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Old 2nd October 2012, 10:16 AM   #1431
SY is offline SY  United States
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Quote:
Originally Posted by staccatiss View Post
You mention the "inductor trick". What is that?
See the input stage of the Jensen 990.
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Old 2nd October 2012, 11:05 AM   #1432
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Originally Posted by qusp View Post
'using as' P channel (acting as, not changing the atomic structure, didnt I make this correction already?)


re J113: hmm no I dont think thats the fet, i'm going to have to do some more searching to see where this was discussed, one of the many threads lamenting the lack of P-channels
You may have been lost in the complementary discussions. It is typical that many devices are called complemets but in actuality they are not exact compliments. Euvl has done measurements and worked with source resistors etc. to generate more complimentary behaviour in some circuits. I beleive even after these tweaks, you are sill left with non equivalent input Cs.
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Old 2nd October 2012, 12:26 PM   #1433
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> perhaps Patrick may have mentioned it....

On 2 occassions, including a recent pdf which showed measurements to illustrate that all Toshiba, Sanyo and 2N5xxx JFETs that we have tested are all D-S reversible. Don't ask me to find the link for you .......




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Old 2nd October 2012, 02:30 PM   #1434
qusp is offline qusp  Australia
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Originally Posted by flg View Post
You may have been lost in the complementary discussions. It is typical that many devices are called complemets but in actuality they are not exact compliments. Euvl has done measurements and worked with source resistors etc. to generate more complimentary behaviour in some circuits. I beleive even after these tweaks, you are sill left with non equivalent input Cs.
nope, its not that simple i'm aware that some compliments are more complimentary than others, the toshiba (particularly the MOSFETS) are better than most, but still many require asymmetric degeneration, to bring better, but not complete symmetry

Quote:
Originally Posted by EUVL View Post
> perhaps Patrick may have mentioned it....

On 2 occassions, including a recent pdf which showed measurements to illustrate that all Toshiba, Sanyo and 2N5xxx JFETs that we have tested are all D-S reversible. Don't ask me to find the link for you .......




Patrick
aha!! right OK I knew one of you had been doing some work in this area and I had an inkling it may have been you, perhaps in the initial thread for your mini jfet opamps. no worries that'll hopefully be enough info to find it. thankyou, I thought I was losing it
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Old 2nd October 2012, 02:38 PM   #1435
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Quote:
Originally Posted by flg View Post
You may have been lost in the complementary discussions. It is typical that many devices are called complemets but in actuality they are not exact compliments. Euvl has done measurements and worked with source resistors etc. to generate more complimentary behaviour in some circuits. I beleive even after these tweaks, you are sill left with non equivalent input Cs.
I compliment those who use "complement".

Yes, because P-silicon has a lower mobility of majority charge carriers than does N-silicon, holes versus electrons, P devices with the same transconductance and comparable breakdown voltages must be larger than N devices. Due to those larger areas the capacitances are higher, so at high frequencies they will not be complementary --- the same behavior except for a polarity inversion. At audio frequencies, for most applications it's not as much of a limitation.

Toshiba in particular went to great lengths to make a series of very good P-channel devices, the most famous the 2SJ74, whose obsolescence is much lamented. Rumor has it that Linear Integrated Systems is working on a replacement. Wish them well.
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Old 2nd October 2012, 02:50 PM   #1436
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And postscript: it's important to distinguish the drain - source reversibility of JFETs from the complementarity of specific N devices and P devices. All JFETs are, to a large extent, reversible, and some manufacturers even mention this by saying that they are symmetrical. No JFETs change their effective polarity under a swap of drain and source leads.

I've verified experimentally the reversibility of the drain - source connections of the Toshiba dual N device, the 2SK2145, which is apparently a two-chip dual using 2SK117 devices, probably plucked from adjacent positions on a wafer. Since they elected to hard-wire the two channels and use only a 5 lead package, the reversibility helps to make the part a lot more versatile. I suspect Toshiba just expected us to use it as a conventional differential pair. On earlier single-chip devices like the obsolete 2SK389, the two "source" leads were brought out, as well as a substrate connection, in a seven-lead package.
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Old 2nd October 2012, 04:00 PM   #1437
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Originally Posted by fas42 View Post
Just to let people know I've whipped up an LTspice version of Scott's 2nd, complimentary version so no-one really needs to duplicate this (the easiest one first!), and it works, how amazing, ! Of course, not being an amp designer, nowhere near it, took me a little bit to realise that pfets were need -- still need to insert real, reasonably accurate models of the actives, so won't post for the moment ...

Something to play with in an idle moment ...

Frank
Remember to trim R18 to set the OS standing current, 8mA is enough for non-switching behavior into 600 Ohms 20V p-p
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Old 2nd October 2012, 04:11 PM   #1438
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Originally Posted by kgrlee View Post
In particular the reasons for

-all the cross-coupling
- certain diodes like Q12.
- what does Q15 do and how does it do it
The cross-coupling just gets the phases right some times it's just an artifact of order drawn.

Q12, Some of the diodes just get the voltage to match across the output of diff-pairs, it can be a small effect.

Q15 just samples a voltage to drive the current sources for the output stage, this saves some devices and keeps all currents set by the input stage. It also provides a slew boost to the output devices, not much benefit here at band limited audio but it makes prettier square wave pictures.

Sorry about the bad JPEG conversion that dropped some 1 pixel wide lines, post #1387 has a schematic that caught this.
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Old 2nd October 2012, 04:17 PM   #1439
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Originally Posted by bcarso View Post
Toshiba in particular went to great lengths to make a series of very good P-channel devices, the most famous the 2SJ74, whose obsolescence is much lamented. Rumor has it that Linear Integrated Systems is working on a replacement. Wish them well.
I saw John Hall at the Analog Affictionados Party. They sent samples of all grades and more than one lot was represented, so it looks like there is progress. I do worry in that John is WAY past retirement and hope there are folks to carry on.
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Old 2nd October 2012, 04:40 PM   #1440
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This is my simulation with no transistor selection, just took it from LTspice librery, exept jfets.
I moved the compensation cap and distortion halved.
dado
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