High efficiency Amplifier for Boombox

squeaks

Member
2010-12-06 1:46 am
Hi all,

I just found this forum and I think I have found the right place.

I want to build boom box that is built into an ammo can for use on rafting trips. I could just buy one, but after all I am an engineer (mechanical though) and I love taking on new projects.

I am trying to bring into this project a few different technologies and my main goals are:

1. I want to learn how to work with Li batteries as a power source
2. I want to build, or at least start from some basic level, the different components of the project
3. I want maximum efficiency, for superior battery life
4. Maximum durability

After all I could just use a car receiver and speakers and a lead acid battery, but how much fun would that be?

From the highly knowledgeable people on this form I am looking to be pointed in the right direction, or just get outright answers :), on the following questions:

1. What is the best amplifier type for efficiency
2. How will power supply requirements such as voltage change with different amp types
3. Speaker choice
4. Am I doomed?

I will greatly appreciate any advice I get.

Thank you very much,

Eric Harvey
 
Eric,

Yes, this is the right place, for sure. Lots of information here already, so do some searching. Most of the relevant stuff is in the Class D forum. That's the amp type best suited to your project. Look especially at the Boominator thread, as a lot of your topics have been discussed there, like efficiency, battery type, etc.

Car receivers use a lot of power, so not well suited for a portable boombox.

Look also at the "T-amp" or TriPath oriented threads. There is a nominally 25wpc amp that runs on 12v that's a good choice for boomboxes, and they're available on eBay and other places for pretty cheap--great sound, too. For more power, you will need to go to 24v or higher, which complicates the battery situation. Lots of 12v options out there.

For batteries, the lithium iron phosphate seem to be the best right now for various reasons, including longevity, but they tend to be expensive. There are gobs of lithium polymer ones for cheap as they're used in RC cars, planes, etc.

For speakers, look at projects out there that are about the same volume as your ammo can--that's the one thing you can't change. Search for a site by a guy named Zaph, who has some well-thought-out and well-researched projects you can use as a starting point for the speaker part. Efficiency of the drivers will make a big difference in the amount of sound you'll get at any given wattage, but this is higher in larger speakers, generally, but they don't work so well in small boxes, so, well you can see it's complicated. Be aware that metal boxes are not generally a good choice because they resonate, so you'll probably need to build some inner box out of MDF or something to seriously dampen the metal.

You are not doomed. With a lot of work and research, you will be the life of the party--or raft, and the envy of all the fishies.

Don't forget the solar charger.

--Buckapound
 
Depending on the shape and construction of the can, you might be able to get away with just lining it with Dynamat to help get rid of resonance. Since you mentioned this will be used for rafting trips, I would suggest using a pair of coaxial marine speakers.

A decent sized lithium pack along with the control/protection board and a charger is probably going to be your biggest cost here.
 

squeaks

Member
2010-12-06 1:46 am
Thanks for the info above, I will go through the posts today.

As far a cost goes, as always cost is a factor, but I am also looking for a cool project to work on and happiness is priceless right?


I have a question about the reason for using aplifiers that opperate at higher voltages. What would be a reason to use an amplifier that operates at 24V vs 12v?
 

squeaks

Member
2010-12-06 1:46 am
I am narrowing down my choices for my boom box.

Would it work to just use a speak like these:
Dayton PS220-8 8" Point Source Full-Range Neo Driver


They seem to have a good sensitivity and a large range.

I am think of using two of these mounted back to back.

Also, I think I will use the AMP10. However I have a question about this. When I get one with the power supply on board, what does that mean?

From what I can tell the amp needs one powersupply at what ever the main voltage is that will be used and one at 5V to run the chips on the amp. If I get one with the power supply on board does this mean that I can just feed the primary voltage to the amp?

Thanks,
Eric
 
Also, I think I will use the AMP10. However I have a question about this. When I get one with the power supply on board, what does that mean?

From what I can tell the amp needs one powersupply at what ever the main voltage is that will be used and one at 5V to run the chips on the amp. If I get one with the power supply on board does this mean that I can just feed the primary voltage to the amp?

Yep! Not household voltage though, but yeah, something according to what the you want the rail voltage to be.
 

squeaks

Member
2010-12-06 1:46 am
Come on... I want all the answers NOW! :)

Although this question may best be asked somewhere else I would like to keep it in this thread.

