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PowerDAC V2

HPTOY_iOS.png

iOS App

You can call it USB DAC + Headphone amplifier(HPA) >600mW@15ohm but actually, PowerDAC has no HPA at all. Yes, PowerDAC V2 can, as an example, drive LCD3 with 600mW but only as powerful enough DAC, no analog amplification and no feedback are implemented there. It's a quite similar to Fully Digital power Amplifiers(FDA) like Sharp SM-SX100(probably earliest FDA), TACT-Millennium, Lingdorf, Wadia etc $5-10K legendary toys. PowerDAC V2 uses the same or similar Ti digital PWM modulator chip TAS5558 but of course different output stage for headphone. 

HPTOY_Android.png

Android App

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 PowerDAC V2 doesn't need drivers to convert stream PCM up to 24/192 from PC/Mac. iOS, Android or Linux, however, if you wish to get full control of the built-in DSP, you need to install iOS or Android app.

A few reasons why you could wish to use the app:

a) Volume slider with classical Fletcher–Munson loudness curves

b) Familiar HiFi Bass/Treble sliders

c) Intuitive controllable filters i.e. 7 parametric EQs, left/right gestures control frequency, up/down gain, zoom in/out Q-factor. Also available LPF/HPF and APF for phase alignment and text form Biquad control just in case(actually, it comes from another my project HiFiTOY crazy-tiny 250W@4ohm PowerDAC where LPF/HPF/APF needed for bi/tri-amping)

d) Compressor/Limiter, I believe this function really useful for an open back planars to "compensate" ambient noise. And limiter keeps sound distortion-free at high volumes, also you can see the output clipping indication in the app

e) Preset manager allows to save/load presets and export/import(email/skype/www etc) as well to share PowerDAC settings between users

f) I prepared a few EQs presets to transform frequency response one headphone to another or to the "ideal Harman" curve. I using www.innerfidelity.com measurements data + short Matlab script to obtain EQ compensation

Specifications:

Status:                            production

Retail cost:                     TBD($50)

Materials:                       sandblasted/anodized aluminum, mirror polished stainless steel

                                         with laser marking

Dimensions:                   75x45.5x19mm


Weight:                           68g


Power:                             USB 5V power rail no internal battery, 250mA idle current, the device                                                   contains up to 5000uF of capacitance and IOS/Android devices can

                                         start OTG operation only with Camera_Adapter and USB OTG Y-splitter                                                 cable respectively


Input:                               USB PCM up to 24b/192kHz


Output:                            digitally generated PWM 384kHz + passive LC demodulation

                                          balanced output 2.5mm jack 5mm shaft stopper, A&K pinout

                                          No adaptors allowed! You can kill the DAC.


Output impedance:       1.5Ohm@1000Hz FFT flat top -6dbFS 32Ohm/open load, -.4db drop 

Output power:                >320mW@32Ohm@1kHz@THD=1%

Output power:                >580mW@16Ohm@1kHz@THD=1%

measured in 24b/44.1k mode +.6dbFS level, typical PC USB2 port powered. In case USB power-splitter aka USB-C Y-cable used i.e. USB data goes from Android and 5V power rail from 5.2V 2A charger the max power will be seriously higher see tech plots in the appendix
 

Frequency response:    20Hz-20kHz +/-.2db(+/-.15db typical)

                                        10Hz-30kHz +/-.5db(+/-.3db typical)

                                         2.5Hz-46kHz +/-3db


S/N ratio:                      -108db(A) (-109db(A) typical)


THD+N@1kHz@0dbFS <.05%


THD+N@1kHz@-3dbFS <.03%


THD+N@1kHz@-6dbFS <.02%


THD+N@1kHz@-10dbFS <.01%


THD+N@6.3kHz@-10dbFS .01% typical


THD+N@100Hz@-10dbFS .03% typical(depends on USB power quality)


THD+N@1kHz@-20dbFS .01% typical


IMD 19kHz(-10dbFS)+20kHz(-10dbFS) -80db typical (THD and IMD measured with 32ohm load in 24b/44.1k mode)

Crosstalk:                     <-92db@1kHz

iOS/Android HPTOY App, practical consideration.


