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Caffeine Wolf posted:If you want to use anything in an IC you need to power it hence it is active. clredwolf posted:Also, ICs almost by definition have to consist of transistors, which are active devices. I think there might be one or two out there that are not active (but I have no idea what those would be, I just know it's possible), but 99% of them are active devices. Sorry, but these are both just wrong. Resistor networks, integrated capacitor networks, and diode networks are all "Integrated Circuits" and none of them are active or contain transistors (with the exception that diodes are active or passive depending on who you ask). Any number of devices packaged in a self-contained unit is an Integrated Circuit, and there is no "definition" for integrated circuits which says they are active. I work in the semiconductor industry and I can (and have) design(ed) ICs with no active elements. They aren't terribly useful in a large circuit, mind you, but there you have it. Edit: Just wanted to make a point. The confusion about diodes comes from the fact that if you look at it from the perspective that they consume and do not produce energy, then they are passive. The problem is that a passive network (a circuit made of only passive elements) has the same V-I characteristics as the passive elements (that is that they will have a measurable resistance, capacitance, and/or inductance, depending on the elements involved) and they will be easily predictable. Once you start throwing diodes and transistors into the mix, that stops being true (diodes and transistors are non-ohmic devices, and therefore their properties change with applied voltage). By that definition they are active. Using a "switch" or "offset" model for diodes reduces the problem significantly though, because then they really are just treated like opens or shorts within the circuit. nchernyy posted:I think the confusion comes from defining electrical current before the discovery of the electron. People knew that there was charge flowing, they just didn't know it was made up of discrete particles that were negative. Benjamin Franklin is the one who caused all the problems. It wasn't a "gently caress up" though. It made perfect sense to believe that current flowed from high potential to low potential. It was just wrong, unfortunately for us. We've made lots of mistakes like that, and quantum particles always seem to slap us in the face just when we though we had the right answer. scholzie fucked around with this message at 04:29 on Jan 9, 2008 |
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Jan 9, 2008 04:21
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clredwolf posted:Much better. Now our circuit looks like this: The power source shouldn't be 5V there anymore since you changed your power source. Also, the spec sheet for that LED gives the Absolute Max. current as 70mA. You're not going to kill it with 5mA over spec as you alluded to. You'll just reduce its lifetime a little if you run it consistently (i.e. long periods of time) at that current. Spec sheets are written by engineers who build safety margins into everything. For true limits you should be looking at the extreme values. If you want to run your LED a little hot, go for it. You're not going to ruin it. It just might die in 13 years instead of 15. Of course if you run it at 75mA you're looking for trouble. Kids, don't test your expensive super-bright LEDs by sticking the leads on a 9V, even for just a second. You're going to waste your money. On the other hand, you'll get to see what melting semiconductors look and smell like. scholzie fucked around with this message at 05:11 on Jan 9, 2008 |
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Jan 9, 2008 05:09
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I got a few really nice super bright LEDs and I accidentally shorted one straight to 9V and it died instantly. I guess it depends on the color (and thus the substrate material the diode is built on). As for your resistor methods, I guess worse things have happened. You're wasting your time though because Ohm's law is just about the easiest thing to do in electronics. Also, you're dealing with voltages and currents that are so low you'll never need more than a 1/4 watt resistor. Assuming your resistor is about 50-75Ω, and your current is about 25mA, P = I2R = 0.03-0.05W. Even that example above, 50mA and 2.9 volts is just 145mW. 1/4W resistors are going to be ok for pretty much anything involving LEDs unless you get some of those crazy Luxeon LEDs with 1.5A max currents.
