Making my own little speaker system

[shovenose]

I picked up a pair of Sony speakers... they seem to be a weird shape, maybe for a TV?
they use standard 2-wire speaker wire, but I'd be interested to make my own little audio amp for them, just as a project, (not because I need more speakers, even though I could always use more :P)

Where do I start?
lol thanks

[mariushm]

Re: Making my own little speaker system

First, open them up and see how powerful the speakers are and their ohm rating. If the speakers are 4-6 watts @ 8 ohm, no point making a 2 x 50 watt amplifier.

The TDA series of amps are simple and it's easy to make amplifiers out of them.

For example, TDA2050 will do up to about 28 real watts @ 4 ohm with a +/- 22v power supply or regular 40-45v. Well, it would do up to 35w but at 10% distortion which you don't want. 28 is the average for 0.5% distortion.

Here's the digikey page: http://search.digikey.com/us/en/prod...28-5-ND/634792

Powered from a simple 12v, for example from a regular computer power supply, it can do about 5 watts.

Here's the datasheet:

Page 4 and Page 5 shows typical designs for split power supply and single power supply.
The split power supply is nicer but if you want the full 28 watts you'd pay extra for a transformer capable of doing 35-45v @ about 3-4A (because you need to power two copies of this circuit, this chip does one channel only)

With the single power supply (the second example) you can just feed each channel with 12v from a power supply which is much cheaper.

[shovenose]

Re: Making my own little speaker system

IIRC it says on the back, I'll look in a bit.
Thanks!

[999999999]

Re: Making my own little speaker system

Even if your speakers are rated for a fairly high wattage, you can still factor how loud you need this to be versus the cost (and sometimes complexity) to get there.

Another consideration is whether you have any parts already, 12V ~ 1A unregulated AC-DC power bricks are common as dirt so if you can settle for a single-digit # of watts that's one way to greatly reduce cost and almost halve the build complexity. Another option moving up to split power rails from transformers with a dual secondary (or center tapped secondary) winding would be a toroidal transformer. Antek is one US supplier with reasonable rates.

http://www.antekinc.com/gview.php?d[]=0

You can find a lot of various amp and power supply examples on audio forums like DIYAudio,

http://www.diyaudio.com/forums/chip-amps/


If you just want both the simplest and cheapest way to get 2 watts out of an unregulated 12V adapter as the PSU, a chip with two channels and fixed gain like LM4752 will do that.
http://www.national.com/pf/LM/LM4752.html

[kaboom]

Re: Making my own little speaker system

Forget a split supply and go BTL with a TDA7297.

Use one of these ICs and an old CPU heatsink will cool it nicely- you'll probably be able to run the fan a 5V or so. The tab is at ground, so no insulator or shoulder washer needed.

[mariushm]

Re: Making my own little speaker system

The devil's in the details...
That chip can do a maximum of 15 watts at about 17-18v.
At 12v, the chip would barely do 6 watts with 1% distortion.

The TDA2050 I recommended above will do about 5 watts at 12v but on the other hand can go up to 28-30 watts with about 40v input.

Considering it has only 5 pins, and it's more compact, it's much more suitable for soldering it on one of those boards with lots of holes (not breadboard, the other name, forgetting now) and you can also use regular heatsinks from spare power supplies to keep them cool (at 5-10 watts, anything higher you need beefier heatsinks)

You're not saving money by going with a single chip vs duplicating a one channel design so that's also not an issue.

[999999999]

Re: Making my own little speaker system

^ Is that the new math? Of course it saves money. A few caps and resistors can be had for under $2 either way (though TDA2050 actually requires a few more of these) while buying two $3 chips instead of one raises cost about 50%... assuming use of an existing PSU like an AC-DC power brick.

Granted, it's not much money relative to a high powered amp, but there's also 50% or more extra wire to the amps, more connector terminals if the wire won't be soldered down, a larger circuit board or two of them instead of one, and if you don't have a project case or what you wanted to use isn't large enough, there's that addt'l cost too.

I'd rather the TDA2050 for higher power operation and think it's worth the extra few dolloars to do so, but it's also exceeding the current capability of a common 12V/1A power brick so add time or cost for a different PSU, you can't get 6W+6W/channel RMS out with only 12VA in with it being < 100% efficient. However, even with that constraint it would still be higher output wattage than LM4752 using 12V/1A PSU.

The real question is how much money to save. If money is no object I'd think about replacing the speakers too which kind of defeats the purpose.

[shovenose]

Re: Making my own little speaker system

Cost needs to be under $20. I can power it with an old laptop power supply if need be

So what's the concensus? which chip should I base it on?
Thanks

[999999999]

Re: Making my own little speaker system

Some people like the distortion caused by cheap brick switching power supply like those used with laptops, and others don't want it. Cost of the amp depends a bit on how many parts you already have and how many places you'll need to order from - shipping on a project like this eats up a small budget fast, though at least places like Digikey or Mouser should have practically everything needed to get the job done but they charge more for some things like transformers or project cases.