The connection between App and PowerDAC V2 establishing automatically, you only need keep turned On Bluetooth (BT) on your smartphone(Android will ask for Location service because the app uses API 26 but not because we need that), and next open the App to see the initial page like that:

Without PowerDAC V2 hardware you can try Demo mode, also please read (i) hints we leave everywhere. If the device(or devices, if hypothetically you'll have many PowerDACs) was found, to start any adjustment please tap on the device name "PowerDAC V2 7E-7E852" and you'll see the main page:

The top-right corner you see "Save" shortcut to the Options/Preset Manager. All adjustments are applying online, virtually no delay, however, these parameters aren't memorized until you save it as a preset.

Volume slider range Mute-0db, if the Loudness Dry/Wet slider >0%, the volume control will operate with loudness function. Loudness Dry/Wet 100% and Loudness_frequency 60Hz are generally recommended but it depends yet and I rather prefer 60% and 50Hz.

Bass/Treble sliders range -12/+12db, pretty much classical thing no need comments on it.

Filters page has up to 7 Intuitive controllable parametric EQs, left/right gestures controls frequency, up/down gain, zoom in/out Q-factor. To select any filter please double-tap on its marker(dashed vertical line). Also available LPF/HPF(double-tap on the first or last orange dot on the filters curve, and drag it down) and APF(tap+hold on 1S on any parametric EQ will turn it into the APF) for phase alignment and text form Biquad control just in case. Actually, for headphone purpose, you need mostly parametric EQs, LPF/HPF/APF/TXT_biquads filters needed only for extensive Bi/Tri-amp filtering i.e. for a speaker amps. We just keep the same Filter page for HPTOY and HiFiTOY apps just in case. For example, you can digitize the signal directly from your turntable cartridge without corrector, next play that wav file or online stream with PowerDAC V2 where RIAA correction will be applied in TXT biquad form. Right, looks weird but anyway better to have it than haven't.

Compressor page contains classical compressor/limiter DSP cell, well familiar to studio producers, however, to use it right way need to know some simple theory of operation, so I recommend you read wiki first or start from my presets. Dry/Wet slider at 0% bypassing the compressor cell. 

Time_const subpage has 3 sliders: Energy, to change detection behavior from Peak(50uS) to RMS(up to 50mS), Attack with range 1-200mS and Decay 10-10000mS.

Options page:


 "Name" subpage, allows renaming device 


 "MAC" it's a BT ID MAC address, the new device will automatically be named as its MAC


Restore_factory_settings is the panic button, tap there if your PowerDAC V2 doing wrong. To be honest, I never had reason to use it so far.


Change_pairing_code helps in case if you and your office-buddy within 5 yards both using PowerDAC V2. Set that code for any value but zero(default pairing code = 0) and the problem solved.

 Preset_manager can save/load/rename/delete/import/export/merge presets. After you changed some parameters, and you are sure it is what you need, you tap on "Save' shortcut to get Preset manager page. Where you'll tap "Save" again to confirm your intention, and the new preset will be saved with the name = Current_Time. About 10S you'll see the App sending the data to the hardware. Next, a good idea to rename that preset for a friendly name or export that preset to share your office-buddy. Tap to (i) symbol opposite new preset to get Preset_Name subpage, and edit current name if you wish, or tap there to share symbol (top-right corner rectangle with an arrow) to export the preset(choose the app for preset sharing, email, skype etc). To import preset need to tap on the received preset file in skype/email app, and preset will be imported into the HPTOY app after you choose that app. This part of GUI slightly different for Android version but the logic of operation the same. If you wish to assemble the new preset from a few old, please try the Merge function and follow its dialogue. iOS app version deleting presets by common delete gesture(tap+drag to left).

