simple kiosk sound system design

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pigeon

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Joined 2005
#1
Hello, I am looking to design a PCB to handle the 3.5mm output of a computer then boost that signal to run standard"" speakers (simple $6.00 per car speaker at walmart ones).

The reason I don't want to use standard computer speakers is because I like the mounting holes for the car speakers, and besides that, at $6.00 per speaker (and I really wouldn't only need one speaker), I could get away with a really inexpensive setup.

Also, this system will only need to handle midrange... the kiosk will 'talk' to people, no heavy bass or high highs.

Does anyone have any suggestions?

I have been looking at radio shack for amp chips (I am not evensure that is the right name), but I have found LM324 chip... but I am afraid (?) that it will not be powerfull enough.

The ability to have the speakers be really loud would be a plus, but not necessary.... Also, I would like the ability to regulate the volume somehow (on the pcb)


Are there any inexpensive solutions (under 15$ for speakers + pcb + parts)?

thanks
Lee
 
#3
well since sound quality is the least of your worries, i would suggest locating an electronic surplus store in your area. you dont need much to get one channel simple chip amp working.

start with finding an LM or TDA chip that gives you the power you need. take the datasheet for it, and just p2p an amp. i dont think a PCB is necessary, and it will blow your budget. most of these chips need half a dozen caps and resistors in all to make a working amp. add a cheapie pot infront, and you have yourself what you need.

oh for power supply, see what your surplus store has lying around, and work from there. with 4 cheap diodes you have yourself a powersupply. but of course, dont forget to snubber it 😉

im sure you could find the appropriate connector to accept 3.5 mm jack from computer and connect to pot. if not, just buy a cable with 3.5 mm jacks, cut one end and directly connect to pot and sound card.
 
#4
agreed. surplus stores will be your friend with this one...

i built a gainclone way back in the days in a cardboard box for $40 for a stereo one with decent parts and dual power supplies.

its "possible" to do what you want, but i would shoot closer to $30 for a budget just so you dont completely sacrifice things. little bits and pieces always add up ($1 for 3.5mm connector, wires, ac input cord or jack, etc...).
 
#6
exactly. it all depends on what you have. i built a pair of aleph3's with cases, caps, etc... for $350 for two monoblocks. you could NOT do that if you didnt have stuff laying around. all the wire, caps, fets, resistors, and other bits and pieces were just already in my shop. i just added transformer, case, and some other stuff.

resistors and caps for a chip amp are practically free (if you get them surplus or have them), the chip it self costs some cash, and the transformer will be the other cost (but you can get these for $5-$10 if you are lucky. but you will need a case, connectors, wire, etc...

$30 sounds like a fully built amp.
 
#11
it doesn't have to pass anything...

I was looking at something like:
http://www.chipamp.com

for $20 I could have 2 unassembled setups (since I only need mono)...

The downside to me would be, no adjustable speaker control (like the one allelectronics has) and the assembly part.. even though the guy said he could assemble it for me...hmm...

What do you'll think about the allelectronics :
http://www.allelectronics.com/cgi-b...P-30&type=store

option... then what kind of driver would I use with it? just a generic? 8ohm? 6ohm?

thanks
lee
 
#13
Great!

I just ordered:

http://www.allelectronics.com/cgi-bin/category.cgi?category=580&item=SG-4&type=store

http://www.allelectronics.com/cgi-bin/category.cgi?category=580&item=GW-2048&type=store

http://www.allelectronics.com/cgi-bin/category.cgi?category=937&item=AMP-30&type=store

and a 3220 contact breadboard 🙂

I have been waiting a long time to get that bread board.. but just didn't want to order it by itself 🙂

So you'll think the speaker amp combo will be good?

I heard that I should get 8ohm speakers, why is this? I know less ohm = less resistance.. (isn't that right?)

Also, the reason I got this speaker (granted it is under powered) is becasue I could get a grill that fitted it.. and would be a pain for a person to get off and vandilize the machine.

But, where could I also get a speaker/grill solution that is inexpensive?

Many thanks!

Lee
 
#14
Another thing that would work well and not need a transformer is an LM384, a chip that can run off of 12VDC, or a LM4752, a stereo chip that can also run off of 12VDC. Then, power it off of the 12V power supply in the PC.

edit: the impedence you should get depends on the amp. Lower impedence equals more power from the amp, but only if it can handle it. If your amp can't handle the low impedence, then the 8-ohm may be the only chance.

But, you may be able to bridge that amp for 30W (15W per side) by using a DRV134, asusming the amp can handle 4-ohm loads (8 ohms to a bridged amp is 4-ohms). I dobut you would need that much though. For that application even a watt or so is more than enough. Just having a speaker to talk to people is not a task that requries a lot of power or anything. IMO 15W is overkill.
 
#16
I got the components in last week.

I have to turn the AMP to nearly ~80 percent power to get desired sound... And in some environments, I would have to use 100percent power. And possibly more.

My concern is, I don't have enough power and when I turn the AMP up to 80percent power, I hear fuzz/static out of the speaker (what you would expect).



Is there a better option?

I would also like the option to be able to hook up a cable and have a pot on the other end to adjust the volume (so the user can adjust the volume on the front of the machine).

And I would like more power.


Lastly, I need this to look nice.. I will have 2 or 3 other PCB boards in the machine, and I could mount the amp pcb near them.

And oh yeah, Lets say I can spend a little more.. lets say under $50 for the amp setup

PS, what kind of watts does the chipamp.com put out for an 8ohm speaker?


thanks
Lee
 
#17
pigeon said:
Is there a better option?
...
I would like more power.
Click to expand...

The soundcard you are using must have low output...
Depending on the chip, you could increase the gain of the amp.
What chip does that thing use?

Hope it's not a fixed gain chip...:xfingers:
You can always add a gainstage, but there goes your budget.😀
 
#20
pigeon said:
hmm..

Well, is there any already built solutions I could look into? I would hate to have to buy 100 of these amps from allelectronics then have to mod every single one :/
Click to expand...

So, instead of changing one resistor on the amp you prefer to add a gainstage?

I thought your budget was very tight for this...😕
 
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