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Old 22nd March 2011, 02:46 AM   #151
NYCOne is offline NYCOne  United States
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Default Best voltage for the base of the cascode transistor

I've been on a hiatus - real life work is busy. I'm getting some time to play again and was wondering the best target voltage for the base of the cascode transistor. Many have been using an equal voltage divider. With 24V rails that's a ~12V base. I would guess the "sweet spot" voltage is well known for these transistors. Put another way, should I shoot for a 12V base, 8V, 6V?
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Old 22nd March 2011, 05:18 AM   #152
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with 24V rails I dont think there's any need to cascode the jfet
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Old 22nd March 2011, 12:04 PM   #153
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Quote:
Originally Posted by tinitus View Post
with 24V rails I dont think there's any need to cascode the jfet
but there is always a joy in complicating things
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Old 22nd March 2011, 04:59 PM   #154
NYCOne is offline NYCOne  United States
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I'm going back to what NP said - there's always a benefit to a cascode. The 24V rail was a demonstration point, I intend to use a few Xformers until I resolve which I like. Since changing resistors is easy, I thought I'd ask what experience folks have had with cascodes. The PCB is done and populated, the only issue is what voltage divider to use. Or as I put in my last post, what is the sweet spot for the JFETs? I'd think someone has done this before.

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with 24V rails I dont think there's any need to cascode the jfet
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Old 22nd March 2011, 05:36 PM   #155
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Read more. 8Vds iMO
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Old 22nd March 2011, 05:47 PM   #156
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Quote:
Originally Posted by NYCOne View Post
what is the sweet spot for the JFETs?
You may find these links useful
http://www.firstwatt.com/pdf/art_sweet_spot.pdf
http://www.firstwatt.com/pdf/art_zv9.pdf
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Old 24th March 2011, 03:14 AM   #157
NYCOne is offline NYCOne  United States
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Maybe it wasn't obvious in my post, I was referring to these articles and Nelson's comments in the forum when I posed the question in this thread. I may have missed the portion of the articles where they show 2SK170BL and 2SJ74BL cascode results, but that's what I was hoping to elicit.

Basically, assuming there's a benefit to cascoding, as we're all pointing to the same articles, what have folks experienced in terms of best base voltage for the front end transistors in the F5?

8V has been put forth by one person, any other experiences?




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Old 24th March 2011, 03:38 AM   #158
tinitus is offline tinitus  Europe
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I think from Nelson's point of view, the cascode holds 'technical' advantages
lower distortion figures have been mentioned
but in lack of skills, I really dont know much about any of this

but those here who have tried haven't been able to actually hear any difference

well, could be it comes down to careful implementing and adjusting
maybe thats one part we are missing still

and ofcourse there's the possibility to drive the curcuit harder
which is the obvious one

but again, I'm always cautious about what other people claim to hear, or not
like reviews, always taken with a grain of salt, so to speak
I want to hear it myself, before forming any opinion about it
not good to just pass on other peoples opinions, unquestioningly

but honestly
when I build something that seems to work to my satisfaction, I leave it be as is
once it works ok, I do not experiment further
maybe I will miss out on something, I dont know
my personal opinion is that many so called 'improvements' are merely just changes
no worse no better
in many cases just a matter of personal preferences, and as such very individual
could just exclusively relate to a certain setup
and in the end subjective and personal

oh, well, adjustments, yes
that I can do forever, and never ending
simple ones, ofcourse
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Old 24th March 2011, 04:59 AM   #159
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Earlier in this thread someone suggested 8 to 10 volts for the cascode.
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Old 24th March 2011, 05:23 AM   #160
NYCOne is offline NYCOne  United States
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True, 8V has been mentioned a few times.

I bought a 12V 800VA transformer for the Balanced-Cascoded circuit. I hope to have time to try it in 2 weeks. I have a 26V transformer for testing, but its too small for the final version.

Based on NP's advice, I'm pushing toward a Balanced-Cascoded amp with 12V xformer, and a standard Cascoded F5 with 26V xformer.

I was able to finish my OB speakers, so I have a real means of evaluating differences in the amps (finally).

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Earlier in this thread someone suggested 8 to 10 volts for the cascode.
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