The background for this preamp - Passive line stages and the TCJ stepped attenuator & NO-Gain/No-Pain Tube Line Stage
This is my 2nd attempt with this design. The 1st attempt ended poorly ! 94v @ 15ma & 12.6v @ 400ma. Voltage multiplier for the b+ & +/- 15v for the servo / filaments. Start up with 45 sec delay plus shut down muting. Khozmo 10k ladder attenuator. 6 layer PCB with 2 ground planes. No dc protection..
currently using this preamp with my 5w JJ 2a3-40 SET.
Dwight
This is my 2nd attempt with this design. The 1st attempt ended poorly ! 94v @ 15ma & 12.6v @ 400ma. Voltage multiplier for the b+ & +/- 15v for the servo / filaments. Start up with 45 sec delay plus shut down muting. Khozmo 10k ladder attenuator. 6 layer PCB with 2 ground planes. No dc protection..
currently using this preamp with my 5w JJ 2a3-40 SET. Dwight
Attachments
Depan,
Here you go ! 1st attempt with a servo. I still have much to Learn. All measurements are on a 16bit Picoscope. I use a choke + gyrator for the b+. Servo cutoff @ 1.6hz. I attempted a servo cutoff @ 0.33hz but the baseline was unacceptable. I need to filter the B+ more on the next version so I can lower the servo cutoff. @1.6hz there is some phase error @ 20hz. Looks like I am using the servo to filter power supply noise.. not sure that is a great accomplishment 😕
1st pic - b+ ac coupled, output dc coupled to show offset. Scale : 20mv / 2s
2nd pic - square wave, 1khz
3rd pic - FFT turned up to show higher order harmonics.
Here you go ! 1st attempt with a servo. I still have much to Learn. All measurements are on a 16bit Picoscope. I use a choke + gyrator for the b+. Servo cutoff @ 1.6hz. I attempted a servo cutoff @ 0.33hz but the baseline was unacceptable. I need to filter the B+ more on the next version so I can lower the servo cutoff. @1.6hz there is some phase error @ 20hz. Looks like I am using the servo to filter power supply noise.. not sure that is a great accomplishment 😕
1st pic - b+ ac coupled, output dc coupled to show offset. Scale : 20mv / 2s
2nd pic - square wave, 1khz
3rd pic - FFT turned up to show higher order harmonics.
