'Fully Digital power amplifier' DAC/AMP: PowerDAC V2

Discussion in 'Digital: DACs, USB converters, decrapifiers' started by Baten, Aug 16, 2019.

  1. Baten

    Baten Almost "Made"

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    Found no mention of this product yet and wanted to discuss its principles. Original design discussion sparked on diyaudio forum. It is an FDA amp with PWM modulator in the analog conversion stage. I haven't really run into anything like it yet, but I'm very intrigued. It uses direct drive, no feedback output over 2.5mm balanced. See design label:

    [​IMG]

    On top of that it has an iOS/Android app called HPTOY that can tweak DSP settings over bluetooth, including PEQ profiles. Asking price over contact form/paypal is like $60-ish bucks, $5 if you want a usb split cable to use external power (for using with smartphone for example). Pretty cheap, no?

    Seems like a fun toy. Website and details here.
     
    Last edited: Aug 16, 2019
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  2. joeexp

    joeexp Don't ship this man FD-X1 ever

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    Just testing this; Sounds surprisingly analogue but very slightly "plasticky/splashy" with certain types of music. Plenty of power and a fantastic app to remote control the thingy via Bluetooth.


    PS: Make sure you turn down the volume all the way down at the start. This thing packs a punch!
    Also getting quite warm; Not sure a Smartphone would be able to power this for very long.

    Design inspired by Altoids Peppermint mints box is an absolut fingerprint magnet.
     
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  3. ultrabike

    ultrabike Measurbator - Admin

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    Somewhat interesting, with some possible issues. The design is based on the TAS5558.

    The TAS5558 seems to be designed with a "DVD receiver" (or AV receiver) in mind (see section 8.2 of the paper bellow):
    http://www.ti.com/lit/ds/symlink/tas5558.pdf
    On section 8.2.1.2 "Detailed Design Procedure" I read "Possible headphone out that would require an output filter"

    I look at their website here:
    https://e1dashz.wixsite.com/index/products
    And there I find their frequency response measurement climbing up > 20 kHz.

    I'm not sure, but I'm a bit concerned about them completely neglecting to implement the output filter. If so, I would be hesitant to recommend this.
     
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  4. Baten

    Baten Almost "Made"

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    The app addon seems particularly interesting, especially at its seemingly ridiculous low price.
    I might just buy one, "surprisingly analogue" sounds tempting ;)

    Good catch. I see what you mean...

    In the product description it says "PowerDAC V2 uses Ti digital PWM modulator chip TAS5558 but of course different output stage for headphone." so that does make it sound proper care has been given to the output. Given the many filterless DACs out there, you think neglecting the output filter can have big consequences for headphones?
     
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  5. ultrabike

    ultrabike Measurbator - Admin

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    That's not what I get when I read this from their website:

    "That gates can be tied in parallel to provide more than enough current to feed your planars, with near to perfect switching quality(LVC gate has about 1nS..."

    "To check that idea in the reality I took the same Texas Instrument's digital PWM modulator as used in monsters FDA only different power stage, in my case it looked like an array of logic ICs."

    "The very first proto PowerDAC showed that the idea to use logic gates array as a power stage isn't wrong"

    And when I see this in their website:

    PowerDACV2_FR32Ohm.PNG

    Things don't look so hot above 20 kHz IMO.

    Again, I don't think this guys are using an LPF as required by the App note.
     
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  6. joeexp

    joeexp Don't ship this man FD-X1 ever

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    Last edited: Aug 16, 2019
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  7. bengo

    bengo Friend

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  8. ultrabike

    ultrabike Measurbator - Admin

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    It does seem to have a low order passive LPF. I believe that's what is engraved in the cover (LVDS with two inductors and a cap per channel). But that's pretty low order and AFTER the amp. Indeed, the Sharp SM-SX100 seems to claim the same according to that Sterephile article (perhaps minus the LPF after the amp: which means lots of power going to the LPF trash bin).

    It would be nice to see the measured frequency response all the way to 100 kHz to a 20 kHz bandlimited input signal.

    Anyhow. You guys know my main concern. It may be nothing. Carry on.
     
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  9. ultrabike

    ultrabike Measurbator - Admin

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    Alright, I'll go a little further since this, for some reason, got me interested.

    There is an EVM from TI for the TAS5558 (for $100):
    http://www.ti.com/tool/TAS5548EVM

    The solution uses the TPA6138A2PW as the headphone driver of the EVM. Looking at the TPA6138A2PW specs and the EVM board schematic (see EVM User's Guide linky below for the schematic in section 5.2), it seems the EVM is using the headphone driver. The configuration has the headphone driver in differential active second order MFB low pass filter mode to suppress out of band noise (see 9.4.2. of the spec bellow):
    http://www.ti.com/lit/ds/symlink/tpa6138a2.pdf

    It may be that the EVM cannot claim "no feedback" whatever. But IMO, while perhaps lower in output power, this reference design appears to be miles ahead of the PowerDAC2 in terms of noise supression, unless I'm missing something.

