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Old 26th January 2012, 03:37 PM   #121
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If you go to the http://www.firstwatt.com/prod.html site you can read the articles on the more recent Aleph J's, Aleph X and the F series amps amongst the others.
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Old 26th January 2012, 03:38 PM   #122
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Quote:
Originally Posted by pdhanwada View Post
50 W class A.
Define 50W Class A.

(normal 50W Class A is an amp that is able to deliver 3.5A peak output current without cross-over distortion due to part of the output stage closing shop)
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Old 26th January 2012, 04:01 PM   #123
a.wayne is offline a.wayne  United States
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Originally Posted by pdhanwada View Post
I get your point. I feel Alpeh4 is little too much for my place. It will turn out be a furnace generating about 600 to 800 watts of heat continously.

My place has 9 months of summer to 3 months of winter. Is there any other design which will get me 50 W class A.

Thanks
Pandu

Do the CViller cascode dual output version, this version can deliver 50watts /ch ....
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Old 26th January 2012, 04:10 PM   #124
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I had a look at the DIY-Audio store on the Cascoded F5 but the schematic images seem corrupted ?
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Old 26th January 2012, 05:50 PM   #125
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http://www.diyaudio.com/forums/blogs...version-2.html
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Old 26th January 2012, 05:56 PM   #126
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That certainly clears matters up. On The DIY-AUDIO schematic everything is BLACK, the colours indicate the options available.
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Old 26th January 2012, 07:51 PM   #127
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Originally Posted by jacco vermeulen View Post
What is there to say ?
Thanks for the explanation. Now I understand the reference to the 0.5 factor.
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Old 11th March 2012, 06:34 PM   #128
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Just searched for "F5 power" to check my calcs, and came across this; some good info.

I would just like to see if some of my thoughts/calculations are right. This is what I calculate:

Regarding the power of an F5, I calculate about 100W into 8ohms. This is assuming 40Vp-p output (a best-guess with +/- 25v rails). This gives P=Vrms^2/R=((20*sqrt(2))^2)/8=20^2*(2/8)=400/4=100w (if that notation makes any sense!). You can bias as you wish - or really has heat permits. The manual says bias to 25w, but I'm seeing this Class A power as "arbitrary" - is that right?

EDIT: At 100W, that calculates to 5Ap-p current output, so there is no current limit before 100W.

The same cannot be said for a Single Ended Class A. In that case, the MOSFETs are biased to their mid-operating point. The power of the amp is then its Class A power only.

So if the Aleph 4 is SE, and 100W Class A, and the F5 is 100W Class A/B (25W Class A), they both have basically the same "driving" ability.

This assumes massive PSUs which don't limit anything. Have I made any massive errors here?

Having completed my own F5 amp, I would say it is good - very good. I'm not being down on it here, but I would say that it sounds like a very solid, well designed amp. Its not "out of this world", but I suppose what I would expect for a £2k transistor amp - and that was about its retail. Clearly, I'm pretty chuffed for the £400 outlay, but I do prefer my Sugden - the mid range has just a slightly more correct timbre to the instruments, and doesn't really loose anywhere else.

Of course, the main temptation now is to try another First Watt variation!

Last edited by jt1000; 11th March 2012 at 06:38 PM.
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Old 11th March 2012, 07:53 PM   #129
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F5 is for 1.3A bias current.

25w class A / 25w classAB / into 8 ohms
12.5w classA / 50w classAB / into 4 ohms
6.25w classA / 100W classAB / into 2 ohms

Last edited by bobodioulasso; 11th March 2012 at 07:56 PM.
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Old 11th March 2012, 08:17 PM   #130
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Can you please explain why its only 25W Class AB into 8Ω? The Class A figures you give seem to add up to my calcs, but I cannot see how you arrived at the class AB figures. What am I missing?

Also, why do you say that the F5 is 1.3A bias? The comercial version was set to that, but as far as I can see, it will be a valid design at less than that (and maybe a bit more if you can keep the MOSFETS cool).

Just curious!
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