Hi Mr. Dean, yes I can accept that. But I have different way to look at this issue or situation. In my view (not just view actually because I know precisely what I'm after), sound reproduction is far from perfect. What I can hear is that these amps and those amps, all have their own flaws. When nothing is perfect, then everyone is legitimate to choose what kind of imperfection or 'effect box' that they prefer.
But the objective, preference and design direction should be the "perfect sound", which of course, not everyone has a firm idea of what it is.
I disagree about the other extreme you mentioned. The pure undistorted zero THD is not at the 'end' of the spectrum. It is not an extreme. The other extreme is the perfect sound nobody perhaps can yet create. But it is possible to have a clue of what and how it is.
It's been posted a few times in various threads here that Naim and a number of other high-end, big ticket brand amplifiers, are what engineers often dismiss as "effects boxes". If you want evidence, you only have to look at the distortion spectrum of Naim amplifiers (NAP and early Nait series) and wonder how else they could wind up with such a dominant second harmonic when there is an LTP input. Just look at the topology and IPS current imbalance, look at the high capacitance VAS transistors, Quasi-complementary output stage and a few more tricks and consequences too.
Some believe, perhaps guided by professional ethics, that only zero distortion amplification is worthy of aspiring to. Therefore, as the reasoning goes, DIYs and pros alike should always strive for lowest possible THD, noise etc. Enthusiasm for these "effects boxes" here though, tells quite a different story. Look at the long threads - see how many newbies are attracted and keep returning to these so-called effects boxes but how many follow the grand, ultra low distortion, SOTA projects? Why are audio enthusiasts so interested in the old legends of mid-fi whilst ignoring the often complex and verbose refinements of the classic linear amplifier that small audio industries still strive for?
For DIY, simplicity is a big factor in interest and one look at the schematic and a brief listen to the evergreen JLH69, will tell you how important a contribution to both simplicity and sound quality Linsley-Hood made there. The NAP design's commercial product focus makes it a little harder to understand but still easily constructed from an inexpensive kit. If you also note the peculiarities of the design and the parts issues, it doesn't take too long or require many changes and $$ to get the clones quite close to Naim sound, if that's your desire.
Only a few small parts are critical to Naim sound - other semis and the PCBs have been changed about from the original products through many models and revisions with mostly subtle rather than significant differences in sound quality for a given model, IMHO. When you get into using SNAPS and Hicap power supplies and cable/connector arguments, I'm afraid the issues begin to evaporate into fancy and conjecture for me so I 'll leave well enough alone.
I'm sure we'll find a few more facts and surprises here though, when Big'n gets his TGM10 going. 'looking forward to it and hope it all goes smoothly to plan, Gareth. 🙂
Some believe, perhaps guided by professional ethics, that only zero distortion amplification is worthy of aspiring to. Therefore, as the reasoning goes, DIYs and pros alike should always strive for lowest possible THD, noise etc. Enthusiasm for these "effects boxes" here though, tells quite a different story. Look at the long threads - see how many newbies are attracted and keep returning to these so-called effects boxes but how many follow the grand, ultra low distortion, SOTA projects? Why are audio enthusiasts so interested in the old legends of mid-fi whilst ignoring the often complex and verbose refinements of the classic linear amplifier that small audio industries still strive for?
For DIY, simplicity is a big factor in interest and one look at the schematic and a brief listen to the evergreen JLH69, will tell you how important a contribution to both simplicity and sound quality Linsley-Hood made there. The NAP design's commercial product focus makes it a little harder to understand but still easily constructed from an inexpensive kit. If you also note the peculiarities of the design and the parts issues, it doesn't take too long or require many changes and $$ to get the clones quite close to Naim sound, if that's your desire.
Only a few small parts are critical to Naim sound - other semis and the PCBs have been changed about from the original products through many models and revisions with mostly subtle rather than significant differences in sound quality for a given model, IMHO. When you get into using SNAPS and Hicap power supplies and cable/connector arguments, I'm afraid the issues begin to evaporate into fancy and conjecture for me so I 'll leave well enough alone.
I'm sure we'll find a few more facts and surprises here though, when Big'n gets his TGM10 going. 'looking forward to it and hope it all goes smoothly to plan, Gareth. 🙂
THD shouldn't be the only design goal or parameter. Imho, it is the most important parameter BUT not the only one which determines the sound quality. If the other quality parameters have no dependency on THD then the problem is simple. But the other parameters DO have dependency on THD and on each other!
So the key is to have minimum thresholds for each of these parameters, so we have a better chance in having all the parameter tickboxes ticked.
How can we set the minimum threshold for THD (let's talk about 1kHz THD to simplify the issue)? Well, if we believe that we cannot perceive 0 THD, why should we strive for 0 THD? Big mistake here, because (1) the designer has no idea how this number will affect perception (2) the designer doesn't understand that once he lowers the THD something else goes up.
Complexity is one thing as you have mentioned. But really, does the often complex and verbose refinement of the classic linear amplifier that small audio industries still strive for, correlate with 'perfect sound'? Not necessarily so
I believe I can see what the objectivists see, but I believe that I can see what the subjectivists see too.
Lohk already mentioned that he has never heard a clone that sounds as good as the original. This is possible. IF you believe that amplifiers sound is only determined by THD and noise, then I don't believe that you can easily copy the Naim sound.
And I'm not so sure that Bigun's work will yield answer to these questions. Because Bigun is not using the proper models for the Naim transistors.
There is commercial objective and strategy, I believe you understand that. First, by having a transistor that nobody has the exact substitute.
Then there is a possibility that the Naim designer just did trial and error until they get a sound that is "unique" and "selling". This may sound strange to you, but whatever the circuit, if you tweak it to death using sensitive ears, I believe you may find sound that is so enchanting.
