm loads with a low turns ratio Output Transformer. The advantage of this is that it much easier to wind a good quality output transformer (ie Low Capacitance and Leakage Inductance) when you have a low turns ratio. This amp is likely to sound very different again than the standard push pull or SET designs.

CONCLUSION: There is always more than one way to skin a cat and none of them are pleasant for the cat.

Cheers,
Ginger

[ginger]

Hugh,
Missed the SET line up inquiry in initial read of your post. I had the bottom off for a quick look inside but have'nt done a full trace. This is what I think it is from my short look inside.

The 845 SET is as follows:
Russian 6N9P (6SL7) SRPP Front end
Direct Coupled to
Russian 6N8P (6SN7) Common Cathode Amp direct coupled to Cathode Follower to drive 845 Grid.
845 run cathode bias with +850V on the anode.
Its NOT Parallel Feed or any of that fancy stuff.

This is a made in China job - cost was $2500 Australian  - ie 3 times the cost of a 100W Nivarna Kitted AKSA. Supplier is Thompson Audio Design
in your home town of Melbourne.

Cheers,
Ginger

[stvnharr]

Ginger,
I believe Victor K. first designed an OTL amp, but didn't like it, so came up with the VK-60.   He also mentioned that the best way to improve the bass was to get a second VK-60 and use them in bridged mono.  Great if you got $10k sitting around.   However when I replaced the C-J Premier 11a with the VK-60, it seemed like I got ss like bass.  Over time, the VK-60 did have a nice tube sound w/adequate bass.
Still, the little Aksa Twin 55's are more naturally neutrally sounding.
I listen mostly to classical and value a natural neutral sound.

Pity the Poor Cat!

[audiojerry]

Wow, I'm glad I picked up on this thread - great commentary from several posters! This looks like a classy place to hang out -  

Hugh, I love the way you meld social issues, philosphy, and audio all into a thread about amplifier design - you make me feel guilty for owning my ARC VT200 (16 6550 output tubes, 900 watts power consumption - at idle).
I'm gonna have to sell it to some guy who can load it on the back of his SUV Hummer.

Sincerely, future AKSA owner

[stvnharr]

You'll be happy with an AKSA.   Although you may have to install a heater in your music room to replace all the heat that will no longer be there from the 16 6550's.    Big tube amps are great in winter though!!

[Larry]

Having listened to my gears switched back and forth for some time, I can now tell what my preferences are, based on the time I ended up listening to each of them.

- Ella ultralinear push-pull valve amp  
   Used most for audiophile recordings;

(Chinese KT88/6DJ8; Russian 6SN7GT; upgraded with AudioNote caps in the signal path; Available both in HongKong and US as complete kit for about US$600 including upgrades)

- Nirvana AKSA100 SS push-pull amp
  Used most for pop music, particularly those mixed and with electric instruments; played at high volumes.

(for about AU$1300, including kits and self supplied parts)
 
- SiliconChips 15W class A SS push-pull amp
  Used most for slow and soft music like blues and solo strings; played at late night at low volumes.

(Upgraded all caps with Panasonic and Elna Starget etc; for about AU$600 including kit and self supplied parts and upgrades)

All of them are driven by an upgraded GK-1 and helped by an REL active subwoofer. An Ultra-Curve Pro DSP 8024 is also used in the digital front for room correction and system balance, which makes significant differences in final sound quality.