unusual request regarding small speakers and amp

[pmdevlin]

Hi all

yes, its a noobie her! but please read on, you might be able to help with an unusual request. I have a radio controlled scratch built replica of the jaws boat, Orca

It has a custom made sound unit using a technobots mp3 , with a sd card that has recordings of music and dialogue from the film, operated using a trigger system from the radio transmitter. All good so far, but, I cannot work out a speaker/amp combo that gives clear sound, with a reasonable volume (speakers are enclosed inside the boat). I currently have tried a number of things, all seem to fail as I do not understand the ohms, watts etc. Power source is 14v, depleting as the boat is used, so the amp need to be able to handle this. Speakers are currently 50mm 2w 8 ohms, all equipment needs to be small and light, mylar preferably due to possibility of water

The amp is from ebay, cheap chinese thing, now useless, speakers are from technobots, now useless as they are really bad distortion so I have probably ruined them! I have tried pc speakers (bit heavy) and pc speaker amp

Can someone please explain if speakers are for example 8 ohms 2w, what amp wattage should I use, would 4 ohms be better, a link to a UK supplier would be fantastic, told you it was different!

 

[Fardringle]

What are the physical dimensions of the space available to hold the amp and speakers? And what is your available budget for the parts?

 

[vi edit]

Is the current amp something like this?
http://www.ebay.com/itm/2-2W-4-PAM8..._Audio_Amplifiers_Preamps&hash=item35ad5a9159

 

[pmdevlin]

many thanks for replies,

this is the mp3 board

http://www.technobotsonline.com/embedded-mp3-player-v2.html

current (duff!) speakers (stereo not important, mono would do, but the tracks that are recorded are stereo, I thought it would sound better, the tracks are recorded using a download called audacity, and are music with dialogue and an engine sound overlayed on each other)

the boat runing (I need to get out more

speakers (now probably also duff!)

http://www.technobotsonline.com/2w-50mm-plastic-cone-loudspeaker-8-ohm.html

amp, (I doubt this is now ok, so need to replace)

"Chip: TDA7297 Dual-Channel Amplifier Chip
Power Supply: DC 9-18V, Recommend 12V 2A
Output Impedance:4-8 ohms
and will be running on approx 14v,"

http://www.ebay.co.uk/itm/TDA7297F-..._HomeAudioHiFi_Amplifiers&hash=item43b0df0af7

I have a reasonably good space, boat is 3 1/2 feet long, I cannot fathom out how to post pics yet ( I click the insert image icon above, and post the url, but it will not work?) which I suppose would help, as regards to budget, I would say speakers and amps something not too excpensive, maybe £25 $38??, less would be better!

weight is the enemy, hence everything is relatively small, the size of the amp from the link provided above is perfect!,



thanks

 

[vi edit]

You had the right idea, but I think your amp was throwing way too much juice at the speakers. Those were rated at 2w with a maximum of 3w. You more than quintupled the amount of juice they were rated to take with that 15w amp. The other issue with some of this low end Chinese junk is that it's just very "dirty" power and that could easily interfere with stuff and cause some of the issues you were having.

Throwing more power at speakers than they are rated won't instantly kill them, but going past a certain threshold of volume/excursion will definitely fry the motor/voice coil. I'm admittedly not that familiar with speakers of this size. I'm more used to the home audio side of things.

But it looks like you can get this little amp from Ebay.uk
http://www.ebay.co.uk/itm/2-2W-4-PA...4182&pid=100033&prg=1011&rk=1&#ht_4602wt_1144

That's 2w a channel, which is right in line with the power requirements of those speakers you linked. That should be a decent combo. The Sure amps had decent reviews from some other sites I've followed.

 

[pmdevlin]

that amp link looks ideal, but how do you reckon the volume is controlled? I cant see anything that resembles a vol knob,

thanks

 

[sdifox]

maybe this?

http://www.youtube.com/watch?v=obX2gYpMr-Q&feature=fvwrel

 

[pmdevlin]

found these on same site, not sure how you would control volume on the first link

http://www.ebay.co.uk/itm/110712859817?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

and this

http://www.ebay.co.uk/itm/350480722297?ssPageName=STRK:MEWAX:IT&_trksid=p3984.m1423.l2649

 

[joetekubi]

Here's what I'd suggest, very small, pretty powerful. Runs fine on 12V DC
http://www.parts-express.com/pe/showdetl.cfm?Partnumber=310-300

 

[Rio Rebel]

You should have bought a bigger boat.

(I can't believe I'm the first one to post that.)

