[Transcendence]

Hello Head-Fi'ers,
 
I have this idea that i'm working on that would require a battery powered amp + 2 basic speakers. I don't need super great sound quality, but i do need the components to be thin, and have the ability to be encased in resin (the speaker won't be encased, just the amp circuit)
 
Basically i'm looking to either buy or get:
 
1) a simple-ish circuit for [or a prebuilt] basic stereo amp that can be run off of 18 volts worth of battery power that will run the speakers discussed in #2 at decent volume for a ideally a couple of hours off 2600 mAh battery although i can beef up the battery capacity if i'm kidding myself here. 
 
2) suggestions for two approximately 3" diameter speakers that are no thicker than 1" that will sound OK, but high-fi is not a real necessity. I'm thinking basic desktop computer speakers here. 
 
The amp circuit will be encased in resin, and wires will run in and out for power and data, but there will be no connectors on the board itself. Both parts should be less that an inch thick. I'm hoping to spend <$75 for both but maybe that's unrealistic?
 
Thanks for your input!
 
--Transcendence

 

[cfcubed]

Looks a little out there, that & fact its your 1st post, haven't mentioned builds/designs to date & you've not posted the research you should have done on your queries may be keeping some from replying.
 
But as I got silly & actually did encase something (a CTH headamp) in clear resin I guess I'll toss in some thoughts.
*  the last thing on your mind should be the encasing in resin.  You've got a bunch of design questions to get answered & prototyping to do 1st.
*  think you'd be looking at a class D something & there's lots of info about them + some about battery-powering + charging over at diyaudio
*  get on parts express or something & research your speakers & how'd you'd case them up
*  other than the obsession w/thinness think there's a bunch of similar commercial/chinese offerings
When all that is done then you can fool around trying to encase a prototype in resin - there'd be lots of concerns there esp. safety ones regarding the batteries.   

 

[Transcendence]

Quote:

Looks a little out there, that & fact its your 1st post, haven't mentioned builds/designs to date & you've not posted the research you should have done on your queries may be keeping some from replying.
 
But as I got silly & actually did encase something (a CTH headamp) in clear resin I guess I'll toss in some thoughts.
*  the last thing on your mind should be the encasing in resin.  You've got a bunch of design questions to get answered & prototyping to do 1st.
*  think you'd be looking at a class D something & there's lots of info about them + some about battery-powering + charging over at diyaudio
*  get on parts express or something & research your speakers & how'd you'd case them up
*  other than the obsession w/thinness think there's a bunch of similar commercial/chinese offerings
When all that is done then you can fool around trying to encase a prototype in resin - there'd be lots of concerns there esp. safety ones regarding the batteries.   

Yes, this project is a bit "out there", and yeah this is my first post with this account.. I had a different one a few years back linked to a now defunct email address but it didn't have a significant number of posts either. 
 
I've built a CMOY with a friend, and i looked a bit at different small builds, specifically the gainclones. the whole thing needs to be pretty thin, and a SLA battery is completely out of the question which rules out a number of small amps. I'm hoping to run off a medium sized RC car style Li-Poly battery.
 
Having done a bit more reasearch on this i'm thinking im going to go very low quality and buy a set of two "portable ipod speakers" ex: http://www.amazon.com/Altec-Lansing-Technologies-IMT227-Portable/dp/B006KZ0R1Q/ref=pd_sim_e_5. I would remove them from their cases and ditch the batteries in favor of a lipo. Then either buy or make a splitter for the stereo output of the player to send a it's channel to the appropriate speaker (which are mono speakers). I'm going to run it all off a smallish LIPO with a switch to allow for charging, off, or on modes. 
 
 
Anyways thanks for the advice on the rest of the stuff, i'll check out diyaudio's class d amps and see if anything fits the bill. Thanks again! If you have any sudden realizations of what the perfect thing is let me know!

 

[wakibaki]

You want an amp that is very efficient if you're going to case it in resin. A class D amp fits the bill, http://www.ebay.com/sch/i.html?_odkw=t+amp&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313&_nkw=ta2024+amp&_sacat=0 I like the Sure electronics boards, I've used them. They call these T-amps because they use a Tripath TA2024 chip.You might like to look on diyaudio.com to see if there are any mods recommended, there used to be when these first became available but Sure might have changed them by now. It's only a difference in a couple of small caps or remove a resistor or so. Don't bother about some of the more exotic changes some people have done.
 
