Jfet/bipolar PCB and Schematic (finaly)

[peranders]

Sonny, I just checked the schematic. The input stage with JFET's seems very

100 ohms in drain resistors and 2 kohms at the sources???? OK you have a folded cascode but still?

In order to get low noise, shouldn't R1 and R2 be of a low value or just a wire?

[sonnya]

Yes you are right. I will go for 100R - 200R myself.

I cant remember why it was set at 2K.. it must be an mistake. I do not have the board right here, but i do think i have set it for 200R => GPBW of ~8MHz.

[sonnya]

Read my first page......

Originally posted by sonnya
First the schematic...

Match Q1 and Q2 (J111 - J113) to a current difference of 100uA when measuring IDSS.

Change R1 and R2 to 470R.
Change R3, R4, R14 and R15 to ~ 200R
Change R10 and R13 to 500R (multiturn)
Change R18 to 2K0

Set ID on Q3 to 6 - 8 mA.

Set ID on Q6 to ~ 6 mA.

Set ID on Q2 o ~ 2 mA.

Then it should idle around 30 - 35 mA.

The feedback is outside the PCB. Remember short tracks!.

Slewrate is ~+/- 75V/usec.

at unitygain -3dB is ~4MHz.

It is stable with 1nF load (No overshoot! at squarewave signal).

Try it!, i have mounted it inside my CD player and it have in my system better treble perfomance than OP275GP when driving
1K || 220pF load.

Sonny

[WaltJ]

Hi Sonnya, Thanks for the links; two were new to me! Please find also below a link to a article by Walt Jung. He uses a similar buffer you do but with LED's in the current sources! GaAsP is just chemical shorthand for the chemical elements of gallium, arsenic and phosphorus used in the semiconductor. It looks very scientific but it is just a normal red LED [I am a chemist BTW] http://www.planetee.com/planetee/se...?ArticleID=2800

This link and the other 'Walt's Tools and Tips' columns are apparently gone into the ether, from an ED website purge.

I have posted the 4 part ED op amp series on my website page under "Links, PDFs". This includes the discrete buffer referenced above with an LED Isource.

See: http://home.comcast.net/~walt-jung/wsb/


Enjoy.

wj

[peranders]

Walt, your articles _can_ be found but I don't know the logic beacuse they can't be found through search.

http://www.elecdesign.com/Globals/Pl...tent/2800.html

I have now tried and tried. Why aren't "walt Jung" any good as search words? I have tried other words too without success.

[sonnya]

Hi Walt.

Nice to see you in the forum.

And your work back on your homepage.