Class-T portable Boom Box

[nige838]

I'm designing a portable Class T Amp.

parts:
Lapai LP-2020...$20
-Parts...........$10

5 1/4" Full Range Dayton...$45
Parts-Express.comayton PA130-8 5" Full Range PA Driver | 5" woofer 5 inch woofer midbass driver pro sound sound reinforcement PA

misc.................$25

I plan on using 11mil plywood. enclosure size is 30" x 15" x 12"

Power will be supplied by 8 C cells

I'm wondering if using a tweeter would be necessary?...It will be used mostly for HipHop and Grateful Dead music.

Any suggestions?

[theAnonymous1]

Originally Posted by nige838

Power will be supplied by 8 C cells.

That's soooooooo 1985.

I hope those are going to be NiMH cells.

[sadim1223]

Originally Posted by theAnonymous1

That's soooooooo 1985.

I hope those are going to be NiMH cells.

lol... I vote SLA... Seriously.

[Saturnus]

Originally Posted by sadim1223

lol... I vote SLA... Seriously.

Make it LFP cells and you're in the right century too.

[nige838]

Constructive critism please....I did a test run on the beach during spring break and powered a pair of 6X9s for 30+ hours off of AAs, so with C cells, and more efficent speakers, this should be worthwhile

[mfong]

If you can get 30 hours of play time from AA batteries, I'm not sure why you would want to go to C cells. More than that and you'd be on a long boat passage or something or a week long camping trip. In either case, the extra weight and bulk would matter in those situations.

On the battery end, people do seem to prefer SLA batteries for sonic reasons (less resistance, etc.) over nimh, but nimh still sounds very good and with 5 inch full range speakers I suspect you won't hear that much of a difference between the two. Lead Acids are heavy and they need to be topped off all the time to perform best. Neither quality is good for portable use.

I run a t2020 amp at home on 10 nimh AA batteries. I got something like 20 hours of play time into a pair of 6.5" two way speakers at mostly moderate to high volume. The other nice thing about AA batteries is that they're cheap and you can buy them most anywhere at any time, keep backup sets with you without adding much weight, etc. My issue with rechargeable C cells is that they're not easy to find retail. You also have to be careful, when it was nicad batteries, the C +D cells were really just AA's packed into the bigger form factor.

[Saturnus]

I'd seriously consider LFP cells. Some can be recharged at up to 2C, meaning 42 minutes recharge time from completely empty to full, and they still have 2000 cycles before 10% deterioration and have linear deterioration thereafter so 5000 cycles is still only 25%.

Any nimh/nicad/standard li-ion would be completely and utterly dead long before even reaching 2000 cycles. That means LFPs are basically drop and forget. You don't have to take into account the ability to change batteries ever. With your use they'll probably last 20+ years before you'd notice lower capacity.

That's just one of the many advantages LFP cells have over any other battery type. The only drawback is their roughly 20% lower capacity than standard li-ions in the same package size and weight. Otherwise they're superior in every aspect to any battery type.

[mfong]

On the other hand ni-mh AA sell for about a 1.25 each (so about fifteen dollars for the battery holder and the batteries) are good for a few hundred cycles not in the same class as the LFPs, but definitely not in the buy new batteries 6 months from now.

I don't know how much 12 volts of LFP's would be, but my guess is that 15 dollars won't get you there even though they run at 3.3 volts instead of 1.2 so you don't need as many.

fwiw, I would suggest the arjen helder 2002 mk 3 board instead of the Lepai if you're going to build an enclosure for the contraption anyway. You won't have to modify it and it should give you more flexibility for placement etc.

[nige838]

the MKIII isn't a ta2020, it's the ta2024...loss of 7 watts

I'm using C cells because I don't want to have to change the batteries very often and will prob. require taking out a speaker to get into the box.

Anyways, my real question so far is if the 5" full range will produce good base and decent highs...

[mfong]

I thought Arjen's latest ta2020 was the MkIII, but whatever his latest version of this 2020 board.

If you're going to seal the batteries into a box with no door or gate to get inside, then definitely don't use sealed lead acid. You might want to have a charger built in so you can plug the charger into the wall through a connector of some kind.

In terms of your real question, it depends on which 5" driver you use, how it's implemented (box volume, etc.) , and the match between your source and the t-amp. fwiw no 5" driver produces really good bass or great highs. If you go that route, you're really looking for passable not "great" or even really good. I don't know if you've looked at the "boominator" thread, but those guys have put a lot of time into a pretty similar problem and may have some very helpful specific suggestions about driver choice and speaker loading, etc. even though they seem to be using much bigger drivers. There are some things about outdoor or portable use that are a bit different from indoor applications. For one, stereo doesn't make sense in a boombox and low bass just doesn't happen much so you do things to make the upper bass really loud. Anyway, those guys have figured that stuff out.

with the amp, I might look into the Sure 2050 board with 2 12 volt lithium ion batteries used for radio controlled cars and airplanes for 24 volts reasonable size and easy recharge options.