These amps only work up to ~13.6V, car battery voltages, but they will give quite a respectable (loud) output from a 2600mAH for a couple of hours or more if you keep the volume down. You'll find it hard to get 3" speakers that'll handle the 15 watts per channel max that the amp is capable of. You can regulate 18V down to 12V but the regulator will get hot and it's a waste of power so better to go with a 12V battery if you can. 10 NiCads or NiMh in series would be ideal.
 
As for speakers, I could google for them, but you can just as easy do that yourself...
 
w

 

[Transcendence]

Quote:

You want an amp that is very efficient if you're going to case it in resin. A class D amp fits the bill, http://www.ebay.com/sch/i.html?_odkw=t+amp&_osacat=0&_from=R40&_trksid=p2045573.m570.l1313&_nkw=ta2024+amp&_sacat=0
 
These amps only work up to ~13.6V, car battery voltages, but they will give quite a respectable (loud) output from a 2600mAH for a couple of hours or more if you keep the volume down. You'll find it hard to get 3" speakers that'll handle the 15 watts per channel max that the amp is capable of. You can regulate 18V down to 12V but the regulator will get hot and it's a waste of power so better to go with a 12V battery if you can. 10 NiCads or NiMh in series would be ideal.
 
As for speakers, I could google for them, but you can just as easy do that yourself...
 
w

Ah this looks awesome! do you think i could run this one http://www.ebay.com/itm/Mini-MKll-TA2024-Tested-PCB-Power-Digital-Audio-AMP-Amplifier-Board-12V-2x15W-/290810092558?pt=US_Home_Audio_Amplifiers_Preamps&hash=item43b5a1dc0e off of something like http://www.hobbyking.com/hobbyking/store/__11911__Turnigy_nano_tech_2200mah_3S_25_50C_Lipo_Pack.html or would it not provide the necessary power. Also, Yes i can definitely google for some speakers but if you have a strong preference or previous knowledge as to some good cheap ones i'm all ears
 
EDIT: Note that this battery is 11.1 Volts, is this problematic?

 

[MisterX]

PartSEXpress has a pretty nice assortment of small amplifier kits and mini speakers.
 
Examples:
 
http://www.parts-express.com/pe/showdetl.cfm?partnumber=297-210
 
http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-329
 
 
How are you going to deal with the heat when the amplifier is encased in resin?
And...a DIY fast charger for high capacity, multi cell batteries is easier said then done.

 

[Transcendence]

Quote:

PartSEXpress has a pretty nice assortment of small amplifier kits and mini speakers.
 
Examples:
 
http://www.parts-express.com/pe/showdetl.cfm?partnumber=297-210
 
http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-329
 
 
How are you going to deal with the heat when the amplifier is encased in resin?
And...a DIY fast charger for high capacity, multi cell batteries is easier said then done.

Very helpful links thanks. 
 
The heat is definitely an issue, hoping that i can get something efficient enough to be okay.. if not i could either make air holes or i don't know what at this point. 
 
Also, the charger wouldn't be a DIY, I would leave the current leads on the lipo and charge it via my normal DC charger that i use for my RC plane Lipos 

 

[cfcubed]

Some IMOs & info FWIW:
*  ID your basic requirements - e.g. sizing, SQ, amplitude/battery-life, input/volume control/battery-charging, discrete # of pieces
*  ID a couple/few class D / T-amps, perhaps pre-built, that might work w/assoc battery targets (wouldn't cast batteries in resin)
*  ID possible speakers / speaker enclosure arrangements - getting decent sound from little speaker / 1" max depth would be a challenge I'd think.  The smallest speakers I remember somewhat liking were my apple mac cube ones - but they may have had some EQing in their dedicated amp:
http://www.atpm.com/15.07/segments.shtml
*  May not have to worry about heat much w/a class D in resin - the output buffer & rail splitter & heater SMPS parts in my encased CTH get warm and are hanging in there.
*  Would consider jacks in resin for all I/O vs wires dangling from resin - the whole shebang would need tossing if even one of its I/O wires broke.
*  But every part able to be invaded by the resin needs some form of sealing from it, e.g. jacks, volume pot (if any)
*  Consider testing your resin casting skills on something other than a precious prototype.  Use proper mold material & pour in layers instead of all at once.  I failed to do that.  Related links:
http://runawaybrainz.blogspot.co.uk/2012/04/audio-crystal-cmoy-freeform-headphone.html
http://dotmatrixdesign.tumblr.com/
http://www.flickr.com/photos/davidnin/sets/72157603372291689/
*  I was able to pick up Castin' Craft Clear Casting Resin + Catalyst at a Michael's Craft store nearby - avoiding shipping costs. 
Good luck.

