Computer Speakers

[luvdunhill]

Hi all, I was wondering if someone might be able to point me in the right direction for creating a pair of glorified computer speakers. I was thinking something small with a single 3-4" driver that could be plugged directly into a line out. Thus, the speakers would have mini amplification circuits located in their respective housings. I was wondering if it would be possible to adapt a cmoy/pimata design to do something like this, or if there's possible another design that's small and compact, yet powerful enough to drive a single speaker? A single tube or tube-hybrid design would be a bonus

This creation would be more of a conversation device than a real audio system, or perhaps gifts for people to replace their cheap computer speakers with. More specifically, I'm thinking of the TANG BAND speakers over at partsexpress.com. Am I even going down the right path looking to adapt a cmoy/pimeta design, or is there another compact, inexpensive design I should be looking at.

Thanks in advance!
-Marc

 

[mono]

I'm a little skeptical that you could cost-effectively build a pair of single 3-4" driver, amped speakers that would be a cost or time effective upgrade for a computer. It seems easy enough but the incidental expenses start adding up so unless it were very high-end, it might not be better than just buying (better) speakers, whether "PC" or just bookshelfs.

Anyway, for moderate volume you could take an opamp (elaborate on the CMOY or Pimeta design as the foundation), give it enough gain and sufficiently sized buffers on the output to drive your load (whatever the impedance is of those speakers) to at least a few watts, but I think I'd look in a different direction, at a chipamp like a Gainclone, perhaps with an LM4780 chip but you don't have to build it for max output. Then again lower current chips may have lower quiescent power so at the typical modest volume levels you might find they are easier to 'sink and cool inside a small speaker cabinet.

I'd probably put both amp channels in one of the speakers too instead of a mono in each, as either way you have to string the cables for the audio and power.

Exactly what path you take could ultimately depend on the size, cost, your experience level. Even taking the guts out of a Sonic Impact T-amp could have a good result but it's not nearly as hands-on, not AS much tweaking possible. It is small, relatively cheap and easy though, as well as low heat for being inside a small speaker.

 

[Uncle Erik]

I don't know if these would be too tall for you, but I've always found the Zigmahornet very charming. Take a look here:

http://melhuish.org/audio/DIYTQ12.html

The drivers are pretty inexpensive, too, and can be found at Madisound, as well as other dealers.

Any fleawatt amp would work with these, so you could use something like the $140 or so K-502 kit over at AES:

http://www.tubesandmore.com

A Bottlehead S.E.X. would drive them, too, as well as a pair of headphones.

 

[luvdunhill]

mono:

Thanks for your help! I think this chipamp approach is exactly what I'm looking for! The kits at http://www.chipamp.com look like they'd work just fine. I'm assuming these are the Gainclone kits you were referring to. Also, it looks like they're right about at my skill level. If you have any other suggestions, or ideas I'd appreciate them. As for now, I'm going to read the kit manuals and see what I think. Has anyone else used/build one of these kits?

-Marc

 

[mono]

I've built gainclones but I used a board I etched myself instead of the kit, which was even larger than the kit board.

Keep in mind that while the kit looks small, once you start adding up the space for two amp boards, power board and transformer, it won't fit inside a normal box for a 3-4" driver. With creative mounting you could get all but the transformer in, probably, and indeed that's what many smaller speakers do already is have the transformer as a wall-wart, though it's hardly a wall-wart to shoot towards the upper bounds, typically at least a 4" x 2.5" toroidal transformer would get it's own case.

the possiblities are seemingly endless though, everybody from Toshiba to Philips to TI, etc, etc has chipamp chips and their datasheet example circuits are a good place to start.

If you go with one of those kits it should work fine, but for small drivers I'd consider using less than the default gain (many use about 20?), but you'll have to try it and see.

Having both a gainclone and modded/recased Sonic Impact, I think I'd lean towards the T-amp for a pair of 3-4" drivers because they cant' be expected to produce much bass anyway and the T-amp sounds very fast, great detail. Don't discount my brief words about cooling either, a gainclone can need substantial sized heatsink (relative to a cabinet for a 3-4" driver) while T-amp is arguably ok with just the preassembled PCB-as-sink, though I think later versions of the T-amp didn't have the chip's 'sink plate soldered down and it made them run hotter, I VERy carefully added solder to mine as well as making the back of the board-sink area a central ground point so there were also several moderate gauge wires 'sinking away heat. The t-amp also uses a significantly less expensive and smaller transformer, any typical 1-2A 12V (keep it at 13.x V or lower as implemented) will do, and are dirt cheap contrasted with the typical $35-80 toroid used on many gainclones (but again, the amount of power you want from the gainclone dictates transformer size, power output).

