F2 Initial Listening Impressions

[steenoe]

Biosonar and Jon, I forgot to mention this: What a nice reading you two gent's post's are

Steen

[Nelson Pass]

Originally posted by Jon Ver Halen
Your only excuse would be if you have a high impedance driver and wish to wait for the F3.

Yes, Jon has been torturing me about the F3. It is a special
version of the F2, optimized around a 16 ohm load, and so you
can imagine that the voltage and current have been adjusted,
but there is also something else unusual, not seen
previously in the Zen genre. I put some more work into it today,
and it is definitely better if your load is 16 ohms or so. Below
12 ohms, you're better off with an F2. I expect availability in
late August, early September.

[Biosonar]

While I own many cameras, none are digital.

[sklimek]

Originally posted by Biosonar
While I own many cameras, none are digital.

Hi,

I love those cameras as well, which ones do you have?

Stan

[jh6you]

Nobody sells digital cameras there . . . ?
Nobody sells Fostex, Lowther or Jordan here . . .


Regards
jH

[Nelson Pass]

Originally posted by apassgear Steenoe and myself are working on a “back engineered” F2 based on all the tips that Nelson has shared.

That is not exactly it, but I believe it will work well enough.

Originally posted by steenoe
I dont suppose any of the happy (lucky ) owners of the F2, would care to take the lid off the amp and post apicture, would you

I think www.6moons.com put up a nice interior shot.

[lumanauw]

Hi, Mr. Pass,

Does F2 has output capacitor or DC coupled at output?

NP's Fseries should be better than SET (single ended tube) because both are current sources (SET makes a current source via its OT secondary windings), while NP's Fseries makes a current source via nothing at all (at least in F1, don't know about F2). Output transformers are not linear. Direct connection are.

People usually comparing tubes SET (eg. 300B) with transistors (Mosfet/Bipolar) and say tubes sounds better. I think it is useless to compare tubes and transistor while SET is current source and transistors amp are voltage sources.

Now, those people can make tube vs transistor comparison one more time with equal topology (current sources) offcourse.

[tmblack]

How do the F1 and F2 sound using typical 8 ohm 2 way bass reflex speakers?

Tom

[AD]

Mr. Pass wrote:

"I think www.6moons.com put up a nice interior shot."

They certainly did put out a nice clear picture of the interior. A lot of questions have been answered this way, like what kind of power supply is being used and what kind of components as well.

But I found it easier to locate the review of F2 via Google search than navigating on the .6 moons web site...

Andrej

[Biosonar]

Originally posted by tmblack
How do the F1 and F2 sound using typical 8 ohm 2 way bass reflex speakers?

Tom

I can't give you an answer based on actual listening. However, I expect 2 problems that won't give you the results you are hoping for: the crossover and base response.

Nelson has covered the question of how current-sourced crossovers are different than voltage-sourced crossovers in his "Current Source Crossover Filters" article which can be downloaded off the Articles page of the First Watt site, www.firstwatt.com. While possible workaround solutions of building a current-sourced crossover, or using an active or passive voltage-sourced crossover between the preamp and F1/F2 look attactive, none deal with the second problem: interaction of the Box and BR port resonance with the base driver low frequency (LF) resonance.

With both the F1 and F2, the base driver LF response is extended by adding a resistor in parallel with the driver, resulting in an adjustable LF peak at driver's resonance. (See Dick Olsher's panther and leopard projects at www.enjoythemusic.com for clever examples of this LF extension using a closed box solution.) The problem with a BR design is that the interaction between port tuning and driver resonance is messed up by the change of the driver's resonance characteristics brought about by the current-sourced amplifier and its LF damping.

The upshot is amps like the F1 and F2 can be used with BR designs. One just has to take into account the changed nature of LF response that current-souced amps like the F1 and F2 cause when designing the box. I have a base driver with an Fs of 31 Hz and an effective bandwidth product of 96, indicating a BR design. So I am grappling with this design isssue. Any insights are welcome.