The questions I posed were rhetorical but a designer does know these things if he/she is a qualified professional. They will know far more than is revealed in a few audio products but most will have little choice in the final design, once the product specification is handed to them. So when a manufacturer says the performance specs will be <0.001% THD, that is what happens or no job.
If you own a company and design the initial products yourself as JV did, then I guess you could make the product choices, design and tinker with sound quality to suit yourself etc. - a bit like DIY when we can afford to do as we please.
@Traderbam. There is a lot to cover there over several years, a few forums and threads and some of my own soundcard plots actually so I don't plan to spend the hours in detailed reply. You might look at Wahab's posts 255, 257 and AndrewT's comments on The LTP imbalance (around #2230 in the big thread) for starters though. However, as far as critical parts are concerned, I refer to the specific ZTX753/653 VAS pair, as without these being much as in the original products, the SQ of any NAP or clone just sucks, even if the Cob is compensated in a higher Cdom. A selected mismatch of the LTP transistors is also needed to counter the DC offset from the leg current imbalance.
Perhaps there are also issues with the cap types and current options that I simply haven't checked out but I find most other components and layout of the clones I've used, to be uncritical. It seems there were benefits in dropping some of JV's ideas about power transistors though.
In his last interview, Vereker outlined his early struggles with high speed switching transistors, regardless of linearity concerns and went on to talk about the switch to their NA001 type but seemed to leave out the long sojourn with Sanken 2SC2922 LAPTs which began back in the chrome bumper era and AFAIK, still continues. I usually take the interviews with a grain of salt, but they are now the only insight we have.
I suggest the changes amounted to accepting the benefits of earlier Japanese semiconductor superiority and the significant developments in audio semis that had been going on apace in Japan. Meanwhile, many UK manufacturers were still using switching transistors or other local and US sourced power devices with poor gain linearity.
There's a lot that I could respond to that has been said about he "sound" or other nuances present in the performance of an amplifier and, noting that, I wonder if any of you have any thoughts about the significance of gain and phase margins obtained after feedback has been applied?
Graham
Graham
I know its Gareth's thread but hi Graham, it seems you are fairly new to the forum. Are you thinking in terms of Naim models and clones or about audio amplifiers in general?
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I agree.
It's a perfectly legitimate goal to design for the lowest achievable THD and with modern components, materials and design software this goal is within the reach of rank amateurs like myself - thanks in no small part to the exchange of knowledge on the internet. Back in the day JV did not have access to all this. And his amplifiers had to be heard through speakers that were also designed and built to ancient standards. I suspect that tweaking by ear was one of the more reliable approaches to achieving a good result.
Today we are free to choose between very low THD and something else. Given that amplifier manufacturers are in a competitive world it's not easy to differentiate anymore on the fight to lowest THD.
Amplifier and speaker manufacturers have the least control over what you hear. That power goes to the recording and mixing artists/engineers. They control almost all of what you hear. If you are going to design and sell amplifiers and speakers the last thing you want is to be rigidly held to a common set of 'perfect replay' specifications. You can't thrive. To sell to people who will spend decent money you have to sell based on emotion not on a spec. sheet alone. You have to retain some control over the brand, appearance and the sound. The ability to 'voice' your amplifier, or your speaker cross-over is very important.
For me, building something like the famous NAIM amplifier is a celebration of times past, a spot of industrial archaeology. And by designing and building it myself I get to put myself into the 'chairs' occupied by people in the past which I find very interesting. Clearly, the goal is not lowest possible THD. Clearly the goal is not to hear as perfectly as possible an old NAIM amplifier as I could easily buy one today.
I think JV realized that fast transistors were important for helping control cross-conduction and other parasitics in the output stage. He prioritized this above linearity - of course he did, BJTs are by their nature non-linear, so you design accordingly, which is why we need some feedback whether global or local degeneration.
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I'm talking about amplifiers in general. But as far as the JV quasi design is concerned, for example, a lead (R/C) in the driver circuit changed the audible character, presumably without changing the open loop gain or the feedback. Is my observation correct?
Graham
In the early Nait series of amplifiers there were no stopper resistors in the driver transistor bases. For the modest power 5 MHz power devices could be used and the compensation adapted to suit.
For better performance specifications faster transistors are needed and the compensation eased up to extend the bandwidth.
That would uncover the mismatch in phase between output halves partially hidden in the Nait amplifiers.
For more on this see post 57 on page 6 and post 98 on page 10.
Bigun,
Have you got all your parts yet...will this weekend be the big build? 🙂
Regarding the LTP. You'll want the transistors to be identical and you'll want their Ic to be the same. Ha! You can use your trimmer to adjust the Ic and if you get too much dc offset you could try hand-matching parts from a small pool of transistors.
Have you got all your parts yet...will this weekend be the big build? 🙂
Regarding the LTP. You'll want the transistors to be identical and you'll want their Ic to be the same. Ha! You can use your trimmer to adjust the Ic and if you get too much dc offset you could try hand-matching parts from a small pool of transistors.
The Naims seem to need a very unbalanced LTP to produce the THD that JV thought necessary for "his sound".
If one is building a Naim clone then one NEEDS to copy all of it.
If one wants true "reproduction" then choose a better reproducer, not an effects machine.
I believe there are more terms in the contract beside minimum THD. Nowadays, getting THD below 0.001% is quite easy when there is no more limitation or other requirements from the circuit.
We can lower THD by adding (unnecessary) complexity 😀
This could be a challenging question: 0.001% at 100W with LATFET output, how many transistors do we need? 12?
mosFETs require 4 times the maximum output power.
Thus for a 100W amplifier you would select 400W for the Pmax of the output stage.
2pair of 100W devices will give a reliable 100W amplifier driving severe reactance speaker if the heatsink maintains a sensible Tc.
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