[kyrill]

Dear
Hugh

In the positive development of the Aspen line the Soraya and the potted  magical "black box" have arisen and gave new meaning to transparency and quickness ( the rising and fading of micro transients among other things)
May i ask from a very humble thinking of mind?

my understanding is the GK-1 is originally developed and listened at with SS Aksa's in mind with the TLP philosophy at its basis. The TLP's function being a wonderful tube cathode follower to add this wonderful tube sound to the SS line combining the best of two worlds . So too the GK-1 has this Cathode follower with "starving" feed to its eh plate (?)
tubey harmonic distortions were not meant to be brought back to zero point zero (zero )levels.

The LF extended the Aksa with vanishing low distortion and a (much) better beautiful transparency and focus of minute details. Then the Soraya extended those properties further and a highly transparent and musical amp arose.

well now my question
IS it possible to change the character of the GK-1 to make it more transparent than it already is? Even with a little sacrifice of this wonderful tube characteristic?
Not with major new path ways or topology but wit small "mods"?
How to bring the "distortion" to  lower levels, do we have to change some resistors in the FB loop?
what would happen sonically if we slightly rise the voltage feed to this "plate" ( dunno the real name

So my question is  NOT how to improve the GK-1, all earlier mods addressed this question already but how to make a slightly different GK-1 with  different sound characteristics to support more the characteristics for an extreme transparent amp like the Soraya?

Of course i can anticipate the answer
My dear friend dont worry
as the GK-1 already is, it is as transparent and focused as the mind of Buddha, you dont need any change

[AKSA]

Hi Kyrill,

I dread these questions.  They go to the core of the audio design paradigm, reveal my philosophies, and are very hard work to explain in logical terms.  I design more by intuition than by pure logic (I am not an engineer!) and having to explain these difficult issues is a challenge for me.

I will present my POV in bullet points;  it's a bit easier to follow.  What I write is pretty heavy stuff!

#1  There are two schools of thought on audio;  subjective v. objective.  The disagreements are bitter, trenchant, and expose vested interest, intellectual snobbery, club membership, passionate belief, and marketing hype.  It would seem one has to choose which camp to inhabit, a difficult choice, particularly as in life the best approach is often the middle course.

#2  If we choose objective, then on current convention the approach should be lowest possible distortion.  This is a beguiling quest, as reduction of distortion to almost immeasureable levels is certainly possible and a most rewarding pursuit.  But there appears to be limited correlation with the subjective listening experience, which I would define as the likes/dislikes of a group of a 100 non-technical audiophiles across an ownership of a couple of months on all musical genres.  Wide ranging?  Of course, that is the consumer, the designer must accommodate the consumer in all his diversity, just as in other technologies.  There is promising work being done in this field, however, and in time this may bear fruit.

#3  If we choose subjective, then this means designing by hit and miss, lots of listening tests, not too much distortion analysis, and a general touchy feely/mystical approach much despised by engineers the world over, perhaps with good reason.  However, another way of looking at this is designing according to engineering principles, but testing over a long period with subjective listening tests.  This is how John Linsley Hood, Arthur Bailey, John Curl, Nelson Pass and many other successful designers do it.

#4  When one looks at the standard western chromatic scale, it is quite evident that it does not much favour odd order harmonic distortions.  So 3rd, 5th, 7th, 9th etc tend to sound harsh, and unmusical.  Even order distortion, however, is a different story, with 2nd and 4th sounding warm, intimate, if a little indistinct.  Because of the transfer curves, push pull SS amplifiers tend to produce a spray of harmonics, frequently monotonically decreasing, from H2 through H3 to about H13.  The odd order harmonics tend, for psychoacoustic reasons, to confer a hard, 'surgical' sound.  Indeed, this has always been the main criticism of SS when compared to the more melifluous tube, which has a lower order transfer curve (exp. 1.5) and thus produces large quantities of H2 and H3 and some H4 and not much beyond.

