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Old 25th January 2010, 02:34 PM   #1
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Default First Watt F2 J-fet

My First Watt F2 was recently re-worked by Nelson with J-Fet's in place of the original Mosfets. Thought I would write a few words about it.

As usual, the unit requires 15 minutes of warmup to sound good, and 30 minutes for critical listening. It does not take long to realize this is a special amp. Although it is difficult to recall the exact nature of the F2 mosfet sound, this amplifier is obviously cleaner, with lower distortion. The "rose shaded glasses" effect of the F2 is now gone. But, more importantly, the sound is now much sweeter, as if cut from whole cloth and part of the musical fabric. Imaging seems improved, but that my be more my memory than fact.

As before, very dynamic when mated with efficient speakers. The current source F2 may require a special filters to sound its best with different speakers. For more information, see the White Paper "Current Source Amplifiers and Sensitive Drivers: by Nelson Pass" on the First Watt site. With only 5 watts, high efficiency speakers are a must.

As an extra added prize, the LED's have been dimmed. So last night was a late night listening session. Vinyl was spinning, the lights were off, and a bit of cognac involved. But it was the sound which was truly intoxicating. Extended listening showed no signs of "listener fatigue", and the few words above do not accurately portray how much fun it is to hear this amp. Very, very nice.
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Old 25th January 2010, 05:22 PM   #2
Zen Mod is offline Zen Mod  Serbia
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well Jon , I'm glad that you're glad .

funny thing is - that nothing less we don't expect from Papa .

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Old 25th January 2010, 06:24 PM   #3
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I wonder if a similar FET replacement could be done on the F1...
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Old 25th January 2010, 07:00 PM   #4
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No doubt it could.

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Old 25th January 2010, 08:00 PM   #5
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Nelson, is there a hand drawing of the new schematic to share?
I have some of the R100's that could be used.
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Old 25th January 2010, 08:47 PM   #6
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Quote:
Originally Posted by Tea-Bag View Post
Nelson, is there .......
greedy boy .........
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Old 25th January 2010, 10:02 PM   #7
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Quote:
Originally Posted by Tea-Bag View Post
Nelson, is there a hand drawing of the new schematic to share?
I have some of the R100's that could be used.
This is reference to what product?

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Old 26th January 2010, 12:15 AM   #8
eyoung is offline eyoung  United States
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I hope it was the F1 as I am building one, that being said I would like to hear both as I am sure they are different sounding...

Regards, Elwood
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Old 26th January 2010, 12:32 AM   #9
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Quote:
Originally Posted by Nelson Pass View Post
This is reference to what product?

Oops, The F2 I was referring to, and I have SemiSouth SJEP120R100's.

The F2 is the first pass amp I built. It's worth revisiting.
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Old 26th January 2010, 08:23 AM   #10
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No doubt it could.

Cool
I'm wondering if can be changed to provide more power, even leaving class A...? Any tip?
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