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Old 18th October 2012, 09:05 PM   #331
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Quote:
Originally Posted by Joachim Gerhard View Post
There is no way around paralleling when you want to use J-Fets balanced unless you get yourself some Interfets. I can not second your opinion. I made several Fet stages, all parallel symmetric, some commercial, that have 4 x 2SJ74 plus 4 x 2SK170 that sound wounderful in the midrange and treble.
This is what I don't understand. Why wouldn't paralleling more BFs would equal having interfet from a gain standpoint?
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Old 18th October 2012, 09:19 PM   #332
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Because Gm doubles with each doubling of Fets. The Interfet inside may just be several JFets in parallel on the same chip.
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Old 18th October 2012, 09:24 PM   #333
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Prof. Faulkner in England was the first that had the paralleling idea in the 60th, it was with BJT at the time but equally valid with Fets. Noise impedance falls by 3dB with each doubling and Gm goes up by a factor of two.
Maybe you should study a book like this :Browse Results - SpringerLink
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Old 18th October 2012, 09:26 PM   #334
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Originally Posted by Joachim Gerhard View Post
Because Gm doubles with each doubling of Fets. The Interfet inside may just be several JFets in parallel on the same chip.
Right...so 10 pairs of bf would have 450mS gm so what I was saying what is the difference...beside matching and thermal tracking, between paralleling 10 pairs of BFs and having a pair of IF? I don't get it..
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Old 18th October 2012, 09:33 PM   #335
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The difference is that one is a BJt design and the other a Fet design so you can direct couple the Fet without problem plus self bias so no elcaps like in the Paradise .
The BJT version will likely be better in terms of 1/F noise so the bass is cleaner of noise.
Fans of Fet argue that this difference is swapped because of psycho acoustics ( A filtering ).i can hear the difference, ear on speaker, but in the listening space my Fet phonos are dead quiet. The BF862 is very good on 1/F noise by the way. Better then the 2SK170 plus lower input capacitance. It is certainly my first choice for low noise phono with only N-channel. how good the 1/F noise is on the Interfet i can not tell.
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Old 18th October 2012, 09:35 PM   #336
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I posted in the same moment you posted yours.
Maybe that book answers to my question...dunno!
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Old 18th October 2012, 09:37 PM   #337
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Ok, yes, paralleling 10 pairs of BF862 gives you one Interfet on the cheep.
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Old 18th October 2012, 09:42 PM   #338
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Quote:
Originally Posted by Joachim Gerhard View Post
The difference is that one is a BJt design and the other a Fet design so you can direct couple the Fet without problem plus self bias so no elcaps like in the Paradise .
The BJT version will likely be better in terms of 1/F noise so the bass is cleaner of noise.
Fans of Fet argue that this difference is swapped because of psycho acoustics ( A filtering ).i can hear the difference, ear on speaker, but in the listening space my Fet phonos are dead quiet. The BF862 is very good on 1/F noise by the way. Better then the 2SK170 plus lower input capacitance. It is certainly my first choice for low noise phono with only N-channel. how good the 1/F noise is on the Interfet i can not tell.
Maybe I wasn't clear. I wasn't asking what is the difference between the bjt paradise style and the jfets approach.
I was saying lets say I try the r7 schematic only n ch and use bf862. Would I be able to parallel 10 and get the gain needed? You said I can only do it with the IF part and I was asking why not with BFs?
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Old 18th October 2012, 09:44 PM   #339
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Originally Posted by Joachim Gerhard View Post
Ok, yes, paralleling 10 pairs of BF862 gives you one Interfet on the cheep.
Thanks you answered. So I can move forward and try out the only n ch design and paralleling 10 BFs and see if I can get up to the needed gain.
Do you think that this circuit has potential?
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Old 18th October 2012, 09:49 PM   #340
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I can not tell if it has potential.
To make it clear YOU do not want to parallel, so the Interfet is the only choice.
If you accept paralleling forget the Interfet. 10x BF862 is not the same but to a first order approximation extremely similar.
Yes, that paralleling solves the gain and the noise problem-
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