Cascoded jfet in X-BOSOZ?? - diyAudio
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Old 20th January 2006, 01:12 PM   #1
Magura is offline Magura  Denmark
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Default Cascoded jfet in X-BOSOZ??

I have set this special time aside for making a fool of myself

I simply can't figure if there woulod be a benefit of using the cascoded jfet approach for the X-BOSOZ ??

It should be fairly easy to adapt existing ones to accepting an extra board with the few extra parts, but I would like to understand why or why not to do that.

Cheers

Magura
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Old 20th January 2006, 06:49 PM   #2
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Yes, I believe it would work quite well.
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Old 20th January 2006, 08:12 PM   #3
steenoe is offline steenoe  Denmark
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Is it necessary to cascode the J-fets in a preamp?? I mean, if you adjust the railvoltages to an appropiate level for the Lovoltech J-fets, and maybe a few other component adjustments (I wouldnt know ) Wouldnt that be pretty good for a BosoZ variant? I can understand the cascoding thing for a poweramp, but for a preamp?? I asked something here, so you can keep track:
http://www.diyaudio.com/forums/showt...111#post819111
Metalman suggested the railvoltage adjustment.
I guess I put this time aside for making a fool of myself, too

Steen
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Old 20th January 2006, 08:24 PM   #4
moe29 is offline moe29  United States
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i think Grey said he had some thoughts on this, but i think we've
used up any free time he may have had to work on projects with
the group buy!

it seems like a lot of us were thinking the same thing at the same time...

BJFETZLS

BXJFETZLS

BXCCSJFETZLS


LOL!


...maybe once the parts get out there and things settle down a bit
we'll see something really cool in the Zen Line Stage bent.
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Old 20th January 2006, 08:30 PM   #5
steenoe is offline steenoe  Denmark
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Quote:
BXCCSJFETZLS
I can do better
"B-CC-CCS-X-JFET-ZLS" Beat that one

Steen
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Old 20th January 2006, 08:49 PM   #6
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Hi,

funny how suddenly everyone starts to think about J-Fets

I also had some thoughts about modifying the cs-ccs-x-bosoz:

please correct me if Im wrong

What you would need is a jfet wich can take around 80mA of current and some 10V (cascoded). The rest should be simple........

With the smaller jfets the output impedance of a bosoz type amp would be very high because of the bigger drain resistors needed to get the same voltage swing with less current.

Im not shure if the X-feedback can bring it down enough to be of practical use.

When using the lovoltechs you will have to look at the input capacitance so cascoding would still be a nice thing.


William
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Old 20th January 2006, 09:28 PM   #7
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I don't know if the Lovoltech's are the best JFET device for the BZLS. I think the 2SK389 would be the better JFET. Cascoded it should be able to handle the current level, and the cascode should also help with achieving a decent output impedance too. I've been mulling over this idea for about a year, but haven't got around to really looking properly at a design.

On the other hand, if the positive rail voltage is lowered to say 20V, the Lovoltech coud be used without needing the cascode.

Now what else can we do to make that acronym even longer ...
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Old 20th January 2006, 10:22 PM   #8
steenoe is offline steenoe  Denmark
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Quote:
Now what else can we do to make that acronym even longer ...
Not a whole lot I guess I agree with you on the Toshiba J-fet for low level signals! Maybe it would'nt be absolutely necessary to use those Lovoltech's everywhere! They are pretty fancy right now, but maybe not the best for a preamp!!
The Japanese J-fets like 2sk170 and dual sk389's has been long regarded as the best in handling low level's. But I guess this is not Nelson Pass country then? Except for RIAA's and the Aleph-J input circuit we didnt see a lot of those japanese J-fets in NP's amp's I think Still, it would be kind of cool with a BosoZ like J-fet preamp I will built one if I get the opportunity

Steen
BTW the J-fet used in the Aleph-J is a 2sj109 device. One of those small dual fet devices in a single house! Pretty cool
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Old 21st January 2006, 08:00 AM   #9
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Hi,

with the 2sk170 is the the max Idss is 20mA (v-spec). To bias it properly you would need something like 15mA or lower and max. 30-32V of positive rail. The drain resistors would be around 1k for 16V at the ouputs. The max. input voltage swing is then 0,2 - 0,3 volts maximum so you would need a voltage divider or pot at the input.

Just read the Borbely Audio articles (new frontiers part 2). There a BOSOZ with 2sk389 is featured along with the ad-and disadvantages.

william
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Old 23rd January 2006, 07:07 AM   #10
Magura is offline Magura  Denmark
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So the conclusion is that it would be worth doing, well that's the good part.

The bad part is that I still don't understand why ?

Cheers

Magura
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