Clipping_setting value depends on the hardware and in case of PowerDAC V2 suppose be 0db. That value using to set clipping indication threshold. The clipping indication is embedded into the header of each page of the HPTOY app, you'll see that as red highlighting in the header in case if the output will reach the Clipping threshold value. For instance, you can set the threshold for -2db and your clipping indication will work like early caution of clipping.

Advertise_mode let you reduce BT 2.4GHz disturbance and noise if you going to use PowerDAC V2 without a smartphone. In that case please switch Advertise_mode to the After_1_minute_off position, and your PowerDAC V2 will be discoverable only during 1 minute after turning On.

Tech appendix

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PowerDAC as USB/Headphone interface

This story started as an idea to implement a pure digital USB/headphone interface, similar to Fully Digital power Amplifiers(FDA) like Sharp SM-SX100, TACT, Lingdorf, Wadia etc.

 Actually, I just bought HE400i headphones and found that I have not enough power/voltage to drive it from my phone or laptop. HE400i is awfully low sensitive headphones as many of planars. So between trivial DAC+Amp solution, I decided to get a PowerDAC, and due to my professional background(500A SMPS, thousands watts class D amps, DSP and so on) and also because I didn't find pure digital headphone solutions on the market, I decided to make my own truly DIY PowerDAC project. I have to say that Tact/Lyndorf FDA's are expensive but not only because of high-end-brand or so, technically the task to get high-quality audio output 5-10 Ampers and 30-100V from the open-loop topology (without the feedback loop), is quite challenging. Today we have some GaAs/GaN power stages for that and it is not cheap again. Well, fortunately, the headphone doesn't need hundreds of watts and tens Ampers as well, so we can try to use there something widely available and inexpensive for example standard logic gates! 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 per edge that's probably even better than bloody expensive GaAs/GaN power stage), and 5V USB rail can handle almost 2ch x 400mW@32ohm(with USB power splitter to get solid 5.0V from a power-bank instead of weak 4.2V from a smartphone's USB) or about 120db SPL undistorted sound. As to me, that is loud, maybe for some else really need louder but certainly not to me. 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. I living 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 so - 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 that 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).

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Conventional PC USB2 port, 32ohm load power sweep, THD+N = 1% at 320mW

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Conventional PC USB2 port, 16ohm load power sweep, THD+N = 1% at 580mW

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Conventional PC USB2 port, HFM HE400i load power sweep, THD+N = 1% at 290mW

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Conventional PC USB2 port, 16ohm load crosstalk -92.64db

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Frequency response 32ohm load

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FFT 0dbfs HFM HE400i load, USB power splitter to 5.2V 2A charger THD+N =.032%

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FFT -3dbfs HFM HE400i load, USB power splitter to 5.2V 2A charger THD+N =.023%

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FFT -6dbfs HFM HE400i load, USB power splitter to 5.2V 2A charger THD+N =.014%

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FFT -10dbfs, 50% of the PC volume slider, HFM HE400i load, USB power splitter to 5.2V 2A charger THD+N =.0074%

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FFT -20dbfs HFM HE400i load, USB power splitter to 5.2V 2A charger THD+N =.0065%

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FFT -10dbfs 6.6kHz HFM HE400i load, USB power splitter to 5.2V 2A charger THD+N =.0095%

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FFT -10dbfs 100Hz HFM HE400i load, USB power splitter to 5.2V 2A charger THD+N =.025%

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FFT +.6dbfs 3.46VRMS 374mW 32ohmload, USB power splitter to 5.2V 2A charger THD+N =1%

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FFT +.6dbfs 3.32VRMS 688mW 16ohmload, USB power splitter to 5.2V 2A charger THD+N =1%

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FFT +.6dbfs 3.5VRMS 350mW HFM HE400i, USB power splitter to 5.2V 2A charger THD+N =1%

Presets

HPtoy  App has 29 presets built-in.

Latest presets are below.

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