    EDIT: BTW, here is the EVM User's Guide convinient linky, in case some crazy dude wants to play with it:
    http://www.ti.com/lit/ug/slou351b/slou351b.pdf
     
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  10. Baten

    Baten Almost "Made"

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    Here's what he had to say on feedback, design stage, etc:

    I live in China so to order sample of proto PCB is very easy and fast over here. Probably next week after I got an idea regarding logic gates array as power stage, I got it listened to. The first point is that's is really the same sound signature as other FDA i.e. it is razor-like detailed sound. I know that not all audiophiles like that typical PowerDAC/FDA sound, they like to explain it as - we have to listen to music rather than its details. However, if you like a max transparent and max detailed sound, bingo, here you go! The very first proto PowerDAC showed that the idea to use logic gates array as a power stage isn't wrong. I got THD about .02%@-3dbfs(200mW) with no feedback at all, it means that the linearity of such power stage is simply exceptional. Someone can say - .02% isn't something WOW at all, my old HiFi had the same at 100W. And he'll be right, however, everyone class A/AB whatever tube or solid i.e. linear amp use tonnes of feedback amount to reduce THD and their initial linearity never being so high to show even 1% of distortions without feedback.
    That's why the feedback-less analog amp doesn't exist. In fact, people, including music production stuff, never heard feedback-less amps before FDA(and actually modern digital modulators are not really pure-digital as well and not really feedback free due to noise-shaper but this is a different story yet). Next 5-7 iterations of the project brought Signal/Noise ratio improvement up to <-108db(A), THD and jitter(with WM8804) was a bit improved as well, and Bluetooth Low Energy interface for DSP control by IOS/Android with preset sharing by skype/email/www etc. Also the BOM cost was optimized, finally, was found the way to get high-performance PowerDAC for headphones with balanced 4 wire interface and IOS/Android app control with moderate BOM cost(expected retail cost $50, no brands/distributors/robbers involved).


    So does seem to be more or less feedback-less. Less/little noise suppression. About 3.3V output over 2.5mm balanced. And mostly: $50 expected retail cost including the free android/iOS app is kinda nuts.

    Idk, I'm still curious :) I'll have to give this thing a try. The -10dBFS graph looks not too bad and does look more or less as expected from supposed no feedback design
    [​IMG]
     
  11. joeexp

    joeexp Don't ship this man FD-X1 ever

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  12. MrTeaRex

    MrTeaRex His head's not fat, he's my brother!

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    Exogal (former Wadia engineers) has a PowerDAC power amplifier that connects to their Comet DAC using a digital HDMI cable for a similar fully digital DAC/Amp combo (as a result, the PowerDAC amplifier has no analog inputs and must be used with the Comet DAC). However, they claim not to need PWM for their implementation.

    https://www.exogal.com/images/PDFs/EXOGAL_DAC_and_PowerDAC_White_Paper.pdf
     
  13. ultrabike

    ultrabike Measurbator - Admin

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    It looks like he is using 4 outputs per channel, using gates to digitally amplify + adding current, and passing it through a maybe about ~50 kHz RLC LPF, maybe. Seems second order.

    Would be nice if he provided the following:
    1. Frequency response showing out of band noise.
    2. Power dissipated through the output filter vs. power delivered (efficiency).
    3. RF emisions: Will I be able to hook up my Wi-Fi/phone to this thing and still browse SBAF?
    EDIT: Anyway. Maybe this is a good option.
     
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  14. joeexp

    joeexp Don't ship this man FD-X1 ever

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    I just tried and yes you are still able to hook up to WIFI/Phone next to the dongle. Perhaps that's why the box is metal on all sides but limiting the bluetooth radius to 2m/6ft ...
     
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  15. joeexp

    joeexp Don't ship this man FD-X1 ever

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    I'd like to nominate the PowerDAC V2 for a Golden Schlong Award.
    Best DAC/AMP/Dongle for under $60;

    Although not the final word in resolution, this is very easy to listen to. Fantastic graphical equaliser with an option to load in a FR background Image. Bluetooth Remote Control. Power to even drive some FullSize Headphones.
    All for less then 60 bucks; That's less than I paid for some USB cables.


    https://www.aliexpress.com/item/4000078625548.html?spm=2114.12010615.8148356.4.24d159699eaF2B

    PS: I am not affiliated with the designer/producer of this product.


    [​IMG]
     
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