Hi Gabor,
Actually I did not build the A Class PSU, so I cannot confirm, I do think one member here has mentioned that any jfet will work in the circuit, perhaps Sir Miles could help us out here.
My simulation shows that it is a fully working circuit.
@apexaudio:
With my Apex A23 Board i added 3K8 resistors in parallel to the 3K3, resulting roughly in 1K7. Now I'm getting +-14,8V at the Opamp. But I still can't get any bias current in the output stage on any trimpot value between 0 and 200R.
I've just taken some bias measurements in the attached picture. For me seems like the input stage is a bit asymmetrical and the bias servo voltage is a way too low. I appreciate any help 🙂.
regards
With my Apex A23 Board i added 3K8 resistors in parallel to the 3K3, resulting roughly in 1K7. Now I'm getting +-14,8V at the Opamp. But I still can't get any bias current in the output stage on any trimpot value between 0 and 200R.
I've just taken some bias measurements in the attached picture. For me seems like the input stage is a bit asymmetrical and the bias servo voltage is a way too low. I appreciate any help 🙂.
regards
Attachments
There must be wrong resistor value 4k7 or 680R in Vbe multiplayer.
Vce on BD139 must be from 3,5V to 4,5V.
Regards
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I use BF245A with pin out GDS.
As for others I use BC546/556, BC639/640 and TIP31C/32C.
This PSU has been working for long time. The desired adjusted voltage is
rock stable.
Bingo! Not the resistors- more the BD139 was connected wrong. What is recommended quiescent current per output pair?
With highest Trimpot Resistance (mine is 200 Ohm) I'm getting about 320mA per Pair. Uce of Bias Servo is 3,7V. Sound is very nice 😀. Should I try 1k instead of 680R?
I've added 150R in series, that helped a lot. Maybe I will take it with to work this week for distortion Measurements. Thank you Apex!
Is this amplifier better than A40? As I remember, A40 did not have a simulation.....
Thank you !
Thank you !
A40 is working design, this is only simulation.
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Finished layout for A15, pcb size 87mm X 85.8mm. Now its time to check mistakes and revision.
Nice pcb, thank you.
Regards
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Wow layout is too good...congrats.
Placing of resistor inside inductor, will it change the characteristics of inductor?. It may not be critical, but just want to have an opinion of others.
Reg
Prasi
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Hi Guys,
An update about my A class PSU. I ordered some BF245A's and they came in today. I installed them and the PSU still didn't work. With further investigation I discovered that I had installed 500R trimmers rather than 5K. I swapped out the 5k trimmers and reinstalled the BF246 jfets and it works flawlessly. Sorry for all the fuss. If anyone wants my layout for the BF246 just let me know and I'll post the files.
Blessings, Terry
An update about my A class PSU. I ordered some BF245A's and they came in today. I installed them and the PSU still didn't work. With further investigation I discovered that I had installed 500R trimmers rather than 5K. I swapped out the 5k trimmers and reinstalled the BF246 jfets and it works flawlessly. Sorry for all the fuss. If anyone wants my layout for the BF246 just let me know and I'll post the files.
Blessings, Terry