[wgscott]

Are there any DIY kits (or instructions) for a DIY "Direct Digital" amp?

What I have in mind is something akin to the NAD C390DD.

The idea is that the Class D-like amp itself is also the DAC; it uses the switching properties to do the sampling.

The 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. Its 35-bit architecture and 108MHz master clock also make Direct Digital one of the most accurate DAC technologies available.

[wgscott]

Using google, I was searching today for an answer and found my own still-born thread.  Any recent developments?

[G Georgopoulos]

The concept is not new,fm radio rides on similar waves,and it has done for decades,whats most important these amplifiers are very efficient,very little signal power is burned as heat,class-d is complex their linearity is so and so and from what ive seen so far and is not going to take over from other traditional amplifier technologies
especially tubes...

[Speedskater]

How many new commercial units are there?

[ebag4]

How many new commercial units are there?

This is a link to Core Audio's version:

http://www.coreaudiotechnology.com/kratos-fully-digital-amplifier/

[fiveoclockfriday]

Not DIY, but in response to the question about what commercial options are out there, Nuforce makes the DDA-100, which is pretty great for the size/price.

https://www.nuforce.com/index.php?option=com_k2&view=item&layout=item&id=306&Itemid=370/index.php

[wgscott]

NAD has 3, as mentioned there is the Nuforce DDA-100, and the Vanatoo powered speakers are direct-digital.

[JoshK]

I think there are some avenues to explore in this concept, but I am skeptical of the benefits.  Namely, keeping a digital signal preserved all the way through without lots of noise and jitter introduction seems a high standard.   TACT did it first, or Pioneer as I recall but reviews seemed mixed as to whether it was a better solution.   ADC I believe is still the most problematic conversion, so I'd hope your system is all digital all the way, no radio, no TT, etc.

Lots of Class-D amps are analog amps, only using a switching output stage, much like a switch power supply, so digital isn't really a fair description of the modus operandi.  In fact I think most class D amps fall in this range, so is a direct digital input beneficial?  I don't know, I haven't kept up on the tech. I think TACT and now Lyngdorf is different, but can't recall the deets.

[wakibaki]

You mean a PCM to PWM converter?

w

[JoshK]

You mean a PCM to PWM converter?

w

Likely....its been a long while since I looked into this subject, but I vaguely recall the concepts.

[G Georgopoulos]

BTW I think these product are very good and priced well,the reason i say this is i have also used smps ps in linear amplifiers and they sounded good,i know not many use smps in linear amps...

[JohnR]

Here's a commercial unit, not DIY but cheap enough to experiment with:

http://hifimediy.com/index.php?route=product/product&path=59_71&product_id=146

I have one on the way.

There's also a little brother:

http://hifimediy.com/index.php?route=product/product&path=59_71&product_id=129

[G Georgopoulos]

Thanks for the links john

In the future we'll see more and more of these products
they are not going to go away,it reminds me of the vcr
wars between beta,vhs,others,if that happens we'll see
more and more digital sources with digital interconnects
only,this would split analog and digital only systems.

we'll see in the future?

[Brad]

Here's a commercial unit, not DIY but cheap enough to experiment with:

http://hifimediy.com/index.php?route=product/product&path=59_71&product_id=146

I have one on the way.

There's also a little brother:

http://hifimediy.com/index.php?route=product/product&path=59_71&product_id=129

Nice link John. 
Like you said, cheap enough to experiment with easily.


I had one of the Sony receivers back in the day, that took a single-bit signal direct in from their SACD players.

[wakibaki]

I remembered about the PCM to PWM converter. It has some practical problems.

One trouble with PWM is that you need a 2.8GHz clock to get the same resolution as 16/44k1, and even then there's something about the difference between the kind of PWM generated using a gate and a sawtooth and the digitally generated kind typically used to control a motor.

Eventually my brain lurched into gear and I started to think about how a digital amplifier is implemented in the now. Of course, it's PDM.  20-bit PDM manages to work at ~2.8MHz, so if you can run a switch that fast, then the audio output power is just a reflection of the voltage and current the switch will bear. In fact a typical chip offers 2.7W with 3 or 6 MHz operation and a spread-spectrum modulation said to obviate the necessitate for output filters. This is not a huge power, but it is definitely a power device, being capable of driving a transducer directly, unlike a DAC, and from a 5V supply.

OK, here is a demo board for a PDM amplifier based on a TI chip:- http://www.nxp.com/demoboard/TFA9881D.html.

When you start to look, these things are all over the place like a rash. Life races onwards despite resistance in some quarters.

w

[JohnR]

I got it. It's punchy! I need to make a better set of desktop speakers to test it out properly.

The surprise, completely obvious in retrospect: it is totally silent! No noise at all. Important for a desktop setup where you are less than a meter from the speakers.

[Markvdv]

I am curious about this one too. I have the 320. This should be an improved version. Could you post a pic of the inside?

[JohnR]

Me? Why do you want a pic of the inside...?

[Markvdv]

I know sound a bit crazy, but look at 320 amp, that is what I know, looked at it and modded it quite some times. if you say it is 90% equal to UD20 which is on website "open'' I will also know it is different from boxed 320 without display and usb instead of spdiffs:)

[JohnR]

From appearance alone, it looks fairly similar to the UD20 but with a heatsink, two PSU caps instead of four.

What mods did you do to the 320?