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Jan 9, 2008 08:38
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SkunkDuster posted:The reason I do it that way is because of the unknown LED values and lack of data sheets. Looking at this reference chart, it show a range of 1.5V to 3.8V at 20mA depending on what color LED you have. Also, the resistance of an LED changes based on how much current it is using, so you'd have to figure out that value as well if you planned on running them at something other than 20mA. I find it is just easier to plug the LEDs into the breadboard, hook up the multimeter, and try a few different resistor values. The above example used a 5V source and a 2.1 V drop across the diode. Therefore, the drop across the resistor was 2.9V @ 50mA. Also, as Komputernauta already mentioned, you don't have to worry about the strange I-V characteristics of an active diode. Once the LED is active it's almost a perfect ohmic device with a fairly steady resistance. The only portion of the curve where its not is during the short span between 0V and ~0.7-1.3V before the diode is saturated. All you need to do is decide at what voltage and current to run the LED. Nearly all the time you will have a spec sheet (or at least know enough about your LED to find one). In the event you don't, 25mA @ 3V is pretty much the standard spec for generic grab-bag LEDs. You can easily find a good starting resistance based on your input voltage using Ohm's law. Regardless, I see your point, but I think that's a bad way of going about design, even from a hobbyist standpoint. Sure, it works for one LED, but what if you have 10 of them, neither in parallel nor in series? 25? 50? You have no choice but to do a little math, and if you've made yourself so comfortable not using it in the past then you're just going to get tired and likely give up. In the end, Ohm's law is so straight-forward and simple it usually takes more time to do the trial and error method (not to mention the fact that not everyone has a wealth of parts to play with at their disposal; they have to buy everything as they need it). Even if you don't know the LED specs, 25mA @ 3V always works for generic LEDs. Then you can tweak if it's not bright enough. Sorry to nitpick so much, but if this thread is all about getting started in electronics, I think people should get started doing it the right way so that they are covered when something more complicated comes along. scholzie fucked around with this message at 15:36 on Jan 9, 2008 |
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Jan 9, 2008 15:34
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It's worth mentioning that flux used in electronics is pretty weak. Gloves wouldn't hurt, but they certainly aren't necessary. I think the danger of flux is far outweighed by the danger of holding a branding iron and molten lead.
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Jan 9, 2008 16:54
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I sometimes gauge my productiveness by how many burns I got that day. It's usually because I'm up way too late and I lose concentration. But burning flesh tends to wake you right back up again. Also, everyone needs one of these. http://www.a-msystems.com/electronics/soldering/helpinghands.aspx The mag glass is useless though. Just throw it out and get one of those arm lamps with a magnifier on it if you are old and/or blind and really need it. Edit: Maybe someone (or I) should do a soldering tutorial. If there's interest maybe I can do it. I'm sure there are plenty out there on the net already though. scholzie fucked around with this message at 17:17 on Jan 9, 2008 |
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Jan 9, 2008 17:12
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joebuddah posted:I want a nematic arm to to move up to turn on a light switch when I break the beam. 1) http://tinyurl.com/2md9ot 2) Why do it so complicated? Just rig a relay to switch when the beam is triggered. I'm assuming you're using some sort of laser/CCD combination, so just use the CCD to activate the relay and switch on power to the light.
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Jan 9, 2008 19:07
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It pains me to see how much of a moron you actually are. Sorry, but anyone who figures out what resistances to use by mixing and matching until they hit the right one has no right correcting anything anyone says. But ok, let's go. SkunkDuster posted:Here we are talking about using a 12V supply to light up LEDs (first mention of 12V). SkunkDuster posted:Here is a 1/4W (250mW) resistor failing miserably in Scholzie's scenario (second mention of 12V): Ahem, SkunkDuster posted:You're right that at 12V and below in the 20-25mA range that a .25W resistor should be fine for whatever you are doing. When I mentioned using a higher wattage resistor or multiple lower wattage resistors, I was getting another project where I had to do that mixed up with some of the LED stuff I've worked on. I guess it's my fault that I replied to something you admittedly hosed up