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Old 1st October 2012, 09:40 PM   #1411
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Quote:
Originally Posted by scott wurcer View Post
A comment on the frequency selection, I don't think the non-common factors of the bins is that important. An IM tone only needs to fall in a bin not exactly on the bins center frequency to go into a tone bin rather than a "noise" bin.
Scott, is that with rectangular windowing?
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Old 1st October 2012, 09:44 PM   #1412
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1N4148 should be fine, I used the 2N4401/4403 in those plots. The 2N5550/5401 seems a little less good but the 2SA970/SC2240 look much better and very encouraging for lower closed loop gain versions.

The .1u caps in the input might not do anything anymore, a holdover from some experiments.
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Old 1st October 2012, 09:55 PM   #1413
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Guru Wurcer, we grovel at your feet.

But could you give the unwashed masses (us) an explanation of perhaps one of the simpler circuits you have deigned to show us? eg the one in your #1380 post.

In particular the reasons for

-all the cross-coupling
- certain diodes like Q12.
- what does Q15 do and how does it do it
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Old 1st October 2012, 11:20 PM   #1414
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is there any noise penalty for using actual diodes vs diode connected transistors? I was thinking of trying 2sk246/j103 or perhaps even some confused bisexual 2sk170 for both positions in the front end differential; any opinions?
I don't get it with the 2SK170.
Could you elaborate?
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Old 2nd October 2012, 12:06 AM   #1415
qusp is offline qusp  Australia
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Originally Posted by Wowozange View Post
I don't get it with the 2SK170.
Could you elaborate?
while k170 are not truly symmetrical, they are reversible to a degree, so you can use them as a P channel by reversing the pins. some say performance is fine like this and they are pretty much as close as many complimentaries, others disagree. they work and work quite well like this depending on parameters of the circuit, but whether the change will mean it functions here or not I cant say.

Last edited by qusp; 2nd October 2012 at 12:09 AM.
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Old 2nd October 2012, 12:19 AM   #1416
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Originally Posted by qusp View Post
while k170 are not truly symmetrical, they are reversible to a degree, so you can use them as a P channel by reversing the pins. some say performance is fine like this and they are pretty much as close as many complimentaries, others disagree. they work and work quite well like this depending on parameters of the circuit, but whether the change will mean it functions here or not I cant say.
I was thinking myself also at that property, and I wonder why nobody tried yet (AFAIK), leaving the search for complementaries in the dust. LSK389 is in this list? Because if it is, our life is much easier.
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Old 2nd October 2012, 12:20 AM   #1417
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Quote:
Originally Posted by qusp View Post
while k170 are not truly symmetrical, they are reversible to a degree, so you can use them as a P channel by reversing the pins. some say performance is fine like this and they are pretty much as close as many complimentaries, others disagree. they work and work quite well like this depending on parameters of the circuit, but whether the change will mean it functions here or not I cant say.
No way. JFETs are symmetrical, mostly, for an interchange of the leads labeled "source" and "drain", but that doesn't make them function like P channel parts. Life would be nicer if they did, although very confusing for solid state physics.
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Old 2nd October 2012, 12:22 AM   #1418
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Quote:
Originally Posted by qusp View Post
while k170 are not truly symmetrical, they are reversible to a degree, so you can use them as a P channel by reversing the pins. some say performance is fine like this and they are pretty much as close as many complimentaries, others disagree. they work and work quite well like this depending on parameters of the circuit, but whether the change will mean it functions here or not I cant say.
You may be able to use them as n channel
with source and drain switched, but not as
p channel.
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Old 2nd October 2012, 12:25 AM   #1419
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Where do you get the idea that there is asymmetry in the Toshiba 2SK170, 2SJ74 jfets? Are you confusing these with American jfets?
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Old 2nd October 2012, 12:45 AM   #1420
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aahhaa the distinction, sorry yes badly described and conceived. use them as reversed N channel in a differential then. completely right guys, thanks for the correction. 'acting as P channel', but not actually complimentary. so what does this mean for harmonics cancellation?

army of responders haha, OK so I havent bothered to actually do this in an amplifier due to lack of info, i've only read about it a few times. last time I read about it, there was mention of a small difference in.... Ciss perhaps, something, not completely the same one way or the other (for these jfets in particular). maybe John Curl can clarify, it was discussed in his blowtorch thread.


obviously the polarities of the supplies will be switched if you are using it in place of a Pchannel, will it actually work, or not? my google-fu was unable to get much info on it last time or this time, but I have seen it discussed several times on the forum.

doh morning head, now i'm not sure at all... was a throwaway line to throw a cat amongst the pigeons to maybe get some into from people who know, its so rarely mentioned and I have a crapload of k170, not many j74

Last edited by qusp; 2nd October 2012 at 01:05 AM.
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