Learning curve of electronics is steeper than I expected
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 3rd February 2014, 04:17 AM #1 diyAudio Member   Join Date: Jun 2013 Learning curve of electronics is steeper than I expected On the input of most (if not all?) amplifiers is a capacitor. Why? Transistors don't work on AC. The capacitor takes the AC signal and turns it into (by magic to me) a varying DC signal. Let's imagine the flow of electrons as automobiles. In an AC signal the automobiles travel in one direction, turn around, and travel in the other. In a varying DC, the automobiles accelerate, peak, then decelerate to a trough, and so on. THE AUTOMOBILES NEVER CHANGE DIRECTION! So? So! So what if your signal goes from +4V to -6V! How can an automobile accelerate to 4mph and decelerate back 6mph ...all while traveling in the same direction! Impossible! Transistors also confuse me. Maybe it's best I explain to you how I think they work. Now crystals are small, and so are junctions, so I'm going to falsely explain how a signal is amplified with a triode (vacuum tube). Okay, 3 terminals. One in the center and two at opposing ends. Hook those two opposing ends of the tube up to a battery (amplifiers can't create power out of nowhere). Now you should have a really strong current flowing through the tube. Now take on of the wires from your input and wire it to the center tube. Well I don't know where that other wire goes from the input signal. I'm just hoping to get across the idea that I see nothing special about a triode vacuum tube. How is that any different than wiring in a battery either in series or parallel with the signal? (I do understand the importance of the diode in my crystal set, but you dont need to AM your signal from your receiver to your speakers, so there's no reason to extract any signal here) Thanks!
 3rd February 2014, 05:54 AM #2 diyAudio Member   Join Date: Dec 2010 Location: wigan The input capacitor blocks Direct current it will also act as a high pass filter its frequency of operation is dependent on the capacitor value and any resistance that follows.. Ps Transistors do amplify AC. To simplify try looking at a transistor as an electronic controlled variable resistor it may help a little regards Last edited by madtecchy; 3rd February 2014 at 06:01 AM. Reason: ps
 3rd February 2014, 12:06 PM #3 diyAudio Member   Join Date: Dec 2009 Location: Md LOL. Well, I have a degree in electronics with 40 years of experience and I know almost NOTHING. You will spend your entire life learning electronics. If you have not had the basic electronics classes, you really need to. The WEB is full of basic classes for free, or try and find one you can pick up as an elective whatever your major is. (We are not prejudicial of art history majors here). I find I can explain electronics better with plumbing analogies than cars. The electrons actually DO change directions, in a simplistic sense. That is the DEFINITION of AC. What you are thinking about is an AC with a DC offset.
 3rd February 2014, 02:04 PM #4 expert in tautology diyAudio Member     Join Date: Apr 2002 Location: New York State USA AC. Think of a rope tied in a circle, around two pulleys (clothes line). Pull back and forth = AC Pull in one direction only = DC Capacitor in this application *blocks* DC, but passes AC (magic). Tube, transistor, etc. It's a VALVE. Just like a water valve. Big pipe coming in. Big pipe going out. Nothing goes through until you turn the valve. You can't stop the water with your finger, but you can use your finger (small force) to turn the valve. The valve will adjust the flow from nothing, to something, to everything. So, what a tube or transistor does is to permit a small force (small signal) to control the flow of a much LARGER signal. This is called *amplification*. The amount that the replication of the small signal - aka amplification - or "the output' is different, does not track perfectly, or varies from the small signal ("control signal"/finger on the valve) we call DISTORTION! Now armed with this information get thee to a website or book that tells you the rest of the story. Go to your library (ur in college, right?) and get a copy of The Art Of Electronics, by Horowitz and Hill. That give nice plain language explanations of all of this. _-_- __________________ _-_-bear http://www.bearlabs.com -- Btw, I don't actually know anything, FYI -- [...2SJ74 Toshiba bogus asian parts - beware! ] Last edited by bear; 3rd February 2014 at 02:06 PM.
 3rd February 2014, 02:15 PM #5 diyAudio Member   Join Date: Jul 2004 Location: Scottish Borders I'm unfamiliar with steep learning curves. All my learning is done quite slowly. Did I hear someone whispering "baby steps"? __________________ regards Andrew T.
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Quote:
 Originally Posted by MinnesotaStateUniver Let's imagine the flow of electrons as automobiles. In an AC signal the automobiles travel in one direction, turn around, and travel in the other. In a varying DC, the automobiles accelerate, peak, then decelerate to a trough, and so on. THE AUTOMOBILES NEVER CHANGE DIRECTION! So? So! So what if your signal goes from +4V to -6V! How can an automobile accelerate to 4mph and decelerate back 6mph ...all while traveling in the same direction! Impossible!
Lesson learned: it's a bad analogy.
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Quote:
 Originally Posted by tvrgeek LOL. Well, I have a degree in electronics with 40 years of experience and I know almost NOTHING. You will spend your entire life learning electronics.
I have been doing it 36 years. Mostly software and electronic design.

I recently got into class d amplifiers and LLC SMPS and realised I knew very little ! I started to get into the realm of high frequencies and that's when things change radically. PCB layout and decoupling becomes vital.
I also got into SMPS transformers and it turns out to be very complicated.
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 3rd February 2014, 10:18 PM #8 diyAudio Member   Join Date: Jun 2013 My major is EE, but I have nothing but math under me. Circuit Analysis isn't until next semester. I'm under the impression that transistors can only amplify DC signals, because transistors themselves are powered with DC sources. But according to Lenz, when you speak into a mic, you'll get an AC signal. So how are you supposed to amplify an AC signal when transistors will only amplify DC signals? You can cheat and wire a capacitor in series at the input to get a DC offset. It may be DC, but it's still AC in nature. See it all works out. ^I understand this is incorrect, but I'm just showing you where my logic is at.
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Quote:
 Originally Posted by SY Lesson learned: it's a bad analogy.
You're looking at my analogy and thinking this is how I understand AC.

That is incorrect. That analogy explains my understanding of DC offset. That is, a signal with electrons flowing in one direction only, but vary in amplitude over time. And if the signal is varying in amplitude over time, then the signal is AC in nature, regardless of electron flow.

 3rd February 2014, 10:27 PM #10 diyAudio Member     Join Date: Feb 2004 Location: Silicon Valley Get this book - Malvino Electronic Principles - Albert Paul Malvino - Google Books You can find used older copies for less than the price of a cheap 6-pack. It is one of the more pragmatic treatments of basic electronics I've seen, and still useful as a basic reference for old dogs. There is just enough math for basic understanding, not so much as to overwhelm.

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