Compact series - CFA / VFA, including tube hybrids (4 amps)
Dear friends!
I was more or less keeping silence during the last few weeks. But I did not waste any time 😉 I was "cooking". As a result, I am pleased to present a series of rather compact (PCB size is 5.5 x 3 inch for the whole channel) amplifiers. 2 pairs of IRFPs and +/-50V rails ensure solid 120W per channel at 8 ohm. Low distortion, easy to build. The previous version of the first design is auditioned earlier with excellent results (mentioned in some previous posts).
Short description of key "specialties" of each design:
1) Compact CFA V1.2 - further improvement of the earlier design with singleton CFP input stage (jFET + BJT) and EF2+IRFPs output stage. DC servo is added for those who likes to be sure the offset stays within a couple of mV (although it stays within +/-20mV even without the servo - tested on 4 channels live).
2) 6DJ8 Compact CFA - same topology (singleton CFP input, current feedback), but with 6DJ8 tube . It would be interesting to compare the sound with the previous one. Looks very promising.
3) ALLFET V2.0 - further development of the ALLFET topology. Balanced front-end based on IRF610/9610 (emitter followers are added in front of VAS mosfets - increasing VAS linearity dramatically). IRFP-based OPS is driven directly from the high-current VAS stage - simple and efficient. No problem with IRFPs' high input capacitance at this kind of VAS current.
4) 6DJ8 Compact VFA - same topology, but having the tube at the input LTP. Dynamic load is added to compensate the lower gain of the tube - front-end shows rather high overall linearity. AC analysis shows very good stability margins.
All designs are rather high-speed (especially CFAs). Both VFAs have got bootstrapped VAS load.
In order to fit the compact PCBs, I had to use SMD parts, placed on both sides of the board. VFAs also utilize SMD source resistors at the output pairs (5 x 1W resistors in parallel for each source).
Sorry, these PCBs are not etching-friendly, but rather easy to build as soon as they are manufactured at the workshop.
Designs will be presented in the next 4 posts (one per post).
Have fun! 😛
Valery
Dear friends!
I was more or less keeping silence during the last few weeks. But I did not waste any time 😉 I was "cooking". As a result, I am pleased to present a series of rather compact (PCB size is 5.5 x 3 inch for the whole channel) amplifiers. 2 pairs of IRFPs and +/-50V rails ensure solid 120W per channel at 8 ohm. Low distortion, easy to build. The previous version of the first design is auditioned earlier with excellent results (mentioned in some previous posts).
Short description of key "specialties" of each design:
1) Compact CFA V1.2 - further improvement of the earlier design with singleton CFP input stage (jFET + BJT) and EF2+IRFPs output stage. DC servo is added for those who likes to be sure the offset stays within a couple of mV (although it stays within +/-20mV even without the servo - tested on 4 channels live).
2) 6DJ8 Compact CFA - same topology (singleton CFP input, current feedback), but with 6DJ8 tube . It would be interesting to compare the sound with the previous one. Looks very promising.
3) ALLFET V2.0 - further development of the ALLFET topology. Balanced front-end based on IRF610/9610 (emitter followers are added in front of VAS mosfets - increasing VAS linearity dramatically). IRFP-based OPS is driven directly from the high-current VAS stage - simple and efficient. No problem with IRFPs' high input capacitance at this kind of VAS current.
4) 6DJ8 Compact VFA - same topology, but having the tube at the input LTP. Dynamic load is added to compensate the lower gain of the tube - front-end shows rather high overall linearity. AC analysis shows very good stability margins.
All designs are rather high-speed (especially CFAs). Both VFAs have got bootstrapped VAS load.
In order to fit the compact PCBs, I had to use SMD parts, placed on both sides of the board. VFAs also utilize SMD source resistors at the output pairs (5 x 1W resistors in parallel for each source).
Sorry, these PCBs are not etching-friendly, but rather easy to build as soon as they are manufactured at the workshop.
