Can someone help me build an amp?  - Page 1
Forum section: electronics / beginners

author: haglered
author_rank: Contributor
timestamp: October 21, 2010, 02:53:39 am
content: I am a relatively inexperienced at building anything electronic but I have had some experience at it.I would like to build a simple relatively low power amp (between 5 and 20 watts).I need help in finding a simple but effective design. It needs to be made from parts I can get from Radio Shack or scrounge from old equipment (Like an old speaker I can get from a Thrift store.)I need help in knowing what to look for.I am a soundman and want to use this unit as a small portable amp for occasional outdoor use. It will need to be powered by batteries and accept 1 mic. So it will need to include a small pre amp for at least one mike.I intend to amplify voice so the mid range is the important range to amplify.I don't have much in the way of equipment. I have a radio shack iron and a few other tools.

author: Simon
author_rank: Unknown
timestamp: October 21, 2010, 05:57:53 am
content: perhaps you can find a kit from radio shack ? otherwise there are many many audio amplifier IC's around that will do the job, just remember that wattage to some extent depends on voltage supply. Try the TDA2009 or TDA2035 (I may have got all of those wrong mind you it's a long time sice I used them and apparantrly they are out of date)

author: david77
author_rank: Frequent Contributor
timestamp: October 21, 2010, 07:09:17 am
content: Maybe have a look around here:http://www.sound.westhost.comI've used some of his circuits in the past with excellent results.Do you need a stereo amp or would mono be enough, e.g. just for monitoring a sum from a mixer?I agree with Simon, have a look at the TDA2009's datasheethttp://www.datasheetcatalog.org/datasheets/208/378193_DS.pdfI'd suggest using the circuit shown in Fig. 16, that should give something like 8W power into 8Ohms, ifrun from a lead acid 12V battery. You'd need that circuit twice for stereo, obviously.If weight is not much of an issue you could use two lead acid batteries to increase the power output.Then you'd only need to add a small preamp to use the thing with a microphone. Have a look at the linkI posted above, he's got it all there.

author: Zero999
author_rank: Super Contributor
timestamp: October 21, 2010, 10:47:41 am
content: Quote from: david77 on October 21, 2010, 07:09:17 amIt think that's a little optimistic, especially when usable power and distortion are taken into account.Although your theory is correct, you haven't allowed for the extra transistor saturation losses. The graph in figure 4 says the power output is just under 2W into 8R with at 12V supply. Bridging will theoretically quadruple the power to 8W output but the current will be higher so the saturation voltages in the driver transistors so it will be a bit lower. A good guess for bridge is to double the the power output for a 4R load, since it will be using the same current as 4R with 8R at double the voltage, I make it 7W maximum.Then there's the actual usable power output which will be much lower. Figure 4 is at 10% THD (clipping) which sounds so bad it's useless. Looking at figure 3 will give a better indication of the usable power so going by the double the power for 4R rule of thumb again, we get 6W of power with a THD of 1% which is pretty usable.

author: DJPhil
author_rank: Frequent Contributor
timestamp: October 21, 2010, 11:00:32 am
content: All good advice. TheTDA series from ST Microis all around what you're looking for, and the example circuits in the datasheets will get you rolling on a power amp section.The best advice I can give is to get a few chips and start tinkering. I got sidetracked reading into the details for far too long before jumping in when I started tinkering with chip amps. It all comes together really quick once you start building them.

author: Simon
author_rank: Unknown
timestamp: October 21, 2010, 11:43:31 am
content: Quote from: Hero999 on October 21, 2010, 10:47:41 amif your already on the lowest speaker impedance for max power it will only double it as you will have to double the speaker impedance as you've doubled the voltage but can't pull any more current

author: Mechatrommer
author_rank: Super Contributor
timestamp: October 21, 2010, 12:10:17 pm
content: good infos so far, i like it, keep it coming, will be a good reference later

author: Zero999
author_rank: Super Contributor
timestamp: October 21, 2010, 12:58:17 pm
content: Quote from: Simon on October 21, 2010, 11:43:31 amBut the TDA2009 is rated for 4R so bridging and driving 8R won't be a problem.Quote from: DJPhil on October 21, 2010, 11:00:32 amIt depends on what power level he's after.The power output from a TDA2003 will be a quarter of a bridged TDA2009 driving the same speaker or half if he goes down from 8R to 4R.You'll only get 10W from the TDA2003 with a 2R load, a 14.4V power supply with it driven to clipping giving crappy 10% distortion.With 12V, a 4R load and an acceptable distortion level, the usable power will be around 3W.The maximum theoretical power output from a 12V bridged amplifier into a 4R load = V2/(2R) = 122/(2*4) = 18W, for a non-bridged amplifier V needs to be halved. In practise the actual usable power will be much less due to losses in the driver transistors and the fact you don't want to drive it to distortion. As low power speakers with a lower impedance than 4R aren't widely available, the only way to get more power is to boost the supply voltage or parallel the speakers.For 10W into 4R with low distortion and a 12V supply, you need the the TDA2005.http://www.st.com/stonline/products/literature/ds/1451/tda2005.pdf

