Camping Music Box - PROJECT

[stuee]

Hi, i regularly gofishing/campoing with aload of mates and always someone gets a flat car battery from music on. So my idea is.......

A Box with a small sub and midrange speakers, a amp and mabey a mp3/radio player inside..

Now for all this i would like a smallish battery mabey 6-9v rechargeable and i want to put a solar panel on the box lid so it keeps charging it, (in aussie we have lots of sun) Its not a high powered system just a system for some background music.
So any i help / ideas?
I havce speakers already, i just need some 6-9v amp schematic (Mono no more than 100w or less is great prob around the 50w mark) that i can just plug the earphone socket of the mp3 player into the box and ,turn on and off we go.

Also the solar panel, ive not had much dealing with them so any advice for what i would need. size, Wattage or voltage.

Thanks all in advance
Stu

[audioguru]

Hi Stuee,
Doing some number crunching with your 6V rechargable battery and 100W requirements, if the amp is 60% efficient then it will use 167W and pull about 28A from the battery. The battery charge might last only a few seconds.

Your amp will need a DC to DC stepup converter (like a high-power car amp) to produce 100W into an 8 ohm speaker. With only a 6V supply, a bootstrapped single-ended amp will produce about 5Vp-p which is 0.4W into an 8 ohm speaker at clipping. An ordinary LM386 amp will produce 0.25W. If you use a bootstrapped bridged amp it will produce about 1.3W.

100W into an 8 ohm speaker is 80Vp-p and a single-ended amp will need at least an 86V power supply. A bridged amp will need a 46V supply. The DC to DC stepup converter will have some loss so a 6V battery will have 35A discharge when the amp is producing 100W into an 8 ohm speaker. Of course the battery must be rated for about 70A/hours to be able to play loud music for 4 hours each evening and consist of about 140 rechargable Ni-MH AA cells.

Solar cells? The expensive ones made for trickle charging a car battery are rated at only 15W. Maybe you could cut it in half to charge your 6V battery. After a day in the sunshine it will provide enough battery charge to play full-power music for a couple of hours. ;D   

[stuee]

like i said its only for background music or radio, mabey 100w is a bit loud the same as 50w. mabey a 30w or less system. What do you think and do you know of anmy schematics so i can make a coupkle and try them.

[ante]

Hi stu,

You can buy two small 12V 17Ah sealed lead acids and wire them in series, that will keep the losses low since you can use 24V without and DC-DC converter. Or, you can buy a boat battery with a handle 12V 75Ah and use conventional car stereo parts in your box. Solar panels are still expensive about US$ 4 /W, I guess you are not going to spend US$ 800 on this project! ;D

[audioguru]

Hi Stuee,
You can use an amplifier designed for a car radio and power it from a motorcycle battery:
The TDA1552 is a simple circuit that will provide 12W per stereo channel at clipping into 4 ohm speakers.

The TDA1564 is very efficient since it switches fom single-ended at low power to bridged at high power and will provide 16W for each stereo channel.
http://www.semiconductors.philips.com/acrobat/datasheets/TDA1564_4.pdf

The TDA1562 has a built-in voltage doubler that is used only on demand of high power. It provides about 40W to a single 4 ohm speaker at clipping.
http://www.semiconductors.philips.com/acrobat/datasheets/TDA1562Q_ST_SD_2.pdf

Don't believe the amplifier manufacturers' claims for output power. They use a 14.4V supply and the amps are heavily over-driven to produce 10% distorted square-waves. ;D

[Guest Alun]

How about using a class D amplifier at least for the bass element of the amplifier?

[audioguru]

Good idea, Alun. ;D
TI have a nice "240W" class-D amplifier IC. It would provide about 35W into a 4 ohm speaker at clipping with a 24V battery and is so efficient that it doesn't need a heatsink.
It has 36 pins and is a tiny surface-mounted thingy so it would be difficult for Stuee to solder. I think even its bottom must be soldered to the pcb's ground-plane somehow for its heatsink. ???

tas5152.pdf

[Guest Alun]

I've done a quick search and the LM4651 looks easier to build.