Designs will be presented in the next 4 posts (one per post).
Have fun! 😛
Valery
Compact CFA V1.2
Here we go.
For those, who wants to add DC servo to the previously built initial version of the amp, I have designed a standalone servo that can be mounted on top of the PCB and connected to the main PCB with 5 wires (including ground).
Here we go.
For those, who wants to add DC servo to the previously built initial version of the amp, I have designed a standalone servo that can be mounted on top of the PCB and connected to the main PCB with 5 wires (including ground).
Attachments
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01-Compact-CFA-V1.2-Sch.jpg -
05-Compact-CFA-V1.2-Silk-Top-SERVO.JPG -
03-Compact-CFA-V1.2-3D-Top-SERVO.JPG -
02-Compact-CFA-V1.2-PCB-SERVO.jpg -
01-Compact-CFA-V1.2-Sch-SERVO.jpg -
06-Compact-CFA-V1.2-Silk-Bot.JPG -
05-Compact-CFA-V1.2-Silk-Top.JPG -
04-Compact-CFA-V1.2-3D-Bot.JPG -
03-Compact-CFA-V1.2-3D-Top.JPG -
02-Compact-CFA-V1.2-PCB.JPG
6DJ8 Compact CFA
This is a pretty interesting one. Tube-based CFA 🙄 I expect it sounding very cool 😉
This is a pretty interesting one. Tube-based CFA 🙄 I expect it sounding very cool 😉
Attachments
ALLFET V2.0
Initial version of the front-end was tested by me and Terry. This one is significantly improved with EFs in front of the VAS mosfets - my tests have shown dramatic linearity improvement.
Now it comes bundled with OPS, however it is easy to use just the front-end - in this case it will fit the "standard" 3 x 4 inch board, same as any other front-end in this series.
It's got 2 BJTs now, but I still call it ALLFET... well, it's FET enough 😀
Initial version of the front-end was tested by me and Terry. This one is significantly improved with EFs in front of the VAS mosfets - my tests have shown dramatic linearity improvement.
Now it comes bundled with OPS, however it is easy to use just the front-end - in this case it will fit the "standard" 3 x 4 inch board, same as any other front-end in this series.
It's got 2 BJTs now, but I still call it ALLFET... well, it's FET enough 😀
Attachments
6DJ8 Compact VFA
Pretty cool balanced front-end with 6DJ8 at the input and high-current bootstrapped mosfet VAS.
I try to keep the compensation as simple and light as possible, which is especially true with this particular design.
Pretty cool balanced front-end with 6DJ8 at the input and high-current bootstrapped mosfet VAS.
I try to keep the compensation as simple and light as possible, which is especially true with this particular design.
Attachments
Output pairs and Vbe multiplier are shown on top of the PCB instead of hanging underneath - that's just because Diptrace cannot draw them the right way 🙂 Use your imagination 😉
I'm interested. I wonder if there are enough guys interested here in North America to make some board orders worthwhile. I'm starting to get too many extra boards laying around.
Great work vallery,as usual, but not diy friendly pcb😱
Can you post dimensions,for price test😉
Can you post dimensions,for price test😉
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Since I mentioned the possibility of making the electrolytic caps SMD/through hole capable, I wait for that before asking for gerbers. I really appreciate all the hard work you do for us.
Blessings, Terry
Blessings, Terry
All of them are 5.5 x 3 inch = 139.7 x 76.2 mm. VFAs have got those cutouts on the sides 🙂
For 10 pieces cost is $44 except shipping cost.
I really appreciate all the hard work you do for us.
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I was thinking about them at some point - now I will definitely make them 😉
Good price for PCBs by the way. I think, my local workshop would charge around 50-70% more than that...
Chinese manufacturer.PCBWAY
Chosen to deliver by simple post, not fast courier, the final cost is much cheaper.
Chosen to deliver by simple post, not fast courier, the final cost is much cheaper.
Attachments
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