Home of the Squeezebox™ & Transporter® network music players.

1. ## Has anyone listened to the NAD C 390DD?

I'm curious as this is a "digital" amp.

According to the NAD website "C 390DD has no analogue stages in the signal path, keeping music in the digital domain right up to the speaker outputs. All preamp functions are executed in the digital domain without the phase shift, noise and distortion that plagues all analogue designs regardless of price or pedigree."

It sounds like it would work well with a Squeezebox, as it is a DAC, pre-amp and power amp all in one.

2. So how does this work? Does the amplifier send "jagged" (digitized) waveforms out the speaker terminals, and the speaker coil itself effectively does the D-to-A conversion by simply smoothing out the jaggies?

3. Originally Posted by Henry66
So how does this work? Does the amplifier send "jagged" (digitized) waveforms out the speaker terminals, and the speaker coil itself effectively does the D-to-A conversion by simply smoothing out the jaggies?
*cough*
There are no "jagged waveforms". This is an urban myth. Those images of staircase waveforms on the Internet are all part of the "great lie about how digital audio actually works".
Each sample contains mathematical information ( to be precise, a numeic value) that when sequentially replayed at the correct frequency describe exactly how the frequency and amplitude of the original source vary over time. In order to turn that information into an analogue form that can be heard via speakers, each sample is converted to a voltage. The number of possible values of that voltage is determined by the bit-depth... 16-bit=65,000 values. the discrete sample voltages pass through a filter which integrates the values over time, at which point they become an analogue waveform. Normally this all happens inside the DAC or CD player or whatever. In amps like the NAD (and there are many others) the conversion happens very very close to the speaker terminals.
At no point ever does the "jagged waveform" actually exist as an analogue representation of the signal... That is just a metaphor to explain how things work. Unfortunately it has lead to all sorts of misunderstandings and religious beliefs about analogue vs digital. For example, there is NO missing information between each step... For a signal frequency less than half the sampling frequency, capturing each step faster does NOT capture more information...

The theory behind this has given us the mobile phone, HDTV, transatlantic multplex cables, satellite comms and the Internet (amongst many other things)... Technologies that are far more demanding than reproducing audio frequencies from 20hz to 20kHz from a CD or music file.

Erm, so the answer to your question is no, there are no jagged waveforms so they can't be sent anywhere. Digital information in the form of bitstreams are sent to the amp and nice analogue waveforms are produced from them right at the speaker terminals.

4. It's a switchmode amp how they are modulated is a bit of science bitstream like high frequency something / pwm like and there is a filter at the output .

In the simplest for as I understands it switchmode amp is a kind of pwm (pulse width modulator ) . On and off pulses with a length, the filter then converts length to amplitude ( simplified ) you are charging the output filter to create an wave form .

So somewhere there is a PCM to PWM conversion and a filter .

There is some rocket science to make switch amplifiers good nowadays the cheaper ones are not as good as an traditional a/b amp but they are cheap small cool and energy efficient .

There is some cult around the simpler class D amps often of very low power , but that might be a novelty for the audiophile to have some other kind of coloration to wax about

An odd french design http://www.devialet.com/ which have claimed performance that is extremely good in any amp (but this is not cheap ).

Required output filter may rise the output impedance of the design at higher frequncy not as bad as a tube amp but to some extent .

This should get cheaper and better over time, they are already standard in subwoofers .

5. All that makes sense...but in that case could someone explain the staircase output in the Stereophile measurements for many DACs? These very often show distinct voltage level steps in an undithered 16 bit tone at -90db.

I'm not questioning what has been said, I am genuinely curious.
Darren

Sent from my HTC Sensation Z710e using Tapatalk

6. Tech data is interesting ! good development to up the performance of switchmode

7. Originally Posted by Mnyb
An odd french design http://www.devialet.com/ which have claimed performance that is extremely good in any amp (but this is not cheap ).
I was able to listen to this amp in a hi-end setup in a store and for a few hours in my setup at home: WOW! Sounded excitingly neutral/dynamic and controlled the loudspeakers extremly well. But what else would a expect from a €13k amp?

It's just a pity that they did only release an iTunes compatible (16b, CD quaility) version of their AIR streaming functionality.

8. Originally Posted by darrenyeats
All that makes sense...but in that case could someone explain the staircase output in the Stereophile measurements for many DACs? These very often show distinct voltage level steps in an undithered 16 bit tone at -90db.

I'm not questioning what has been said, I am genuinely curious.
Darren

Sent from my HTC Sensation Z710e using Tapatalk
Depends where you measure it i guess?
I don't read Stereophile... Nor do I worry Much about -90db signals :-)
I'll look into it...

9. Originally Posted by darrenyeats
All that makes sense...but in that case could someone explain the staircase output in the Stereophile measurements for many DACs? These very often show distinct voltage level steps in an undithered 16 bit tone at -90db.

I'm not questioning what has been said, I am genuinely curious.
Darren

Sent from my HTC Sensation Z710e using Tapatalk
Erm... At -90db a 16-bit DAC only has 1 bit to play with... This test might say something about DAC linearity but it won't say anything about what music sounds like, given the fact that at normal listening levels a -90db signal is going to be way way below the level of audibility If there is any other signal happening at the same time. The ONLY way to hear such a signal is to listen tothe very end of a reverb tail with your amp on full volume. Be careful!

I can't find any of these Stereophile staircase plots... I can find plenty of rough looking sine waves... Do you have an example?

10. Originally Posted by Phil Leigh
Erm... At -90db a 16-bit DAC only has 1 bit to play with... This test might say something about DAC linearity but it won't say anything about what music sounds like, given the fact that at normal listening levels a -90db signal is going to be way way below the level of audibility If there is any other signal happening at the same time. The ONLY way to hear such a signal is to listen tothe very end of a reverb tail with your amp on full volume. Be careful!

I can't find any of these Stereophile staircase plots... I can find plenty of rough looking sine waves... Do you have an example?
I was thinking of these (figure 5 in each case):
http://www.stereophile.com/content/b...r-measurements
http://www.stereophile.com/content/s...r-measurements

Though, I imagine the dithered versions would appear smooth.

#### Posting Permissions

• You may not post new threads
• You may not post replies
• You may not post attachments
• You may not edit your posts
•