5W=U^2/50R
5W x 50R=U^2
(5W x 50R)^1/2=U
=15V8 RMS = 44V7p-p
what means that you need even slightly higher rails for that F4
30db gain means (30/20)inv-log = around 31 x
so , with 2 in , you'll get 62 out ........ if stage is not clipping before that
using balanced will double possible swing , but gain remains the same
5W x 50R=U^2
(5W x 50R)^1/2=U
=15V8 RMS = 44V7p-p
what means that you need even slightly higher rails for that F4
30db gain means (30/20)inv-log = around 31 x
so , with 2 in , you'll get 62 out ........ if stage is not clipping before that
using balanced will double possible swing , but gain remains the same
Any hint with topology, mosfet used, number of stage, etc?
But there is no way you can swing more than the rails, right? So the gain stage would have to be the higher voltage version with 32v rails...
@ Jay
ask Wayne .......
make BA-3 FE
Oh... BBA3 with excessive bias for the mosfet... Ok, thanks
how big P1 in your amp?
the question is
- can b1/b2/b3 increase gain on F4 to drive 87 db speaker ?
- or better to use double F4 / use 4 pcb to drive 87 db speaker ?
- which b1/2/3 better for f4 ?
thank you Zen
my F4 ( Papa's Koan ) is plain F4 made by R1 schematic , so P1 is 5K
for F4 , of all B's , only B3 is adequate
but - observe what's written on B3 page : http://tinyurl.com/d34lzku
for your spks ( some other things are also important , besides db/W - room size , your listening habits ...... ) safe bet is using F4 as balanced ....
lacking B3 , best thing for now is combining BA3 Balanced front end with input buffer-less balanced F4 ......... and that combo is simply BA3 amp , balanced
for my spks (94db/W/m , 16R ) I'm feeding F4 as SE , ditto from DAC output and I'm having max 600mW as result
still lacking some 6db of voltage swing for full blast , but I'm lazy bstrd
hi zen
i got aleph p 1.7 setting on the highest output ( 1-0-0-1 )
and the X2 preamp, it is enough to feed F4 ?
i was interest with glassware audio like pjgregory did on the post #3179
but after i think view times got an original product maybe better for me
i will think about B3 front end on the next step
now making chassis for the F4, walter burkhard give me a lot of homework
to make a beautiful chassis ( i bought heatsink from him )
i got aleph p 1.7 setting on the highest output ( 1-0-0-1 )
and the X2 preamp, it is enough to feed F4 ?
i was interest with glassware audio like pjgregory did on the post #3179
but after i think view times got an original product maybe better for me
i will think about B3 front end on the next step
now making chassis for the F4, walter burkhard give me a lot of homework
to make a beautiful chassis ( i bought heatsink from him )
Zen Mod,
I am surprised you are not recommending your creation, The Pumpkin. What gives?
Pumpkin is, of course ........ 
but , there are few reasons why I'm not mention it :
-I'm still Paypal-less , and tired of inventing new ways to have it ,
-I hate advertising in every possible place
Pocoyo - X2 is wonderful little gadget , but not optimized for output swing needed for balanced F4
X2's output stage is having ~ 10mA Iq , not enough for your purpose ( at least in my book ) while changing/tweaking that is almost impossible , considering it's physical layout
make full BA3 , balanced and use X2 to drive it
but , there are few reasons why I'm not mention it :
-I'm still Paypal-less , and tired of inventing new ways to have it ,
-I hate advertising in every possible place
Pocoyo - X2 is wonderful little gadget , but not optimized for output swing needed for balanced F4
X2's output stage is having ~ 10mA Iq , not enough for your purpose ( at least in my book ) while changing/tweaking that is almost impossible , considering it's physical layout
make full BA3 , balanced and use X2 to drive it
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Yes Sir ... Allright Sir !
I will search the BA-3 green PCB
BTW can i connect the BA-3 supply
from F4 PSU ?