[audioguru]

Yeah, the LM4651 and its controller mate are easy to make. National was going to cancel them this year but extended the cancellation until next year.

[ante]

For better economy this might be an alternative for the beach party: http://www.greeleynet.com/~cmorrison/WindMachine.html  ;D

[stuee]

So can someone please look at these projects and tell me if any of these are suitable for me and the time they would last for, i dont want it for blasting music out, jsut as background music for a quite fishing spot we always goto....also i only want it in MONO not stereo so would that make these last alot longer as im only using one chanel?


http://www.aaroncake.net/circuits/amp20w.htm

http://www.reconnsworld.com/audio_16wattamp.html

http://www.maxim-ic.com/quick_view2.cfm/qv_pk/4834

[Guest Alun]

The first one is stereo not mono, and all of these projects are probably far too loud for you, a 1W amplifier made with the TDA7052  should be more than loud enough.

[audioguru]

Hi Stuee,
100W would scare away the fish and anyone about 1km away. You need only a few watts for background music when fishing.
Most amps you posted are designed for 4 ohm speakers and therefore have double the idle current of an amp designed for 8 ohm speakers. The stereo ones have double the idle current again for the channel that is wasted.

The "20W" amp will provide about 4.5W at clipping into an 8 ohm speaker. Its max idle current will consume 2.1W.
The 2nd amp will be about the same except its LM383 ICs haven't been produced for many years.
The 3rd amp uses a surface-mount IC with umpteen number of pins (64) and you will probably be able to hear its distortion at high frequencies.

Maybe Alun's 1W amp won't be loud enough.

Years ago I made portable dual mono amplifiers to take to the beach. They gave a few watts output when powered by 6 AA Ni-Cad rechargable cells all day long. Now with modern Ni-MH cells they play all weekend.
Unfortunately the amp ICs aren't made anymore but Philips has a similar one, their TDA8945S. It has only 9 pins in a row with a heatsink tab. It will supply about 5W into an 8 ohm speaker (it can't drive 4 ohms) at clipping with a 12V battery. and its max idle current wastes only 0.4W. ;D

[stuee]

what type of battery would you reccomend. i might go for the philips amp. I was thinking of getting a spotlight torch and using the mini car batery out of that but finding a 12 is awkward most are 6v or 9v or could i use a load of recharge D batteries so i can stick the solar panel onto it so it keeps them topped up?

Thanks for your help so far. \
Stu

[audioguru]

Hi Stuee,
If you look closely at the spec's for Energizer's AA and D Ni-MH rechargable cells, you will notice that they are exactly the same capacity. Their D cell is simply an AA cell in a big D-size can! ;D

[hamoodyjamal]

Hi,

I have a simple solution for you. However, it does not include a Solar-cell to charge the battery.

I have done this 3 times and worked great!

All you need are some simple desktop speakers, and a rechargeable battery (or you can use normal batteries). The thing is, most simple desktop speakers (ones used for computers) have a built in transformer to drop the voltage to say 12V (in my case, it was always 9V with my speakers). So, you can hack through the transformer and connect the battery as the power supply, your speakers should work and become portable. They provide some what enough power for background music. About 5W.

I used a single 9V rechargeable battery rated 170mAh and it lasted a couple of hours on full charge. However, your speakers may need more/less than 9V (i.e. 6V or 12V ...) you will need to measure the o/p of the transformer. You will, however, get a higher reading than what it is actually. Mine measured 15V when it was actually 9V. I think the 15V is called RMS volts. I don’t know of a specific way to measure the actual voltage, but you can try by playing something and setting the speakers on the loudest. WARNING: YOU WILL BE DEALING WITH 220V SO BE VERY CAREFULL NOT TO TOUCH THE TRANSFORMER INPUT WIRES

My point is that you can use a battery to power simple desktop speakers. You may be wondering what I mean by simple, well, speakers that have minimal knobs, i.e. volume and power. This way, you won’t have to go through the trouble of building a circuit then housing it.

Hope that helps.

