BJT Buffer Circuits?

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I was looking at the JFET article on, and noticed the source-followers shown and was thinking of using such a circuit in a "buffered passive pre-amp" so to speak. When I fell across HarryHaller's thread on his passive preamp and he said he was thinking of doing something along those lines as well.

I was looking at the 16b diagram. But I was thinking, could such a thing be done with BJTs? Or would the input impedence be too low? I'd rather use BJTs for I have some on hand and I'm cheap and all.

Or if annyone knows of simmilar circuits which use BJTs and run off close too +/- 24v, do let me know.

Or if BJTs are not suited for this at all, are MOSFETs more so?
BJT buffer

The input impedance will depend on the Hfe of the transistors and the load that the buffer is driving. Wiith the SC2240 and A970s I would estimate it to be several megaohms. I would use transistors with Hfe greater than 200 at 2 mA. Output impedance should be less than 25 ohms.

The diagram you posted had originally 2N3904's and 2N3906's, but could one use higher power devices (even though it'd be a waste of money, I already have them) like MJL21193/MJL21194 or MJL3281A/MJL1302A. They only have their hfe listed for 8A and 16A, so I dunno. I could always go buy some little small signal transistors, but was wondering if these could do the job, why bother...
I mean, the thing is I can only buy 2N3906s and 2N3904s and simmilar locally. And since I have some MJLXXXXXs, I know it's overkill, but would it work? I just don't want to have to wait for a mail order shipment from the states (but, if I have to, I have to.

Buffer with Jfet Transistors. Jfet buffer with Toshiba K170s biased at 4 mA. Borbely topology based on White cascode follower. Point to point wiring with four nines silver with loose teflon sleeving. Corning RN60D resistors, Sidereal, Wondercap, Panasonic HFQ, and Rifa caps. Silver soldered.



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hi harry,

well it looks like it's been months since anyone posted in this thread but i was just doing a search for "JFET BUFFER" and i came up with your little baby here. could be very useful in Son of Dork! how does it sound? it is capacitor coupled obviously but do you find the strengths of the circuit overcome the coloration of the caps?

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