Looking at the Nelson's schematic from post 1:
What could be the outcome of flipping the S-D connection on the buffer and take the feedback from after the output caps? Still a source follower connection.
Of course the idea is to get rid of the input cap.
Would this result in a higher distortion?
Should we need to change to a N Jfet?
What could be the outcome of flipping the S-D connection on the buffer and take the feedback from after the output caps? Still a source follower connection.
Of course the idea is to get rid of the input cap.
Would this result in a higher distortion?
Should we need to change to a N Jfet?
apassgear said:Looking at the Nelson's schematic from post 1:
What could be the outcome of flipping the S-D connection on the buffer and take the feedback from after the output caps? Still a source follower connection.
Of course the idea is to get rid of the input cap.
Would this result in a higher distortion?
Should we need to change to a N Jfet?
If you flip the SD you would necessarily need to go to an N, but
also the feedback would become positive due to the polarity
inversion of the input device. Still, with some re-arrangement,
you could get something like what you want.
Hi,
Say that you need a line stage buffer...
Perhaps you may want to connect it to your Zen v4 (or some other variation)
Or just want to have a general purpose buffer....
Say that you want to use Jfets...
say that you don't have P-channel Jfets handy...
say that want to use 2sk170 BL
Can this circuit work, as is?
(cut from: http://www.borbelyaudio.com/adobe/ae699bor.pdf)
Vix
Say that you need a line stage buffer...
Perhaps you may want to connect it to your Zen v4 (or some other variation)
Or just want to have a general purpose buffer....
Say that you want to use Jfets...
say that you don't have P-channel Jfets handy...
say that want to use 2sk170 BL
Can this circuit work, as is?
(cut from: http://www.borbelyaudio.com/adobe/ae699bor.pdf)
Vix
Attachments
Thinking of using Buffer for Blues
Quick background: I’ve built the Zen V1-V4 p2p just one channel to experiment and learn. I’m ready to build two V4 channels and install in chassis.
I’m at a point where I could easily adjust the board layout on V4, changing the ZVP3310 P channel Mosfet to the 2sj74 P channel JFet. The original article lists several advantages of the P channel follower over the N channel follower.
First, the input can be direct coupled, as it operates at ground potential, eliminating input capacitor and bias circuit.
Second, it is self-adjusting in the sense that the Source will operate at +Vgs where Vgs is the Gate to Source voltage for the Mosfet, or about 3.5 volts. The amount of current supplied by the resistor is not critical, and can be quite high if desired, as the Mosfet will only dissipate that current time the Vgs value. For the ZVP3310 we will be using, you could run it as high as 50 mA, which is a lot
Third, the P channel non-linearity will tend to operate in opposition to the N channel distortion of the gain Mosfet, giving some distortion cancellation. You can adjust this cancellation a bit by adjusting the bias current and loading of the P channel device.
Fourth, because the input system is at virtual ground, we can swing all the drive current we want without being concerned about the voltages across the input device, since it will be held very close to the constant Vgs of the P channel input. No Miller Effect, hardly any gain or capacitance modulation, better performance.
I’m wondering if these advantages hold true for the P channel Jfet as well as the P channel Mosfet. I notice that the circuit is not direct coupled, using a 1uf capacitor at the input.
Thanks for your advice.
Quick background: I’ve built the Zen V1-V4 p2p just one channel to experiment and learn. I’m ready to build two V4 channels and install in chassis.
I’m at a point where I could easily adjust the board layout on V4, changing the ZVP3310 P channel Mosfet to the 2sj74 P channel JFet. The original article lists several advantages of the P channel follower over the N channel follower.
First, the input can be direct coupled, as it operates at ground potential, eliminating input capacitor and bias circuit.
Second, it is self-adjusting in the sense that the Source will operate at +Vgs where Vgs is the Gate to Source voltage for the Mosfet, or about 3.5 volts. The amount of current supplied by the resistor is not critical, and can be quite high if desired, as the Mosfet will only dissipate that current time the Vgs value. For the ZVP3310 we will be using, you could run it as high as 50 mA, which is a lot
Third, the P channel non-linearity will tend to operate in opposition to the N channel distortion of the gain Mosfet, giving some distortion cancellation. You can adjust this cancellation a bit by adjusting the bias current and loading of the P channel device.
Fourth, because the input system is at virtual ground, we can swing all the drive current we want without being concerned about the voltages across the input device, since it will be held very close to the constant Vgs of the P channel input. No Miller Effect, hardly any gain or capacitance modulation, better performance.
I’m wondering if these advantages hold true for the P channel Jfet as well as the P channel Mosfet. I notice that the circuit is not direct coupled, using a 1uf capacitor at the input.
Thanks for your advice.
Blues said:
Um Blues, I don't really have a favorite anything when it comes to DIY gear. This is it man, it will be my first complete amp when I put two channels together. So you've put things in perspective for me. As much fun as I'm having researching JFET buffers, I need to build the amp with ZVP3310 as a baseline and the retrofit JFET buffer in the future.
Thanks,
Kevin
Nelson Pass said:
As I've indicated, I've been trying the new power JFETs parts in all
the old familiar places, and it appears that we will have to opportunity
to revisit most of them with improved performance.
It's very much anticipated Mr. Pass. Thank you once more for your generosity.
Will we see a complementary part soon?
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