Starting a student project, need some input (chip amp + speaker set)

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Hi guys. I'm new here and come seeking some wisdom. I am an EE student at Auburn University and our campus IEEE group is looking to start an EE project to teach students more about designing a circuit and then constructing the circuit.

Most of what we get is classes is all "book smarts", so the goal of this is to try and give people some practical knowledge about designing, building, and testing a circuit.

I have had a little experience with amps in the past (I did a bit with tube amps in high school, and built a chip amp based off of a Phillips IC, I don't remember the name anymore) so i suggested building a chip amp as it would be a simple enough project that people could actually use and enjoy. The idea was taken to pretty quickly so now we are doing some reading to try and figure out exactly what we want to do.

We will not start this up until spring semmester, but we want to go ahead and plan out the project and build a few of these amps so that those of us in charge are familiar with the design and will be able to answer questions about it.


Ideally we are looking for a design that is relatively simple, has a low parts count, and won't be too expensive to build ( students will buy their own parts. I guess if a student wants a better quality amp, they can choose to buy better parts, but just for the experience, we want it to be able to be built cheaply), and can be built on a pcb easily.

The LM3875 seems to be a very popular choice, along with the LM3886, but I am unsure what would be the best choice for us.


We are also considering giving kids the option of building a speaker set to go along with the amp. If we do, it will probably be zigma hornets or something similar that is easy to build and small enough for a dorm room.

Thanks guys, any input is appreciated.
 
Hi!
It's very good that students are interested to learn and build an audio amplifier.
I start to build amps. since I was 10 years old, and till now I have made a lot, and My present listening amps are also homemade.
My suggestion is that if you like to learn more about audio amps is to start with discrete transistors schematic.So you will able to learn more about all amps circuits input circuit thermal and bias stability, PA circuit, all input and output parameters distortion impedance handling, feedback,, frequency response, slew rate, and other very important thing which I would say that is 40 to 50 percent of the sound , a good power supply.
If you start learn with IC amps you will learn maybe how to solder components etc...
Sorry but I can't give you a schematic but I am sure that you will get a simple transistor schematic here or other places on the internet.
I wish you a good luck with your attempt to build a simple and cheep amp.
 
Some of this stuff we learned the basics of in out Analog Electronics class, but the application of this is what we are looking for mostly.


Ideally, these would be good general purpose amps. There is no way we are going to get an agreement on musical taste to pick out a design, so something that hits about middle of the pack would be best.
 
I'm not sure how much real learning value there is in building a chip amp. After all, the manufacturer has done all the design work, and published detailed application notes on how to use the thing. It's like thinking you're a chef because you added water to a cake mix. IMO, you'd be better off buying a barrel of surplus discrete small signal and power devices, then building up a very simple version of a traditional amp. Get a copy of Doug Self's book on power amps and start there. All the stages are explained in painful detail, but you then get to exercise some judgement based on how complicated you want it, and what parts you have available. That gets you away from the cookbook approach that teaches far less.
 
Perhaps a headphone amplifier?

Sorry, realize this is the chip amp forum, but I feel a headphone amplifier might be better.

Although these are EE students, they are still amatuers. This project will be conducted within the realm of a university, so safety must be considered. As an individual, we can do things which would not be allowed in an institution.

A headphone amplifier can operate from a discarded wall-wart or notebook PC power supply, pushing the onus for safety to another company.

A headphone amp is also more useful in a university setting.

A headphone amp costs a fraction of the stereo power amp, and consumes a smaller portion of the constrained dorm space.

And yet, building a headphone amp will teach almost all the same skills, save off-the-line power supply design.

Your thoughts?
 
Well, I don't really want to do a headphone amp because I don't think anyone would use it. I know I wouldn't.

Most of us have our Ipods and what not and they get used when we are walking around. When we aren't walking around we usually are listening on speakers.

The only time I ever use headphone is when I am playing an online game and need voice chat for team coordination, and when that is the case I am using a USB headset.


The chipamp that I built in high school runs off a wall wart. I don't see why we can't do the same thing with this one.
 
Conrad Hoffman said:
IMO, a headphone amp is a good idea too. If you have to use a chip amp, learn to do a bridge amp. At least there will be more area for discussion beyond the app notes. You can likely do a nice dual purpose amp- headphones, but with just enough power for efficient dorm room speakers as well.

As I said above (you can't see it yet because of the moderation stuff), while a headphone amp may be simpler/smaller/cheaper, I think it's usefulness would be limited.

I dual purpose would be ok, but honestly, I don't see a headphone amp getting used often. Most of us use our ipods, and if we do use headphones otherwise it is usually when we are on computers in the labs, and taking an amp along for that doesn't seem practical.
 
