[kyrill]

Hugh,

IS it possible by altering some values to make the AKSA AB amp more a class A amp?
FOr instance 10 watts class A before it switches to B?
I know of some high end brands which have a high "A" factor in their B, as 90% of all listening is done under 10 watts.
However would it be beneficial for the AKSA? and if not why not?


: )Kyrill

[PSP]

Hi Kyrill,
I don't mean to make light of your question (besides, I am so unqualified to answer it!) but... I am quite sure that when you finally listen to your AKSA all you will be thinking about is the music and the glorious sound.  Class A, class double-Z, class whatever.... it ain't gonna cross your mind, believe me.

Peter

[kyrill]

It would be easier just to enjoy and I am sure I will
But hig end is also about reaching for the  Holy Grail.

Remember the AKSA by itself already sounded very good. But there was room for the nirwana and now there is room for Nirwana plus, and then I suppose it will be very hard to better the potential of the schematics unless a much better sounding transisto arise which can be swapped in th AKSA.
But raising the class A before switching to B is  a possible solution and maybe an easy one. I don't know. the amp will run hotter but not too hot at 5 or 10 watts.

[Occam]

It would be easier just to enjoy and I am sure I will
But hig end is also about reaching for the  Holy Grail.
........
But raising the class A before switching to B is  a possible solution and maybe an easy one. I don't know. the amp will run hotter but not too hot at 5 or 10 watts.

Kyrill,
You might well find the increased distortion subjectively pleasing.....
One of Hugh's most charming characteristics is that while a die-hard subjectivist, he always endeavors to make use of current objective analysis. The output topology used in the AKSA can be described as a Type II EF, or in Self's mischaracterization a 'Blameless Class B', which is really an AB biasing scheme that minimizes crossover distortion by optimizing the bias at a specific low level, and makes use of 'charge suckout' caps.
http://www.dself.dsl.pipex.com/ampins/dipa/dipa.htm#5

Hugh's 'trick' is to implement those technically based improvements, only after verifying that an 'optimal' solution is also a subjective improvement.

This is not to say that real class A (Hugh's design is pure class A up to the output stage), would not be prefferable, for you.... that is a subjective call.
But most commercial products claiming Class A are not, simply high bias AB.  Nelson Pass's diy designs are true Class A amps, and we could argue our subjective impressions, but I'll simply state that given my constraints, you can't do better that the AKSA.

[kyrill]

It is not fair to assume that high bias class a is by definition introducing more distortion. That completely depends on the topology of the amp, and thus on the vision of its designer. It will, if I hear you right do this in the AKSA configuration.
I was just asking by being curious, nothing wrong with that

[Rocket]

Hi Kyrill,

I am the least qualified to answer your query.

Have you had the opportunity to listen to the aksa amp at this stage?  It has a very good sound quality and competes with amps costing many times the cost.

Hugh has refined the components he uses over the years and this is why he offers a stock, nirvana and the soon to be released nirvana plus.  In fact it is the builders and tweekers who have helped hugh to refine the components.

I am sure that it would require a fair amount of redesign to push the amp to operate at higher levels of class a.

Btw i have a 76 watt class a and it is much less dynamic compared to the aksa.

regards

rod

[AKSA]

Hi Kyrill, et al,

The AKSA delivers interesting performance at high bias.  As you increase bias towards about 350mA the bass becomes stronger, but at around 65mA the sound stage starts to contract and by 150mA most of the stunning dynamics of the amp have vanished.

I won't explain the sound stage phenomenon, because it is highly complex, I don't fully understand myself, and my prattle would be inconclusive.  Ginger might have a few comments on this, as he understands the math so much better than I do.  But the increased bass and loss of dynamics are related, and have to do with the increased loading on the voltage amplifier of an output stage operating at high bias.  High bias is not well accommodated by the charge suckout circuit in the output stage, and driving the outputs at high bias pulls back gain in the voltage amplifier, costing feedback ratio, and thus top end clarity and punch, giving an impression of more bass.  This is not well appreciated, but bass can be enhanced simply by pulling back on HF response.

Dynamics are normally the province of the power supply, and its capacity to deliver high current bursts on transients.  With heavy current draw from the power supply, less energy is available for transients and thus the subjective impression of dynamic range is less.  Many Class A amps I've heard (and the AKSA was developed with constant reference to a Sugden A21 as a seminal example of a full-on, genuine Class A) have a dynamic 'greyness' in their presentation which seems to bear this out.  This is also to an extent reflected in many Single Ended Triodes, which have an elegant, refined sound, but, compounded by a lack of power, could hardly be described as dynamic.

Kyrill, I have examined the Bartolucci offering.  The best power transformer they offer would be the M4 potted 150M of 6.2Kgs weight and 133 x 133 x 132 mm dimensions.  However, I'd be very surprised if this transformer was much less than 100 Euro, and since the toroids work so well with the AKSA I really would question the point of all that money.  You can get reputable toroids such as the Antrim series from the UK, and I am absolutely positive Holland will have many, many transformer manufacturers who do as good if not better a job.  If you want a really good transformer, use a double C core from Holland.  I'm not convinced the Italian product will be any better;  often specialty manufacturers of OPT for tube amps will contract out their power transformer manufacture;  it's not a difficult assembly process.

So, you live in Holland's biggest city, check out your Yellow Pages.......

Hope this puts things in perspective and is helpful.  Keep the costs down;  buyers remorse is inevitable in audio, but you are really encouraging it if you spend silly money on flash transformers.  If anything, spend a little more on power supply filter caps;  this has strong influence on the sound, particularly the bass.

Cheers,

Hugh

[kyrill]

O Hugh you are a peach
Suppose to be something positive, but translated in Dutch it sounds strange , especially to a man at least from a man.

I had in the back of my mind, that you must have played with higher bias, but  I forgot that no other reason than what sounds the best biased yr decisions,  except from exaggerate costs and not the original choice for designing a class AB.
You can be faithful to a design principle  and stick to it.
You explained in your papers 2 other designs: The Glass harmony and the Lifeforce

Thanks for yr advice of the Bertoluggi transformers.The man suggested a price of 70 euro's, and then I reacted. But it is much closer then 120 ! I found a Dutch toroid manufacturer 225 VA 25-0-25 4,5 A 7% regulation and for 41 euro. Those specs are within your overall specs.

I thought, that exclusive more expensive trafo manufacturers known for their good set output trafo's would also be good for the AKSA, especially as in your papers you point to how important an power transf is. I had no idea that they are so over expensive that you may call it silly money.
thanks for another pair of lessons