F3 vs J2 for a SET guy - diyAudio
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Old 25th May 2010, 05:56 PM   #1
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Default F3 vs J2 for a SET guy

Hi,

My current reference amp, a JE Labs SRPP 45 SET, had a problem and so I borrowed an F3 clone. And was promptly reminded how much I love that amp. I've previously owned an F3 clone and a Pass F3. I am now considering buying either a Pass F3 or J2.

My speakers are now a Fostex BLH and will be (shortly) Tonian Labs Classic 12s using the 12" PHY driver. I listen at moderate volumes and have found the 45 enough power for speakers in the 95 dB/W range that are an easy load in my large room so power is not really an issue.

I like the SET sound but realize the FWs are not quite SETs (just different, and better in many ways). But I what I value more than anything else are body, timbre, and smoothness! I cannot handle an amp that sounds not quite fleshed out or lacking proper timbre. I found that the F3 absolutely did NOT have problems of this sort. In fact I only went back to SET due to boredom, the occasionally need to hear that "magic big vocalist" thing, and an apparent unconscious fetish for tubes.

I guess what I'm getting around to is this: could someone compare the F3 to the J2 for me in the criteria I outlined above? Are the mids and highs very similar? Anything else I should know about?

Since the designs are so similar I would expect a lot of similarity. The J2 seems to have newer/"better" parts which maybe does something. The F3 I believe is one gain stage which to me is an advantage as I don't need the extra gain or power.

The techie nerd in me is wondering about the differences in NFB as well.
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Old 26th May 2010, 02:42 AM   #2
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Default J2 v F3

Man, if you like an SET, and enjoy the F3, you will love the J2. It sounds much closer to an SET than the F3, with that "sweet" sound that SET's have. But it comes with the extended bandwidth and top to bottom coherence of SS. Neat trick.

So good even my teenage son is coming home and listening to music after school. Never had that happen before.
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Old 26th May 2010, 02:55 AM   #3
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I know I want a (DIY) J2. I'm ready for that schematic! Time to start gathering bits and pieces!
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Old 26th May 2010, 03:20 AM   #4
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Thanks for the feedback, John!

I assume you are running Lowthers?

What linestage? I am thinking the F3 might be better with higher-gain linestages given its low gain. With such a linestage its single gain stage could be an advantage. OTOH the J2 might sound better with passive or low-gain line stages?
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Old 26th May 2010, 03:23 AM   #5
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The difference between the J2 & F3 is going to be more about output impedance. J2 (from what i understand an F2 with the JFET output devices) will have an output impedance more akin to the SET. F3 is a voltage amp.

dave
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Old 26th May 2010, 03:31 AM   #6
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Quote:
Originally Posted by planet10 View Post
The difference between the J2 & F3 is going to be more about output impedance. J2 (from what i understand an F2 with the JFET output devices) will have an output impedance more akin to the SET. F3 is a voltage amp.

dave
According to FW site it's .4 ohms (J2) vs 1 ohm - a pretty trivial difference into almost any load, I think. But maybe not.
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Old 26th May 2010, 03:46 AM   #7
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A factor of 2.5.

Into an 8 ohm driver, damping of 8 vrs 20.

I did expect a higher output impedance on the J2 (ie similar to the F2)

Nelson was talking about updating F2s with the JFET outputs. If it retains the high output impedance, that is what i'd want.

dave
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Old 26th May 2010, 03:52 AM   #8
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Quote:
Originally Posted by planet10 View Post
A factor of 2.5.

Into an 8 ohm driver, damping of 8 vrs 20.

I did expect a higher output impedance on the J2 (ie similar to the F2)

dave
I have often found no real diff in DF once it gets above 3-4. Of course that is very speaker-dependent.

For the most part I think most widebanders sound as good or better with low DF. So I think that is a + for the F3 if anything.
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Old 26th May 2010, 03:53 PM   #9
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Default F3 vs. J2

Personally, I'd give the nod to the J2 particularly for how it handles the treble. But as you suspect, it's a close call. I'd not think you'd give up anything in the midrange. I just had the J2 on my Rethm Saadhanas (Lowther DX-55 modified) and liked it better than my Yamamoto 300B. Sacrilege and holy cows gone to hell but there it is
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Old 26th May 2010, 04:14 PM   #10
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Quote:
Originally Posted by Paul Folbrecht View Post
For the most part I think most widebanders sound as good or better with low DF. So I think that is a + for the F3 if anything.
Yes. My comment was based on the wrong assumption that like the F2 the J2 output impedance was 15 ohms... looks like the F2J (thats the one i want, alas i'll have to live with the F2 until the output devices become more reaonably prices or i become richer)

dave
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