I am new to posting here ('cept for selling stuff) but am ready to take the plunge!
been lurking for ages.
I have scoped out the OPA 2134 for my first stage. total gain (over several stages) must be ? 80? There seems to be quite a range of problems when working at 1 meg input. (I got, allegedly, 2.0 mV @ 1 megohm to amplify)
The OPA spec sheet says to correlate your input imp with the resistance in your feedback loop, but that might mean 1.5 meg//250K (to ground) which seems a bit out of whack.
Also it would appear difficult to get much gain in this stage, also. that i could live with, but 9 or 10 sure would be nice.
Do i need a Jfet or complementary Jfet input buffer here?
I have no design skills to speak of --just cookbook competence.
Advice, please. I'll happily use a 6DJ8 if I have to. Would i know what Im doing? No.
I am also correct that the inverting input is out of the question?
been lurking for ages.
I have scoped out the OPA 2134 for my first stage. total gain (over several stages) must be ? 80? There seems to be quite a range of problems when working at 1 meg input. (I got, allegedly, 2.0 mV @ 1 megohm to amplify)
The OPA spec sheet says to correlate your input imp with the resistance in your feedback loop, but that might mean 1.5 meg//250K (to ground) which seems a bit out of whack.
Also it would appear difficult to get much gain in this stage, also. that i could live with, but 9 or 10 sure would be nice.
Do i need a Jfet or complementary Jfet input buffer here?
I have no design skills to speak of --just cookbook competence.
Advice, please. I'll happily use a 6DJ8 if I have to. Would i know what Im doing? No.
I am also correct that the inverting input is out of the question?
Long delayed thanks to Juma! I see that Q8 is set up as a current source??
Done some more reading in Horowitz et al. I had previously no real notion of Jfets.
Am I to assume that distortion is not an issue? Normally i think of any amplifier stage as being enclosed in a feedback loop--
My text sez "you can build discrete Jfet stages, but normally one looks at Op-amps that use Jfets in the input stage." Hello TL072?
Done some more reading in Horowitz et al. I had previously no real notion of Jfets.
Am I to assume that distortion is not an issue? Normally i think of any amplifier stage as being enclosed in a feedback loop--
My text sez "you can build discrete Jfet stages, but normally one looks at Op-amps that use Jfets in the input stage." Hello TL072?
Yes, Q8 represents a working load for Source Follower Q7.
Not at all.
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