Some of the full rage speakers like the Dayton or Tang Bang stuff look like they have delicate pieces to the speaker. Are they as fragile as they look?


-Eric
 
I'd actually take a different amp - Amp4 or Amp11. Mostly because the Amp10 needs a split supply, positive and negative.

Edit - more detail - I'd consider these 41Hz amps:
Amp4 / Amp11: Crazy good sound quality - these are implementations of the TK2050 chipset, they're as good as they get. They're SMD though ... I love SMD soldering myself, but it's not everybody's cup of tea.
Amp9: Four channels, rugged, simple to build, lots of power. Hole-mount.
Amp6-BASIC: Very easy build, through-hole, but only runs off ~12V max.

The efficiency is about the same with all these. The idle currents vary ... I think you can squeeze the idle current lowest with the Amp6 and Amp4, and the Amp9 is hungriest AFAIK.

I'd take an Amp6-BASIC and see if you need more power later. Or, if you've done some SMD or are OK with learning, get an Amp4 + STA517B power chip upgrade.

Then if you want to go nuts, you can add a tiny switchmode preregulator to cut down on idle losses in the regulators. (The 41Hz PS4 is quite cool.)
 
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Squeaks, most of us who are doing boomboxes are using the Amp 6 or some other module with the 2020 chip. It makes a good deal of noise with its nominal 25wpc. Remember, to double the sound level, you need ten times the wattage, so going from 25 to 60 doesn't get you as much as it might seem. IMO, not worth the extra expense of a 24v power supply.

It may be worth adding a buffer such as the arjenhelder tube buffer (eBay). If you're running an iPod, this will get you a little more sound, especially noticeably more bass. And, it runs off 12v, so it's easy to hook up, efficient to run. You'll get a bit better battery life on the iPod as well.

--Buckapound.
 

squeaks

Member
2010-12-06 1:46 am
Thanks for the replies.

Questions:

1. What is SMD?
2. What is a switchmode preregulator?
3. What is a Tube Buffer?

As far as wattage goes, I want the sytem to be as loud as a car system so at least 2 x 50W. However, the speakers that I am looking at seem way nicer than what is in my dodge pickup, so I am not sure the impact that they will have on loudness.

-Eric.
 
1. What is SMD?
2. What is a switchmode preregulator?
3. What is a Tube Buffer?

As far as wattage goes, I want the sytem to be as loud as a car system so at least 2 x 50W. However, the speakers that I am looking at seem way nicer than what is in my dodge pickup, so I am not sure the impact that they will have on loudness.

SMD stands for "surface mount device" - this stuff: Surface-mount technology - Wikipedia, the free encyclopedia ... I suggest you avoid it for the time being. There's enough to wrap your head around without unnecessarily dealing with a less-straightforward soldering technique :) (It's easier once you get the hang, but it's a significant step up in complexity when you're planning everything out in the beginning ...)

A switchmode preregulator is a different kind of voltage regulator. It wastes less energy than an ordinary regulator. There are voltage regulators to create 9V and 5V sections in most of these amps, and these are places where you can do minor optimisations of idle-power consumption. I'd advise staying away from that too for the time being :) It's not worth the complexity either.

Others will answer the tube buffer question.

The crucial part here: BY FAR the single most significant arbiter of the final volume are the speaker drivers! Notably their decibel-per-Watt sensitivity. A 10W amplifier and a 92dB/W speaker will give you as much volume as a 100W amplifier and an 82dB/W speaker. With 10dB higher sensitivity speakers, the batteries will more than three times longer, the power supply will be much cheaper, simpler, and easier to obtain – and the same goes for the amp.
 
A buffer is a type of preamp, I believe one that does not provide a lot of gain (voltage increase), but that increases the available current to drive the next stage. This should make an easier load to drive for whatever source you're using, and theoretically should make for better sound.

The arjenhelder tube buffer on eBay is just one product out there. It does offer some gain, so maybe it technically is more of a preamp--but honestly I'm sure where the line is, if there is one. At any rate, it offers good sound, runs on 12v, uses little current, and will give you better bass, a higher level of sound and better battery life when used with an iPod. Other sources may not benefit. It also has a volume control built into it.

--Buckapound