Borbely JFET buffer

[dorkus]

i built the Borbely JFET buffer, a very simple 2-transistor design. for more info, please check out my Son of Dork thread:

http://www.diyaudio.com/forums/showthread.php?postid=46275#post46275

sorry for the re-direct but i am trying to keep discussion in there for the purposes of the project. for a background on the circuit here is a very good thread:

http://www.diyaudio.com/forums/showthread.php?threadid=2281

p.s. thanks Freddie + Harry for all the great tips in that thread

 

[mikek]

this configuration is not i fear, due to borbely....it goes back to the tube era, when push-pull action could only be induced in this fashion as there are no complementary tubes....indeed it was used in all-BJT form by douglas self in his 1976 pre-amplifier article in electronics world..

 

[dorkus]

yeah, borbely calls it a "White cathode follower" in reference to the fellow who invented the topology for tubes i assume. he doesn't make any claims to coming up with the circuit concept, only the JFET implementation. read borbely's JFET papers, he is no hack.

 

[Nicke]

Have you compared this circuit to a regular JFET follower(type 15C i Borbely´s article) ?
These buffers looks really interesting...

Nicke

 

[Nelson Pass]

The circuit has indeed been around a long time. I pulled
up some old notes on it using 2SK170's (same device but
singles) with no source resistance.

The distortion figures I got were quite good, around .002%
across the band into 10 Kohm at ordinary signal levels ( 2
Volts or so) and +/-15 volt rails.

The distortion will deteriorate at a figure inversely proportional
to the load, so at 5K you get twice the distortion and so on.

 

[dorkus]

hello Mr. Pass,

that is what i am using, two SK170's. your distortion figures line up with what Borbely has measured. in my prototype, the sound is good but a little flat and electronic... perhaps a power supply fix (i'm using your pass-transistor regulator design, but i have a small parasitic oscillation in my voltage references) and parts upgrades will improve matters. it has a lot of promise, in many regards it is very transparent.

Nicke, i have not tried the other design in Borbely's article (Fig. 15C)... i might give it a shot later on for comparson purposes. interestingly, this "White cathode follower" design here was used in Borbely's original JFET SE preamp design, but the latest version has the tradtional 15C follower. maybe it is more transparent w/o the feedback cap?