Does this type of Desktop Digital Audio player exist?

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#61
I did a quick search, turned up this patent which refers to 'digital PWM' several times : https://patents.google.com/patent/US7286009B2/en

Short excerpt :

Amplifiers ... have sometimes been called ‘digital’ in the popular press, but we shall describe them as ‘analog’, because the timings of the edges of the rectangular waves can vary continuously in sympathy with the audio. We shall reserve the word ‘digital’ for an amplifier in which the edge timings are quantized, so that the edge timings can be represented digitally and the edges can be generated by counting pulses produced by a high-precision, high-frequency clock, such as a crystal oscillator.
 
#62
yeah, thats dubious lol. if the only useful hits are a patent from 2005, thats a pretty low bar IMO. how about we call all of them 'digital' amplifiers (compulsory quote marks)? arent the edge timings 'quantised' (in effect only) in ANY PWM driven by a clock? ie. if the input is digital and the design sufficiently accurate, then the output edge timings could be read digitally. doesnt make it any more digital IMO, not least, because the output isnt read, or used digitally; even if it could be. that definition also fits the output of a DSD DAC and the output of dacs are analogue, wouldnt you agree?

btw, the patent also says this

An analog-to-digital converter (ADC) may be provided to convert the output audio signal to a digital signal for input to the subtractor. Filtering may be implemented before or after the ADC, and a decimator may be placed after the ADC if it is an oversampling ADC.
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if the output was digital, you wouldnt need an ADC.
 
#63
Indeed the output is analog - wasn't one of your earlier claims that a feedback loop couldn't include an ADC because latency?

That wasn't the 'only useful hit' it just happened to be the first one I opened.

<edit> Attached another relevant paper (IEEE circuits), should I hold my breath for it to be dismissed because its from 2004?
 

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#64
I didnt mean it couldnt, obviously latency doesnt prohibit something from being possible, it just adds latency and increases 'loop area' in a completely new way and increasing latency and loop area in a power amp feedback loop seems, at least to me ... stupid. You wouldnt (or at least I wouldnt, not for a power amp, since I tend to favor wide bandwidth amps). it seems lots of trouble to go to to solve a problem that is already solved. Some have in the past. I believe the chips that were used in the NAD AVR units from several years ago used an ADC for feedback in exactly this way, but thats all proprietary and thus not well publicised, so I dont know the details. They claimed they were 'Fully Digital Amplifiers' too.
 
#66
InspectorGadget said:
I didnt mean it couldnt, obviously latency doesnt prohibit something from being possible, it just adds latency and increases 'loop area' in a completely new way and increasing latency and loop area in a power amp feedback loop seems, at least to me ... stupid.
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You used it to dismiss the notion that the block outlined in red (post #45) could be a pure digital block if I recall correctly.
 
#67
I didnt need that to dismiss it, since I had not accepted that a digital in->out PWM was even a thing; so no, that is not what I did.

I dismissed it, because the digital to PWM convertor, to me is not much different to a DAC and its driving a fully analogue power stage.
 
#68
Ah, but you mentioned it was a patent and that it came from 2005 as qualifications for it being 'a low bar', so was I unreasonable to assume you weren't dismissing it for being a patent?

Oh, I see we're now talking about two different 'dismissals' here. Perhaps time for me to quit 😛
 
#69
Try "(digital to pwm) assignee🙁Texas Instruments Incorporated)" in Google Patents.

US 7492,217 B2 (2009) says; "PCM to PWM conversion function 21 in this conventional class D audio amplifier is preferably implemented by digital circuitry that digitally calculates the times at which rising and falling edges of the PWM output signals are to be issued. In this manner, the reference triangle waveform may simply be a high-speed clock signal. The digital circuitry can simply receive the input PCM signal on line PCM in, and digitally calculate the edges of the differential PWM pulses, including the desired filtering. Conventional high-speed digital signal processing circuitry is capable of carrying out these calculations sufficiently rapidly for driving digital audio output PWM signals, as known in the art."

