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Old 3rd May 2009, 09:25 PM   #11
Zen Mod is offline Zen Mod  Serbia
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good enough

go for +/-20V , and use 2 pairs , as you say ;

Papa use 3 pairs to make amp capable of delivering proper output current ;

if your speakers aren't current hungry , you can make compromises ;
if they are , think about using original circuitry
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Old 3rd May 2009, 09:32 PM   #12
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Quote:
Originally posted by Zen Mod
good enough

go for +/-20V , and use 2 pairs , as you say ;

Papa use 3 pairs to make amp capable of delivering proper output current ;
Actually, the plan is to use three pairs if the heatsinks will take it, two if not...
Any idea what power output 2 pairs would give?

Quote:

if your speakers aren't current hungry , you can make compromises ;
if they are , think about using original circuitry
How can you tell how current hungry speakers are? (A reference for me to read up would be great...)

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Old 3rd May 2009, 09:58 PM   #13
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which speakers you intend to use ?
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Old 3rd May 2009, 10:05 PM   #14
njepitt is offline njepitt  United Kingdom
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Quote:
Originally posted by Zen Mod
which speakers you intend to use ?
I'll probably try it with my B&W CDM2s in the living room, but I expect to use it more with the FE127es I have in my office. (If I replace the B&Ws in the living room in the near future it'll probably be for some other diy design based on Fostex's of some sort. I'd love the Jordans but they're too much money for the time being.)

Does this mean "current hunger" is just an empirical thing? Or can it be deduced for t-S parameters or something?

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Old 3rd May 2009, 10:19 PM   #15
Zen Mod is offline Zen Mod  Serbia
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current hungry - at least when we are speaking about "normal" home speakers -is more related to nice ( ie. flattest as possible , without heavy dips) speaker impedance .

anyway - if you think tat you're almost there with 8W Hiraga , then F4 will give you necessary boost - but only current wise .

amp power is nothing else than ratio of voltage and current at load ( speakers)

F4 is power follower - it will push exactly same voltage you threw it in , but it will feed more current through load if needed , than yur wimpy amp you use to drive it ( generally speaking , even if Hiraga 8W is certainly proper candidate to call it wimpy )

re-read few times F4 pdf . Papa already answered there on most of your questions

regarding amp power calc - just google , you'll find several tutorials , certainly better explanation than I can type right now .....
in any case - with +/-20V you'll have little less W at output , but don't loose sleep about that ....
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Old 3rd May 2009, 10:25 PM   #16
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ZM: Many thanks. I'll read up on all this (including the F4.pdf again) and meanwhile carry on building.... Let's see how it all fits together!

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Old 3rd May 2009, 10:29 PM   #17
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Oh, and I forgot to add that I'm still looking at the Pumpkin stuff. If the F4 goes well this may be next project

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Old 8th May 2009, 11:55 PM   #18
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I'm still doing the metalwork on heatsinks, and tomorrow I'll ttry to buy compenents.

Here's a question for someone with more experience than I have: I need to match mosfets for the outputs on the F4. I presume it's OK to match in threes; that is, the three N-fets on one channel need to be matched to each other, but not necessarily matched too closely channel-to -channel. So here's the question: experience says I will likely need how many IRFP240's to get two sets of three matched? I ask because unlike many people on the forum it'll be a long time before I use up a large number of extra mosfets, so I don't want to exaggerate on numbers... Does 8 sound overoptimistic?

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Old 9th May 2009, 03:48 PM   #19
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Default Mosfet alternatives?

Hi all. I've just got back from my local electronics supplier, whom I like to support when possible. The output mosfets are going to be really pricy - the IRFP9240 is US$5 each, so buying a reasonable number for matching is probably not practical. I can try and buy online, which might help a bit, but importing brings its own problems of import taxes....
I should add, in light of my questions above, that I am hoping the heatsinks will take three pairs per channel, and will only reduce to two if necessary.

(I also checked the Fairchild equivalents - I can buy the FQA12P20 from Farnell online, but the N-channel equivalent is still extremely expensive - nearly US$6 each.)

There are a few places in the big F4 thread where people talk about alternative mosfets, so I was wondering if people had suggestions for more economical alternatives.... If I understand correctly, the Int. Rectifier codes start "IRF", for instance IRF9610, and the ones that start "IRFP", for instance IRFP9240 are higher power ones, or something. Are the lower power ones going to be adequate? They are only biased at 0.5A, after all...

So, any ideas? Anyone else had the same problem?

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Old 9th May 2009, 06:11 PM   #20
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i have 25 FQA12P20 spare. Email me off list if you are interested.
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