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Old 8th January 2013, 03:14 AM   #881
dazed2 is offline dazed2  Canada
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Quote:
Originally Posted by AudioSan View Post
ZM. a question. i have pr now R5/6 at 1Kohm, and 7.1mA J-fets(i forgot to calculate a reise of the resistance)
i can solder in some 2.2Kohm resistors. or i have another set of 7.1mA J-fets i can solder in, to dobble up the J-fets. what would you do? i don't know if 2.2K will be enough for 7.1mA fets. but with dual 7.1mA fets, 1Kohm chould be enough? right?
Audiosan or ZM , could you please explain this? Wouldn't the cascode take care of it already and not require more? I'm going to be building a 4pr w 50V rails should I have more than one pair of jfets?
What am I missing?
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Old 8th January 2013, 03:24 AM   #882
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the cascoding takes care of the voltage the J-fets get. but the J-fets need to drive the the output fets, that demands some current. you can drive 4 output pairs with a single pair of J-fets. but it may be a little more narrow bandwith. you may also need to up the resistance for R5/6 to reach any bias current for the outputs.
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Old 8th January 2013, 05:06 AM   #883
anilva is offline anilva  India
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Quote:
Originally Posted by AudioSan View Post
the cascoding takes care of the voltage the J-fets get. but the J-fets need to drive the the output fets, that demands some current. you can drive 4 output pairs with a single pair of J-fets. but it may be a little more narrow bandwith. you may also need to up the resistance for R5/6 to reach any bias current for the outputs.
I had no problems in driving 4 pairs of outputs with a single pair of J-Fets in a cascoded mode and also did not require any change in resistances. I did two channels in a large enclosure with natural cooling but could not sustain it. Have now resorted to forced air cooling and the amp works fine at 375mV bias on each source resistor.
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Old 8th January 2013, 09:51 AM   #884
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i guess you have around 10mA J-fets then?
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Old 8th January 2013, 09:58 AM   #885
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anilva,
Since you have active F5, F5TV2, and F5TV3. Perhaps you would like to comment on the differences.
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Old 8th January 2013, 01:12 PM   #886
dazed2 is offline dazed2  Canada
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If I'm not mistaken the Toshiba 2SK170 and 2SJ74 both have Ig = +/-10mA.
Would this then be ok with 4pr without deviating from Pass's schematic?
Thanks Anilva, I take it you're using the toshiba's as well?
Yes also what are you impressions of all 3 F5 variants?

Last edited by dazed2; 8th January 2013 at 01:15 PM.
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Old 8th January 2013, 02:36 PM   #887
anilva is offline anilva  India
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Originally Posted by buzzforb View Post
anilva,
Since you have active F5, F5TV2, and F5TV3. Perhaps you would like to comment on the differences.
Yes, I am using the Toshiba JFETS at 10mA IDSS.

As fas listening impressions are concerned, I have written elsewhere as well, but I will repeat again. The F5 has absolutely high resolution and very clean sound with tad weakness on the bass.

The V2 comes across lot more powerful and controlled and with tight bass but at the same time has very F5 nature of sound in term high resolution and detail.

The V3 takes it further in terms of more headroom and dynamics with very controlled performance across the spectrum particularly bass and ofcourse the classic F5 resolution.

Mind you, I have not tweaked P3 in any of these setups and is at midpoint. May be the character will change if tweaked. I also have a dual output Toshiba F5 which has slightly different but warmer character than the standard F5, but definitely not as powerful as V2 or V3.

My listening tests are done with a full range back loaded horn based on fostex FE206 and with another setup consisting of active altec 515 LF and Altec 288K HF with a Le'Cleach horn.

Hope this helps. YMMV.

Cheers.
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Old 8th January 2013, 03:23 PM   #888
Renron is offline Renron  United States
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Quote:
Originally Posted by dazed2 View Post
If I'm not mistaken the Toshiba 2SK170 and 2SJ74 both have Ig = +/-10mA.
It depends on their grade.
GR = +/-2.6 to +/-6.5mA
BL = +/-6.0 to +/-12mA
V = +/-10 to +/-20mA

Ron
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Old 8th January 2013, 03:30 PM   #889
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Originally Posted by nrg2009 View Post
I have my fingers crossed that someone will come through with an F5Tv2 in a 5U chassis from the store as a dual channel amp. I know that at least someone has thought about that setup.. it must be..
That's my plan, unless funding forces me to build one like my first F-5 build. Variac said this case (5U) would be perfect for this project, (V2), or 2 4U cases for monoblocks.

Russellc
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Old 8th January 2013, 03:40 PM   #890
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Originally Posted by 6L6 View Post
I'm hoping to have a dedicated 30KW solar array and deep-cycle battery storage system dedicated to my audio system.

To listen to headphones.

Back on topic...

I hope to be getting my PCB and heatsinks in the next few days!
Alright, and great idea! Taking class A Green!

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