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Old 13th July 2012, 04:01 PM   #451
OllBoll is offline OllBoll  Sweden
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Quote:
Originally Posted by Lazybutt View Post
Everything is possible within reason... or rather ... within components specs.
With such a simple circuit, you can play with U and I by just playing with components values.
Just check Umax and Pmax of every components, and keep a safety margin.

I is set by R16//R17 in the current source... if it's not obvious to you (it wasn't to me), read the Zen Amp series articles to understand how, but in essence, increase R16//R17 to reduce I
Nice, thanks for answering =)

I've read the Zen articles which is what gave me the idea since Nelson experiments with lots of different voltages and the F2 is if I remember correctly based on the Zen. I'm no electronics expert though so I thought I'd also ask to be sure

So now another question if someone knows, is current linear in proportion to R16/R17 or is it some exponential whatnot such that I ideally need a pot to dial in amount of current?
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Old 13th July 2012, 05:28 PM   #452
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Quote:
is current linear in proportion to R16/R17 or is it some exponential whatnot such that I ideally need a pot to dial in amount of current?
It is inversely proportional. That is; I=0.66/R or, R=0.66/I
Read first Zen article for describing this type of current source in better detail.
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Old 13th July 2012, 06:19 PM   #453
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In other words it's just simply Ohm's Law. R16/R17 are current sensing resistors. The circuit is designed to keep the voltage drop across R16/R17 at 0.66V.
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Old 2nd December 2012, 02:42 PM   #454
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Red face F2J DIYer needs help

Hi, I've been a 2A3 amp user a while but like to go SS with the F2J...... keep hearing about boards available from Daniel.. how do I get in touch with him ? And is Bias adjustments etc. requiring a lot of equipment ?

Lot of Thanks, Mike
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Old 2nd December 2012, 02:59 PM   #455
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Peter Daniel
Or PM from the Forum
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Old 2nd January 2013, 03:44 PM   #456
OllBoll is offline OllBoll  Sweden
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Hello there again,

I'm considering adding an input transformer since I have a balanced source. If I've understood correctly the Jensen JT-11P-1 works well for this area.

So now the question: The Jensen is 10k:10k, and the F2J has 10k input impedance so I should just hook up the trafo before the F2J without putting any extra resistors on either side?

Thanks in advance,
Olle
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Old 2nd January 2013, 07:42 PM   #457
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most probably

don't be lazy - put link to datasheet , so we can check it together
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Old 2nd January 2013, 08:17 PM   #458
OllBoll is offline OllBoll  Sweden
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Forgot that =)
http://www.jensen-transformers.com/datashts/11p1.pdf
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Old 2nd January 2013, 08:41 PM   #459
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just go with typical application pic , having R1+C1 combo across secondary
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Old 16th January 2013, 07:05 PM   #460
OllBoll is offline OllBoll  Sweden
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Just powered up and measured my F2J with the input trafo and 48V rail voltages and halved current

Max clean output @ 8 ohm is ~ 4 Vrms so 2W if I've understood correctly.

Much more than 24V but still not a lot and hoped for more, I think it will be enough though since it will drive 300 and upwards with 94 db efficient drivers.
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