Starting point

[lofi]

I have been building bits n bobs for a while, but am really fed up with not knowing whats happening. I have a slew of books about electronics, and i dabble in the reading of. Theres a problem though, they are general and encompass electronics, from nuclear to theoretical. i have never been very good at book learn in theory, but point me to an item and explain why that works and its in, cataloged, sorted and ready for use.

do any of you know of a 'heres a schematic and an explanation of how it works' sites? you know the 'idiots guide to audio engineering' type thing. just wondering.

Iain

[mediatechnology]

Have you every looked at "The Art of Electronics" Horowitz & Hill? That's one of the most recommended books around. If you can find a copy of Walt Jung's "Op Amp Cookbook" get one. They're out of print but still available. Walt has some sources on his website and there's a lot of really good information there: www.waltjung.org

[JR.]

I am basically self taught and have also longed for such a book, especially when the end of the chapter shows me a schematic of the design I'm trying to accomplish. Unfortunately for me life isn't that neat.

First I would ask how deep do you want to get into design? if you want to dig all the way down to component level you will need to familiarize yourself with how these basic building blocks work. I'd start with real simple stuff. Like an LED, battery and resistor and see what happens if you connect them in different ways. Read a book to see how they should act, then hook them up and see how they really act. Then start messing with first a one transistor circuit, then two.

Understanding electronic circuits is the cumulative effect of all these individual tidbits in concert. Once you arm yourself with how the basic tidbits work, you can deconstruct larger circuits that are just a bunch of little blocks working together.

My general advice is to dive in and melt some solder. Of course don't start at the deepest end of the pool, it takes time to get up to speed, but once you reach a critical mass of understanding things will fall in place and start making sense.

JR

[mediatechnology]

My general advice is to dive in and melt some solder. Of course don't start at the deepest end of the pool, it takes time to get up to speed, but once you reach a critical mass of understanding things will fall in place and start making sense.

That's really how I did it too. I've been interested in electronics since I was 6 and went to a prototype high school in Dallas named Skyline. Half my day was spent on electronics doing college level lab work. We had a lot of theory, but those written tests were taken in front of the test equipment on the workbench. They spent a lot of money on test equipment and the one I remembered most was the Tek 576? Curve Tracer. So not only did we learn about load-lines we saw them and then had a well-stocked parts room to build the circuit.

I also recommend a small protoboard. While they're not great for doing HF work where you need low capacitance, they do allow you to try out stuff quickly. As to soldering yes, learn to do that well. Buy a good soldering iron and use good solder. The worst thing you can do is go to Radio Shack and buy their irons and solder. Heck, I couldn't use them and a lot of the cheap solder just isn't "clean." RoHS will make things a little more difficult for you I'm told.

One thing about Horowitz and Hill, which was one of my later purchases, was they have a section in many chapters with "bad" circuits. Not only do they show what works, but what doesn't and the mistakes made in them. I had never seen that before.

[lofi]

Thanks Wayne and John for the replys.

I have the Art or Electronics light reading aint it

I am looking for something that would help explain whats happening in the circuit. at the moment i find it hard to get free time with an iron (i left some green pres on the kitchen table for a couple of weeks white i tried to get them done, the wife went spare!!!) as i have to be in the studio to do it. its some reading when i am at home.

when you guys are designing you will throw a capacitor in to do some thing, then one of the others here will read your schemo and think that caps there to do such n such. just looking for some schems that the info is there. think i might pick one and start doing that myself.

so ... set me some home work!!! post a schematic and i will try to fathom out how and why it will work, might help some others that also struggle with the first steps as i write back my observations

Iain

[mediatechnology]

lofi

Can you do an Ohm's law calculation or calculate power? I would think that's probably the most basic thing I use. Somewhere I recall a circle-looking thing that had all the variables, R, E, I and P with the formulas inside the circle. Probably the second-most often used calculation by me is capacitive reactance.

This one may be easy for you but a good practical place to start:

A simple circuit to analyze would be calculating the correct series current-limiting resistor value for an LED. Let's say you have a 15 V supply and an LED with a 2V forward drop. You can't connect it directly to 15V or excessive current will flow so you need to burn of some voltage off as heat in an "R." You want the current through the series string of resistor and LED to be 10 mA.