on. Let's flame scholzie! My original point still stands, considering most LEDs (go ahead and try to prove me wrong) run around 25mA at ~3V. I've personally never seen any normal LED running at 50mA within spec. This is clearly a special case. I've wired up hundreds of LEDs in my lifetime and have never needed higher than a 1/4W resistor. Since you said only care about hobbyists wiring blooooo LEDs into their PS2 controllers, you should be in agreement that 1/4W will be fine for everything you'll ever need. Sorry I didn't add a catchall clause for every situation using every voltage and every power supply ever. Ever. Yes, if you run a 3V LED on a 12V supply, dropping 9V across a resistor at 50mA, you will need a half watt resistor. (Btw, instead of running the circuit for 5 minutes and feeling it with my hands, which really can't tell if a resistor is too hot or not, I could do a 5 second calculation P = 9V*50mA = 450mW and know right away) SkunkDuster posted:
SkunkDuster posted:And some more poo poo that is dead wrong: Most people don't sit in front of their DC LED circuit and loving crank a variable resistor to change current. Once you pick a voltage drop and stick to it, the math falls in place. If you're going to sit here and try to argue semantics then you've got way too much time on your hands. We (real engineers, not pretend ones like you) model diodes as ohmic devices all the time and no one has died from it. Incidentally, you didn't supply plots, just a bunch of numbers. This is a true diode IV characteristic:  See that nice straight line after the curvy bit? That's I/V. That slope is equal to 1/R (= S [edit: I means S as in Siemens, not S as in the graph's "S=10-4"). If you set your voltage well past the threshold, you do NOT have to worry about changing resistance. SkunkDuster posted:
SkunkDuster posted:I'd have to consult Schrödinger on that one. SkunkDuster posted:
SkunkDuster posted:Your math and formulas are dead on correct, but some of the stuff you have posted in this thread ranges from unclear to completely wrong. This is a great thread and I agree that SkunkDuster posted:so please take a couple minutes to look over your replies to make sure you are talking about the same thing the person you are replying to is (12V vs 5V) and your facts are correct (75mA PEAK voltage). SkunkDuster posted:I'm also looking forward to this: Can we move on now? Christ Almighty. scholzie fucked around with this message at 09:26 on Jan 11, 2008 |
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Jan 10, 2008 00:46
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Circumcision Hater posted:Well, I definitely need to upgrade something. Desoldering a single part can take me half an hour or more if it's stubborn and has a lot of leads. If you're having problems desoldering standard parts (meaning the cheap throwaway ones), I'd go ahead and solder them in with a bit more lead on the device side next time. That way, if you need to take them out you can just snip the part off (try to save as much as you can so you can use it again down the line). Then you can hold the board with some Helping Hands (see an earlier post), hold the lead with some pliers, and then heat the joint with the iron. The lead will pull right out, and you can then press some desoldering braid on the joint to clean up the excess solder. For more expensive or limited supply parts, you might considering using sockets rather than hardwiring the device in. This is especially useful with ICs and hard to find special order transistors (like new old stock germanium ones from the 60s). This has the added benefit of protecting the more sensitive devices from too much heat when soldering since you can just install them after you're finished applying heat. Lastly, if you find yourself doing a lot of prototyping, you'd be smart to pick up a Wire Wrap Gun. These will allow you to make some very strong connections with a perfboard, without making them permanent. You'll be able to fully test the device, then unwrap if necessary to fix anything. Bonus: once you've verified it's all working, you can solder right over the wire wrap if you don't care about it being messy. Now you won't lose anything in the translation from wrap to solder.
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Jan 10, 2008 01:35
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mtwieg posted:Jairbrekr would you be mad if I stole your gimmick and did a a minilesson on transistors? FYI, it's not Jairbrekr's gimmick. His are pretty good though. There was a whole thread dedicated to explaining things with foul language. I was actually going to post the links that Thumposaurus posted above. They're great resources (especially geofex, if you're actually interested in learning HOW effects work). I used a fuzz face schematic from General Guitar Gadgets with matching germanium transistors purchased from small bear, and it came out pretty good. It has two volume knobs, though, because I messed up my wiring. I keep putting off the debugging because I've been happy with it as it is, but I guess it's probably a good idea to see what's wrong.
