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Old 26th June 2002, 10:04 PM   #11
Duo is offline Duo  Canada
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Ok, thanks, I'll look at the pages... I do use google already, and I agree, it's a very good search engine...
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Old 26th June 2002, 10:13 PM   #12
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Quote:
Originally posted by Duo
Also, my intention was to drive the amplifier from the output of another hifi amplifier (since they are designed for low impedance loads) and even if it would work for a sub amplifier (100hz and down)
Hey, hey, hey, you really ARE crazy!

Seriously, go for the concept AMPLIFIER, not a buffer. First, if you anyway will try that, how much gain do you need. I'd say not more than 5. Now you have 2000 (haven't done any calculating). Roughly 1 mA + 1kohms = 40, 10 mA - >400. 50 mA -> 2000. The speed of the transistor is around a couple of MHz. This means bandwith approx. a few kilohertz!

The DC at the output? Avoid big caps in series with the load. >10000 uF/50-100V.

If you are going to do a bass amp, it's VERY easy with MOSFET's because the demand very little drive power. The amp I have to my subwoofer needs only 4 mA at 160 V! delivers 500 Watts
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Old 26th June 2002, 10:26 PM   #13
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Do I shoot my mouth off arrogently? Nah, if you want to hear that, go follow SliceMaster101's threads. My problem has just been that people would say I couldn't do it and I was asking for trouble (I had this direct-line rectification thing, 900W amps with +/-160V supply, series-parallel speakers, and stuff) and I wouldn't take it from them. Just don't be like that and you'll be fine. I've just been kind of think-headed, not arrogent, I think people will agree. Now that I'm on the right track (well, better), some people can't quite grasp the concept. I'm no expert, but I do try to help with whatever I do know.

Anyway, like Peranders said, you need an amp, not a buffer, and some MJ15003/MJ15004 output devices, or maybe MOSFETs if you really do want class A. Power amps tend to be just like a big descrete op-amp.
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Old 26th June 2002, 10:54 PM   #14
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Ok, but like I said I have some a1492 and c3856 transistors, do you think I'd be better off making a class ab amp instead with these transistors, I know that they are for audio so I figure they can't be bad...
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Old 26th June 2002, 11:10 PM   #15
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I would think so, but of course you could still do class A if you really want to, but at 450W, I don't know what you would do with all that heat, unless you use water cooling.

P.S. Aud_Mot, it's not "Randy Slone: Audio Power Amplifier Design Handbook" He wrote the "High Power Audio Amplifier Construction Manual" They are very long titles, I know.
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Old 27th June 2002, 12:04 AM   #16
haldor is offline haldor  United States
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Quote:
Originally posted by Kilowatt
Do I shoot my mouth off arrogently?
...
My problem has just been that people would say I couldn't do it and I was asking for trouble
...
I've just been kind of think-headed, not arrogent, I think people will agree.
...
I'm no expert, but I do try to help with whatever I do know.
Hi Kilowatt.

I've got to say you have really grown and matured in this art. Your comments to Dug have been helpful and right on the money.

P.S. I never thought you were arrogent, just not very likely to see your 17th birthday. ;^) Not everyone can learn from the experiances of others, glad to see you can.

P.P.S. Can't wait to hear your outdoor system when you get it built. I expect I might be able to hear it from my home in South Carolina. (Joke) "imitating Jocko"

Phil
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Old 27th June 2002, 12:08 AM   #17
Duo is offline Duo  Canada
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Yeah, I noticed that he wrote the wrong name for the book, but I knew what he meant, I porbably would've done that too, seeing that it's such a long name... Anyway, thanks for your opinion on the other transistors, I guess it is possible to do class A with complementary pairs isn't it?
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Old 27th June 2002, 12:37 AM   #18
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Sure it is. It's just that Mr. Pass likes single ended MOSFET class A, I've heard those sound sweet, but I haven't actually heard any. Mr. Slone has a complementary 40W class A design that can do 0.0018%THD (and he doesn't exaggerate). You say you have 4 pairs of A1492/C3856, you could make a 2 channel version of something like that and use them, you'd have just enough.
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Old 27th June 2002, 12:49 AM   #19
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You mean a two channel version at 40 watts or at a much higher level... I don't need to work for things lik .0018% THD just yet but I would like moderate quality... I have heard many class ab amps that sound wonderful, right now, I use a Harman/Kardon HK A402
with 60 watts a side which is AB and it has a very clean finesse to it's sound, I got it from an audiophile with a pair of ATC SCM100 speakers with builtin pure class A mosfet amps, triamped with 400 watts an amp... He says that the Harman/Kardon has comparable quality to the Krell amps in the ATC's. I would be happy to design a push pull amp with more power, one aim is to be able to give my speakers more power so they can really pack their punch, I don't care if the quality of the amp isn't that of pure class A, but I also don't want to fry my speakers, which would also be quite hard to do... I used to have an amp that had four channels, each class AB using an a1302 and c3856 pair which was bridgeable to stereo with 350watts a side into two ohms...
But I don't have it anymore...
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Old 27th June 2002, 01:17 AM   #20
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With class A you couldn't get more than maybe 80W total out of those transistors, but class AB you could get like 300 or 400W. I assume you want to go class AB, and class AB amps can be made to have like 0.003% or less THD, but it's fairly complex if you want numbers like that (and numbers aren't everything anyway). Even a really simple class AB amp can sound great though, like that project3A from your other thread, for example. You could get like 700-800W total with those 30 2N3055s (a pair will make a 60W amp), even though they do kind of suck by today's standards. Whatever you do, I hope it turns out great.
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