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Old 26th June 2002, 09:24 AM   #1
Duo is offline Duo  Canada
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Post My amplifier ideas (crazy)

Well, I tried a taste of some ohm-slaw and transistor theory
and got up a crazy idea to design and build a set of 450 watt low gain amplifiers for my speakers which are rated at about 600 watts rms. Trust me, I won't need to go as far as 600 watts unless I'm trying to level a building, which can wait till I'm really sure of what I'm doing ... Anyhow, I'd like some opinions from the more experienced people out there on this amp I designed before I attempt to build it. Please look at the attached diagram and say if you think
it'll even power up without frying and also what might be done to make it a better amp. I biased it so that each of the 2n3055's(except for the darlington drivers) is idling at one amp, making a Q current of 10 amps just for the main O/T transistors. Thanks for
any suggestions or to point out that I'm completely nuts! Duo
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Old 26th June 2002, 09:35 AM   #2
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Default Darn, forgot the file on the last post...

Heres's the diagram for the 450 watt amp in the prev. post...
Attached Images
File Type: jpg 450rms.jpg (64.8 KB, 1132 views)
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Old 26th June 2002, 10:20 AM   #3
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Well, I must say that schematic barely resembles anything suitable for a 450W amp. It looks more like something you'd find in a tiny cheap radio or a Gameboy or something. I don't think that design would work so well for a power amp, but you should take it from the more experienced people here than me. I see it's class A too, you're going to be dissapating a LOT of heat if you do it that way. Plan on cooling it with a pair of truck radiators? I've never heard of a 450W amp with that much bias current. Also, why don't you use differential input stage? I see you have no global NFB either. You also need a way higher supply voltage, you need plenty of headroom, it's not based just on ohm's law alone. You need a lot more than ohm's law and transistor theory to design a 450W amp. There are so many things that modern amps incorporate into their designs that your circuit lacks.

To get a good foothold in audio design, you should check out web sites like http://sound.westhost.com, he has a page there on audio amp basics, and read some books on amplifier design, like Randy Slone's "High Power Audio Amplifier Construction Manual" and Doug Self's "Audio Power Amplifier Design Handbook". I remember when I was where you are, it wasn't so long ago. You just need to read up a little more.

Good Luck!

P.S. I'm building some 450W amps too, but they're for 2 ohm operation. I have quite an extensive thread on it ("1kW MOSFET amplifier") you should check it out. My reputation here still suffers from this project, (it was worse before I decided to make 14x450W amps and 8x112W amps instead of 8x900W into 12 ohm amps) so watch out if you dive into something big too early, people will critisize you mercilessly if you don't follow their every bit of advice.

P.P.S. It's great to have more young people like myself here. I'm 16. Even though I think it scares some of the elders.
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Old 26th June 2002, 01:30 PM   #4
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The old ones are too conservative, that's the problem.

Duo, you might need an extra darlington transistor on the drive stage to manage all the current without upsetting the I/P stage.

/Marcus
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Old 26th June 2002, 01:41 PM   #5
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HI Duo. This is a pretty safe forum for putting forth ideas you might consider "crazy". The people here will only "criticise you mercilessly" if you know little *and* shoot your mouth off arrogantly. Knowing little is not in itself a bad thing. Also if someone unjustly criticises you, watch and see if hordes of others don't come to the rescue.

As for your amplifier, I think you are asking *way* too much of '3055's. Look up "safe operating area" or "SOAR". Your'e gunna pop them for sure. Thomas Edison said that invention is "1% inspiration, 99% perspiration". Power electronics, including amplifier design is all blood sweat and tears, all three factor vying for supremacy. Other than that, keep thinking amps, dude! You'll get there!

GP.

"With power electronics you are always only a microsecond away from misery".
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Old 26th June 2002, 05:43 PM   #6
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Duo, since you are 16 I suspect that you know not as much as a pro.

First of all: If you have an idea and can't analyze it theoreticly test the circuit with small signal transistor. If can't get it work, it probely won't work with higher voltage and bigger transistors.

My opinion of your idea:

You have no control over the DC-level (at the output) and working currents.

The input impedance is practically nothing (may be a problem if the signal source can't deliver enough)

The output stage is working in class-A (is it by purpose?), lots of heat! Class A is not a bad thing if yoou really want it.

Worst of all: The distortion will probely be horrible.

Conclusion: You must create stable working conditions. Chosen transistors are slow, the amp may be too slow.

My best advice is to look around and see how have others have done. Check my stuff, check Nelson Pass' stuff, Check Rod Elliott's stuff, check Lars Clausen's amps, check schematics from commercial amps (I have learned of lot by that). Try also to get knowledge about each transistor circuit and feedback theory, otherwise it will be only a struck of luck if you succeed. Start to learn how a simple standard amp works, then it will be easier to develop ideas of your own.

http://www.lcaudio.dk/
http://www.passdiy.com/
http://www.sound.au.com/
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Old 26th June 2002, 07:57 PM   #7
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Default Hmmm

OK, I know what you guys mean, that's kinda what I was thinking about, overcurrent for the transistors and problems with control... I wasn't sure about the 3055's being slow because I can't find any good spec sheets on them... By the way, the design was intended to be class A and run quite hot, (I calculated that it would idle about 2500 watts at the connection to the electrics... Quite a light dimmer, i'd need a dryer outlet for it...
Anyway, back to the point, even if I had some good spec sheets(with curves) and some literature, I'm pretty sure I could make something that's work... I'm just real bad at finding that kind of information.
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Old 26th June 2002, 08:11 PM   #8
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Actually, I thought of something I should of mentioned earlier..
I'm not really aiming for perfect audio characteristics just yet,
even if I got it to power up and add some dirty current to a signal, I'd be quite happy. Also, the main reason I picked the 3055's is because I have about 30 of them in a tray on my bench.
Though I do have 4 pairs of A1492 & C3856, do you guys think those transistors would be a good choice for such great power output? 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) I'd be satisfied. I could later add things to make it better and better until I am sure of how everything works.
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Old 26th June 2002, 08:22 PM   #9
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Duo,

Education and Understanding is key.

2 books: Pick 1 of the 2. For you, I would say the Randy Slone book. He is more PA and musical instrument amp oriented. Seems to understand the need for high power.

Randy Slone: Audio Power Amplifier Design Handbook
Doug Self: Audio Power Amplifier Design Handbook

A very good book and worth every penny: You should ge this.

Paul Horowitz, Winfield Hill: The Art of Electonics

Aud_Mot
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Old 26th June 2002, 10:00 PM   #10
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Default Re: Hmmm

Quote:
Originally posted by Duo
:I wasn't sure about the 3055's being slow because I can't find any good spec sheets on them... By the way, the design was intended to be class A and run quite hot, (I calculated that it would idle about 2500 watts at the connection to the electrics... Quite a light dimmer, i'd need a dryer outlet for it...
Try http://www.questlink.com a goldmine for pros and amatuers.

Quote:
Originally posted by Duo

Anyway, back to the point, even if I had some good spec sheets(with curves) and some literature, I'm pretty sure I could make something that's work... I'm just real bad at finding that kind of information.
Check all link collections, check MY link page! Check this site's link collections!

Try search engines. Google is good, IX search is good, Dogpile OK, Altavista OK

http://home5.swipnet.se/~w-50719/lin...#searchengines
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