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Old 23rd November 2005, 11:30 AM   #1
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Default FET experts advice needed

Hello !

Could someone give me an advice on this HexFet based power amp Schematic.
I'm thinking to build it - but with different output fets IRFP240 and IRFP9240 and with +/- 50V DC on the power supply. I'm not shure if this project is worth to build (I'm not expert in fet based amps) so I ask You experts for an opinion.

Thanks for all info
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Old 23rd November 2005, 12:17 PM   #2
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The FETs should swap fine, but 50V might be a bit too high with a 4 ohm load.
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Old 23rd November 2005, 05:30 PM   #3
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The load will be 8 ohm. How many watts can I espect on 8 ohm load with +/- 50V DC with this setup ?

Cheers
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Old 23rd November 2005, 05:39 PM   #4
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Even for 8 Ohm load you have to take into account impedance dips to some 5 Ohm (I assume you are not going to listen to the sound of pure resistor).

What is worse, the speaker is a reactive load with considerable impedance phase shifts. So peak current and peak power is the issue. +/- 50V is really a lot for just one pair of output devices.
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Old 24th November 2005, 01:52 AM   #5
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Hi bostjancek,

You should look at the other thread regarding the instability with this Giesbert design -

Need help with Giesberts HEXFET AMP

Or you could look to my Simple Killer amp -

Simple Killer Amp!

or check on my website for the simple, elegant GB150D. Mine is stable.

http://members.dodo.com.au/~gregball/guru_004.htm

Cheers,
Greg
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