US 7,262,658 B2 (2007) says: "Various approaches exist to implement pulse Width modulation (PWM). The pulse Width modulation is obtained by taking a stream of pulses and varying their Widths as a function of a control input. One form of PWM generation, Which is called Natural-PWM (NPWM), involves comparing an analog input Waveform With a triangle Wave at a carrier frequency of fc. The continuing expansion of digital techniques in the field of audio has led to a different form of PWM generation called Uniform-PWM (UPM), Which typically uses a higher order digital modulator to convert a digital Pulse Coded Modulation (PCM) signal to a uniformly sampled PWM signal."

I believe these statements make it clear that they have something using all Digital techniques to go from PCM to PWM. I believe the amplifier chips used in the Zoudio amp use this particular technology.

The 2007 patent has a diagram (Fig 2) which looks suspiciously like the feedback arrangement shown in the TAS5825 block diagram. It may be or maybe not be how that part is done; as the feedback is taken from the switching PWM output, while in the TAS5825 block diagram, that specific connection isnt exactly clear.

I'm sure if one digs hard enough, you'll find a patent on how the TAS5825 feedback scheme works. I certainly dont understand how the feedback described in US 7,262,658 B2 (2007) works!
 
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#70
jjasniew said:
What I'm referring to, re the Zoudio amp, is this little fellow in the particular amp chips used - outlined in red;

View attachment 1010160

I've seen the diagrams of other TI chips, where the output of a DAC is brought out of the chip as an analog signal on a pin. It goes through a nice, cheap MLC cap (in the implementations I've seen) and then back into the amp (via a second pin) to be converted to PWM for the output drive. That's the difference I'm illuminating between this design and such.

Looking at the diagram I can see I was wrong about this amp having no feedback. It does and I have no idea how it works. I've never seen anything more descriptive about it than the above "block", from TI's TAS5825 spec; it doesnt go into details about what the two lines "Close Loop Feedback" exactly are.

I like how it sounds; I wont be going off it anytime soon. Not for tubes, hot JFet class A, nor someone else's fancy pants DAC with analog outs. I'd drive a push-pull tube output stage with this amp as a DAC if I wanted to have more fun playing around with some connect half A to half B system topology first. How's that for just sayin' I'd recommend it, because of what it is and what it can do.
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It could be that they generate a PWM signal digitally and then use a low-latency ADC and some digital signal processing circuitry for the feedback, or that the block called "Digital to PWM conversion" internally consists of a DAC and an analogue PWM generator with analogue feedback. It's hard to tell from this block diagram.

Converting a digital signal digitally into a sigma-delta modulate, PWM signal or combination of both, driving a class-D output stage with it and then driving a loudspeaker without any feedback is possible, but it is not a very good idea if you want high performance. The supply of the class-D stage then acts as the DAC reference, so for good performance, you need a very constant supply with no data-pattern-dependent variations on it. That's hard enough for a normal line-level DAC, it will be very difficult with the kind of currents that flow through loudspeakers.

Looking at US 7,262,658 B2, it looks like they use a PWM DAC (with digitally-generated PWM) or a sigma-delta DAC for digital to analogue conversion, and then an analogue PWM generator with analogue feedback for the class-D stage. They found a clever way to combine the reconstruction filter of the DAC with the PWM generator. That also explains why they have this digital PDM block driving the "Digital to PWM conversion" block, that must be the digital part of the DAC.
 
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#71
Simply interested in what's going on under the hood and these discussions cause me to look into it a little bit more. Make a statement like "Digital all the way to the speaker terminals" perhaps should have been "digital all the way through the output FETs" or something, accounting for what I see as the transformation from a "two-state" style signal to a continuous one, taking place in the amps' output filter.

