Speaker amplifier criteria?

[diegoterc3]

Hello, I am trying to build my own music speaker and for what I have been researching some ways to do this is to use OPAMPs which I think I will use.

Also I have read that I will need to make a filter so that the sound doesn´t sound noisy, and that certain kind of capacitors, inductances and resistances, of certain materials, often can cause improvements or make the sound worse.
I will use the audio plug from my smartphone and use the opamps to amplify the sound also I will use a 100W speaker 10cm diameter

So bassically my main question is:
Which other criteria will I have to take into account in order to have a really decent sound quality?

Other questions:
How can I calculate the filters?
Which components are best or most often used in this kind of circuitery?
How can I attenuate physical phenomenon like echoes and such?

As you can read, quality sound is on the top of the "must have" list also I need the circuit to be as small as possible.

Thank you in advance for your response.

[Rerouter]

Ok, not to sound harsh but you sound a little fresh to this, so i'm going to lay it out a bit

Op amps are the best way to amplify small signals with minimal distortion, however to drive something as big as a 100W speaker you will need what is known as a "push-pull" amplifier driven off that op amp, as it is far to big of a load for a linear op amp.


1. How can i calculate the filters
With audio level, your main ones are a low pass filter, a high pass filter, or a band pass filter, and they do as the name suggests, they either let frequency's above below or between a range pass without "attenuation" in most cases if is a sub-woofer, its a bandpass of 30-300Hz or low pass under 300,

have a read up here on how to calculate them http://www.allaboutcircuits.com/vol_2/chpt_8/1.html

2. Which components are the best
People will swear by just about anything as audiophiles, in most cases for your output coupling capacitors i would recommend a non polarized electrolytic with the lowest ESR you can find, and for the input, I've heard people swear by film capacitors, but i would still think a non polarized electrolytic will do the job.

As for the remainder of the passives, use X5 or X7 ceramic capacitors where you can as they dont get affected by supply voltage as much as the others, avoid tantalumns where you can, and pick the cheapest resistors you can find,

3. Attenuate Echos
You may want to clarify this a bit, my first assumption is that this is a DIY PA system, if so i'll be honest in saying i have no idea how this would be done, as the time delay between it leaving the speaker and it reaching the microphone is not something i can think of an analog based solution.

[AG6QR]

I'd like to back up a bit, and ask, why?

There are many amplifiers you can buy off the shelf, and they'll generally work pretty well.  There are different tradeoffs of cost, power output, fidelity, power consumption, etc.  What is it that you expect to do to improve on what's already available?  Or are you just planning to try and learn something, without necessarily improving on an existing design?  Are you wanting to learn how the design process works, or would you be happy just to assemble something based on a schematic someone else developed?

You say you want to drive a 100W speaker.  Just one, or do you want stereo output?   How much power do you want to put into that speaker (or those speakers)?


For a low power, low voltage audio amp, you could start with the LM386 data sheet, or search the web for LM386-based circuits.  If you want more power, both Sparkfun and Jameco offer kits with more power available.  If you want something even bigger and better, search for "carver amplifier schematics" for some examples of audiophile amplifiers.  These are just a few ideas -- audio amps are so common, there are lots of schematics available.

One note of warning:  Because of the economics of the electronic parts supply chain, if the product you want to end up with is something that's already available off-the-shelf, then it's really hard to build something yourself that's better and cheaper.  If you have some unusual requirements that aren't met by off-the-shelf equipment, then building it yourself is the only way to go, of course.  And sometimes it's fun to build things yourself, despite the fact that it may be more expensive and/or worse performing.


Anyway, that's why I'm asking "why?".  We need to know your motivation in order to offer constructive suggestions.  Do you want top audio quality for the best price?  A commercial unit may be your best bet.  Do you want to learn how op-amps work, and how to design passive and active filters?  Working through the relevant exercises in Horowitz and Hill's "Art of Electronics" might be a starting point, though it will take quite a bit of time to accumulate the knowledge and experience to design your own high performance amplifier.  Do you want to copy an existing design, without necessarily understanding it thoroughly?  Maybe someone can offer some suggestions for kits or schematics.

[TimNJ]

Well I've built some of my own amplifiers and it was very rewarding. I've also failed a few times (see my recent thread )

It will be way more expensive than purchasing something prebuilt. I didn't believe it myself until I rang up a bill of materials of $180 for a 60W x 3 (2.1) amp. However, I'm pretty sure the amp will last longer than I will, so I suppose it was worth it.

