Thin film is fine. 14v is close enough, what is voltage at gate of JFET? Look for cold solder joint on feedback resistor to gate of JFET also.
Couple of things you can try.
1. Add 2200uF plus 0.1uF bypass cap on D of mosfet
2. Move ground of input stage to star hub
3. Remove 10ohm ground lift
4. Add 270ohm bleed off resistor on output
I can send you a PCA PCB to play with if you want. Try it out and you can make sure you don’t have any layout errors. You can solder a TO220 to the SOT223 pads like I did. No charge - just get me your address.
Cheers,
Viet
Couple of things you can try.
1. Add 2200uF plus 0.1uF bypass cap on D of mosfet
2. Move ground of input stage to star hub
3. Remove 10ohm ground lift
4. Add 270ohm bleed off resistor on output
I can send you a PCA PCB to play with if you want. Try it out and you can make sure you don’t have any layout errors. You can solder a TO220 to the SOT223 pads like I did. No charge - just get me your address.
Cheers,
Viet
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Viet, thanks! Doh! 
I just noticed that in your post 539, the simmed voltages are different from the one schematic I grabbed from many moons ago. Ok, so in your post 539, I'm much much closer than I thought. The measured gate voltage at the jfet is 1.38V on my Fluke DMM. That's not too far off from 1.1V you have. I'll try out the mods you suggested and I bet that will get me close enough. Thanks for the help on this one. 🙂
I just noticed that in your post 539, the simmed voltages are different from the one schematic I grabbed from many moons ago. Ok, so in your post 539, I'm much much closer than I thought. The measured gate voltage at the jfet is 1.38V on my Fluke DMM. That's not too far off from 1.1V you have. I'll try out the mods you suggested and I bet that will get me close enough. Thanks for the help on this one. 🙂
I finally had a bit of time to make the changes to my boards and hook everything up. Even though it isn't Xrk's latest version, I really enjoyed the sound of this simple amp. It's been quiet and well behaved, with lots of punch. I'll definitely move forward with the changes I see from Xrk's last posted schematic and whip up some new PCBs.
Great it’s working out for you and that you are enjoying the amp! It has beat many much more complicated and powerful headphone amps in AB blind tests. There’s something to be said for simple circuits.
Hi, I bought some BF862 from various places, Ali/Ebay but they are all fake.
I have now ordered the 2SK209GR from Farnell.
Did anyone do the 2SK209GR variant instead of the BF862 or a simulation? Thanks.
I have now ordered the 2SK209GR from Farnell.
Did anyone do the 2SK209GR variant instead of the BF862 or a simulation? Thanks.
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Yes, the 2SK209BL works well and has slightly different setpoints. I’m sure GR can be made to work too. Here is a table of BF862, 2SK209BL, and 2SK170BL
for this topology:
https://www.diyaudio.com/community/...lifier-hpa-for-melbourne-db-group-buy.334457/
for this topology:
https://www.diyaudio.com/community/...lifier-hpa-for-melbourne-db-group-buy.334457/
For those who want the press & peel files you can find them attached.
It was not done practically, there may be errors. Or not...
It was not done practically, there may be errors. Or not...
The curiosity was great .... 
I assembled the amplifier with the weakest components. Aliexpress carbon resistors and some capacitor ****. 😀
The sound is very interesting. I used 2SK209 BL
Dynamic and comparable to other projects that do not use output capacitors, like Sapphire.
I am going to order a set of quality PCBs and components for the more serious version.
I assembled the amplifier with the weakest components. Aliexpress carbon resistors and some capacitor ****. 😀
The sound is very interesting. I used 2SK209 BL
Dynamic and comparable to other projects that do not use output capacitors, like Sapphire.
I am going to order a set of quality PCBs and components for the more serious version.
Nice work! Nothing wrong with carbon resistors. In fact, I prefer their sound - smoother and dominant 2nd harmonic distortion vs 3rd for thick film. Metal thin film are neutral but less smooth. If you want a premade “serious” PCB then check out the DCA PCB designed by JPS64. It will save you some trouble for doing the layout. Unless that’s what you like to do.
Yes, that is the correct PCB and indeed it should be absolutely silent without any source connected or music playing. The measured noise floor is below limit of typical audio interface. I measured -135dB.
I finished it!
The sound does not describe it, I leave you the pleasure to discover it. You will have a big surprise.
But, as everything is not perfect, I forgot a small route. 😀 😉
,
I have seven pcb left available. Those who are interested can find them in the market section.
,
The sound does not describe it, I leave you the pleasure to discover it. You will have a big surprise.
But, as everything is not perfect, I forgot a small route. 😀 😉
,
I have seven pcb left available. Those who are interested can find them in the market section.
,
I have many 2SK209BL and I would try the first option, the one with BF862.
I would like some recommendations for the values in the diagram for the version with 2sk209bl.
Thanks.
I would like some recommendations for the values in the diagram for the version with 2sk209bl.
Thanks.
I am afraid you will have to play with it, but I dropped the 2SK209BL into the sim and got pretty good figures into 120ohm load. It has not been optimized for lower impedance loads.
Here is predicted distortion for 3Vpp into 120ohm load:
Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+03 1.518e+00 1.000e+00 179.97° 0.00°
2 2.000e+03 3.498e-05 2.304e-05 -88.93° -268.90°
3 3.000e+03 4.391e-06 2.893e-06 -134.30° -314.27°
4 4.000e+03 1.674e-07 1.102e-07 90.20° -89.76°
5 5.000e+03 3.190e-08 2.101e-08 50.95° -129.02°
6 6.000e+03 1.968e-09 1.296e-09 -121.22° -301.19°
7 7.000e+03 1.656e-09 1.091e-09 -171.84° -351.81°
8 8.000e+03 1.731e-09 1.140e-09 179.12° -0.84°
9 9.000e+03 2.018e-09 1.329e-09 179.91° -0.06°
Total Harmonic Distortion: 0.002322%(0.001928%)
LTSpice File Attached.
Here is predicted distortion for 3Vpp into 120ohm load:
Harmonic Frequency Fourier Normalized Phase Normalized
Number [Hz] Component Component [degree] Phase [deg]
1 1.000e+03 1.518e+00 1.000e+00 179.97° 0.00°
2 2.000e+03 3.498e-05 2.304e-05 -88.93° -268.90°
3 3.000e+03 4.391e-06 2.893e-06 -134.30° -314.27°
4 4.000e+03 1.674e-07 1.102e-07 90.20° -89.76°
5 5.000e+03 3.190e-08 2.101e-08 50.95° -129.02°
6 6.000e+03 1.968e-09 1.296e-09 -121.22° -301.19°
7 7.000e+03 1.656e-09 1.091e-09 -171.84° -351.81°
8 8.000e+03 1.731e-09 1.140e-09 179.12° -0.84°
9 9.000e+03 2.018e-09 1.329e-09 179.91° -0.06°
Total Harmonic Distortion: 0.002322%(0.001928%)
LTSpice File Attached.