john curl said:
like Sansui differential diamond ? perefct symetry.
Philippe (now guessing, and hoping to learn later)
Not like the Sansui circuit but looking more like an H, two source resistors are linked together between the N and the P FET. The junction of these 2 resistors is coupled to the other pair's junction by the aforementioned SINGLE DEGENERATION RESISTOR, which, in combination with the outputload defines the stagegain.
Uli
Uli
Assumnig the 2SK389 has indeed an admittance of 20mS a 10R resistor reduces drain current to about 5/6 Idss. This is a current area, where the FET is very linear without drawing a significant amount of gate current (about 1 - 1.5 pA, when the DS voltage is not too high).
Uli
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Edit: the admittance depends heavily on drain current. To achieve a certain amount of gain without making the outputresitance impracticably high, it's sometimes necessary to pump up the drain current. Maybe a reason to use violet FETs, to gain some linear voltage swing across the load resistance.
Uli
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Edit: the admittance depends heavily on drain current. To achieve a certain amount of gain without making the outputresitance impracticably high, it's sometimes necessary to pump up the drain current. Maybe a reason to use violet FETs, to gain some linear voltage swing across the load resistance.
I have the problem, that in simulation with LTSpice a higher Rsource gives me qiute lower distortion than the mentioned 10R (80R, in my case). This with a variation of the (assumed) BT-circuit.
The models of the 2SK170 and 2SJ74 seem not to reflect gate leakage current as well.
Am I the only one seeing this effect?
Rüdiger
The models of the 2SK170 and 2SJ74 seem not to reflect gate leakage current as well.
Am I the only one seeing this effect?
Rüdiger
i'd suspect there are not any good ltspice models for those (or any?) jfets.
i wish there were ...
mlloyd1
i wish there were ...
mlloyd1
Onvinyl said:Pavel, I'm so happy you think so...
... however, do you care to elaborate?
Rüdiger
Hi Uli,
I believe I downloaded them from here; anyway:
.model J2sk170 NJF(Beta=59.86m Rs=4.151 Rd=4.151 Betatce=-.5 Lambda=1.923m Vto=-.5024 Vtotc=-2.5m Cgd=20p M=.3805 Pb=.4746 Fc=.5 Cgs=25.48p Isr=84.77p Nr=2 Is=8.477p N=1 Xti=3 Alpha=10u Vk=100 Kf=111.3E-18 Af=1)
.model J2sj74 PJF(Beta=92.12m Rs=7.748 Rd=7.748 Betatce=-.5 Lambda=4.464m Vto=-.5428 Vtotc=-2.5m Cgd=85.67p M=.3246 Pb=.3905 Fc=.5 Cgs=78.27p Isr=129.8p Nr=2 Is=12.98p N=1 Xti=3 Alpha=10u Vk=100 Kf=26.64E-18 Af=1)
Rüdiger
I believe I downloaded them from here; anyway:
.model J2sk170 NJF(Beta=59.86m Rs=4.151 Rd=4.151 Betatce=-.5 Lambda=1.923m Vto=-.5024 Vtotc=-2.5m Cgd=20p M=.3805 Pb=.4746 Fc=.5 Cgs=25.48p Isr=84.77p Nr=2 Is=8.477p N=1 Xti=3 Alpha=10u Vk=100 Kf=111.3E-18 Af=1)
.model J2sj74 PJF(Beta=92.12m Rs=7.748 Rd=7.748 Betatce=-.5 Lambda=4.464m Vto=-.5428 Vtotc=-2.5m Cgd=85.67p M=.3246 Pb=.3905 Fc=.5 Cgs=78.27p Isr=129.8p Nr=2 Is=12.98p N=1 Xti=3 Alpha=10u Vk=100 Kf=26.64E-18 Af=1)
Rüdiger
A 10 Ohm Source resistor gives lower Iq and higher noise than 51 Ohms? One of us isn't understanding the other, I guess. Probably me.
Unless the rules of the game have changed (wouldn't be the first time), there used to be--what?--six different noise mechanisms for resistors (quoting from memory, as I'm at work). If I recall correctly, one of the inescapable ones was that as the resistance rose, so did the noise.
And if higher resistance at the Source results in lower Iq, then I've really lost sight of what's going on, because just last night I was using a 2N5457 with a resistor under its tail to make a quick-'n-dirty current source to sort some optocouplers.
It's been a long day...and if I'm this far out of sync with the world, then it's been even longer than I thought...
Grey
Unless the rules of the game have changed (wouldn't be the first time), there used to be--what?--six different noise mechanisms for resistors (quoting from memory, as I'm at work). If I recall correctly, one of the inescapable ones was that as the resistance rose, so did the noise.
And if higher resistance at the Source results in lower Iq, then I've really lost sight of what's going on, because just last night I was using a 2N5457 with a resistor under its tail to make a quick-'n-dirty current source to sort some optocouplers.
It's been a long day...and if I'm this far out of sync with the world, then it's been even longer than I thought...
Grey
Grey, it is again a language problem. 51 ohms gives low Iq and slightly higher noise. 10 ohms gives optimum Iq, BUT not optimum degeneration, so you have to add the 5th resistor of 200 ohms or so.
My previous post perhaps wasn't as clear as it should have been. Oh well, I'll blame it on the germs.
Okay, so lemme see if I've got this...each open endpoint of an H represents a 10 Ohm resistor and goes to a JFET's Source--the crossbar is the 200 Ohm, yes?
Grey
Okay, so lemme see if I've got this...each open endpoint of an H represents a 10 Ohm resistor and goes to a JFET's Source--the crossbar is the 200 Ohm, yes?
Grey
Ah, so...much better.
I've used a--for want of a better term--a sideways H, with each Source in closer communication (say, a 10 Ohm resistor to each Source of the same differential--thus there's 20 Ohms between each of the two Sources), then a resistor connecting each midpoint between the N-ch & P-ch differentials. But I haven't tried your way. I can see that it might be lower distortion, but does it phase split as well--meaning if I put a signal in the left side of the circuit, does the right side generate something like a reasonable out of phase signal?
Grey
I've used a--for want of a better term--a sideways H, with each Source in closer communication (say, a 10 Ohm resistor to each Source of the same differential--thus there's 20 Ohms between each of the two Sources), then a resistor connecting each midpoint between the N-ch & P-ch differentials. But I haven't tried your way. I can see that it might be lower distortion, but does it phase split as well--meaning if I put a signal in the left side of the circuit, does the right side generate something like a reasonable out of phase signal?
Grey
John can correct me if I'm wrong, but I believe that his circuits use the "sideways H" that you describe.
Okay, I get it...the two of you are ganging up to torment me...
(Wouldn't it be great to see the e-mails that are, at this very moment, flying between California and Colorado? John sez, "I'll hit 'im high." Charles responds, "Great idea! I'll hit 'im low. Between us we can reduce him to a quivering blob of protoplasm in no time!")
Charles,
Is the scheme I outlined above what you were describing to me a week or two ago? I was having trouble figuring out which way your H went.
Grey
(Wouldn't it be great to see the e-mails that are, at this very moment, flying between California and Colorado? John sez, "I'll hit 'im high." Charles responds, "Great idea! I'll hit 'im low. Between us we can reduce him to a quivering blob of protoplasm in no time!")
Charles,
Is the scheme I outlined above what you were describing to me a week or two ago? I was having trouble figuring out which way your H went.
Grey
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