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Class D Switching Power Amplifiers and Power D/A conversion

Extremely portable mini stereo - Help with parts
Extremely portable mini stereo - Help with parts
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Old 26th February 2011, 12:13 AM   #1
voyage is offline voyage
diyAudio Member
Join Date: Feb 2011
Default Extremely portable mini stereo - Help with parts


I'm thinking of beginning with a new project.

Last summer I built a festival stereo consisting of 2x6.5", a 12Ah MC battery and a cheap T-amp from Ebay. Everything was put together in a box made of 7mm plywood (if I remember correctly). I also put in a iPod/iPhone dock that was hooked up with to the amp and to the battery, with a switch that made it possible to choose when the iPod/iPhone should be charged.

All in all I was very content with the end result, since it was the first time I built anything like this. The battery lasted throughout the whole festival (5 days, with maybe 5-6 hours of listening each day).

End result here: http://dl.dropbox.com/u/3618143/IMG_5105.JPG

I want to start with a new project. A stereo which should be even easier to bring with me. Think of it as a stereo to bring for short visits in parks, maybe a festival and for small barbeque parties.

So, for this project I would like to focus on make a stereo that is:
Lightweight (Last project was 12kilos, little bit too heavy)
iPod/iPhone connectivity (with possibility to charge)
Possibility to charge the stereo without having to pull out the batteries
Maybe possibility to hook up computer at the same time as iPod/iPhone

(And ultimately, if possible, being able to mix between the two audio source. Now, this is not a priority, just a feature I thought would be neat. So please think of the above as critical, compared to this wish.)

Been looking around and I've understood that using car speakers, that I did last time, isn't ideal and that I should aim for something else. This is where I need your help: What kind of speakers should I get?

What kind of batteries should I use?
In a dream world I'd like to have the same battery life as my last project.

The only thing I'm fairly certain of, is that I should be using AMP6 for a project like this. So please, if you have any input for this, please help me out.

Thanks in advance

Last edited by voyage; 26th February 2011 at 12:39 AM.
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Old 26th February 2011, 07:11 AM   #2
dragonxwas is offline dragonxwas  India
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Join Date: Feb 2010
for best power to weight ratio a.k.a power density, lithium ion batteries are the best, but having low voltages is a downpoint for amplifier project..
car speakers will not perform well in open air scenarios..
also depends on how loud you want it to be the lesser the battery life will be..

I bet most of the weight of your old project will be due to the weight of the batteries, must have used lead acid type..
My thought for a project like this will not be stereo, nobody cares about the stereo imaging in parties, its all about more sound..
would suggest a 8-12" driver in a vented enclosure, and a mono class D amp, with li-ion batteries, I don't know what they call it in your place ,but here we get them as PCO or coin telephone batteries, they are rated at 1500Mah 3.7v nominal and are 1USD each, I use them in a huge accumulator combination with many of them connected in series and many of them connected in parallel, my last project with about 30 of them resulted in a package weighing only 2.3Kg for only batteries and an output voltage of 18.5-0-18.5 (yeah dual supply) at 4.5Ah each side.. try to get these..

also the mixing stage could be taken care by using 2 different input channels and mixing them togather after the volume pot , after a 10k resistor in line, you could just cross-fade tracks like a pro dj :P
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Old 26th February 2011, 09:42 AM   #3
voyage is offline voyage
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Join Date: Feb 2011
Hi, thanks for your reply.

It's true that I used a lead acid battery, but the weight of the battery was "only" around 4 kilos, which I think is quite good, considering how long it lasted me.

So just one element? Can I still get it fairly loud? These are the speakers I used last time, and I thought they were loud enough for the purpose:

So something along the lines of that performance would be great. Do you have any concrete tips on speakers?

Any ideas how I would solve how to charge the batteries right there in the actual stereo? Would also like it to be so that when plugged into the wall it runs from the wall socket instead of the batteries, that then get charged.
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Old 27th February 2011, 02:50 AM   #4
Johnny2Bad is offline Johnny2Bad  Canada
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Join Date: May 2010
If you use lead-acid, the CTEK chargers work very well .... very low ripple, very compact, an unusually well engineered device for this class of product. For example if you were to run the unit for many days at an event and take the battery down to about 9V the CTEK will bring the battery back to full charge; many chargers won't be able to charge a Lead Acid battery that is below 10V or so. It will also charge batteries that have gone into sulfation.

I'm testing some T-amp builds that will be run off 12V, and for my listening testing I have a lead-acid battery and a CTEK (Sweden) charger always connected. You can just barely hear a slight amount of noise when you place your ear right at the speaker with the charger connected vs battery alone.

You could mount the charger inside permanently connected to the battery, have the unit run off battery all the time, no need to use a switch. I find with a T-amp playing the charger sits right at the maintenance trigger voltage of 14.2V so you won't have a problem playing the unit and charging at the same time. I have the model 3300 but you could use the less expensive one; I need the 3300 because I have an Absorbed Glass Matt (AGM) battery in one of my vehicles.

I'm very happy with the performance of this charger, I've sold my other lead acid chargers.
" ... Go back to the beginning of a technology before the priesthood was established; that was the time when people were communicating information, not proving why there needs to be Priests. This is why the old texts tend to be so good. ..."

Last edited by Johnny2Bad; 27th February 2011 at 03:07 AM.
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Old 27th February 2011, 03:33 AM   #5
picowallspeaker is offline picowallspeaker  Italy
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Battery considerations aside , I agree with DragonXwax that stereo is unnecessary . Power availability is crucial . I finished something like that this week . I had an old subwoofer project laying around ,and when a friend of mine asked me if I could do something portable , I immediately looked at it .
Took the amplifier section out of a boombox and built an IC crossover -it didn't work ! So I went passive and after 5 minutes I blew one Pioneer 100W car tweeter Low power amplifier produce nasty things when 'pushed hard'....
So I ended in using a little 2"1/2 speaker ,crossed with 22 uF.
No volume controls ,just two 22 KOhm resistors to mix left and right and a 3.3 uF BP electrolityc before the two (joined together) amp's inputs.

If doing it again , I would take time to develop a little PCB containing active circuits such mixing between two sources ,mixing the channels ,and an active crossover ,tailored to the chosen drivers . Amplifier for the woofer would be double the power of the tweeter.
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