Read this page a couple of times for a comparison with F5.
6moons audioreviews: FirstWatt F7
6moons audioreviews: FirstWatt F7
I have read the reviews and built some approximation to the F7, listening to it with the Kairos speakers by Jeff Bagby. The amplifier is as good as the 6Moons Review says and it should sell like hotcakes. That means that Papa should sell a pile of them quickly and the DIY world might see the official design sooner rather than later. Amazing sound for such a simple design.
D` accord. Another ingenious design anyway. I am very pleased with the performance of my take of the F7. Due to the lack of a distortion analyzer I did not check nor optimize the harmonics 2nd and 3rd. I am using this amp since two weeks with a pair of Joe`s Elsinores which I like so much. I prefer the F7 considerably over my J2 mono clones and my F1J current amp. Further on I´d say that the F7 is more or less on par with my KT88 CFB tube amplifier which resembles more or less a VSE DPA-150 for the poors but with better low frequency output.
To summarize the F7 design basics as I see it:
-symmetrical push-pull amplifier
-fairly low open loop gain
-fairly low closed loop gain
-comparably high output impedance before applying positive current feedback
-modern approach to solid state amplifier technique, adapted from the tube era
By now it seems that only very few forum members built an amp. It would be interesting to hear about the experience of more F7 builders.
And not to forget: Thanks a lot again to Mr. Pass for making all this possible. Maybe he is not completely happy with the way this F7 diy evolved as another gentleman already mentioned…….
That is what I understood too. To be fair, if you are not absolutely sure you have built a real clone of the F7 then do not call your amp an F7. When I build an amp which can be similar to another amp I use the "clown" designation instead of "clone"....
Having said that I still appreciate the takes of the few members that have built their clown!
Fab
Well, I am decided....
An M2 to build until the F7 is, if Pappa continues to be generous, released to us Dodos.
[I do not have adequate knowledge to improvise on the hard info. available at present. But I have bought the transformers......would also like to obtain the better output devises for both F7 and M2...Heatsinks on order and a good quantity of 8mm alloy sheet in the garage. ]
An M2 to build until the F7 is, if Pappa continues to be generous, released to us Dodos.
[I do not have adequate knowledge to improvise on the hard info. available at present. But I have bought the transformers......would also like to obtain the better output devises for both F7 and M2...Heatsinks on order and a good quantity of 8mm alloy sheet in the garage. ]Actually, this is PL version of what's already on 6moons.com. We wanted to list my impressions in ENG in the first place.
Well, I am decided....
An M2 to build until the F7 is, if Pappa continues to be generous, released to us Dodos.
2SK1530/2SJ201 for M2 , any of Hitachi 2SJ50/2SK135 lookalikes for F7
you can , one day , compare F7 iterations with both output options
That's a 85-ish db, 2-way speaker with a pretty flat 8-ohm impedance, right? Interesting. What Pass amps do you have to compare it to (if any)? I wonder how the F7 behaves into low-z loads compared to a multiple output F5, or F5T. Also, how hot do you have your F7 clone biased?
My comparison is with my XA30.8-Guess. My F7-approximation sounds quite similar. My bias current is 1.25A. The Kairos is described here: http://meniscusaudio.com/images/The Kairos Monitor Speaker by Jeff Bagby.pdf
I have a pair of Druids here, recently arrived. Previously having heard
other Zu models, I did not experience how spectacular the Druids are if
you appreciate really articulate midrange without annoying artifacts.
It does take a little work to get the bass right.
These were a pair that had suffered some cosmetic damage to the enclosure,
but Sean will not be getting them back.
other Zu models, I did not experience how spectacular the Druids are if
you appreciate really articulate midrange without annoying artifacts.
It does take a little work to get the bass right.
These were a pair that had suffered some cosmetic damage to the enclosure,
but Sean will not be getting them back.
There is plenty on the table for you guys to get it right, and the absence of
the official schematic serves everybody's needs if you think about it.
Positive current feedback is very simple, works well when applied in very
moderate doses, and provide all manner of new entertainment.
Lynn has shown you a varied set of topologies, along with equations that
you can plug into your calculator. The best part is that you can even do this
with amps you have already built, and impress your audio buddies
with the awesome and mysterious power of positive feedback!
There is plenty on the table for you guys to get it right, and the absence of
the official schematic serves everybody's needs if you think about it.
Positive current feedback is very simple, works well when applied in very
moderate doses, and provide all manner of new entertainment.
Lynn has shown you a varied set of topologies, along with equations that
you can plug into your calculator. The best part is that you can even do this
with amps you have already built, and impress your audio buddies
with the awesome and mysterious power of positive feedback!
Many thanks for your blessing.
will send you one...towel!