So I only need four resistors? You're saying leave off the first "R" in my alphabet soup? So it will be Cap MX -> CRCRCRCR -> PCA. Thanks.
Today is a very special day in my hi-fi life.
Today I listened to this head amp with Status OB-1 headphones. The headphone amp has been with me since april. but didnt have proper headphone to listen.
I didnt want to spoil the moment with some ordinary headphone.
Last week I received the headphones and the batteries yesterday.
Xrk, I must congratulate you on this, its superb amp, gives new life to tracks, no details lost and gives kindof goosebumps .
Wow!. Many many thanks for doing this. A very very satisfied customer of xrk audio
regards
Prasi
Today I listened to this head amp with Status OB-1 headphones. The headphone amp has been with me since april. but didnt have proper headphone to listen.
I didnt want to spoil the moment with some ordinary headphone.
Last week I received the headphones and the batteries yesterday.
Xrk, I must congratulate you on this, its superb amp, gives new life to tracks, no details lost and gives kindof goosebumps .
Wow!. Many many thanks for doing this. A very very satisfied customer of xrk audio
regards
Prasi
+1 from another happy owner.
You should really consider to EQ these headphones for much improved results IMO. Posts by BYRTT on that starts here:
xrk971 Pocket Class A Headamp GB
Slightly turbo charged PCA
Finally got around to stick heatsinks (made for raspberry pi) on the mosfets of my desktop PCA this weekend. Also changed the regulator circuit according to a recommendation by BYRTT in a previous post for cleaner power.
The plan was to also swap the input caps for electrolytics, and swap the output caps for Panasonic FR’s – but I could not get it over my heart to de-solder the components
– too scared I might mess up a good working amp.
My PCA is now running on 19V at a bias of slightly more than 76mA. Does it sound better? Difficult to say since it’s been a while between the last listen and the upgrade, but I believe it does indeed. I could not stop listening all over to all my favorite reference tracks. The highs are crystal clear, the vocals accurate, acoustics brilliant, the bass, man the bass, is sooo nice – low, tight and well defined attack. I LOVE this little amp.
Finally got around to stick heatsinks (made for raspberry pi) on the mosfets of my desktop PCA this weekend. Also changed the regulator circuit according to a recommendation by BYRTT in a previous post for cleaner power.
The plan was to also swap the input caps for electrolytics, and swap the output caps for Panasonic FR’s – but I could not get it over my heart to de-solder the components
– too scared I might mess up a good working amp.My PCA is now running on 19V at a bias of slightly more than 76mA. Does it sound better? Difficult to say since it’s been a while between the last listen and the upgrade, but I believe it does indeed. I could not stop listening all over to all my favorite reference tracks. The highs are crystal clear, the vocals accurate, acoustics brilliant, the bass, man the bass, is sooo nice – low, tight and well defined attack. I LOVE this little amp.
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Hi Twocents,
Super looking and sounding amp there. I need to get these little heatsinks! Are they double sided taped on? Glad you love the sound. I was listening to mine last night (with 1000uF FR's on output and 10uF Silmic II on input). Yes, the bass, and everything sounds so nice. It can keep up with my desktop amps for most anything. Don't be afraid to desolder caps a few times. The board is pretty rugged.
Super looking and sounding amp there. I need to get these little heatsinks! Are they double sided taped on? Glad you love the sound. I was listening to mine last night (with 1000uF FR's on output and 10uF Silmic II on input). Yes, the bass, and everything sounds so nice. It can keep up with my desktop amps for most anything. Don't be afraid to desolder caps a few times. The board is pretty rugged.
Just a thin layer of 3M adhesive glue (probably the same as used on double sided tape) on the back of the heatsink - just peel and stick.
i finally got some time and put it together, first time smt soldering with a crappy soldering iron ! it turned out ok i guess. the sound is fantastic, the bass is the first thing you'll notice, but i did not test it on my main headphones because of the loud click when powering the amp on and off ! is it normal ?!
and after like 5 minutes i noticed the mosfets got very hot ! the board was hot, the caps were hot, everything got hot pretty quick, one side was warmer than the other side, not sure what i did wrong. 
what do you think ?
and after like 5 minutes i noticed the mosfets got very hot ! the board was hot, the caps were hot, everything got hot pretty quick, one side was warmer than the other side, not sure what i did wrong.
what do you think ?
The turn on click is normal as the output caps get biased to the midpoint of the rails at circa 9v. But that happens once st turn on. Don't plug your headphones in until after you turn on power.
The heat is normal - it is Class A after all. Correctly built, it will all feel warm but the MOSFETs and corner of amp with heatsink tab will be around 45C to 50C. That's normal. If one side is hotter than other it may mean bias currents are different. Did you match JFETS and MOSFETs ? Check bias current by measuring voltage at source of MOSFETs. A 7.5v reading divided by 117.5ohms (4x470R parallel) is 64mA for example. If your JFET is "hot" running and MOSFETs are also hot running you could be in a situation where bias is greater than 75mA and that may be too much heat for the little heatsink copper planes on the PCB to dissipate. 75mA x 8v is 600mW through ea MOSFET and resirtors take rest. But total heatload is 0.150amps x 16v (typical voltage)=2.4w for amp and that's a bit high. Try to stay below 2W total.
The heat is normal - it is Class A after all. Correctly built, it will all feel warm but the MOSFETs and corner of amp with heatsink tab will be around 45C to 50C. That's normal. If one side is hotter than other it may mean bias currents are different. Did you match JFETS and MOSFETs ? Check bias current by measuring voltage at source of MOSFETs. A 7.5v reading divided by 117.5ohms (4x470R parallel) is 64mA for example. If your JFET is "hot" running and MOSFETs are also hot running you could be in a situation where bias is greater than 75mA and that may be too much heat for the little heatsink copper planes on the PCB to dissipate. 75mA x 8v is 600mW through ea MOSFET and resirtors take rest. But total heatload is 0.150amps x 16v (typical voltage)=2.4w for amp and that's a bit high. Try to stay below 2W total.
thanks for the input,
i did not matched the JFETs or the MOSFETs, but i did a reading on MOSFETs source, one is around 7v the other one is around 8.5v , not sure if that much difference is normal, but both are below 75mA then , mosfets are hot but jfets are warm and i think it's because of the mosfets heat, lemme know what you think.
gonna do some listening tonight
i did not matched the JFETs or the MOSFETs, but i did a reading on MOSFETs source, one is around 7v the other one is around 8.5v , not sure if that much difference is normal, but both are below 75mA then , mosfets are hot but jfets are warm and i think it's because of the mosfets heat, lemme know what you think.
gonna do some listening tonight