author: david77
author_rank: Frequent Contributor
timestamp: October 21, 2010, 01:36:12 pm
content: Right, 10% distortion ispretty badhorrendous, but might still be usable if he only wants a "command" amp, for shouting "orders" around.There's a more modern version around: TDA7350, that gives about 10W into 4R at 12V with 1% distortion.

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 21, 2010, 03:27:29 pm
content: I am in the middle of a project using the TDA2050 amp chip. (two, actually, since they are mono single channel amps)There are plenty of web projects that show 35 to 50 watts out of this thing, but that's at 10% thd.I'm holding it to 20 watts and using a bipolar supply so the distortion should be around 0.04%.Just google "TDA2050 circuit" and you'll see a bunch of applications, most of which just lift the circuit from the data sheet.A totally different approach is to scavenge some old computer speakers. I've bought a number of Altek Lansing GCS100 sets at thrift stores for a few dollars each. I strip them all down and put both speakers and the amp in one enclosure to make "worksite" style iPod amps. They're only 4 watts per channel, but you could run a mono signal into both sides and effectively get 8. And they really do sound awesome. They came standard with Gateway PC a number of years ago, so there are gobs of them around.

author: Simon
author_rank: Unknown
timestamp: October 21, 2010, 04:23:38 pm
content: well you could even get some pc speakers and just run them off a battery as most use 9-12V, and you would get a free transformer unless you want to keep it dual supply

author: sonicj
author_rank: Frequent Contributor
timestamp: October 21, 2010, 05:26:59 pm
content: i recently pulled a pair of|pp=[t=pip,i=TDA8561Q]]tda8561q'sfrom a old clarion cd player. pretty neat little chip. 4x12W or 2x24W, few extra components needed, standby, mute. your local independent car audio retailer likely has a box or shelf full of dead or unwanted headunits. if you go in with a good attitude, you can likely leave with a few free units to hack on.-sj

author: Zero999
author_rank: Super Contributor
timestamp: October 21, 2010, 08:58:43 pm
content: Quote from: sonicj on October 21, 2010, 05:26:59 pmAs with all audio amplifier ICs, treat those specifications with caution. You need to look at the graphs to get an idea of what the performance will really be like. Checkout figure 12: with a 14.4V supply and a 4R load, the distortion rapidly increases to an unacceptable level when the output power goes above 13W. With a 12V it will be worse. By how much? See figure 13, curve 3, the maximum power output with a THD of 0.5% and a 12V supply is about 11W.http://www.nxp.com/documents/data_sheet/TDA8561Q.pdfDon't get me wrong, it's a good IC, it's just Ohm's law which dictates that it's not possible to get more than around 10W into a 4R load with low distortion from an amplifier run from 12VDC and no boost converter.

author: haglered
author_rank: Contributor
timestamp: October 22, 2010, 01:01:49 am
content: I'm just looking to amplify voice to a level that can be heard at 10 yards over some background city noise. So it only needs to be a single channel amp.I am not wanting to buy a kit to build it. I want to do it myself so I can learn a little about electronics design.I have built kits before and I have never really understood why I am putting it together the way I am.I am hoping one or two of you could design a simple amp that I can build and understand.I also have a practical use for such an amp. I could save up and buy something professional but that would not be any fun.I plan on building a simple wooden case for it. I am wanting to use it about twice a month for an hour each time. It doesn't have to be a real good amp only enough to amplify human voice in a P.A. application.

author: Simon
author_rank: Unknown
timestamp: October 22, 2010, 06:37:24 am
content: if you want someone here to design it then your still merely making a kit, only that you may have to make the pcb yourself. most amp IC datasheets have example circuits that you can use, they are drawn up by the IC manufacturer and a PCB layout is usually provided.

author: haglered
author_rank: Contributor
timestamp: October 22, 2010, 07:06:11 am
content: yes but then I can ask things like why do I need a resistor here or why that size capacitor there.I have never understood things like that. Maybe if I can ask someone that understands I can finally get it.Like I said I am a nube at this and want to learn more.