#5  The feedback question is pivotal for the following reason.  SS devices have very, very high transconductance, and thus in common emitter configuration yield very high gain.  Feedback is necessary to bring this gain back to realistic levels.  Tubes have much, much lower transconductance, and thus finite, measureable gain, typically in open loop around the 20 mark. Because of their more elongated, linear transfer regions, they are usually operated without global feedback, unlike their SS brethren.  This means the distortion spectrum, reputedly of more significance than THD these days, is concentrated at the low order;  mostly H2 and H3.  It's high, around 2-3% on a good day, but low order, and largely musical.  Add to this the fact that largish levels of low order distortion have a masking effect on the human ear (it's been estimated that the ear itself introduces around 30% H2 to all signals coming in), these levels effectively reduce the harsh effects of residual high, odd order distortion, and so you can see why tubes work so well.  But the absence of feedback with tubes, pretty much mandatory in SS amplifiers, has problems, to do with bass response, drive, and frequency response.

#6  Global negative feedback reduces absolute levels of distortion, but is increasingly ineffective at the very high speeds at crossover.  At the crossover point most of the high order artefacts are produced as devices switch on and off when one side of the output stage hands over to the other.  Furthermore, GNFB tends to 'blenderise' lower distortion levels, morphing them into higher order distortions by intermodulation mechanisms, albeit at very low levels.  The low levels are nevertheless objectionable in long listening sessions and usually show as 'listener fatigue'.  When you realise that the masking effect of highish levels of H2 and H3 is lost with GNFB, you can see why it's a mixed blessing.  There are other reasons too why GNFB is not ideal;  chiefly in the way the error signal is extracted.  This process itself can be inaccurate, leading to inappropriate correction.



OK, so that's the philosophy.  Let's talk about the GK1.

Input stage is a discrete Opamp, with a long tailed pair, a common emitter voltage amplifier, a single ended output stage and heavy global feedback.  With high levels of feedback, and a deliberately engineered level of H2 and H3, this has very low overall distortion largely because there is no push pull output stage.  The power supplies help too;  they are regulated, and have falling impedance with rising current draw.  The fb factor, however, is high;  with more than 60dB of feedback, the distortion levels are incredibly low, and the output impedance is a very low 30 ohms.  This is ideal for driving a potentiometer, a considerable source of distortion (loss of resolution) in most amplifiers.  The output from this first stage is exceptionally clean, with just sufficient H2/H3 to mask the nasties we normally associate with SS designs of this conventional nature.  So, you see nothing unique, just a very careful balancing of operating points and dimensions.

The tube output stage is a self-biased cathode follower, using a variable mu tube.  A plate loaded triode traditionally has high levels of distortion;  the cathode follower around 15% of these levels according to the Radiotron Handbook by Fritz Langford Smith.  Since we want a bit of H2/H3, we can easily achieve this by choosing a special kind of tube with variable mu, so that Vgk varies that bit more in operation than if we had a fixed mu tube.  These tubes were used as automatic gain control devices in AM radios, and in recent years have been much in demand for Fairchild 670 tube limiters, used in the recording industry and to this day the standard for such devices.  I use the 6ES8, and if you google Pendulum ES8 you will find something very interesting, no coincidence.

The operating point of the tube in the GK1 is chosen to give best sonics;  this was a long quest, as many factors must balance.  We want low order distortion in very small quantities, but we want strong, tight bass as well, one of the big problems for tube circuits.

I won't reveal all the details, but I will say that a great deal of the so called 'tube sound' is related to the tube's interaction with the power supply.  This is why different designs using the same tubes sound quite different!  For best effect on low level stages (and NOT transformer output stages, which are very different!), the supply should be high impedance, but should also be frequency dependent, ideally with low impedance at low frequencies and high impedance at high frequencies.  This is done on the GK1 through some fairly trick circuitry.  The result is that very little H2 and H3 is added by the tube at low frequencies, giving tight, punchy bass, but increasingly more is added to 'romanticise' the sound at higher frequencies.

