I was looking at the JFET article on www.borbelyaudio.com, 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?
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
This circuit is from the The Audio Amateur 2/88 and I adapted from 15 volt to 24V rails. You might want to put an output cap since I don't know what the offset voltage is. I would use C2240s and A970 if possible.
H.H.
This circuit is from the The Audio Amateur 2/88 and I adapted from 15 volt to 24V rails. You might want to put an output cap since I don't know what the offset voltage is. I would use C2240s and A970 if possible.
H.H.
Ah, thanks. I'll give it a try.
But you wouldn't by any chance know what the input and output impedences are supposed to be with this circuit?
But you wouldn't by any chance know what the input and output impedences are supposed to be with this circuit?
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.
H.H.
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.
H.H.
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...
Here is an article by Walt Jung describing a discrete BJT buffer:
http://www.planetee.com/planetee/servlet/DisplayDocument?ArticleID=2800
http://www.planetee.com/planetee/servlet/DisplayDocument?ArticleID=2800
It is a bit overkill with MJLxxxx for a basicbuffer.
You will get some good results, when using ztx453/553 as output types biased around 20 - 30 mA... i think 1$/each.. As a start use them and 2sa970/2240 as input @ 2mA like Harry writes... Then you should be flying... Can be better but it is a really good start.
Sonny
You will get some good results, when using ztx453/553 as output types biased around 20 - 30 mA... i think 1$/each.. As a start use them and 2sa970/2240 as input @ 2mA like Harry writes... Then you should be flying... Can be better but it is a really good start.
Sonny
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.
Try something like 2n3904/6 as inputpair and MJL1302a/3281a as output pair.
R1 = R2 = 3.3ohm => idle current in MJL @ 82mA
R3 = R5 = 100ohm
R4 = R6 = 10k.
And a output cap to block ~100mV offset.
Should work. with something like -3dB@~3MHz
Sonny
R1 = R2 = 3.3ohm => idle current in MJL @ 82mA
R3 = R5 = 100ohm
R4 = R6 = 10k.
And a output cap to block ~100mV offset.
Should work. with something like -3dB@~3MHz
Sonny
Sure, I'll tell you how it goes.
But one more query. Would keeping the 2N3904/6 as the input pair degrade the sound that much? For I know they aren't the most linear devices...
But one more query. Would keeping the 2N3904/6 as the input pair degrade the sound that much? For I know they aren't the most linear devices...
Hi JoeBob, maybe try 2n5401/5551 instead, but they have higher parasitic caps and less currentgain than 2n3904/6.
They are more linear but will maybe generate more offset at a given input resistance compared to 2n3904/6.
Sonny
They are more linear but will maybe generate more offset at a given input resistance compared to 2n3904/6.
Sonny
Douglas Self has a set of very good articles based around the BJT, including unity gain emitter followers. Not exactly what you need, but very educational.
http://www.dself.demon.co.uk/
http://www.dself.demon.co.uk/
Joe Bob:
You need some better parts! I'll give you some....if you pay postage.
Just don't ask for a thousand or so.
Jocko
You need some better parts! I'll give you some....if you pay postage.
Just don't ask for a thousand or so.
Jocko
Jocko is right!!
There is a reason why whe all mention parts like zetex or toshiba.
But if you can't get other parts like 2nXXXX or BCXXX etc.. Then you have a little problem.. There must be some audio/video parts store in your country.. They will have parts like 2sc2240 2sa970.
Sonny
There is a reason why whe all mention parts like zetex or toshiba.
But if you can't get other parts like 2nXXXX or BCXXX etc.. Then you have a little problem.. There must be some audio/video parts store in your country.. They will have parts like 2sc2240 2sa970.
Sonny
B.J.T.
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.
H.H.
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.
H.H.
Attachments
cool!
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?
cheers,
dorkus
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?
cheers,
dorkus
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