F4 power amplifier

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#1,021
mpmarino said:


Yes, very appealing! Sounds like the perfect winter setup😉 Also, the fact that you would even mention building 12 channels of an amp tells me you truly like it beyond what you've stated. Well, since you've built everything else 'round here already your opinion carries weight😀


I need to settle on a low power, high resolution, very quiet, and balanced amp for the 'drek squeaks'. I'd do a 'crippled F4' but it's not balanced. Suggestions??

I think a bridged f4 can handle the woofs.

EDIT: what is a KSA? besides a Krell🙂

Septic?
Click to expand...

The thought has been buzzin' in my head for a few days. Nothing decided yet, though.
As for a balanced tweeter-amp, a "Mini-Babelfish" or simply a Babelfish, would be a good choice😉 Balanced input, J-fet frontend; what is there to be wished for, other than that? For tweeters, the J-fet frontend is a real bonus.
The KSA is in fact a Krell😀

🙂

PS ZM, those Bylund brothers are indeed doin' great.
 
#1,022
Russ White said:
BPA is always an option I think, but why not just add more output devices to scale the current?
Click to expand...
Hi Russ. Yes, that would probably be a more sane way to do it.
Actually I was playing around with the idea of putting the F4's in a SUSY FB-loop, using your TXD's. Not sure if the TXD's can swing enough voltage, but with effective speakers it would likely be enough. Another appealing thought.



🙂
 
#1,023
steenoe said:

Hi Russ. Yes, that would probably be a more sane way to do it.
Actually I was playing around with the idea of putting the F4's in a SUSY FB-loop, using your TXD's. Not sure if the TXD's can swing enough voltage, but with effective speakers it would likely be enough. Another appealing thought.



🙂
Click to expand...

Indeed... 🙂 In fact i will share something here that may be even more appealing... 🙂

Cheers!
Russ
 
#1,025
Bfish:
Balanced input, J-fet frontend; what is there to be wished for, other than that?
Click to expand...

D'oh! I didn't think the babelfish was balanced:xeye:

Hi Russ!

I'm probably in total cranial shutdown but - what is BPA?:xeye:

oops, found it. It's a chip, right? You know good and well I'm not ready for those yet:clown: . I certainly know who to call when I am though

😉
 
#1,026
how about something like this?

Essentially its a discrete THS41xx type opamp. I have not tested it fully yet, at least not in this configuration, but I have a similar prototype working.

I wonder what Nelson would think... It seems to be a good combination to me. 🙂

Cheers!
Russ
 

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#1,030
Ok another factoid. 🙂

If you have an atteuator with a sufficiently low constant(or close) output impedance, you can omit the input(gain) resistors(R17, R18) and scale the feedback resistors(R16,R18) to suit your needs.

Example for AV of 10 you could use a "Joshua Tree" attenuator which has 750R output impedance and use 7.5K resistors for FB. This works very well actually.

Cheers!
Russ
 
#1,031
mpmarino said:
Bfish:


D'oh! I didn't think the babelfish was balanced:xeye:

Hi Russ!

I'm probably in total cranial shutdown but - what is BPA?:xeye:

oops, found it. It's a chip, right? You know good and well I'm not ready for those yet:clown: . I certainly know who to call when I am though

😉
Click to expand...


BPA is Bridged-Parallel-Amp.

Printing Russ's schematic right now🙂 Sure looks like a nice gainstage.

🙂
 
#1,032
steenoe said:
Taking it one step further would be to use the one I posted as woofer amp's, together with a pair of the stock bridged F4's for the fullranger (High/Mid) when the active crossover hits the download area at F-W. Spells powerfull, fully balanced setup😎
Appealing thought, but maybe 12 channels worth of F4's for a stereoamp is going a bit overboard? (No it aint😀 )
🙂
Click to expand...

This is the confirmation I was waiting for....Yes, you are NUTZ!
😀
 
#1,037
Nelson, congrats on the fine review😎 Those of us that build and listened to the F4 knew all that😉 We also knew about the preamps importance with this poweramp😀 You better build 150 preamps to go with those F4's😉 (And post the schematic here...he-he)

Steen🙂 :cheers:
 
#1,038
I want to mention

that the review is not yet complete. I'm sure he will add one or more pages talking about the various ways to implement the F4 and how it performs in these configurations.

It is of course in this early stage an extremely positive review and I look forward to building mine after I acquire a few heatsinks and the rest of the BOM.

C
 
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