 

[tjohnusa]

I think heat will be a factor even with a class d.....airholes would not be sufficient in my opinion. In regards to the speakers what kind of cabinet volume are you going to have? It sounds to me your whole design will be based on astetics and not sound quality. Is space an issue? Here is a link to a PartsExpress project that is large but looks awesome and the amp will meet your power requirements: http://www.parts-express.com/project-gallery/home-audio-projects/

 

[wakibaki]

Yes, you could run the amplifier in the link from the battery in the other link, the reduced supply voltage will not be a big problem, you will get a bit less volume, in fact it may actually make things easier as regards heat.
 
As you can see though, most people (including me) have concerns about the amplifier overheating, resin is a pretty good thermal insulator.
 
That said, that particular amplifier probably has the best chance of surviving the experience, but it will depend on how long you run it before allowing it to cool down, and at what power level. You could do better with a lower powered amplifier though, if you are prepared to accept a reduced volume capability, the problem is identifying a built-up class D amplifier in the range you require, I just picked one in the range I thought would best suit you at a price that is unlikely to break the bank if it does blow up.
 
One thing you could consider is providing a path to the outside world for the heat, you could embed a chunk of aluminium in the resin, in contact with the amplifier chip itself and stuck on using some conductive thermal tape. http://www.ebay.com/sch/i.html?_trksid=p5197.m570.l1313&_nkw=sekisui+thermal+tape&_sacat=0&_from=R40 Fins on the heatsink would help, poking out into the air, it all depends on the lengths to which you are prepared to go, maybe cut up a heatsink off an old PC processor or graphics board.
 
w 

 

[tjohnusa]

don't forget that resistors heat up also.

 

[no_eye_dear]

You need a low profile board and this would work well. It's probably the best TA2024 board available and very cheap.
You then need a plate of aluminium or copper to stick to the top of the chip, use superglue, I've built a lot of T-amps and it gets the job done.
You don't need fins, just a wider surface area of the plate will do it. I have potted a complete Sure PCB this way and it' still going 3 years later....
In fact if anything, it prevents the inductors on the outputs from resonating.
 
As long as the supply voltage doesn't drop below 9V the amp will continue to sing... batteries last a surprisingly long time with these efficient amps
Look at the sonic Impact that this whole craze started from..... 4 x AA's if I remember?
 
As far as SQ is concerned, you aren't going to get much from that size of speaker but have you considered exciters?
You know, the one's you stick to doors and flat surfaces....
 
EDIT: Like these

 

[Transcendence]

Lots of good info here guys thanks so much!
 
I'm going to start with the wiring + design and get it solid and sounding good without being cast in the resin, and then hopefully move to that once i'm liking how the whole design is working. 
 
 
 
Current parts list is looking something like:
 

1. 2200 MaH Lipo    http://www.hobbyking.com/hobbyking/store/__8932__Turnigy_2200mAh_3S_20C_Lipo_Pack.html                                     $7.89
2. Lipo Charger                   http://www.hobbyking.com/hobbyking/store/__8247__Turnigy_2S_3S_Balance_Charger_Direct_110_240v_Input.html          $11.44
3. Speaker (X2)                   http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=297-210                                                                          $17.58
4. RCA Plugs  (X2)              http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=092-112                                                                          $1.28
5. 2.5mm DC power plug     http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=090-498                                                                          $1.49
6. Amp                              http://www.parts-express.com/pe/pshowdetl.cfm?&Partnumber=320-330                                                                          $16.48

 
 

1. Bluetooth Module http://www.parts-express.com/pe/showdetl.cfm?partnumber=320-352                                                                                         $19.98
2. 4 Battery Holder + Switch http://adafruit.com/products/830                                                                                                                                  $2.95

 
I'll let you guys know how it goes!