Anyone who has heard the GK1 will agree that it is subtle;  the effect creeps up on you as you listen more and more.  The warmth of the midrange, and crystalline purity of the top end, with the wide image, the wonderful dynamics and very tight, strong bass is a revelation.  None of this is terribly evident after ten minutes, but it really endears itself to you after a few weeks ownership.  So how do we improve upon this for the new generation Aspen amps, the Lifeforce and the Soraya, which are specifically designed for very low distortion?

First off, use a teflon input cap.  That really makes an impact by improving resolution.

Second, redesign the first stage for all single ended circuitry, so that any distortion will be principally even, and even only.

Third, redesign the tubestage for cathode follower operation but in half pentode, half triode.  This is achieved with trick screen grid circuitry, and should give the best of both worlds.

And that, Kyrill, is the basis of my next generation Swift, which will use just this thinking.

If I ever get around to it.........  In my semi-retirement and my advancing years, I'm starting to get a little tired!!

If this does not answer all your questions, do please send me an email, and don't worry about stepping on eggshells.  I'm pretty confident of my products, and criticism is absolutely no problem.  Two heads are always better than one.......

Cheers,

Hugh

[whubbard]

Hugh,
Considering I will be using a GK-1m & lifeforce...that is a very informative, and useful post, thank you.

I must ask though, if you do ever release the next gen swift, would you consider offering some sort of 'upgrade' for all of us GK-1 users. Maybe just a new board, or a list of components changes. Maybe the next gen swift will be different, but considering the currently swift is just a GK-1 in a retail box, it might not be too hard.

Thanks again for the long, detailed post.

[AKSA]

Hi West,

For the Lifeforce, I would not recommend going beyond the teflon input cap on the GK1!   

The Soraya, maybe, but have to design, build, listen and consider first - we are jumping the gun a bit here!

The new Swift, which is not even on the drawing board (a teflon will be used on future Swifts as an effective upgrade), would likely use completely different bits.  New pcbs, new tube, different front end, power supplies - the whole shebang.  I doubt upgrades would be viable, either for sale or for building, you'd really have to have another product.   

But don't be concerned, West, because what you have is the best I currently offer, and it ain't half bad, man!!   

Cheers,

Hugh

[whubbard]

Hugh,
I'm very aware that what I have is not only the best you have to offer, but is the best there is! 
I can't wait to get it all up and running!

Thanks Again!

[AKSA]

West,

this is philosophy - the best there is generally is always outdated in time, and there's the rub......

I will certainly keep you, and all others, informed!

Hugh

[whubbard]

Yes,
It is sad that the best always get outdated...
...just one more reason why you should retire any time soon 

[LM]

Hugh, a fascinating and informative post, some of which we have discussed over the years whilst consuming a coffee or three.  Please don’t retire yet mate, I still have a few upgrades left in me and I sure you have a few mind bubbles that need to be turned into realities.

If the change Kyrill is mentioning is really limited to subtle and refining change such as improved transparency, then great.  But whilst it took me a while to get there, I really do consider the current GK1 as the soul of my system and would only essentially want it to be tweaked.   Only Hugh can know how much it might have hurt when despite having his demonstrator Swift in my Lifeforce based system for quite a while, I wasn’t 100% sure and kept demoing other brand items rather than ordering Aspen.  One item in particular I tried had bags of precise, detail commensurate with its price but every time I switched back to the Swift, I felt how alive my system became and how much more lifelike and less sterile.  Once I realised how irrelevant my little criticisms were compared to the bigger picture of just how much else the GK1 brought to the table, I was happy.  I must admit that here I mean the Platinum upgrade that was, to me, profound.

With the Lifeforce now a Soraya as the heart of my system, the component harmony is superb.  So whilst I wouldn’t doubt for an instant that one day there will be a generation 2 GK or Swift and likely a post Soraya amp to mate it to, I hope and trust it will retain the same essential GK1 character of making music rather than providing a precise but etched facsimile of musicians and singers like some of the alternatives.