author: Zero999
author_rank: Super Contributor
timestamp: October 22, 2010, 07:40:30 am
content: As Simon said, if you get someone else to design it for you then you won't learn much more than you would if you built it from a kit. People on forums generally don't design projects when others ask them to because it doesn't help them.If you want a circuit, look at the links datasheets for the ICs posted above. The TDA7350 seems to be the most suited to your application, see the circuit in figure 3 and the PCB design in figure 4. Use a 15W 4R speaker and a nice chunky 5Ah sealed lead acid battery.http://www.datasheetcatalog.org/datasheet2/3/07wekepw0qlowr5upksuaioej1yy.pdfYou'll also need a pre-amplifier, the gain will depend on your choice of mic.Using ICs isn't the best way to learn. The best way to learn is to use discrete components but building a bridge from discrete is a pain to set up because the quiescent current through the speaker needs to be trimmed to near zero. You could use a non-bridged amplifier but the maximum power output will be under 3W.Why not buy a kit and ask questions about it on the forum? We will help but this is not a free design service and bear in mind that there's no guarantee because this place is manned by volunteers.

author: Simon
author_rank: Unknown
timestamp: October 22, 2010, 02:11:29 pm
content: if your making an IC based amp the only person that can tell you what all the parts do is the IC manufacturer, anyone anywhere wanting an amp is going to start with the recommended schematic from the IC maker and then adapt it slightly. essentially you need to learn how to chose an IC, then follow the datasheets guide lines in putting a circuit around it and then learn to interface different circuits for example a preamp and power amp.

author: Zero999
author_rank: Super Contributor
timestamp: October 22, 2010, 04:32:55 pm
content: Some datasheets show a simplified schematic.For example, check out page 5 of the TDA2005 datasheet.http://www.st.com/stonline/books/pdf/docs/1451.pdf

author: Simon
author_rank: Unknown
timestamp: October 22, 2010, 04:37:15 pm
content: Ah, I found the TDA2002 to be good but really there is a whole series, 2002, 2005, 2009 and many more that are similar, will take a few more volts each and make more power

author: sonicj
author_rank: Frequent Contributor
timestamp: October 22, 2010, 07:31:45 pm
content: Quote from: Hero999 on October 21, 2010, 08:58:43 pmagreed, those numbers are almost always stretched for car radio amplifiers. i didn't look at the graphs as i have a pretty good idea of what it sounds like. should be enough juice for the op's requirements.-sj

author: Simon
author_rank: Unknown
timestamp: October 22, 2010, 07:36:23 pm
content: what about a nice D class amp ?that's something that can be "designed" although yea there are chips available too. If this is a battery application efficiency is a nice thing to have

author: sonicj
author_rank: Frequent Contributor
timestamp: October 22, 2010, 07:44:54 pm
content: theres nothing wrong with starting with a kit... something like this:link. then if you have questions, someone here can offer answers as to why this or that.kits are a great intro imo even if you don't know all the how's and why's. assembling something with your own hands and seeing it work beats staring at a datasheet trying to figure out what all the cryptic symbols mean and ending the day with nothing but frustration.i would start with the kit. my 2¢ fwiw.-sj

author: Zero999
author_rank: Super Contributor
timestamp: October 22, 2010, 07:49:37 pm
content: Quote from: Simon on October 22, 2010, 07:36:23 pmA class D amplifier will have similar limitations regarding power output to a class AB amplifier unless it has a boost converter but you're right, it'll be much more efficient than but it's much more complicated. Simple class D amplifier ICs do exist but you won't learn much by blindly copying the design on the datasheet.

author: david77
author_rank: Frequent Contributor
timestamp: October 22, 2010, 09:29:33 pm
content: As I suspected all you want is a simple command amplifier, so basically any of the mentioned IC'sdoes the job. Even 10%THD won't matter, so you can have a higher power output.Just look at the datasheet of the TDA7350, all you need to know is in there.Then look up a thing called non-inverting amplifier. That's the thing you need as a mic preamp.There're gazillions of circuits on the web on that matter, have a look at Rod Elliots page. Especially his articles on amplifier theory and construction are worth a read.You can make a circuit board for all that, but it will even work on Veroboard. In that case you'll haveto take care not to get the amp oscillating, though. Keep wires and traces on the board short, especiallyaround the TDA7350. C1 and C6 need to be as close to the IC's pins as possible to avoid oscillation.Use shielded wire for the MIC input and ensure that the outputs and inputs of the single stages are as far apart as possible.Ideally you try to design it "straight through": Mic IN -> Preamp -> Power Amp -> Speaker OUT.This applies to both Veroboard and a purpose made PCB.Maybe your first try will fail. Good. So you can learn something by troubleshooting it.I built my first amps in the days before the internet allowed easy access to datasheets and all sorts ofinformation. All we had back then was books and try-and-fail.