Maybe you should determine the project parameters first, and then select the IC you use. Either start from the output, i. e. how much power do you want or need at which load impedance? Or start from the input, i. e. how much money will you spend or what power supply is available?

If you want to use a wallwart as power supply, the power output will be very limited. And then there is the restriction that most wallwarts are single supplies.

Seems more like a job for smaller and cheaper ICs like LM1875, LM1876, TDA 2003..2051. Or one of those car amplifier ICs that run off 14,4 V single supply like TDA7374 or µPC2500.

OTOH it may be possible to use a powerful symmetric laboratory power supply that should be available at the university for the project, and build a conventional power supply for your private use and experiments and home. Then go for LM3875 or LM3886.
 
zoranaudio said:
. . .My suggestion is that if you like to learn more about audio amps is to start with discrete transistors schematic.
. . .I would say that is 40 to 50 percent of the sound, a good power supply.

Well, have a look at this useful "prototyping style" chipamp project for learning layout and general power circuits:
http://www.diyaudio.com/forums/showthread.php?s=&threadid=123255
Its not a "gainclone" with a limited power circuit, but rather a more general power circuit.
And, in doing the layout yourself, then you can also study how prototyping relates to PCB.
In practice, the usable power output doesn't differ significantly from a LM3875; however, the safety for a class project is greater since LM1875's required voltage is lower. This project works perfectly well with inexpensive EI core (square) center tap transformers.

Perhaps after playing with a chipamp, then a discrete amp can be made that uses the same or similar support circuits? To me, its an interesting prospect to gain some basics with the chipamp and then do a, similar, discrete amp.

Do be aware of the abilities of your students to handle safety concerns. There is high voltage.

There is yet one more hazard. If you score a find like this one: http://cgi.ebay.com/Nippon-2200uf-3...VQQcmdZViewItemQQ_trksidZp1638Q2em118Q2el1247 for quite the bargain on capacitors, then do be aware that these could be new old stock. That's an eye injury hazard. For safer use, charge these for 10 minutes with a 12vdc wall-wart power pack supply to allow the contents to "form" rather than expel at force. Drain them with a 50R 10w sandblock resistor before assuming safe handling.
 
Sneasle,

Nice to see some local interest in amplifier / speaker building. I am in Eufaula, about an hour and a half from Auburn.

One project that has not been suggested so far is the P3A amplifier at Elliott Sound Products. It is a very good little amp circuit, with a few limitations. Boards are available at a reasonable cost, though it is not difficult to make your own (I have). The best part is that the entire design is well described and documented at the page above, thus teaching you some of the background as you build.

I have built all of the projects suggested so far and then some, and would say that I learned the most from the P3A project. It also took me the longest to build, as my first two boards had oscillation issues, and I ended up with 4 revisions before I finalized my design.

By far the most simple and robust amplifier project is a www.chipamp.com kit. You can have two built in under an hour, even if you have never soldered before. If you are interested in designing your own circuit boards, a chipamp will require the fewest revisions of boards as they are very easy to lay out. Chipamps also have internal protection circuitry for shorts and over temperature faults. I haven't noticed a difference between chips, so just pick one based on your needs. Another plus to chipamps is that as students you can get free samples of the chips.

All of that convenience comes with the tradeoff that the circuitry inside the chip is far too complex for a student to fully understand, and the external circuitry is far too simple to teach anything valuable.

I think you need to reach a consensus among your peers as to what level of detail you want to reach in this project and what you expect to get (physically and educationally) out of the project.

You also mentioned a speaker project. There are several good choices out there, but I would have to recommend a small two-way over a full range design. A small two way will be more universally appealing and with the crossover to build, will also serve to provide another source of education. I'm sure you've seen the projects at www.zaphaudio.com, but if not they deserve a look.

Keep us updated on your decision, I for one would like to see what you end up doing, and would love to visit one of your meetings if I could.

Regards,
David Malphurs
 
David:

Thanks for the welcome. I do like the products at chipamp.com, but I would like the students that do this to have the opportunity to make their own boards.

What I am tempted to do right now is use on of the power supplies that he has as a foundation. You think that would work?


If your ever in Auburn let me know. I am a part of many different student teams and we would be more then happy to show you around a bit.


To All:

I like the idea of picking a starting point and going from there. I will talk with the rest of my group and come up with what we think is a reasonable cost to start with.



Can someone explain to me what the differences are between these? Mono vs stereo is easy enough, but what is dual mono?
 
Sneasle said:
Mono vs stereo is easy enough, but what is dual mono? [/B]
Well, it really depends on the context. Sometimes it means that two amplifiers are used for each output channel in a BTL or paralleled configuration. In this case it means 'enough parts to build two mono amplifiers in separate cases'. The only difference is that the kit includes an extra power supply board so you can build two separate 'mono blocks' instead of a single stereo amplifier.
 
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