Not to steer you away from the gainclone though, I think I'd just put it in a separate casing before putting it inside a small speaker cabinet.

 

[happyangryhappy]

For really small and inexpensive fullrange designs you could try a pair of these or these. Or if you look around in the DIYAudio fullrange forum you probably will find something that uses the tang band drivers you mentioned.

 

[luvdunhill]

All:

Thanks for the Zaph link! I think the plans for the Hi-Vi B3S speakers will suit me fine. It seems, looking at the SPL vs Phase / Frequency graphs that I really only need around 8W power, before I start distorting due to X_max. I still would like to go with the dual-mono type setup and stuff one channel of the amp in each enclosure. I would also like to stay with a wall wort transformer and run one transformer to each speaker. I guess my question is whether or not the Sonic Impact T-amp could be split into two amps, and more importantly, if this either the T-amp or the Gainclone is still overkill since I only need max 8W.

Thanks!

 

[luvdunhill]

mono:

one other quick question: what chip is the SI amp based on?

 

[luvdunhill]

mono:

uh nevermind, I found it

so, why not just adapt the example circuit at http://www.tripath.com/downloads/TA2024C.pdf in the datasheet and just use a single channel?! Am I being to naive here?

 

[mono]

I was under the impression you wanted two speakers, so why use only one channel per on two, two channel chips?

Sure, you "could" do that if you wanted to, but don't go trying to make a bridged amp out of two channels because these chips aren't meant to do that.

Were you thinking of making your own amp board? I was suggesting using the ready-made SI board. There are guide on the 'net you can seek to do some alterations such as replacing the input caps and beefing up the supply rail caps but even to start it's a reasonably good sounding amp for what it is and the cost. Many shun it because of low wattage but some uses don't need the power so...

 

[luvdunhill]

mono:

yea, I'm leaning towards the SI board now

I guess all that's left to decide is how to heat sink it. Do you think I could get away with keeping the heat sink sealed inside the sealed speaker cabinet, or will I need a way to "poke" the heat sink out of the back of the enclosure? Another option, would be this kit http://www.41hz.com/main.aspx?pageID=118 which is based on the beefier Tripath TA2020 chip... maybe I can substitute the 2024C chip in place of the TA2020 on this board? I'll check the specs out later on today, but perhaps this might work. These kits are cheap and look easy to build.

Thanks again,
-Marc

 

[mono]

Quote:

Originally Posted by luvdunhill mono: yea, I'm leaning towards the SI board now

It seems I completely overlooked the other *Class-T* alternatives. 41hz.com has prducts that are technically related and may sound better as well as higher wattage. Of course they will end up costing more too, but given that you're going to take the time to build cabinets for the speaker too, they might be a good option. For example this or one of the others but there have been many newer products added to their lineup so i dont' know the specifics of the others besides what they spec on the corresponding pages.

Quote:

I guess all that's left to decide is how to heat sink it. Do you think I could get away with keeping the heat sink sealed inside the sealed speaker cabinet, or will I need a way to "poke" the heat sink out of the back of the enclosure?

There isn't any way to mount a heatsink through the back with the T-amp board, the PCB itself is the whole 'sink. The only option with it to improve cooling is adding solder to the PCB to 'sink the chip to it better (I have done this BUT it is a risk of overheating the chip that many would not do, and I wouldnt' have either if it had been more expensive than it was, and it would require a high wattage iron and care to let chip cool inbeteen passes at adding solder. I almost didn't mention adding the solder at all because of the risk but did anyway in an effort to be thorough on the topic.

Otherwise there is no way to cool it better except having an open speaker cabinet at least enough that passive airflow cools it. It doesn't create much heat though, certainly less than most other alternatives and I think you will be ok with it in a sealed cabinet unless running it with very high voltage or output (dont' recall which has the greater thermal effect at the moment, but when I was checking temp on mine it wasn't getting very hot.

Quote:

Another option, would be this kit http://www.41hz.com/main.aspx?pageID=118 which is based on the beefier Tripath TA2020 chip... maybe I can substitute the 2024C chip in place of the TA2020 on this board? I'll check the specs out later on today, but perhaps this might work. These kits are cheap and look easy to build. Thanks again, -Marc

I need to read ahead more often.

I mentioned above about 41hz.com without reading this. I don't see why you'd want to substitute 2024 for 2020, as 2020 should be even easier to cool because you can add a 'sink substantially larger than just the adjacent PCB copper as 'sink. Also, IF you were willing to put the 'sink out the back of the speaker, this chip will allow that, but with a big enough 'sink I don't think it necessary (but then again, I have not built an enclosed speaker with one, you are a pioneer to a certain extent).