[gerado]

Just curious Hugh,

I think I recall accurately that you designed the GK to sound best with your power amps.
 Why not design a GK-LF integrated amp. Wouldn't this offer added design benefits over separates  apart from the obvious cost savings? You would not have to worry about compatibility with other brands. You can even have 4 or 6 output sections all in one integrated board for those who wanted bi or tri amping.


I know this may be a little silly, but from a layman's position what are the reasons you do not see high end, well designed well built integrated amps sounding as good if not better and cheaper than separates.

[AKSA]

Hi Theo (Gerado, blown your cover!!),

Two reasons: cost and market appeal.

#1  Cost

Developing a power amp takes around a year, with perhaps 300 hours from me, $3-5K from consultant input, and about $10K in inventory.  Developing an integrated would increase this by around 60%, so you would have to return that much again in retail price.

#2  Market appeal

The Japanese pioneered the integrated amp in the seventies as a budget alternative.  The mantle has since been adopted by the Chineses.  The Japanese integrateds were robot assembled, and some, particularly the NAD3020, changed forever the perception of amp value.  Consequently, in an ironic twist of marketing illogic, the integrated amp has double the electronics of a conventional, high end power amp, has a much higher labour and parts input, and sells for half the price.

As you can see, if I produced an integrated, it would be perceived as down market, cost more to make, and sell for less.  Makes no sense at all for a small producer.

Cheers,

Hugh

[gerado]

So what you are saying is that it is largely perception, and marketing. But theoretically, cost aside, a well designed integrated ought to have an advantage?

It is also a surprise that it costs 60% more than the combined cost of developing and building a separate pre and power amp.
But there you go.

Was it the Japanese in the 80s that also tried a pre- pre seperate?

[AKSA]

Hi Theo,

Thanks for your response.......  but not quite what I was meaning, in fact.  My mistake, not well expressed.   

So what you are saying is that it is largely perception, and marketing. But theoretically, cost aside, a well designed integrated ought to have an advantage?

Actually, there is no technical advantage whatever over a pair of matching separates.  In fact, you could argue that with completely separate power supplies (since power supplies are always conjoined with integrateds) it's plausible that separates, monoblocks if you will, have a sonic advantage.

It is also a surprise that it costs 60% more than the combined cost of developing and building a separate pre and power amp.  But there you go.

Ahem, not quite my meaning!  I was comparing it to the cost of developing a power amp alone!!  The cost of developing a separate pre and a separate power is much more than developing an integrated, but then one can sell each for comparable prices, making the separates a better proposition from a profit standpoint.  You have to factor in that R&D is essential to keep pace with the market, and R&D is a dead loss which must be recouped, just like pharmaceutical research.  But advances must be carefully metered, so that the entire income of the company is not exhausted on product development.....  and to keep existing customers, you must produce new products all the time.  I spend around half of company income on product development, just as a small time example.  Marketing costs to find new customers are always high too, because advertising and reviews are costly, so there is a fine balance here.  The best balance is an excellent product with good service and a significant upgrade every two or three years, with a brand new product every five or so.  Aspen always has around three products under development at any one time, but the company does not advertise either.  I can get away with this because of a very strong customer base, who are interested to see what new product is coming!! (Thankfully!!   )  This appears to be the balance in the market;  but a lot of advertising is required to fully exploit the sales potential of any new product, which must not be too radical otherwise the sales will be very slow.

Often what happens is that the performance benefits are technically disguised on release so that novel, untried ideas are not trumpeted until there have been a few good reviews.  Until then, sales based on past reputation should be enough to get the product moving.

Was it the Japanese in the 80s that also tried a pre- pre seperate

Theo, I'm not too sure about this, but I rarely look over my shoulder, so I really don't know.

cheers,

Hugh