My intent was to highlight the PCM -> PWM transformation done by digital logic within the amplifier chips used in that Zoudio amp. As evident by 3 points so far, giving some probability of it being true;

1. The block diagram label implies it
2. TI has relevant period patents mentioning they have that process occurring via digital logic
3. TI has other "TAS" product line designs where an analog signal is brought outside the chip, in anticipation of that being a useful feature for the designer. Not available in the TAS5825 for some reason...

I learned #2 by engaging here and following another thread participant's lead on doing the patent search.
 
#72
something being '2 state' (this is not true either as you suggest with your quote marks, it does try to switch hard and fully from on to off, but that isnt actually what occurs) doesnt make something digital. This conflation of pseudo binary things, with digital things is common, but nonetheless erroneous. That would make any switch digital. I never argued it may be a digitally controlled PWM. I doubted the PWM had a digital output, or that it was achieved digitally and still do. the block diagram doesnt imply one way or the other to me. Marcel appears to think its implied that it doesnt.

searching around for less vague references to digital PCM->PWM brought me to this short thread and a couple posts by esteemed members here. particularly this one by gmarsh https://www.diyaudio.com/community/threads/pcm-to-pwm-conversion-101.205496/post-2884265

unless absolutely everything he says here is nolonger true, it seems very unlikely they are doing this in a tiny $5-10 class D amplifier chip.
 
#74
These types of devices exist, and even in the simplest of them, the DAC should be good enough. I thought of purchasing a DAC for the CD/DVD player but I am not sure I will hear the difference. There is a difference in the DAC sound between mobile phones and also with BT recievers.

Surprise. You don’t need a DAC. If you already own an iPhone / iPad, you could simply plug that into your stereo system using a simple lightning to headphone adapter for less than 10 Euros. Similar adapters exist for Android. Mobile devices are capable of high-resolution playback. So if you’re happy with 75-80% of the quality of a high-end DAC, I would try this route before spending money.
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https://www.musicservertips.com/product-reviews/dac-buyers-guide/
 
#76
These ones look much better: more suitable for using in a system:

https://www.amazon.com.au/Decoder-DC12V-Bluetooth-Module-Lossless/dp/B0999TTL22
https://www.amazon.co.uk/Zopsc-1-Decoder-Player-Decoding-Amplifier-Silver/dp/B09R6FMLNJ
https://www.aliexpress.com/item/100...%3B-1%40salePrice%3BUSD%3Brecommend-recommend
This one is pretty nice:

MP3 Decoder Board Color Screen Bluetooth V5.0 Car MP3 Player USB Recording Module FM AUX Radio For Speaker​

https://www.aliexpress.com/item/100...202203020806366461074673178400006398445_1&s=p
US $3.43 and shipping $0.31
 
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#79
https://www.ebay.com/itm/203829047303 A renowned member here said it's pretty good, sound wise. Costs almost nothing, considering the free shipping.

One thing an experienced audiophile does is leverage off the more experienced - stand on the shoulders of the Giants so to speak.

If 20W isnt good enough, yes its output can be padded down and drive another, more powerful amplifier.

There's https://www.ebay.com/itm/324988697910 which is a MA12070P amp, a chip a lot of people like the sound of; will set you back a whole $30 with ship.
 
#80
Earphones connected to a mobile phone are powered by an amplifier, and can even power small speakers, not very loudly, so the concept has been tested. These are, however relatively high powered amplifiers, so if I preferred the sound of another amplifier (like some use a headphone amplifier) would it cause any undesirable effects, that was my question, really. I want to use my own low power amplifier with this thing, since there is no line out, but it looks pretty good.

This headphone amp has a 3.5 mm input:

11. iFi hip-dac​

This mini DAC/headphone amp delivers high-quality sound on the go.​

SPECIFICATIONS​

Inputs: USB Type-A, USB 3.0, 3.5mm audio
Outputs: 3.5mm, 4.4mm
Bluetooth: No


What I am looking for is a digital decoder board that looks good and has a line out.
 
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