I'd suggest trying to build the amp on your own (i.e. don't buy a PCB off of eBay or some place else). I've done that and I don't think I learned nearly as much from that as when I build them myself on prototyping board...though protoboard can be a nightmare if you have a circuit that's very sensitive to layout and grounding etc.

[diegoterc3]

Happy new year to you all. Thank you for the replies. Yes I am bulding a newamp because I want to learn and have a nice sound made by me. I've build other circuits before and it is a very rewarding experience. By echoe I will put an example that has happened to me. In my car stereo sometimes i echoes when I plug my smatpone. I dont know why is this. I fix it by unplugging and plugging it again. So a push-pull circuit looks great. Any advice on the opamp that I hace to use? It should be 100 W x 4.

[Mark Hennessy]

Investigate the LM3886 - it does 68 watts into 8 ohms. You can bridge a pair of them to get more than 100 watts. You can run them in parallel to get more current capability. There are kit PCBs available, so building them in fairly fool-proof. Building the case, power supply and heat sinking is pretty complicated, of course. Have a look at www.diyaudio.com for more advice.

A properly constructed one of these gives excellent performance - typically less than 0.003% THD+N in my experience.

The "echo" from your smartphone can be ignored here.

As has already been pointed out, it won't sound any better than a commercial product at the same cost.

[NiHaoMike]

At that power level, it makes a lot of sense to go with an analog input class D chip. The TI chips are really good, with one available that can handle 600W in a package smaller than a quarter. You will have to do some surface mount work, so it might be better to buy a premade module.
http://www.ebay.com/itm/2-X-300-Watt-4-Ohm-Class-D-Audio-Amplifier-Board-TAS5630-300W-Stereo-Power-Amp-/350601682056?_trksid=p2054897.l4275
One of those will run nicely from a surplus 48V telecom PSU.

[bgsteiner]

One thing to understand is that in the audio world is that the best way to amplify an audio signal is not to split the frequency range you want to amplify the entire signal through an amplifier then split the signal before getting to the drivers for that frequency by use of a crossover circuit. with the power you are looking at i would go for a class D circuit one that uses high power MOSFETs. In this way you will have clear sound as long as you isolate it from interference and a good crossover that is set for the frequency range of the drivers you use you will end up with the best sound.


If you need any more advice feel free to pm me

The sound engineer.

[Mark Hennessy]

I've just spotted that the OP says that his 100W speaker is 10cm

What sort of "watts" are we talking about here? I'd suggest that the OP reads this, then re-evaluates the whole project: http://en.wikipedia.org/wiki/Audio_power

I stand to be corrected (which will require nothing less than a full datasheet for the drive unit in question), but I suspect that a single LM3886 pushing around 50 real watts (continuous average power) would tear the drive unit apart playing modern hyper-compressed "music". Forget about 300 watt class D modules!

[grumpydoc]

I've just spotted that the OP says that his 100W speaker is 10cm

What sort of "watts" are we talking about here? I'd suggest that the OP reads this, then re-evaluates the whole project:

Car audio I would think - "100W" 10cm units common. Actual RMS handling probably 10-40W

[Bloch]

Actual RMS handling probably 10-40W

I think a 100 Watt amplifier is ok for a 10cm speaker like this http://www.scan-speak.dk/datasheet/pdf/12mu-8731t00.pdf

[Mark Hennessy]

I've just spotted that the OP says that his 100W speaker is 10cm

What sort of "watts" are we talking about here? I'd suggest that the OP reads this, then re-evaluates the whole project:

Car audio I would think - "100W" 10cm units common. Actual RMS handling probably 10-40W

Quite 

[Mark Hennessy]

I think a 100 Watt amplifier is ok for a 10cm speaker like this http://www.scan-speak.dk/datasheet/pdf/12mu-8731t00.pdf

Wrong 

It's a mid-range driver, so the rating (80 watts with noise) is with a 200Hz high-pass filter. Actual power ending up at the voicecoil will be substantially less. In other words, the power rating is a suggested system rating; what you might be able to expect when using it in conjunction with a woofer et al... If you up the crossover frequency, you'll probably be able to increase the system power handling if your woofers are up to it.

[Bloch]

I think a 100 Watt amplifier is ok for a 10cm speaker like this http://www.scan-speak.dk/datasheet/pdf/12mu-8731t00.pdf

Wrong

I stand corrected. The IEC standard was new for me.

[peter.mitchell]

2x STA540s will do you just fine, cheap as chips, will give you the power you want, easy to set up. 10cm speaker, 100w? what is your speaker? a single phase ac motor? lol