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Views on NAIM amps
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Graham Slee View Drop Down
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Joined: 11 Jan 2008
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Points: 16314 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Graham Slee Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2008 at 12:43am
Unfortunately the "digital" amplifier is based on Harry Nyquist's theories from 1928!

I don't think old Harry understood phase response all that well.

The "digital" amp isn't digital at all. It is PWM - pulse width modulation (just like switched mode power supplies) directly applied to an analogue input signal with no ADC or DAC between it and the output.

For a given phase response to be accurate enough, the frequency response needs to be 10 times as wide. This fact seems to have eluded Nyquist, but hey, it was 1928.

However, all digital audio is based on Nyquist theorem with a little improvement by researchers over the intervening period.

Oversampling (and under sampling at the recording end) proves the point about phase response.

For a PWM ("digital") amp to give a realistic sound it would need a bandwidth 10 times that of the audible spectrum - 150kHz should suffice. Then to allow the all so necessary passive output filter a chance of removing the garbage, the modulation frequency should be at least 10 times the bandwidth - even more.

In actual fact the modulation frequency is not much higher than 100kHz.

Why? Try looking up the EMC regulations...

Why bother then? But they do. It's as if they can't or won't understand how to bias an analogue class AB transistor output stage so they go to such ridiculous lengths to avoid doing so. It's not like going to the Dentist LOL, it's easy enough to learn - good grief, I managed to learn it without a tutor from the pages of electronics magazines when I was only 19! Yes, and within three years I was marking A-level "mocks" transistor questions for a head of science that couldn't do biasing also! Take Quad's current dumper, another example of evading the issue! Wink








Edited by Graham Slee - 28 Feb 2008 at 9:04am
That none should be able to park up and enjoy the view without a smartphone and the knowledge in how to use apps
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dvv View Drop Down
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Joined: 12 Jan 2008
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Points: 95 		Post Options Post Options   Thanks (0) Thanks(0)   Quote dvv Quote  Post ReplyReply Direct Link To This Post Posted: 28 Feb 2008 at 8:38pm
Originally posted by Graham Slee Graham Slee wrote:

Unfortunately the "digital" amplifier is based on Harry Nyquist's theories from 1928!

I don't think old Harry understood phase response all that well.
 
Didn't have a clue. In his defence, not many did, and I expect the key person in that field would be the late Bernard Kardon, who kicked off with it in the early 50-ies, about the time Harman/Kardon invented the stereo receiver (yep, with tubes).

Quote The "digital" amp isn't digital at all. It is PWM - pulse width modulation (just like switched mode power supplies) directly applied to an analogue input signal with no ADC or DAC between it and the output.
 
I knew there was a reason why I like you so. Completely agreed! Technically, they are hoodwinking the public - and not for the first time, either.

Quote For a given phase response to be accurate enough, the frequency response needs to be 10 times as wide. This fact seems to have eluded Nyquist, but hey, it was 1928.

However, all digital audio is based on Nyquist theorem with a little improvement by researchers over the intervening period.

Oversampling (and under sampling at the recording end) proves the point about phase response.
 
Completely agreed!

Quote For a PWM ("digital") amp to give a realistic sound it would need a bandwidth 10 times that of the audible spectrum - 150kHz should suffice. Then to allow the all so necessary passive output filter a chance of removing the garbage, the modulation frequency should be at least 10 times the bandwidth - even more.

In actual fact the modulation frequency is not much higher than 100kHz.
 
What, what, WHAT? Do I see this mention of 150 kHz, or is that just wishful thinking? I seem to recollect somebody asking me some years ago why did I insist on full power bandwidth of no less than 300 kHz, and that limited only by the input filter?
 
Oh, how things come around ... LOLLOLLOL
 
But, all was forgiven when you saw the light and adopted the AD 826 AN. Clap


Quote Why? Try looking up the EMC regulations...

Why bother then? But they do. It's as if they can't or won't understand how to bias an analogue class AB transistor output stage so they go to such ridiculous lengths to avoid doing so. It's not like going to the Dentist LOL, it's easy enough to learn - good grief, I managed to learn it without a tutor from the pages of electronics magazines when I was only 19! Yes, and within three years I was marking A-level "mocks" transistor questions for a head of science that couldn't do biasing also! ...
 
Ooooops! Again, I seem to remember some Yorkshire pudding eating Limey asking me some years ago why bias my power amp analog output stage at 100...120 mA per output device, with four pairs of trannies, giving me say half an Amp of quiescent current ... Wink
 
But seriously Graham, I do see you have moved quite a bit towards my side of the road. I sincerely hope the reason is greater experience, i.e. that you have tried and tried and came to se the added benefit of higher-than-typical bias. Judiciously applied, it can bring all the benefits of pure class A in say 99% of the time, without the attendent high cost and liberal size of true pure class A. Not to mention the power bill, which, by the time you get to some reasonable power like 50W/8 Ohms, changes colour from green to very, very red.
 
Quote ... Take Quad's current dumper, another example of evading the issue! Wink 
 
In some cicrles, you could be shot for the above statement. As could I, since I completely agree. The idea is not bad, but the implementation was strictly economy, economy, economy. Never saw what made it so dear to people, not bad, but in no particular way special. As soon as the load dropped to 6 Ohms, God forbid any less, it was done for.
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Dave Millier View Drop Down
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Points: 67 		Post Options Post Options   Thanks (0) Thanks(0)   Quote Dave Millier Quote  Post ReplyReply Direct Link To This Post Posted: 12 Mar 2008 at 3:02pm
I have a Naim 42.5/Flatcap/NAP110.
 
I like the retro looks ("chrome bumper" model) but I have to say it sounds not the slightest bit different from the Onix OA21s or Kenwood AV amps that preceded it.  Nor has the flatcap changed the sound in the slightest.
 
I happen to think that for speaker based systems, the most critical component is the room. The room has a dominating influence on the overall sound.
 
I'm currently in the process of doing some real time spectrum analysis on my living room with a view to taming those room modes that provide rather unhelpful +/- 20dB peaks and troughs in response, particularly below 200Hz...
 
Dave
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