author: Simon
author_rank: Unknown
timestamp: October 22, 2010, 09:35:58 pm
content: be very careful on the veroboard, I wired up a pair of TDA2009's as bridged amps and ended up with a very poor quality and hot running amp that just happened to be oscillating at 6 MHz

author: david77
author_rank: Frequent Contributor
timestamp: October 22, 2010, 09:40:40 pm
content: Well, the same could happen with a PCB if you don't know what to look out for.For one off's and prototypes I really like Veroboard.I prefer the variety with individual solder pads rather than the stripes. The striped Veroboard canbe problematic if you don't cut off excess traces!

author: haglered
author_rank: Contributor
timestamp: October 24, 2010, 06:49:44 pm
content: Quote from: sonicj on October 22, 2010, 07:44:54 pmThat looks like a good option. I think I will order that (next payday) and build it. I will also find a preamp to build as well.I will post it on this forum when I get it and begin the build process. Expect a lot of why questions when I am building it.

author: sonicj
author_rank: Frequent Contributor
timestamp: October 24, 2010, 10:17:08 pm
content: if you want to learn a lot of "whys" then they have more complicated kits on that site, including kits with pre-amps built in (for the same or about the same price). the kit i linked is VERY simple. not much to lurn from that one, it was just the first one i came across that met your requirements.i definitely think you'll be satisfied with a kit as a starting point. even the more complicated designs will be ok as you don't have to fully understand them to assemble a working unit.-sj

author: haglered
author_rank: Contributor
timestamp: October 25, 2010, 03:18:28 am
content: I assembled an FM transmitter kit before and I didn't understand much about that at all.I should probably get a bench iron, even a cheap one to put this project together. I'm not sure how good a job I will be able to do with my radio shack iron.I know you have to make good solder connections and that is a weak area of mine.I am not good in Algebra either, maybe that's why I never learned what I wanted to know about electronics in general.I went out to my shed and dug up some old electronics parts including som resitors and a couple of capacitors I had thrown in an old box. They were still in their packaging from radio shack.I used to want to about learning enough about electronics to tear aprt old radios and tape players to reuse the parts from them. I still have a collection of old electronic equipment in that shed. I brought some of what I found today into the house. There isn't much there still useable but hopefully I will learn more than I have in the past.

author: sonicj
author_rank: Frequent Contributor
timestamp: October 25, 2010, 09:31:03 pm
content: stripping old electronics for parts can be fun. for me, it hasn't been a great a return on the effort, but has helped many times with that one or two components i need to complete a project. the best resource i've found for building up a inventory of parts is the "grab bag" type deals from places likeelectronic goldmine. sorting through one of those is fun and will yield way more usable goodies than stripping junk electronics (for the most part).the aoyue 936 / 937 soldering iron (hakko clone) is a decent starter station foraround $50.

author: DJPhil
author_rank: Frequent Contributor
timestamp: October 26, 2010, 03:28:25 am
content: Quote from: sonicj on October 25, 2010, 09:31:03 pmI love those assortments, I always thought they should offer a quarterly or monthly subscription option.

author: sonicj
author_rank: Frequent Contributor
timestamp: October 26, 2010, 04:02:22 am
content: yea. i want to order another one, but im waiting a bit in hopes of getting a different mix of goodies. sorting through one of those boxes is like a scratch-off lottery for nerds.the $7.95 assortment would cost approximately $1.2 million usd if purchased separately at radioshack.Quote from: DJPhil on October 26, 2010, 03:28:25 amthats a great idea! kinda like arecord pool. i would subscribe!-sj

author: JohnS_AZ
author_rank: Frequent Contributor
timestamp: October 26, 2010, 04:05:19 am
content: @sonic ... So which grab bag did you buy, and what sorts of things were in it? Any grand treasures?

author: sonicj
author_rank: Frequent Contributor
timestamp: October 26, 2010, 04:16:42 am
content: i got the $8 assortment + some of their smaller assortments (led, switches, etc.) and some individual items i wanted. in retrospect, i would order the assortment before ordering any small quantity stuff as a lot of the $1 for 3 type items were in the assortment!basically, i completely filled one of those 39 drawer storage bins with mostly usable parts for less than $50. way more useful values and sizes than i expected. no diamonds in the rough, but a super value non-the-less!heres a good example of the loot you can expect:http://blog.freesideatlanta.org/2010/01/mystery-unboxing.html