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xrk971 Desktop Class A (DCA) Headphone Amp
xrk971 Desktop Class A (DCA) Headphone Amp
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Old 21st June 2019, 10:58 PM   #241
adydula is offline adydula  United States
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Ok are you saying to use the Westell 12vdc 1000ma to feed this internal DC boost convertor?

Alex
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Old 21st June 2019, 11:14 PM   #242
xrk971 is online now xrk971  United States
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xrk971 Desktop Class A (DCA) Headphone Amp
Yes, almost any Class 2 12v wall wart can work.
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Old 22nd June 2019, 12:12 AM   #243
xrk971 is online now xrk971  United States
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xrk971 Desktop Class A (DCA) Headphone Amp
Alternatively, you could use a 24v 500mA Class 2 transformer wall wart without a DC-DC stepup. It will drop about 4v across the cap Mx. You can increase the R value of the CRCRC to drop another volt and be at 18v and not have any DC-DC that may be inject high frequency noise (150kHz) into you amp.
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Old 13th September 2019, 09:25 AM   #244
yourownbuzz is offline yourownbuzz  Australia
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Built one with the low bias current values - the amp works (there's sound out), but when measuring voltages they seem all wrong compared the sim (https://www.diyaudio.com/forums/atta...-schematic-jpg)

My Vcc is a hair above 18.2V (18.2x V) Not sure whats going on...?
Voltage measurements are in red, relative to gnd.
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Old 13th September 2019, 10:46 AM   #245
xrk971 is online now xrk971  United States
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xrk971 Desktop Class A (DCA) Headphone Amp
Looks like your particular BF862 has a lower Idss than one used in simulation. Let me think about it.
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Old 28th September 2019, 08:18 AM   #246
yourownbuzz is offline yourownbuzz  Australia
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hmm those are from the same batch from RS which I've been using all along though. maybe I'll swap them out and see. I was a bit suspicious since it was running totally cold to the touch.
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Old 13th October 2019, 07:33 AM   #247
Dibya is offline Dibya
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This beast is capable of rivaling best tube amps out their . One of my Thai friend own a high end tube amp from schit but i found this amp simply destroys it. As an musician , distortion is not always bad rather second order distortion puts life into your music . . Distortion profile is truly like those of DC Coupled tube amp. I used adapter of my Compaq 620 , it worked flawlessly as power source.
If you are a new to smd , it is better to take help from anyone who repairs SMD boards day in day out like those who repair smartphone , macbook etc for placing JFET on board .

I don't know where xrk971 has fabricated the pcb but they are absolutely top notch as i have used de soldering wig for many time for fixing my stupid mistakes but the board absolutely survived my awful torture . xrk971 always helps you if you have any doubt . Anyway never use Ruby con caps in output stage unless you want some harsh mid range . Vishay BC will give absolutely neutral sound but i will recommend Panasonic FC or Nichicon UFG for clean audio . Use at least 1% resistor from Vishay Dale to archive least distortion . As for film caps use any metallized film like mallory , wima or vishay Roederstein , my favourite .
I actually used every passive components from Vishay as they have excellent supply in india which i cannot say at all for panasonic and wima . I recommend to grab components from Digikey or mouser or farnell to ensure legit components. If you are using 10uf caps in input like Silmic II or Nichicon ues , please kindly give some burn in time before listening . Most importantly , never reverse the supply rail , it will blow your first mosfet in no time .


Lets come to most important thing , how it sounds :
DAC used :: Focusrite Scarlet Solo
Headphone used :: AKG K 240 Semi-Open Studio Headphones
I will compare with OBJECTIVE 2 and OPA1688 based amp of XRK.
Warning : If you have wedding or something important to attend , donot listen to this amp beacuse you cannot stop listening. It literally sings into your ear with awful amount of detail in midrange ,
crystal clear highs with lovely tube like distortion and crisp lows . I have played Yanni Live at the Acropolis [Whole CD] , Skillet Rise [whole album at 24bit ] , Evanescence Synthesis [24 bit ] ,Evanescence Open doors [CD],
Some Metallica[16bit flac ripped from CD] , Enigma Sadness I and II

Yanni Live at the Acropolis [CD] :
First thing i noticed is Piano is quite more profound than any OP AMP based amp i own like OBJECTIVE 2 and OPA1688 based amp of XRK.
In rain must fall , i can feel shout at beginning from different direction which i never heard. I never before distinguished violin in the song properly but this amp did the magic.

Skillet Rise [whole album at 24bit flac] :
In fire and fury , beginning vocal were crystal clear . Objective 2 is crisp but this amp more crystal clear may be due to JFET input stage .
In what i believe , the beginning portion in guitar sounded totally different , man this is not music it is drug . Metal with 2nd order harmonic distortion is totally heaven for those who love rock and role .

Evanescence Synthesis [24 bit]:
In Lithium : In beginning , Vocals of AmyLee were stunning as always but hold on piano never was so crystal clear then the Gothic metal portion enters and this amp blows everything away in distortion profile.
In Bring Me Back to Life : I will call it bring this amp to life , sound quality and timbre of mid range with excellent stereo separation was in another league which objective 2 cannot stand near to it.

Some Metallica[16bit flac ripped from CD]:
In Orion : i cannot say much , this amp is God for listening metal , in orion i heard many stuff first time and i can literally distinguish what kind of effect and type of guitar string they are using . If you play guitar you will
understand what i am saying . I noticed first time the song is on off note .

Enigma Sadness I and II :
In Sadness I, I cannot make much difference between objective 2 , they sounded equally awesome .
In Sadness II , starting was better on DCA but later when beat drop entered both sounded equally well.
In I love you , i will kill : for first time i heard new instruments which felt like Tabla .

My conclusion : if you listen metal , hard rock , soft rock , punk rock or anything like new age instrumental , you will love this amp. This amp is heaven if you love metal .

I am traveling so writing from my phone , Nokia 8 so their may be some typos so forgive me .
If you want to ask me anything , please feel free .

Last edited by Dibya; 13th October 2019 at 07:37 AM.
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Old 13th October 2019, 12:47 PM   #248
xrk971 is online now xrk971  United States
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Dibya,
Thank you for the extensive listening impressions. Glad you like the amp!
Regards,
X
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