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Jan 13, 2008 04:54
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God, I need an oscilloscope. I found one on ebay being sold as-is. It powered on but didn't have a probe so it couldn't be tested. But, it was a newish HP 4-channel scope, and it was $10. I was top bidder until FOUR SECONDS before the end of the auction when someone bid-sniped me. I hope that fucker just bought a broken oscilloscope. Anyway, I don't know what to do. All of the sound card o-scopes suck balls because they only work in the audio range, and they introduce horrible Gibb Effect to anything with hard edges. The PC-based o-scopes are just as expensive as a real one would be. I hope I find a decent old one in a yard sale some day 
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Jan 17, 2008 10:27
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Hillridge posted:Yeah, they're made of PN junctions specifically designed for solar wavelengths. You could also use it to drive the base input of a BJT or something and use the transistor current instead. It's not really practical to use the LEDs when miniature photocells are so cheap (sometimes cheaper than the LED you're using). Zuph posted:My Uncle goes around to government and school surplus auctions buying lots of old electronics, mostly consisting of old scopes and bench power supplies. He fixes up what he can, and sells the rest on ebay. Sometimes, he'll buy a crappy lot, but overall he's well ahead of the game. If you've got some time and skill with a soldering iron, it might be the way to go. It's a pretty sure bet that you'll find something decent under 100MHz. For anything else, you're better just hitting up ebay directly. This sounds like a good idea. The only problem I can find is that I probably wouldn't know what was broken on the scope if it didn't work. I'm handy enough with a soldering iron to fix it once I knew, but... yeah.
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Jan 17, 2008 17:44
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I think a schematic would be infinitely more useful than a breadboard walkthrough. It's a little hard to follow, and ultimately doesn't leave any lasting understanding of how the circuit is constructed. Other than that, it's useful as a basic example of transistor usage. Also, to add: if you do not have NPN transistors but you DO have PNP transistors, you can construct the same circuit by reversing all devices which have polarity. In this case, the diode and the battery need simply be flipped. This is true of any circuit which utilizes PNP or NPN transistors. For those who are wondering, but don't want to get into difficult reading, NPN and PNP refer to the type of materials used to create the transistor. N-type material has an excess of negative charge carriers (electrons) and P-type material has an excess of positive charge carriers (holes). The choice of NPN vs. PNP is mostly arbitrary for most circuits. Audio circuits might benefit from one type over another, but it usually has more to do with the materials used for the devices rather than their orientation. Edit: do you plan to go over basic amplifier circuits and biasing if you're going to start talking about transistors? I'm not sure it's necessary to go through the more complicated circuit analysis techniques once you get through KVL, KCL, Nodal, and Mesh analysis, and amplifiers and biasing are pretty much essentials. scholzie fucked around with this message at 09:18 on Jan 21, 2008 |
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Jan 21, 2008 09:05
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I think you shouldn't bother with the articles. Anyone who wants to learn is going to have a wealth of information available to them at any level of experience by using one of the links posted earlier. The other downside to putting all this effort into writing them and they'll be in the archive 6 months from now  I think it's best to just show some projects or links to projects, and post questions and tips.
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Jan 22, 2008 03:09
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Nerobro posted:It works great. Taht's how I've made most of my PCBs. In the same vein I was considering putting together a kit for a headphone amp. It would be stereo, and if I can fit it in would also have a fuzz or distortion circuit for guitar players. I made the amp so I could play guitar without bothering the neighbors late at night. I want to make it so I could fit it in an altoids tin, so my next project is turning the circuit into a PCB design. Right now I run the guitar into a marshall blues breakers (overdrive) clone circuit, and then the overdrive into the headphone amp, but I should be able to squeeze them all in and switch the fuzz or overdrive with a switch. It's pretty loud, by the way, and it can run off of a 9V battery or 9V wall wart so it's very, very portable. With the proper input adapter (or if this is a kit, the proper jack chosen at purchase time) it would make an excellent amp for high quality iPod headphones (like the Etymotic ER6s or Grados, which should really use an amp for proper frequency response from the ipod). I was figuring I could offer fuzz, overdrive, or distortion for the first stage (or no effect at all), then your choice of input and output jacks (1/8" stereo or 1/4" stereo) and your choice of LED color for the distortion stage.
