BTL

Reli

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Dec 24, 2010
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You can pull up Google images and look at the advertisements to see if they use the word BTL.

But anyway, BTL doesn't necessarily mean better, it's just a decision they made about how to configure the amps. If your box has 2 amp chips, BTL is usually the best way to configure them. But If they had wanted to, they could have gotten even more power from a single big chip like a Sanyo STK, instead of taking a couple minor-league chips and putting them in BTL format. The Aiwa TPR 950/955 is BTL, but it only makes about 2x5 watts lol.

The manufacturer probably sits down and says, "How much power does this box need in order to be competitive", and "How long do we want the batteries to last", then finally "How cheaply can we do that?". So it's all a compromise. Every box could have been more powerful if they had been willing to do it. Check out the heat sink on this TRK-9900, it's got a single STK chip with more power than almost every BTL box. But that's why it requires 10 batteries, and they don't last very long.

TRK9990.jpg
 

Superduper

Member (SA)
Reli,

BTL is definitely better, especially in boomboxes, and for more than just power. They typically have a higher S/N ratio and usually sound better when operated in the sweet spot. If you look at most datasheets, you'll find that distortion at lower operating levels are usually very good, under 1%. When you get to the 10% maximum, in my opinion, it might not blow up, but it's not really listenable unless you don't care about audio quality. So with BTL, you have far greater usable volume before distortion becomes an issue. For the TPR-950, don't forget that the fantastic sound and volume is accomplished with 6 batteries, yep only SIX, not 10. How?

Boomboxes have a huge problem, and it has to do with voltage. In home audio gear, there's plenty of voltage available. In fact, many if not most home audio power supplies have secondaries that are 55V, 70V, maybe even 90V. Boomboxes are limited by the number of cells and battery life. Also battery powered devices usually need to strike a balance between portability and weight. Sure, you can stuff 208 cells in it, so it can power a Prius for a few minutes and miles of travel but are you gonna have a crane with you at all times? The thing is, amplifier output is limited by available voltage. However, in a BTL design, it's possible to realize almost twice the power output compared to SE with the same available voltage. See the benefit to boomboxes and why it's better? How about those mini boomboxes that only have 3V or 4.5V, or 6V available?

So, you are probably wondering, well if voltage is such an issue, how do car amps can have such high power? It's because internally, they operate at much higher voltages due to a DC:DC converter which boosts the voltage typically to 36-40v. Ok, I can already sense your next question... why don't boomboxes do the same thing? Because power is power. Boost voltage and you get increased current consumption. Means battery life is virtually non-existent, especially the DC:DC converter is not going to be 100% efficient.

Now, about the STK-430-II which is what is in that Hitachi... it really feels right at home at very high voltage. Look at the datasheet for 13.2V for power output.... nothing special is it?

Screen Shot 2019-11-03 at 11.57.29 AM.png


As for which boomboxes are BTL and which are not, here's a simple test if you have access to the speaker system, or the boombox has external speaker jacks:

Simply ohm the (-) speaker leads. On SE systems, a common ground is employed and you should read 0 Ω or close to it. On a BTL system, a floating ground would be employed so the negative speaker leads are not grounded together. While you might read some resistance, it won't be 0, or .9 or something small like that.
 

Reli

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Dec 24, 2010
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Well the TRK-9900 is 15V, and that's just with batteries. Who knows how much voltage it has on AC, which is where it really shines. Mine easily matches an M70 in volume, and puts out more bass as well. Very clean sound too. With batteries though it's gonna suck, just like the Telefunkens.

Anyway you're right, BTL is the best and most efficient choice for a 1-piece box that's meant to be used outside with batteries.