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Old 26th September 2012, 03:34 AM   #3491
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Quote:
Originally Posted by buzzforb View Post
If you got the gain, they got the grunt. That is biased at normal levels. If you are quazy, just bias them higher and raise rail voltage and you definitely have no issues. it is current amp, so it laughs at tough load. As for combinations, I have all boards in quesiton populated, its just matter of taking time to throw it together. I have always wanted tro try Lovoltech JFet SRPP FE for F4. Taylor it to specific Zin of jfet free F4 and you got an amp that can swing big V and shoot big I
Buzz - thanks for the input
You have me re-reading this thread and the BA3 thread
I would like to build a "bass" amp (driving SEAS w26s) to replace my Crown K1s.
Having done two headphone F4s with interstage transformers makes me lean to a full F4 with the same - love the simplicity - but there is the appeal of something new - the BA3
I also have been following the F6 thread and that is one intriguing amp. What would we do w/o DIY
Best
Bob
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Old 30th September 2012, 03:49 AM   #3492
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Hooked up my Jensen F4 to the Ravens in my system a couple of days ago
Kept the F3 driving the PHL midranges
Moved the Aleph 30s from Ravens to drive the SEAS W26 bass driver

First of all I must say that I forgot that the Alephs can put out in the lower range.

Overall I find that I have a wider soundstage, better localization of instruments. nice tight bass and a system that I can listen to without fatigue.

The transformer F4 continues to intrigue/fascinate me. Once and if I can get my head around it I would like to build a F6 and try it to drive the PHLs moving the F3 to the Ravens. Maybe the Ravens favor a current amp. Don't know but it could be an interesting experiment.I do know that the Crown K1s may be headed to CraigsList

Maybe a crazy question but could the F3 be used to drive a stock F4 (no interstage transformer)? Same question about the Aleph30 - can it be used to drive stock F4?

Best


Bob
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Old 30th September 2012, 02:49 PM   #3493
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Quote:
Originally Posted by flocchini View Post
.......

Maybe a crazy question but could the F3 be used to drive a stock F4 (no interstage transformer)? Same question about the Aleph30 - can it be used to drive stock F4?

Best


Bob
both can drive F4 , even if real benefit one can expect only in case of F3 feeding F4 , if increased power is goal
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Old 12th November 2012, 10:16 PM   #3494
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I have a quick question for the experts --

Are the transistors that buzzforb sells, the Fairchild FQA19N20C(FQA16n25C) and FQA12P20 , direct substitutes for the IRFP240 / IRFP9240 when building a F4?

Are any changes to the circuit required or suggested?

Thanks,

Jim
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Old 12th November 2012, 11:14 PM   #3495
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just toss them in
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Old 12th November 2012, 11:27 PM   #3496
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I have more rif you need them
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Old 12th November 2012, 11:30 PM   #3497
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Quote:
Originally Posted by Zen Mod View Post
just toss them in
That's what I thought, but it never hurts to double check.



Thanks!
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Old 17th November 2012, 02:15 PM   #3498
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Here's another question - how much input voltage would it take to drive a F4 from the XLR input to get 5 watt into 50ohm?

I know there is a way to compute that, but I haven't a clue to the formula.

Also, does the drive voltage requirement increase or decrease for a given output if you use the balanced vs. the RCA input?
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Old 17th November 2012, 02:33 PM   #3499
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let's go backwards

say that F4 will squeeze +/- 20V sine at output (round number because of clarity ; real life - it's in ballpark )

that's 40Vp-p

that's 40V/2 peak

that's (40V/2)/1.41 RMS

as P is U^2 / R

that's (for 8R) : 14V14^2 / 8 = 25W

now go backwards

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Last edited by Zen Mod; 17th November 2012 at 02:37 PM.
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Old 17th November 2012, 03:22 PM   #3500
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So if you have that same input signal of 40v p-p (14vRMS)

into 50R

14^2 / 50 = 8w ?

Is that correct?

Next question - with a 2v source (computer, Dac, CD player, etc...) how much signal would you get from 30db gain? (such as a BA-3 front end...) I'm not super clear on how db works...

And does using it (the BA-3) balanced change the gain or is it the same?
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