With a $20 budget I would aim higher than LM4752, but basically you need to work up a BOM (bill of materials) needed to fully complete the amp to see what will fit in the budget. Little *optional* things like plugs, jacks, a volume POT and knob, etc. can add up quickly. Truth is, it's probably cheaper to buy a ready made amp board or a solder-it-up-yourself kit off ebay, including something class D IF you want more output power per PSU voltage. These two are just examples, but there are class A/B (like the chips we've mentioned) kits on ebay too.

http://www.ebay.com/itm/NEW-Tripath-...item1c21e17066
http://www.ebay.com/itm/NEW-HI-Q-NEW...item3a6e77b4be

[shovenose]

Re: Making my own little speaker system

Some people like the distortion caused by cheap brick switching power supply like those used with laptops, and others don't want it.

Please clarify this. I don't know much about audio stuff, and I'd be curious to know what distortion you mean and how it could possibly by enjoyable.

http://www.ebay.com/itm/NEW-Tripath-...item1c21e17066

The entire reason I was going to do this was to get practice with curcuit design. However, that almost seems like too good a price to pass up! thing is, where's the input??

[999999999]

Re: Making my own little speaker system

Chipamp PSRR decreases based on ripple frequency. Switching supplies should be avoided unless known to exhibit very low ripple.

I have not bought the amp linked, but looking, the input would be right before the POT.


Sadly the truth is, today you can't buy all the individual parts for practice and end up with as good an amp at same cost, economy of scale means the price can be undercut so long as it involves enough components to offset shipping cost, BUT beware, higher power and more costly amps on ebay may be fakes using generic/relabeled amp chips. OR, that could be considered a positive thing. Depends upon the goal.

Frankly, what will make the most difference isn't the circuit, it's the enclosure you use for these speakers.

[Scenic]

Re: Making my own little speaker system

as for those Tripath T-Amps...

http://www.youtube.com/watch?v=wBsmFoWVmwE
http://www.youtube.com/watch?v=1nNK8Nc73i4

no comment on the second one.. just nuts lol

[kikkoman]

Re: Making my own little speaker system

ya, i've got a nice little DIY TA2024C amp running here.
great sound, it's more than enough for normal listening, and it's got enough to punch to piss off the neighbors even with the small desk speakers.
the thing runs off a 12V 2.5A SMPS brick with some filtering and bulk capacitors. no complaints at all.

too bad Tripath have gone out of business. those amps are still abundant on ebay etc, but IC stocks won't last forever. i wonder how long it's gonna be before the first fakes show up.

and i've got a few MAX9709 samples here ().
should be good enough for my needs. we'll see how it sounds (filterless? hmm), maybe i'll make a sub amp out of it.
it's a TQFN package (bah), but not impossible on a single-sided PCB. it's a bit ugly.

[mariushm]

Re: Making my own little speaker system

Well , I already showed in another post the amp that was pulled from a Phillips TV...

As you can see, quite simple construction, two channels, almost two copies with some glue between them added for some headphone outputs and other stuff the tv used to do.

The TDA2040 do about 25 watts when powered to +/-25v or so ... i don't remember exactly as i don't have the datasheet in front of me... but this one I screwed on the wood board does about 12-15 watts @ 4 ohm with the +/- 16v I give him.

The voltage is simply generated from a transformer with two windings on the secondary which then gets passed through a bridge rectifier to generate the + and - and then each goes through a 3300uF 63v teapo capacitor.

The large blue capacitors do the extra power storage for each amp.

(you can see on the board it says 2x35w but that's with 10% distortion, it's more like 25w @ 1% thd or less)

[999999999]

Re: Making my own little speaker system

Please clarify this. I don't know much about audio stuff, and I'd be curious to know what distortion you mean and how it could possibly by enjoyable.


The entire reason I was going to do this was to get practice with curcuit design. However, that almost seems like too good a price to pass up! thing is, where's the input??

To clarify, on one of the pics you can see the side of the board with the POT and two long yellow film caps. The input is there, a rectangular screened trio of holes marked "S-INPUT"... so at the least you'd also need some wire and whichever type of connectors you choose, as well as terminals or hard-wired connections for the speaker output.

[999999999]

Re: Making my own little speaker system

Please clarify this. I don't know much about audio stuff, and I'd be curious to know what distortion you mean and how it could possibly by enjoyable.

The effect is lower on a digital (class D or T) amp than an analog (class A/B in this topic) but basically rapid voltage fluctuations cause a lot more small uncorrected errors which some feel makes the sound more lively, more of a rough edge to it.

Once you drift into personal sound preferences there are all kinds of deviations from what seems a straightforward, logical engineering decision. Limiting bulk capacitance, using silver plated wire, audiophile grade capacitors instead of industrial low ESR grade, even the feet on the amp case are topics which will be discussed and argued till the end of time. I'm not suggesting any of these things do, or don't matter but there are people quite determined their way is best in audio.

[kikkoman]

Re: Making my own little speaker system

nice! the MAX9709 works fine so far. it's still a little ugly (FrankenAmp?) but sounds good. i love the Tripath, but there's absolutely nothing wrong with this one.
it doesn't have the one downside of the tripath: operating voltage up to 22V (vs. 14V absolute max).
and it only cost a few bucks (everything came from the parts bin or trash, samples were free).