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Jan 22, 2008 17:42
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mrbill posted:I now have a Tek 453 scope on the way. Did you get it on ebay? I was looking at one of those auctions and it was ending soonish.
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Jan 23, 2008 03:19
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There are some scopes out there from sellers who only sell electronics equipment, and they often have a 7 day guarantee on their scopes. Obviously, also look for high ratings and a large (98+%) positive feedback proportion. I am trying to find this one dude who had a ton of scopes, and all of them were fully tested and guaranteed.
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Jan 24, 2008 08:25
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Jonny 290 posted:I'm about to make Futurlec richer and need some advice. For OpAmps, I like TL072s or TL082s. Very low noise for the price. The 72 is a JFET opamp and the 82 is a BiFET opamp. 2N3904/2N3906 are fine for the transistors. If you don't want to get both, stick with the 2N3904s. You'll see them more often, and anywhere you see a PNP transistor in a circuit you can just flip the polarity of the rest of the circuit and use the 3904 instead. Or you could just pick up both... they're cheap enough. Don't forget some diodes. Get an even assortment of 1N400x diodes as well as 1N914 silicon diodes. The only major difference in the 1N400x diodes is the max current. 1N4001s are good up to 1 Amp, and the rest are all higher. (Edit: meant to mention that the reason for picking up the 914s is because they tend to be a little "smoother" when clipping as compared to the 1N400x series. Not that you intend to push them to that point, but when dealing with varying input signals and opamps there's always a chance you'll clip unexpectedly. If you don't really care about clipping characteristics, don't bother getting the 914s) Check out Small Bear Electronics for some nice pre-sorted capacitor sets in film and electrolytic varieties. http://www.smallbearelec.com OOPS Completely missed the part where you said you already had diodes and caps. Oh well. Sorry 
scholzie fucked around with this message at 23:41 on Jan 24, 2008 |
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Jan 24, 2008 23:20
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sithael posted:Anyone know a company that doesn't gently caress up constantly? I've NEVER had a problem with Jameco. I love them. I also like Small Bear Electric, but they are mostly parts geared towards guitar effects and related items. However, they're also a great place to pick up assortments. They're a little pricier than most places you find, but I've never missed with them and they've always had everything I've ever needed. YMMV, obviously.
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Jan 28, 2008 02:23
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You can also do this quite easily with a charge pump and you might actually find the one special part you need from radio shack. Edit: I'm looking for some easy to read information on charge pumps. Here's a fairly simple schematic which uses a 555 timer, some caps and schottky diodes. You can find everything there at radio shack. It's a voltage quadrupler. http://home.pacbell.net/lengal/ip/cpump.pdf Given the pumping nature of this circuit the output tends to be a little rippley, since the caps are discharging and recharging. Putting a relatively large output cap (compared to the others) will smooth that out to near-DC. scholzie fucked around with this message at 19:23 on Jan 28, 2008 |
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Jan 28, 2008 07:35
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mtwieg posted:charge pumps are nice for their simplicity and and efficiency, but they have their limitation. They're limited to low-current loads, since they require low-esr capacitors to work properly, and therefore you really can't just stick a giant electrolytic on the output to reduce ripple. Also, they are unregulated, so you're usually stuck with inverters or doublers. I use them when I want to make a tracking negative power rail for battery powered devices, but beyond that I'll usually go for a boost/buck converter. 35-45mA IS a low current load. And it's not true that you're stuck with inverters or doublers. And you don't need a "giant" electrolytic cap on the output, just enough to smooth the ripple past the point where it's hampering your needs. I doubt it would be much of an issue at all if the load was the laser diode circuit. He could at least try it and see if it worked first. scholzie fucked around with this message at 20:12 on Jan 28, 2008 |
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Jan 28, 2008 19:21
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Azathoth posted:I found this a while back and it's been gnawing at me something fierce. I've always wanted to learn electronics but I've never had something I wanted to build before. Since no one is answering you: If you purchase a printed circuit board and all the parts, this shouldn't be difficult to put together. Just ensure that your soldering iron is 15-20W, because as a novice it's very easy to burn the traces right off with anything more than that. If you don't use a printed circuit board, I would purchase a prototyping breadboard and lay the circuit out on that first to make sure you are reading the schematic clearly. Then you can work on transferring it over to perfboard or something like that. Honestly, though, with your level of experience just order the circuit board pre-printed and you'll be ok. Just learn how to solder on a piece of crap radioshack copper clad perf board and make sure you're doing it right before moving on to the stuff that costs money. Pro Tip: as you fill in parts, whether you use a schematic or a layout diagram, use a highlighter to fill in the parts you have done as you go. That way you can relate where you left off, what you have left to do, and you don't do more than one part at a time, therefore ensuring you make as few mistakes as possible (though you WILL make some).