 

[sdifox]

You should have bought a bigger boat.

(I can't believe I'm the first one to post that.)

quote fail...

"You're going to need a bigger boat."

 

[Rio Rebel]

quote fail...

"You're going to need a bigger boat."

Thanks for the correction.

 

[pmdevlin]

ha ha, well when the sound unit works..... I can play that famous line, along with plenty of others, and the music, really winds up the old guys who sail model boats!

"fair spanish ladies," etc etc, cant beat a bit of capt quint!

 

[pmdevlin]

that is a nice link Joe, but isnt the output too much for my teeny speakers? I am away now for 2 weeks, so its on hold till then, I still like the sure sound link, with volume control as a seperate rotary control, but cant fathom out how its connected, as instructions say dont hand solder, how else I can do it is a mystery!

 

[ericlp]

quote fail...

"You're going to need a bigger boat."

Not sure how big the boat is...

http://www.parts-express.com/pe/showdetl.cfm?Partnumber=300-385

Seems like it would work has a volume control. Can do 9 watts. but more likely for audio quality 4-6 watts.

Tho no input for thumb drive, you could I guess you'd need to get a super small mp3 player.

 

[Modelworks]

I wouldn't use a switching amp setup in your situation. Switching type amps like clean stable supplies and you are not going to get that on most boats without a lot of filtering. Everything from the motors to the lights can add noise to the power and with switching amps that gets translated into spikes that can destroy speakers.



Really thinking about what you need for a model like that I would use a chip called an LM386. It has about 1 watts output, doesn't produce much heat, uses little power, is very stable and also very cheap. If the input voltage drops it will still work as it isn't picky and is sized right for the speakers you listed.

something like this can be found in a lot of different versions. $10
http://www.ebay.com/itm/Low-Voltage...361355001251079&_qi=RTM1062688#ht_6420wt_1163

 

[pmdevlin]

thanks to all for suggestions, I am now home and want to get this sorted, funny you should talk about "noise to the power" modelworks, just before the vacation a friend saw the inside of the boat, its 4 feet long, but due to all the fittings etc there isnt much room for electronics and he said exactly the same, in my ignorance I had all manner of things cable tied together, the amp was touching the electronic speed controller, the speaker cables ran up to the brushed (sparky!) motor, the power source was underneath all this, and so on!
with that ebay link, its a nice size, only prob is one speaker outlet, twin speakers are fitted and the sound recordings are stereo, I seem to think that could itself be a problem if the amp has only mono?
I dont really understand what you mean with "switching" amp?, sussed out the pictures at last!!

speakers are under the 3 forward portholes, sound unit, motor, amp, power supply and lights etc are under the main cabin windows, all the superstructure lifts off in one go so access is easy, space is limited!
thanks

s

 

[Modelworks]

with that ebay link, its a nice size, only prob is one speaker outlet, twin speakers are fitted and the sound recordings are stereo, I seem to think that could itself be a problem if the amp has only mono?
I dont really understand what you mean with "switching" amp?, sussed out the pictures at last!!

Very nice boat ! I like to build RC airplanes but I haven't done one in awhile now.

Here is a board using the lm386 that is stereo.
http://www.electronics123.com/kits-and-modules/1W-Stereo-Amplifier-Module.html

A switching amp like the Class D designs put out a signal that rapidly changes and then is smoothed out by filtering to produce the audio. Class D is very power efficient but requires a stable , clean power supply to output good sound quality. On a Class D amp varying the output voltage from what the device was designed to use results in less than optimal sound and things like hum or noise in the power signal make the output even worse. Class D is great for things like home audio where the power supply is stable but not so great for battery powered devices like RC controlled models.

The LM386 in the link is a class AB which doesn't switch the sound output on and off but instead just increases the levels of the input signal and outputs that to the speaker. The amp is always on , more or less, so it isn't as power efficient, but because of the way it work is better able to tolerate wide voltage swings.


http://en.wikipedia.org/wiki/Electronic_amplifier

 

[pmdevlin]

Very nice boat ! I like to build RC airplanes but I haven't done one in awhile now.

I am just about to come off a buddy lead, done rc helis for a bit (not very good at them!), now learning fixed wing, but we are doing seaplanes, so landing and taking off over water, just for something different!

thanks for that explanation! I understand now, and yes a varying voltage will be the power source, depleting as boat is running, and probably spiking anfter a rest and batteries have that window of recovery, I am using 4 lipo cells 5000mah to power boat, now over to ebay!

many thanks!