suchuwato Posted June 13, 2007 Posted June 13, 2007 If it's beefy enough just use a variable plug-in type power supply... much easier Share this post Link to post Share on other sites More sharing options...
markiemrboo Posted June 13, 2007 Posted June 13, 2007 how hard would it be to build a 12v amp to run car\house speakers on a computer? I don't understand exactly what you are asking. Why 12v and 'car' speakers? Give me more details on what you are planning and I might be able to give a suitable answer. Share this post Link to post Share on other sites More sharing options...
markiemrboo Posted June 18, 2007 Posted June 18, 2007 (edited) Ok, well the Toshiba CD4013's arrived, I 'de-bounced' the switch with a cap and resistor but I am still not happy with how that circuit behaves really. It is much much better, but in about 50 odd pushes it still turned on then immediately off in one push button press once, and a few times it didn't seem to register the button press. This is quite unfortunate, as I did like how simple yet clever the circuit was, and I quite like how the PCB turned out So I started looking towards other options and thought... why not take this opportunity to use a small microprocessor. After all, I do enjoy programming, I seem to enjoy messing with electronics stuff... and I haven't coded anything in a good while now. Research suggested that the "Microchip" PIC series IC's are quite popular, and there was also 'PICAXE' chips, which appear to be based on the former chips but with software pre-programmed to make programming the chip dead easy, and use a form of a BASIC language, rather than the preferred ASM for the PIC's. I must admit that I was looking at the PICAXE chips for a bit, and trying to tell myself that BASIC would be OK, if possibly somewhat limited. They [the picaxe chips] would probably have allowed me to write the code for the power button in all of 5 minutes, they were reasonably priced and do not require any special programming hardware to be built at all, just like three wires from the serial port and a couple of resistors. However, me being me, I eventually decided against this idea. BASIC, while easy, would be quite boring, and I just feel like going with the assembly approach with the Microchip PIC's instead. It just seems like I can have more control over what happens, and no doubt it will be somewhat faster, if that even matters for a simple power switch . I read somewhere that the PICAXE with it's overheads would be something like 10x slower. I have decided to build a 'JDC'-like programmer which can be found here, and to use a PIC12F675 8-pin microprocessor, which is probably really quite overkill for this task really, but hey! As for the IDE, Microchip have free software called MPLAB, so I will use that. To actually program the things with my code, IC-prog seems to be a popular choice. With any luck all the stuff will arrive tomorrow. Farnell are usually pretty good with their deliveries. It doesn't seem like it will be too difficult at all, in fact it seems quite easy, but I will keep you posted! I also rebuilt my preamp on to a new PCB, which further explains the delay in updates. It was probably quite a pointless exercise, as I already have plans for a completely new and much more fancy preamp, but it gave me something to do Perhaps a tiny bit neater, but still not brilliant really. The main thing is that the power supply, which was originally split over four separate boards, is now on a single PCB with the actual preamp. The remaining tiny board is the brief mute for power on / off to stop funny noises reaching the power amp. The original: The new: As for the case situation, well, the rubbish ends have been cut off ready to mark out the dimensions and get it cut... but... I'm in no real rush with it at the moment, as I really really want the power button working first, so pretty much my entire concentration-ness is on that Edited June 18, 2007 by markiemrboo Share this post Link to post Share on other sites More sharing options...
coolcat97 Posted June 18, 2007 Posted June 18, 2007 I don't understand exactly what you are asking. Why 12v and 'car' speakers? Give me more details on what you are planning and I might be able to give a suitable answer. 12V: so it can be powered by a computer and basically by car speakers i just kinda met that i didn't want PC speakers. I have some speakers that i'd like to run on my pc and if i can build a cheap and decent amp then that would be really cool. Share this post Link to post Share on other sites More sharing options...
markiemrboo Posted June 18, 2007 Posted June 18, 2007 12V: so it can be powered by a computer and basically by car speakers i just kinda met that i didn't want PC speakers. I have some speakers that i'd like to run on my pc and if i can build a cheap and decent amp then that would be really cool. I see. With just 12v from a computers PSU you would be looking at only 6v-pp assuming an amplifier of 100% efficiency. Even if it were possible to get 100% efficiency out of the amp (and it's not) this would be a power output of only ... 9W [peak]? in to a 4 ohm load? I think... You can get close to 100% efficiency with a Class D based amp, but these are not the easiest things in the world to design and you would probably be looking at buying a "kit", rather than doing it all totally by yourself. You will obviously still be limited in output power. I believe typical car amplifiers, for example, use switch mode power supplies from the 12v car battery, as current isn't so much of a problem but voltage is. This would enable you to have the much needed higher supply voltage and output power, but building a switch mode power supply is not a task suited for a beginner, at all, either. To be honest it would be easier to just build a 'conventional' amp that plugs in to the mains. The power IC's that I am using (LM3886's) are fairly straight forward (IMO) and sound fine, but of course you do have to be rather careful with the mains... Share this post Link to post Share on other sites More sharing options...
coolcat97 Posted June 18, 2007 Posted June 18, 2007 Is their a simple 110V amp? I have basic to mediocre soldering skills and don't know much about building an amp...nothing... maybe an amp that occupies two 5.25" bays? and I could just drill into the PSU? Share this post Link to post Share on other sites More sharing options...