;D

[audioguru]

Hi Hamoodyjamal,
You have a good idea to use computer self-powered speakers. My new computer came with pretty good-sounding speakers that are powered by a 12VDC/1A wall-wart.
I took one apart now and it has a 3" (77mm) 4 ohm speaker that is very heavy and has the biggest magnet I've seen on such a little speaker.
The circuit has a ST Micro 11-pin stereo amp IC that must be a house number because it doesn't exist on their website. They have other similar amp ICs like their TDA2009A that produces 3W per channel at clipping with my speaker's setup.
Its max idle current is 120mA so it would take a pretty big battery to power it over a weekend. ;D

[stuee]

thanks for the idea. i do have a few ideas and this was one but the speaker system i have here available is a 9v with a sub and 2 l/r speakers i might still go ahead. I was also thinking i might use a
Alarmclock. So i can have the Time, RADIO and also make a line to add on a mp3 player if i want to listen to custom speakers.
I have just purchased a bigish 12v battery rated  12v-18AH/20hr also a 4.5mw 14v solar panel, i did a few calculations ish  and i figure if i dont hammer the music loud i would be able to use the power from the battery for around 10hrs without any charging. But with the solar perm connected it should be fine. I will aslo add a cigarette socket to the box so in my tent i can plug a lamp into it also the airbed pump.

Any ideas now for the music source. I would prefer digital radio not analouge dials. also as here in aus when you go inland abit signals are a little crap to pick up so io might have to make a preamp if its possible.
Thanks

[audioguru]

Hi Stuee,
If you get a clock radio, get a good one (most are crap) and with an LCD display, since an LED display uses a lot of current continuously. ;D

[stuee]

ok thanks, thought LED was real low current, will find a LCD now. Also what else do i need for this solar panel, i have a regulator inline now, would it be ok to just leave the panel perm connected, will it not overload the battery if its full and keeps putting charge to it? im also after a simple battery power status so i can put it on the box and see the battery power.

Thanks

[audioguru]

You said that your solar cell is only 4.5mw? I don't think so. The tiny solar cell on my calculator is rated the same and is the size of my thumbnail.
It is probably 4.5W, and will overcharge the battery and dry it out. You need a circuit to stop the charging when the battery is fully charged.

What are you going to do when the battery is dead and it is cloudy outside? Sing? ;D

[stuee]

Yer been practicing singing :D
Ok im slowly getting there, i got a preamp, a 40w amp and a mp3 256mb player with radio, it all works ok and volume control is ok. I have 3 more questions.

1. How do i get the stereo output to mono as the amp i use is only mono
(can i just join the 2+ of the audio together?)

2. I would like to get a sort of bass boost too or a tone control. It must be mono and <12v

3. I would like some sort of schematic for the solar panel chargig so i dont dry out the battery.

Thanks

[audioguru]

Hi Stuee,
Which amp circuit do you have that gives 40W output with only a 12V battery?

You should never short together stereo outputs of anything to get mono. The outputs will fight each other and might be damaged.

I designed a passive circuit to add the channels with two 10k resistors and give an adjustable bass-boost by attenuating higher frequencies with a pot. When you turn the pot so its resistance gets lower then the higher frequencies will be reduced but the low frequencies stay the same level, therefore sound like they are boosted. I have seen similar circuits somewhere but haven't tried it. For it to work properly the amp must have more than enough gain. Use shielded audio cables. ;D

[ante]

Hi Audioguru,

Don’t get me wrong here but I don’t know if the expression”boost” is correct for a passive circuit! ;D  I can’t see any problems with the circuit though. :-X

[audioguru]

Hi Ante,
My modified clock radio and the radio in my old car had "loudness" controls that passively boosted the bass when they were turned down. As described by the "Fletcher-Munsen" curves of response changes of our hearing at reduced levels. The bass was always at the same level so didn't cause their amplifiers to clip.
Stuee might adjust the bass-boost control only a single time and leave it like that, then use the amp's volume control for loudness. Or he might like the "loudness control" action of the bass-boost control and use it to adjust loudness. ;D