Scott,
Seems indeed I am missing something here.
Seems Wahabs Sim misses something as well.'Mine in Tina/Ti also came up squirely.
If you measure 0.35nV|/Hz then that is what you measure.
Maybe I spend too much time on transformers and not enough on cap's back at Uni. I have gotten this "Cap's and noise" thing wrong twice, seems I misremember an equation (it's possible).
The reason I never questioned the theory was that we did need rather big value input coupling cap's in our transformer coupled Mike Pre's, which where running at rather much more level and source impedance than your circuit. Probably BJT Base noise current related, J-Fet's don't have that.
Well, I learned something that will be useful in future, as it opens up more options in how to design things. Thank you.
I can already "see" a rather cute "head-amp" design for a future project...
Ciao T
Seems indeed I am missing something here.
Seems Wahabs Sim misses something as well.'Mine in Tina/Ti also came up squirely.
If you measure 0.35nV|/Hz then that is what you measure.
Maybe I spend too much time on transformers and not enough on cap's back at Uni. I have gotten this "Cap's and noise" thing wrong twice, seems I misremember an equation (it's possible).
The reason I never questioned the theory was that we did need rather big value input coupling cap's in our transformer coupled Mike Pre's, which where running at rather much more level and source impedance than your circuit. Probably BJT Base noise current related, J-Fet's don't have that.
Well, I learned something that will be useful in future, as it opens up more options in how to design things. Thank you.
I can already "see" a rather cute "head-amp" design for a future project...
Ciao T
My avatar for now, St. Theresa, mystic and self flagelant. I picked a non-relgious quote to stay within forum rules.
Scott, is the function of C1 primarily to reduce a last bit of battery noise, or is it to provide a lower A.C. source impedance to the circuit than can the battery?
Yes, I have to admit that you might be right about the lf noise, Scott. Good trick, but I would use PPS and not ceramic for the input cap, if I were you.
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Thank you.
Man, in these mystic circles, algolagnia is supposed to be related with (and driven by) “love”.
Here among the audiophiles it seems to be related with “lust” (in case you meant to imply something 😀 )
George
Well I worry about noise from chemical activity at discharge, this is well known for flooded lead acid batteries but information is scant in general. Alkaline seem pretty good but here I tried NIMH rechargables. Nakamichi made a fairly low ouput mike with this circuit and a mercury battery with much less than 1000uF, the current substitute for folks that want to stay original is a hard to get 9V tubular alkaline battery and no one complains about noise. The battery noise does see some PSRR since it's at the drain. The battery is basicly a huge F capacitor so the argument as to weather the capacitor is in the signal path could be entertaining.
<nist.gov/general/pdf/1133.pdf>
NIST Manuscript Publication Search - 23k
I can't get a link to the .pdf that works.
Enter "nist 1133.pdf " into google, the first entry gets me the pdf file.
The title is "MEASUREMENT OF VOLTAGE NOISE IN CHEMICAL BATTERIES"
Thanks, I guess no worries they had to make a -200dBV system to find much. I wish I had this a few years ago in an arguement over a battery's shot noise supression. If I do any more tests I'll move to the Pass forums.
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Please keep me informed, I'm seriously interested in this stuff.
It's kinda surreal when I read:
> Still, I think that this problem of noise with the LM317 has now been
> well covered by outside sources and proves that the problem exists
> outside my imagination. (thank goodness) '-)
when it was published in '95 that the 317 is 70 dB worse than a battery.
Gerhard
I think he meant the fancy oscillators. BTW if you flip the battery and make a second one with a PFET the outputs of the two remain ground referenced and push-pull when the inputs are connected together. Just in case it went unnoticed the simplest common source stage usually has no PSRR (RTO).
Well that was stupid, too many inverted ways of looking at things the outputs stay in phase.
Hello Scott
I think Wahab and Thorsten are using bad Jfet spice models in their respective simulations , is it possible to tell us where and how you got the IF3601 models from. I have asked Interfet for them but I have not received them as yet.
Regards
Arthur
I think Wahab and Thorsten are using bad Jfet spice models in their respective simulations , is it possible to tell us where and how you got the IF3601 models from. I have asked Interfet for them but I have not received them as yet.
Regards
Arthur
Pheonix, hope for the best, but I would not necessarily expect samples of this part (IF3601) from Supertex, today. Maybe 5-10 years ago, when I got mine.
I made them myself, see earlier posts. The proceedure is in the Linear Audio article P2. You start with Vgs and Id at two somewhat spaced points and using the basic JFET equations you can get the beta (transconductance parameter) and Vp this will give you what you need, remember the beta is a property of the FET in general (all IF3601's have a beta of ~.2). The capacitances are on the datasheet and their voltage coefficient is physics based (same sort of for all FET's).
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Hi,
I simulated without J-Fet actually and some of my control sim tests gave results that where unexpected and seriously paradoxical (like adding the RC after a resistive source with appreciable resistance dropped the noise from the source!).
So I gave up and simply decided to go with Scott's measurements.
Ciao T
I simulated without J-Fet actually and some of my control sim tests gave results that where unexpected and seriously paradoxical (like adding the RC after a resistive source with appreciable resistance dropped the noise from the source!).
So I gave up and simply decided to go with Scott's measurements.
Ciao T
OH, I doubt if they have a good SPICE model for the IF3601. I just promised them that YOU would furnish one to them for some samples.
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