Verran Posted June 18, 2007 Posted June 18, 2007 Is their a simple 110V amp? I have basic to mediocre soldering skills and don't know much about building an amp...nothing...maybe an amp that occupies two 5.25" bays? and I could just drill into the PSU? Why do you want the amp inside the PC? The speakers would be outside it anyways, so why not just make a standalone amp that runs on 110 and amplifies a line-level feed from the PC? Share this post Link to post Share on other sites More sharing options...
jammin Posted June 18, 2007 Posted June 18, 2007 Not to mention electrical noise from the other components in a PC and the fact that an amp throws out a reasonable amount of heat. An amp inside your case might be nice so you can carry everything around in one box, but it just isn't worth it in my opinion. Share this post Link to post Share on other sites More sharing options...
markiemrboo Posted June 18, 2007 Posted June 18, 2007 (edited) Is their a simple 110V amp? I have basic to mediocre soldering skills and don't know much about building an amp...nothing...maybe an amp that occupies two 5.25" bays? and I could just drill into the PSU? You want a step down transformer with a 110v primary winding and, for simplicities sake, a center tapped secondary winding. The secondary winding voltage will be specified as an AC voltage (VAC). The secondary *must* be rectified and filtered to produce a DC voltage, which will be roughly VAC * 1.414. So if you have a transformer of, say, 12-0-12VAC this can give a rectified / filtered DC voltage of around +-17VDC. The mains may fluctuate, and / or be generally a few volts higher / lower than 110v, and this will influence the secondaries voltage. The transformer VA rating probably depends somewhat on the load that the amp will be driving. For something low power with sensitive, easy to drive speakers you can probably get away with 120VA for both channels. I am using 120VA for each channel and it plays very well with my speakers. I can't be bothered to draw out a simple power supply to explain the above in schematic form, quite frankly. A simple one can be found at http://sound.westhost.com/project04.htm. Armed with a split rail power supply, you can connect this up to some LM3886's (or some other similar chip depending on your requirements) fairly easily. National's Overture series seems to be one of the more popular ones, and they do sound good. The LM3886 is one of the slightly higher power versions which will work better with lower impedance loads, but requires more pins. The 1875 / 3875 need only 5 pins. There is usually a typical application circuit in the datasheet for the chips. Here's a few to get you started: http://www.national.com/ds.cgi/LM/LM3886.pdf http://www.national.com/ds.cgi/LM/LM3875.pdf http://www.national.com/ds.cgi/LM/LM1875.pdf I'm going in to more 'note' formish now. If you really want to build an amp I would suggest you do a bit of research. I would start learning about the power supply first. - Without even a basic 'scope to check things out there is a risk of oscillation, which can and will destroy speakers, and make your IC's put out a lot of heat. - You should pay particular attention to grounding if you want a quiet, hum / buzz free amplifier. Star grounding virtually guarantee's hum free operation, if done correctly, and a loop breaker / disconnecting network, as seen here http://sound.westhost.com/earthing.htm, may also help. This website is a good source of information. - Just because they are small IC's, this does not mean they don't require adequate heatsinking. - Make sure that you connect the +ve supply to the +ve pin, and the -ve supply to the -ve pin. I have had an ordinary opamp explode on me by connecting the supplies the wrong way around accidently, and even that was quite violent. I wouldn't really like to experience the explosion of one of these high power opamps. - Supply bypass close to the chips pins, between the rails, is recommended. Even 100uF and 100nF should be fine. Why do you want the amp inside the PC? The speakers would be outside it anyways, so why not just make a standalone amp that runs on 110 and amplifies a line-level feed from the PC? Not to mention electrical noise from the other components in a PC and the fact that an amp throws out a reasonable amount of heat. Yep. I don't quite understand why it needs to be inside the computer either. I guess it is somewhat unique, and it does sort of remove the need of making much of a case for the completed project, which you all know is the part I actually seem to be having problems with I would still say just build it as a standalone thing outside of the computer case though. Electrical noise may also be a problem, but heat, especially with the lower power class A/B chips (LM1875 / LM3875), should not be that much of a problem to be quite honest. Edited June 18, 2007 by markiemrboo Share this post Link to post Share on other sites More sharing options...
neddamttocs Posted June 18, 2007 Posted June 18, 2007 hmm ... you can de-bounce using (N)AND gates i believe .. let me look it up and ill post a pic later tonight Share this post Link to post Share on other sites More sharing options...
coolcat97 Posted June 18, 2007 Posted June 18, 2007 I was thinking of how nice it would be just to plug speakers in to my comp instead of a million wires. Guess you guys haven't seen my old monitor setup? Anyway, I like just one big thing instead of a thousand small things. Monitor setup(a bit hard too see): Share this post Link to post Share on other sites More sharing options...
Verran Posted June 18, 2007 Posted June 18, 2007 hmm ... you can de-bounce using (N)AND gates i believe .. let me look it up and ill post a pic later tonight You are correct sir! I remember doing this in one of my digital logic classes. All of our switches had to be debounced, and we did it with a simple NAND circuit. I think it was two NAND gates that it needed. I still have some built on my breadboard actually, but I don't remember the pin-outs for the NAND ICs off-hand. EDIT### SR-Latch-style debounce: Share this post Link to post Share on other sites More sharing options...
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