How do I make a high power audio amplifier?

How to build an amplifier?

• Alright, so I have been off the forums (diyma, 12volt, etc) for quite some time now. I am very knowledgeable W/ "mobile audio" & I am a total noob W/ certain things. I can tell you all about characteristics of various cone materials, tweeter composition, slopes, crossover points, & even a bit of pyscho acoustics (diffraction & reflection). However, I still do not know how to build an amplifier! I have a very basic understanding of FETS, transistors, Caps, Resistors, etc. However, I am up for the challenge. I understand there are several types of amplifiers. This will not be a "tube" amplifier. It will be a "mobile audio" amplifier. Now I know those of you who are knowledgeable W/ audio are going to be laughing at me cuz people do make tube amplifiers that run off DC power. -Take a look at McIntosh. Anyways, so the amplifier I will be fabricating will be ran off of DC Power. Now there are several types of amplifiers right? Class D, A, A/b, G-H, etc. So what type? Well, this amplifier will run a set of Mids for now (I will explain crossover below) so I take it I will be using A/B (for whatever reason?). Class D seems more geared towards "subwoofers." Class G-H is beyond me. I believe ARC & Vibe uses this "new" idea or whatever you want to call it & class A amplifiers are not efficient at all. Watts. I take it this will be my next quesiton? My speakers rate 25 watts. yes, RMS so I figure 30-40 watts RMS should be a good target/goal. They run at 8 ohms, yes they are "raw drivers." -Now this is beyond me & I am not sure how this plays a role. Okay, so here is a few other things I know: Most amplifiers, if not all are built off PCB boards, correct? I know there's a lot of youtube tutorials on how to etch your own & I'd be up for it. I have a few starter breadboards that I could play around with. Cooling: LOL, I assume I will be running fans. Now how does this work? I took a look at a few of my amplifiers and it appears as the FETS run off the heatsink. Are the FETS the only things that gets hot? Oh, my active crossovers will be done at the Source so all I need out of this amplifier is raw power. An amplifier is just a voltage booster right? Gain: Okay, I understand the gain is there to match the signal output from the source to the amplifier right. So what if I know the exact voltage coming from my source, than can do I even need a "variable" gain adjuster? Ha, so I know a bit here & there, but if someone could sum it up for me that'd be great!

• Answer:

  You definitely want Douglas Self's 5th edition of "Audio Power Amplifier Design Handbook." First link below. You may also want to read some comments about the book (55 pages of them) from another link (second link below.) There is hardly anything better as one very good, comprehensive, and very systematic design volume. Packed with practical information, too. For the very basics, you need to understand how a differential BJT pair works, what a current mirror is and how to design with them (widlar and wilson, at least), how a VAS works and what role it plays between the input stage and the output stage, how to design a Vbe multiplier and why a collector resistor can improve its performance (and what function it serves just before the output stage), various types of output stages and modes of operation (A, A/B, B, at least) and how to move operation from one to another, power supply design, and some knowledge about negative feedback (global and local.) FETs aren't spec'd for linear operation. At least, none I've seen. In the linear region, they just don't write much specification text. They are used, of course, for the "above class C" modes. But you need to walk before you run. So start with BJTs. Read Doug's book. You don't have to understand all of it to do something good. But it sure helps to have that book handy as you think about things and move forward. Worth each cent you will spend. I'd definitely recommend starting small, too. Like something on the order of 1 or 2 watts. Or less, even. Just to get the ideas down with something cheap to replace when you burn them up. If you don't have an oscilloscope around, I'd seriously think about it. They are so darned cheap these days. Rigol is officially selling their 2-ch, 100MHz scope for under $400, last I checked. (Last link.) And a voltmeter, obviously. Finally, I added Bob Cordell's book, as well. Worth getting as well. 4th link below. I also haven't seen or read Self's other book on small signal audio design, but am including a link to it (5th link.)