What voltage does the resistor need to drop and what value does it need to be to establish 10 mA? Then, what is the power being dissipated in the R?

This example might be too easy for you and you know how to do it. If not, sketch it out on a piece of paper and work it out using Ohms law and power calculations. If you get stuck, ask for help.

Wayne

[JR.]

When I was in the steep part of my learning curve I would devour schematics, and things like the ideas for design in engineering magazines. After a while I found the ideas for design too trivial and moved onto more esoteric stuff.

I would suggest picking a schematic and trying to figure it out. For extra credit not just why a resistor is in a given place but why that value resistor.

Warning, when looking at schematics there are a surprising number of errors, and the occasional very clever bit that looks like an error if you don't understand.

Try to figure out some simple circuit and if hung up on a single point, post an image here and ask "specific" questions. We'll help you over the hard spots, but don't expect hand holding for the whole journey.

Many design texts and papers cover the basics of biasing up discrete devices, and general configurations. Everything can be broken down for analysis into small pieces, while global feedback may impact the overall response of a complex path, the local circuit must be correct to work.

JR

[lofi]

Ok Wayne, where did i go wrong?

i have a 15V supply going through R1 the the LED.

the LED forward drop is 2V so i need to drop the voltage 13V (15V supply - 2V LED) to not over power the LED.

so i take the 13V and divide that by the 10mA and get 1.3K Ohms for the resistor? then its 10mA x 10mA x 1.3K to get the watts? so 0.13w heat

tis a red LED then.

i think i've got somewhere near the ball park?

And to John, gonna go with your suggestion, thanks

Think i am going to go look for a preamp schematic, cant find any here except the 1984 and I cant make it enlarge enough to read ledigbly. if i start working through the 9K pre schematics and get stuck would you mind slapping me around the head till i understand it? i've picked that one as Keith seems to lurk here, i could also go with greens or G9 as i have pcbs for all of them. but if i manage to get the 1984 to enlarge i will go with that.

Iain

[mediatechnology]

OK Iain you nailed it 100%. Very good analysis. You've done an Ohms law and power calculation.

You can right click and save that Benchmark schematic and load it into the windows viewer for a bigger zoom. Al drew that one BTW in pencil and handed it to me. On pink paper it didn't scan too well.

Take a look at this preamp IC. Internally it's very similar to the Cohen's front-end. Read the datasheet where it describes the circuits. Does the gain increase or decrease as Rg becomes smaller?

http://www.thatcorp.com/datashts/1500data.pdf

[lofi]

Ok, I am looking at the pdf now, and i am picking on figure 2 page 4. Its got bits that i take for granted but dunno why, so i am picking on it!!!

C1, C2 & C3. C1 and C2 are the same thing but on opposite legs. now a quick look at the books i have got lead me to believe this is a grounding type thing. i think that its in case of shorts. we want the signal to pass straight through to the THAT, but what if theres a massive spike? its gonna blow the lot. Short circuit protection!! so we have a 470pF cap, audio signals are volts (I always forget the actuals of what it is, noise is noise ~ i like Metal ) so we want them to pass ok, but only the signals. so as i see it we put a capacitor in that refuses to pass the signals as they are too small, but if, (insert your favorite deity here) forbid, it spikes your gonna breach its threshold and its going to start passing electricity.

We have Two legs (-IN & +IN) so each needs a capacitor on each, and a quick look at the image shows that there connected. But what if the electricity spike is more than twice the capacitor threshold? its going to flow straight from one leg into the other and saturate the whole kit bag and caboodle - so we go straight to earth at a convenient point between the two capacitors, think of electricity as water, it always takes the easiest route down. Earth is as far down as you can get. But why C3? whats that for? after all the electricity is only present if things have gone bad, and at that point we want it gone. Its a very small size capacitor, 10% of each of the other two, and i cant see it doing much except maybe as a stop for spikes coming from earth, because then we are going to have a single 47pF and two 470pF before it gets into the system?

How am i doing so far?

Iain