First Watt F2 J-fet

Jon Ver Halen · 25th January 2010, 02:34 PM

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.

Zen Mod · 25th January 2010, 05:22 PM

well Jon , I'm glad that you're glad .

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

Telstar · 25th January 2010, 06:24 PM

I wonder if a similar FET replacement could be done on the F1...

Nelson Pass · 25th January 2010, 07:00 PM

No doubt it could.

Tea-Bag · 25th January 2010, 08:00 PM

Nelson, is there a hand drawing of the new schematic to share?
I have some of the R100's that could be used.

Zen Mod · 25th January 2010, 08:47 PM

Quote:

Originally Posted by Tea-Bag

Nelson, is there .......

greedy boy .........

Nelson Pass · 25th January 2010, 10:02 PM

Quote:

Originally Posted by Tea-Bag

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?

eyoung · 26th January 2010, 12:15 AM

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

Tea-Bag · 26th January 2010, 12:32 AM

Quote:

Originally Posted by Nelson Pass

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.

Telstar · 26th January 2010, 08:23 AM

Quote:

Originally Posted by Nelson Pass

No doubt it could.

Cool

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

25th January 2010, 02:34 PM	#1
Jon Ver Halen diyAudio Member Join Date: Aug 2004 Location: Chicago area	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. __________________ Jon Ver Halen Lowther-America

25th January 2010, 05:22 PM	#2
Zen Mod diyAudio Member Join Date: Jan 2003 Location: ancient Batsch , behind Iron Curtain	well Jon , I'm glad that you're glad . funny thing is - that nothing less we don't expect from Papa . __________________ my Papa is smarter than your Nelson ! tnx to clean thread ; Cook Book ; PSM LS Cook Book ; Baby Diyaudio FORUM ; BAF Forum & Gallery;I'm dumb

25th January 2010, 06:24 PM	#3
Telstar diyAudio Member Join Date: Dec 2007	I wonder if a similar FET replacement could be done on the F1... __________________ The response of the inner ear extends to at least 200khz - Dr W. Tempest

25th January 2010, 08:00 PM	#5
Tea-Bag not politcally affiliated diyAudio Member Join Date: Feb 2006 Location: Kennebunk Blog Entries: 5	Nelson, is there a hand drawing of the new schematic to share? I have some of the R100's that could be used. __________________ DCB1/BiB Sign up Sheet Round #2 2012 CLICK HERE\|SSHV2 Shipping\| F5TConvertible Circuit Board Sign Up Sheet (Shipping)CLICK HERE\|Semisouth R100A/R085 available PM

26th January 2010, 12:15 AM	#8
eyoung diyAudio Member Join Date: Aug 2007 Location: Sunny SC,USA 15 min south of Charlotte NC	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 __________________ "when you open your mind to the imposible, soon you will find the truth...."


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25th January 2010, 07:00 PM	#4
Nelson Pass The one and only Join Date: Mar 2001	No doubt it could.

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