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Old 27th February 2006, 05:04 AM   #1
Tyimo is offline Tyimo  Hungary
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Default JFet BOZ

Hi!

Afther that I read so many good things about the JFets, I would like to ask:
Is it possible to modificate the original BOZ that I would use 2SK389 in stead of the IRF610?
I know "in principle it is possible to replace a 610 with a 389, BUT the BIAS CONDITIONS are very different. Usually, some adjustment will be necessary".

Any ideas?

Greets:

Tyimo
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Old 27th February 2006, 11:35 AM   #2
Zen Mod is offline Zen Mod  Serbia
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Default Re: JFet BOZ

Quote:
Originally posted by Tyimo
Hi!

Afther that I read so many good things about the JFets, I would like to ask:
Is it possible to modificate the original BOZ that I would use 2SK389 in stead of the IRF610?
I know "in principle it is possible to replace a 610 with a 389, BUT the BIAS CONDITIONS are very different. Usually, some adjustment will be necessary".

Any ideas?

Greets:

Tyimo

too wimpy
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Old 27th February 2006, 12:08 PM   #3
Tyimo is offline Tyimo  Hungary
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Quote:
too wimpy
Sorry, but what does it mean: wimpy??
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Old 27th February 2006, 12:16 PM   #4
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The 2sk389 is not a "manly" device, it is a wimp, a weakling compared to the IRF610.

To use the 389 you'd need to reduce both bias and rail voltages to keep the dissipation and voltage in check. There is a thread or two about this if you search. Cascoding is probably a good idea, or you could simply use one of the opamp circuits here or on passdiy without an output stage. The problem with no output stage is that the 389 would not drive low impedance loads well.

Others much more knowledgeable than me may be able to offer better ideas on using the 2sk389 in a BOSOZ type topology.
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Old 27th February 2006, 12:39 PM   #5
Tyimo is offline Tyimo  Hungary
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Hi Bob!

Thanks for the answer! Now I understand what our "taciturn" Choky meant. :-)
The 2sk389 is not so important for me, so now I re- compose my question:
Is it possible to modificate the original BOZ that I would use any kind of JFet in stead of the IRF610?

Greets:

Tyimo
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Old 27th February 2006, 12:43 PM   #6
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Krazy JFET-cascoded Pass BOSOZ

Also look at the Lovoltec amp thread, those devices are suitable.

edit: Isn't slang in a second language fun? I think it's funny that you have learned taciturn before hearing the word wimpy. But then you'd find any attempt by me to speak any language other than English hilarious.
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Old 27th February 2006, 01:50 PM   #7
Tyimo is offline Tyimo  Hungary
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Thanks Bob!

I didn't want to use cascoded and I haven't got Lovoltech power Jfets yet. :-(

Quote:
Isn't slang in a second language fun?
Yes!

Greets:

Tyimo
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Old 27th February 2006, 06:59 PM   #8
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If you limit the supply voltage you can use either the Lovoltechs
or the 2SK389 / 2SK170. The Lovoltechs handle a lot of current
and have high transconductance, but the 2SKs have much lower
input capacitance.
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Old 27th February 2006, 11:50 PM   #9
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Default Re: JFet BOZ

Quote:
Originally posted by Tyimo

Is it possible to modificate the original BOZ that I would use 2SK389 in stead of the IRF610?

Instead of this, try JFET (any of low input capacitance) cascode paired with IRF610 . . . I am sure that it will kiss you softly . . .

jh
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Old 28th February 2006, 12:39 PM   #10
Tyimo is offline Tyimo  Hungary
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Thanks!

Quote:
If you limit the supply voltage you can use either the Lovoltechs or the 2SK389 / 2SK170.
I thought on 36V supply voltage. (?)

Tyimo
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