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Old 30th June 2012, 07:16 PM   #281
acl0056 is offline acl0056  United States
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Can anyone suggest a maximum rail voltage for F5 turbo V2, using IRF devices and/or tell me how to calculate this? I have a spare transformer that would give me 63V rails.
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Old 30th June 2012, 08:09 PM   #282
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that is way to high. with only 2 output pairs you will have very low bis and class A power.
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Old 30th June 2012, 10:57 PM   #283
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Quote:
Originally Posted by acl0056 View Post
63V rails.
Even with an F5T in class AB, that will not work, unless you run them with "normal" loudspeakers.
With regular sensitivity & impedance loudspeakers, there's no point in going for an F5T.

Allowable rail voltage is determined by the maximum dissipation level.
Max dissipation is not set, just by the output device type and number, also by the heatsink size, and the lowest impedance the amp is supposed to handle without breaking down.
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Old 1st July 2012, 12:06 AM   #284
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Quote:
Can anyone suggest a maximum rail voltage for F5 turbo V2, using IRF devices and/or tell me how to calculate this? I have a spare transformer that would give me 63V rails.
Quote:
The more technically astute DIYer may note that the input Jfets are now
being exposed to greater voltage and dissipation, and this might be a
concern. With respect to voltage, the operating point of these devices is
around 30 volts, 5 volts over their rating. In actual testing these devices
break down around 43 volts, and I depend on Toshiba's famed conservatism
to carry the day. If you don't want to trust Toshiba as much as I do, then you can cascode these devices
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Old 1st July 2012, 02:23 AM   #285
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this is no problem. the boards that will be sold here, you can cascode the J-fets.
but with 63V rails and 2 pair of outputs, the max bias will be around 0.6A pr device(around 40W pr device). so 1.2A bias. thats 20W classA in 8ohms. and a dissipation of 150W pr ch.
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Old 1st July 2012, 03:14 AM   #286
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Quote:
Originally Posted by acl0056 View Post
Can anyone suggest a maximum rail voltage for F5 turbo V2, using IRF devices and/or tell me how to calculate this? I have a spare transformer that would give me 63V rails.
You could do 63V at 1A bias, provided you have adequate heatsinking(126W). You will definitely need cascode at the input.
3 pairs at output.
Probably not the most ideal operating parameters, but if you already have the transformer it doesn't hurt to build it.
Hopefully your transformer is around 500VA
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Old 1st July 2012, 03:49 AM   #287
a.wayne is offline a.wayne  United States
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Quote:
Originally Posted by AudioSan View Post
this is no problem. the boards that will be sold here, you can cascode the J-fets.
but with 63V rails and 2 pair of outputs, the max bias will be around 0.6A pr device(around 40W pr device). so 1.2A bias. thats 20W classA in 8ohms. and a dissipation of 150W pr ch.
Did you finish the test boards yet ...?
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Old 1st July 2012, 06:57 AM   #288
acl0056 is offline acl0056  United States
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I think I will try out the transformer I have with a honey badger build, and also build an F5T V2 using the prescribed psu with my matched IRF devices. My wife will be so happy for me... Because naturally I will need to build more speakers too!
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Last edited by acl0056; 1st July 2012 at 07:17 AM.
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Old 1st July 2012, 11:16 AM   #289
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Did you finish the test boards yet ...?
hello. no, i'm waiting for the new output boards. but i have been ordering som parts. the plan is to have them up and running before the winter time
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Old 11th July 2012, 07:02 AM   #290
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hi,
Just got my F5C from the store up and running,I made some mistakes,I lost a output fet,lol.
I used the schematic I've enclosed ,I found alot of variations so This schematic is working good,
I have been reading all the F5 threads,took some time but I'm old school 2n2222,not fets ,lol.But coming up fast,lol.
I have this F5c at 43 vdc,loaded,I have small heatsinks,got fans on them at and biased at .5 there running 95 degrees F,I'll get the screw driver to them in a few days of running,It actually has more power that I need right now,so might bump the bias a little and that's it.
I am using a 5 amp transformer,35A block Bridge,Papa's PS with 6 6800 Nich@63v per side,
I powered a F5 with 2x18 3 amps at 24v with Papa's crc with 8 15,000 Elna,more than enough power,Ready to build a Balanced B-3,I've got the active crossover,almost there!
Happy Listening!
NS
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