The F6 Revisited

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#561
Anand:

I have a dual monaural jfet-based F6 sitting in reserve, waiting to be compared to this new F6 Diamond. I'll give the F6D a few days to burn in and will then compare them before turning this new amp over to its owner. I built him a BA2018 not long ago and he's excited to start listening to his new system. If I have anything trenchant to offer regarding the jfet/Diamond comparison, happy to do so.

Thanks again,
Scott
 
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#562
Scott,

Good to see that your new DIY F6 with Diamond Buffer is working now - congratulations on another successful build!

Look forward to your listening impressions once you go more hours on the new amp, and some quality listening time. 🙂
 
#565
Folks:

Please take the following ruminations regarding an F6 Diamond with a large grain of salt.

Here is some context: the amplifiers in my main system are F5 Turbo V3 monoblocks, which have been in place for about 10 years. I am unquestionably biased by their sound, having tweaked, loved and listened to them for so long. I built an F6 (with a jfet-based front end) a few years ago; it has a dual mono power supply but is otherwise a fairly standard build, and it is periodically swapped in for the F5 Turbos. My F5Ts and F6 are share many sonic qualities (they offer competing versions of Nelson Pass’ “house sound”) but are very easily distinguishable from one another; the F5Ts are more dynamic and neutral and they create a broad and deep soundstage. I’ve heard amps that create performances that are larger than life. My F5Ts don’t do that, but they do favor larger scale recording venues. My F6, on the other hand, creates a smaller, more intimate soundstage. Where the F5Ts’ soundstage extends beyond the width of my speakers, the F6’s soundstage does not. My F6’s tone is warmer than the F5Ts and its notes sound more “rounded” – there’s a plumpness to the F6 that is at times alluring, but whether it sounds more “real” than my F5Ts is debatable. On my F6, Michael Jackson’s “Human Nature” is almost holographic and Jeff Beck’s “Freeway Jam” is electric, but between the two amps I favor the rawness, dynamics, scale and clarity of the F5Ts. Simply put, the F5Ts are the more commanding amp, though there are times when my F6 seems alive.

A friend asked me to assemble an amplifier for his small system. I built him an F6 Diamond and, after burning it in nonstop for 2 days, I have been listening to it for the past week, comparing it to my F5Ts and F6.

The differences between my F6 and the F6 Diamond are subtle. Each is seductive. Separation is good (but not great) on both. Their soundstages are very similar: intimate, existing slightly inside the width of the speakers and not terribly deep. Both are slightly forward and inviting, offering the impression of being seated in one of the front rows at a small to medium-sized venue. My F6 has a weightier lower end. The F6 Diamond’s tone is very slightly warmer than my F6. Sibilants on both my F6 and the F6 Diamond sizzle realistically (Margo Timmins sings “Sweet Jane” on The Trinity Sessions with just a hint of raspiness) and both F6 versions present soloists beautifully (Leo Kottke played “Vaseline Machine Gun” eight feet in front of me and Pat Metheny’s “And Time Goes On” was near-field and mesmerizing), but both also soften music relative to the F5Ts. “Human Nature” is the tiniest bit softer on the F6 Diamond than my F6 and the F6 Diamond has a slightly blacker background, but both are tonally rich. “Babalou” by the enchanting Angelique Kidjo is terrific on both amps, but it is more romantic on the F6 Diamond (the same can be said for “Suite in F Major: Air” from Handel’s Water Musick (McGegan conducting)). At the risk of being way too precious, I thought “Babalou” was more haunting on my F6. The Trinity Sessions was recorded in a stone church and both amps did an admirable job recreating the sense of space, but “Sweet Jane” was more compelling on the F6 Diamond.

Choosing between the two F6 designs is difficult. The F6 Diamond is very well suited for small ensembles and solo performers and I suspect it would respond very well to a smaller performance space (my listening room is 20’ x 22’, seemingly on the large side for both F6 designs). I like my F6 a lot. That said, the F6 Diamond is an equally satisfying amplifier.

A point of further consideration: my F5Ts have 250,000 uF of power supply capacitance in each monoblock and my dual mono F6 has 96,000 uF for each channel. The F6 Diamond I built has 120,000 uF of capacitance in its single power supply, and the smaller single power supply (relative to the F5Ts and my F6) may have contributed to my perceptions of the F6 Diamond (i.e., slightly more power supply capacitance could be a good thing).

I hope this was helpful (and not too prissy). Kudos and thanks to TungstenAudio and mikerodrig27 for their efforts in making the F6 Diamond available to the masses.

Regards,
Scott
 
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#570
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#571
When using a single PSU that is shared between the two channels, there is an option to add some amount of capacitance that is separate for each channel. The new F6 boards have extra mounting holes which make it fairly easy to add motor run caps next to each channel. I recommend 60 uF or better of CBB60, 250V type. 80 uF is good if space permits. This is remarkably effective at extending the stereo separation beyond the boundaries of the speakers.
 
#573
Anand:

Thank you. Listening to the amps and writing the assessment was difficult and fun, but it's a little hard avoiding sounding either like a professional-critic-of-old-wannabee or a pompous ***. To the extent I failed, mea culpa to all.

TungstenAudio:

Understood. For the record, the power supply used in that F6 Diamond was Jeff Young's design, which he calls "Dual Rail / Decoupled Stereo." Bottlehead calls the same design a "pseudo dual mono" power supply. It's a CRC where the first C is shared by both channels and then separates into two discrete sets of rails for the remaining RC. In my build, there isn't a lot of remaining floor space for the motor run caps (even though the capacitor board is perched above the toroid). I'd suggest a 400mm deep chassis when its likely the builder wants the option of adding those capacitors. Your mileage, naturally, might vary.

Regards to all,
Scott
 
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#574
Jeff Young possibly did his PCB following Mr. Pass's schematic. 🙂
 

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#575
SRMcGee said:
Thank you. Listening to the amps and writing the assessment was difficult and fun, but it's a little hard avoiding sounding either like a professional-critic-of-old-wannabee or a pompous ***. To the extent I failed, mea culpa to all.
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I appreciate your listening impressions. Seems people shy away from doing a lot in the forum. No other way of having an idea of what something sounds like otherwise, maybe if you attend BAF. People buy or build things all the time based on other people’s subjective impressions, that is literally everything on Amazon.

While subjective impressions are inherently personal and can be biased, they offer rich, nuanced insights that objective measures may miss.
 
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