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Feb 6, 2008 20:25
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Jdohyeah posted:ACHTUALLY I don't understand what you're trying to say here. Jarbrekr made an image of exactly what you just posted... he just left Franklin out of the discussion.
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Feb 8, 2008 03:16
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Jabab posted:Easy question: No freebies - 3 LEDs, 3.5V each... that's 10.5 volts, yes? 12 - 10.5 = 1.5V Your resistor must drop 1.5V. I'm assuming you meant 30mA not 30mW. That's 0.03A. So: R = V/I. V = 1.5V, I=0.03A. Do the math, pick the closest standard nominal value to the calculated R. scholzie fucked around with this message at 07:37 on Mar 2, 2008 |
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Mar 2, 2008 07:27
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wuddup posted:Edit: I won't ruin the fun You referring to my [/ma] or something else? I've been up for close to 30 hours now because I was moving and I'm probably nothing (edit: "not" - see?) thinking straight enough to be posting on the internet. I'm too wired from caffeine to go to sleep though.
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Mar 2, 2008 07:38
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oh, ok. I am apparently paranoid, too 
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Mar 2, 2008 07:42
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babyeatingpsychopath posted:Nope, connected in series, the same current flows through all components. If 30mA is going through one, it goes through them all. Once you find your resistor's value, you can calculate the power with P=I^2*R. .03 W / 1.5 V = 20mA, not 200mA. You can't divide a number by a number > 1 (edit: oops) and get a bigger number than you started with. You'd need a 75Ω resistor. scholzie fucked around with this message at 23:13 on Mar 2, 2008 |
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Mar 2, 2008 17:37
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ryanmfw posted:I think you mean "number > 1" Yes that is exactly what I meant  oops.
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Mar 2, 2008 23:13
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Comrade Milton posted:
Well let me just do everything for you. How about you start by reading up about 10-15 posts ago where someone asked pretty much the same exact question. No one is going to grind through some stupid easy math and email you an answer, especially a question that's already been answered.
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Mar 15, 2008 06:18
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Comrade Milton posted:Well, if by "do everything" you mean by a lazy poo poo who'd rather write a paragraph of sarcastic, self-righteous, contemptuous poo poo rather than a one or two word answer to a simple question, then yes, you did everything. Your own loving question was answered a few posts ago. All you have to do is change the voltage and do the same calculation which was laid out in plain, easy to understand terms. So, yes, nearly everything was done and made out for you. Stop being a lazy pile of poo poo and read a thread before posting in it. In the time you took to post and reply to whine about how mean I am, you could have read the solution already. (Yes, I realize I could have also just answered you, but I'm trying to make a point, dammit!  )I don't, nor does anyone else in this thread, feel like giving away answers like we're some sort of nerd calculation factory. If you want to learn something, which I naively assumed was the point of the thread, then try to learn something. If you want someone to give you answers, pay them. Sorry for the derail, but that really pisses me off. Has anyone been playing with guitar effects lately? I built a Marshall Blues Breakers clone on my breadboard (I got the schematic from General Guitar Gadgets) and it's pretty slick - probably one of the better crunchy overdrives I've made. What's I'm really looking to do is build a headphone amp with a switchable distortion channel that can fit completely in something like an altoids can. Maybe make a little kit out of it once I get everything right.
