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Old 2nd March 2010, 12:54 AM   #1
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Default scaling down F4

Hello everybody,

I'm newbie as far as audio electronics are concerned so sorry for any stupid questions.
My problem is as follows: I don't need nowhere near 25W that F4 can produce so I thought about scaling it down to about 5W. Looking at the schematic, I suppose I should use just one pair of hexfets, but I don't really know how/if to modify protection circuit or scale drain resistors to achieve mentioned output watts. I'll be driving it with a tube akido-style preamp.

I'd be gratefull for your help.

Michal
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Old 2nd March 2010, 12:58 AM   #2
Zen Mod is offline Zen Mod  Serbia
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first few pages of F4 thread
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Old 2nd March 2010, 01:32 AM   #3
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Thanks for the answer. I've found your schematic. Did you built that circuit? What was the output power?

thanks,
Michał
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Old 2nd March 2010, 08:24 AM   #4
Zen Mod is offline Zen Mod  Serbia
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I didn't but few DiyAs were , including headphone amp iteration ;

for your needs - you can build it with any PSU voltages going from +/-15V and up , and from Iq going from 500mA and up

less than 15V PSU and amp will suffer in linearity , same for bias - less than 500mA ......

make it , then let your ears decide when is lowest bias you can use
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Old 3rd March 2010, 10:31 PM   #5
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I have built an F4 variant that has 5 pairs of IRF610/IRF9610 mosfets on the output. It works and sounds great as a DI box for bass guitar. It has an advantage over Zen Mod's excellent circuit in that the output bias is spread over many devices eliminating the need for heat sinks. It would probably make a good headphone amp. I figure the output to be about 2.5W.

One of these days I'll start a thread on the project. But you don't need my schematic. It's easy enough to design your own. After all - we're fearless DIY'ers here!

Graeme
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Old 3rd March 2010, 11:00 PM   #6
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I've built the headphone ZM Variant. I like it very much. I really like the top-end presentation.
Mines biased at 250mv at 15-16v. As much as the puny tranny can do.
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