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Mar 16, 2008 06:37
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Comrade Milton posted:Unless you're looking to make this happen, I'd suggest you stop being a cocksucker. My whole reason for getting pissed off is that electronics (hobby or otherwise) isn't something you just pick up by asking people for answers (or as someone earlier mentioned, switching parts out until they stop getting hot). It takes hard work to learn and understand this stuff, and many, many people in this thread have spent 4 or more years of their life learning this stuff. So, it kind of trivializes all that work when someone asks for an answer without trying to figure it out himself. A simple Google search for "LED resistor" brings up hundreds of calculators and you would have had an answer even faster than posting here in the first place. I admit that I could have been nicer about it at the start, but to me it looked like you were looking for fast answers and not having to put anything into it. Especially because you asked people to go out of their way to email you. That, coupled with having a really bad day made me go kind of Patrick Bateman. So, for what it's worth, I apologize for being a dick about it.
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Mar 17, 2008 04:13
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Delta-Wye posted:You didn't miss a period, by the way, you missed a decimal point, which had a significant change to the values you had given. While it is pedagogical for me to not simply put it back in, these kind of mistakes are pretty obvious and should have been caught with a little bit of proofreading (but I guess you were too lazy...) Not too lazy. In a hurry! QUICK! I NEED BLUE LEDS STAT. On the issue of travel guitar amps: I really, really like the TL072/82. They have a little more meatiness in the mid-rages and the FETs do a pretty good job of reacting to input signal spikes (smoother, like a solid-state tube). Last LM386 amp I built was a little tinny sounding, even after adding an active low pass filter. Also, as Delta-Wye said, a 9V won't supply a bi-polar 6V source without a charge pump. The LM386 should be more than happy with a +/- 4.5V supply though, and making a bi-polar supply is as simple as adding 2 resistors and 2 capacitors into the circuit (just 2 resistors would do it, but in a circuit where signals are involved you want to use caps to keep the voltages stable WRT the common lead).
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Mar 20, 2008 21:40
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Corla Plankun posted:I actually built a really ghetto single op-amp amplifier for my guitar a couple weeks ago. I used a 9 volt AC adapter, and absolutely no fancy split-power supply. It sounds really distorted (and awesome, for my application: playing a super crappy squier into a pair of headphones) and I just assumed thats what Op-Amps did, and thats why they're 50 cents a piece at radio shack. Yes, that's the suggestion. Keep in mind that it's not called a split power supply though. A bi-polar (or dual) supply isn't really "split," it's just acting as a negative and positive supply with respect to a common ground (which, in this case, is a floating ground. Don't use earth ground or the ground from another supply.) Splitting something usually gives two or more lines with the same signal on each one. Anyway, you don't NEED a bi-polar supply as long as your signal fits completely within the voltage supply you're feeding the op-amp. That means that if your guitar gives off a signal with a maximum amplitude of +/- 3V (that's pretty high for a guitar), then you need to offset your input signal with +3V DC (at least) in order to make sure it's centered well within the range of your power supply. Essentially, you only need a negative lead into the op-amp if your circuit will be dealing with signals which go negative. If you bump up your entire signal by a few volts, it will always stay positive, and you can get away with feeding a normal voltage source into the op-amp's power terminals. But at the end, you're now left with a signal which is centered around whatever your DC offset voltage was, which might not work with whatever next stage you're feeding the signal into. In that case you'll need to drop the signal back down to center around ground (negative DC offset, 1:1 transformer, or something like that). If you're going to headphones I think it would be fine as long as you used your DC offset source as the "ground" for the headphones. It's a lot easier to just throw 2 resistors and 2 caps in to give yourself a bi-polar supply to use with the op-amp. Delta-Wye posted:If adding a bipolar supply and having negative feedback cleans it up, and you want a dirty signal again, adding two diodes back to back across the feedback resistor should get you some clipping. Ought to be a bit better sounding than what you currently have, at any rate. You can also build an overdrive stage by using a dual op-amp design. Use one opamp to amplify, and one to clip (or vice versa). Diode clipping can tend to be really tinny and gross, but red LEDs sound nice as clipping diodes (the color of the LED actually makes a difference!). Overdrive is the act of driving a signal to clip before outputting it. Just make your first amp stage's gain high enough to clip the signal (by designing a gain higher than the opamp source rail voltage), then feed that signal into your output amp stage. scholzie fucked around with this message at 04:23 on Mar 22, 2008 |
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Mar 21, 2008 10:46
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the wizards beard posted:Actually, diode clipping sounds pretty good, it's very common in overdrive and distortion pedals. Clipping an op-amp sounds pretty bad, op-amps are not designed to be operated this way and usually don't handle clipping very gracefully. If you look at the Bluesbreaker schematic again, you can see that the first stage amplifies the signal to usable level and acts as an input buffer. The second op-amp has 4 diodes in it's feedback loop, this is where the clipping takes place. The first gain stage is completely "clean", and in the newer version of the Bluesbreaker you can bypass the second stage for clean boost. You're right about the BB - I linked it without even really checking it out because I was recalling it differently. I could have saved us both the trouble if I looked at the second stage. There's another design out there somewhere that I recently built on my breadboard that sounded great, and it used 1 dual opamp (or maybe a 3/4 on a quad opamp). If I can find it I'll post link. What I meant about diode clipping sounding bad, but didn't phrase right at all, was that the choice of diodes makes a huge impact on the sound you get. A pair of 1N400x diodes sounds horrible, but 914s sound great. LEDs sound great if you get the right ones. So yeah I didn't mean to imply that diodes weren't used for overdrive - they're used all the time, but the FET driven overdrives tend to have a more tube-like distortion. scholzie fucked around with this message at 04:26 on Mar 22, 2008 |
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Mar 22, 2008 04:21
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radioactivelego posted:I'm looking to do a little project that uses multi-color LED's that react to sound. Imagine an 80's LED tachometer except it reacts to sound (or hey if frequencies are possibly even cooler). It'd be hooked up to a computer microphone and would be aimed at a sound. dB or frequencies I want 5 different color LED's (like a blue to white gradient) that react and light up based on levels. I would imagine some form of resistors would be in order and would revolver around voltage dropping etc. Some sort of variable potentiometer? http://www.google.com/search?q=led+VU+meter There are many circuits out there that do exactly what you want, but lots of them vary the extent to which they do. I had one on my old PC that went from blue to white to red to indicate volume levels. You could also route the signal through a few parallel bandpass filters in order to get VU levels at specific frequencies. That would require some design work though, and I don't know if you're up to that. I'm sure there are more designs for exactly that out there, but it would just take some digging. You could control "sensitivity" a few ways: a potentiometer before the LEDs to scale back the driving voltage (in this case your output signal), or a potentiometer on the signal input. It would really just depend on the circuit design which way you'd choose. If the signal is small, you might need to run it through an amplifier to get it to a point where it can control the LED circuitry, so you can also add a pot to change the gain of the amplifier. That's probably the closest to a "sensitivity" setting as I can think of. If you have a better idea of exactly what you want, it's much easier to come up with a solution.
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Mar 25, 2008 22:07
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FPS_Sage posted:I would guess that's a 3.3 kilo-ohm resistor (rated to 100V). They probably put that in series with the other resistor in order to get the spec'd resistance because nobody makes resistors of that particular value (i.e. a 10k + your 3.3k = 13.3k, and that part is probably hard to find). The good news is, if that really is the broken part, you should be able to fairly easily (and very cheaply) replace it. This really doesn't make sense. A 3.3k resistor "rated to" 100V would only be 300mW. You could easily get away with a basic 1/2 Watt 3.3k resistor. They typically also don't put max voltages on resistors because there's almost always no point. A picture might be useful if you can get one. Also, wrapped wire capacitor? Do you mean one of these? 
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Mar 28, 2008 22:26
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For some reason (probably because it's 5:30 AM and I just got up) I thought you said you were going to put 50 LEDs on your bicycle helmet, and I thought to myself "Jesus Christ what a loving nerd." But I approve of LED bicycle headlights
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Apr 1, 2008 10:35
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