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Chip Amps Amplifiers based on integrated circuits

Need an amp for computer speakers.
Need an amp for computer speakers.
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Old 10th November 2008, 02:37 PM   #1
jdraughn is offline jdraughn  United States
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Default Need an amp for computer speakers.

I have a notebook with built in bluetooth, makes it really nice to pull out my mouse and just have it work with no protruding dongles from my notebook.

Now if I pull out my external speakers (I work in a loud enviroment and like to listen to music off my laptop) I have to untangle the audio cable between the speakers, the audio input cable to the notebook AND the ac adapter wire.

The ac adapter actually isin't that bad, since it's easy to wind the wire around it, but the speakers... not so easy.

So I am in the process of putting together a set of custom speakers for my notebook that work wirelessly (except for the one wire between the speakers).

I ordered a bluetooth stereo receiver off of newegg.com that should do the trick as far as getting a audio signal to an amp, now I need to figure out which amp chip will work best.

I have a few thoughts about what I want, so let me tell you my thoughts, and you guys with a little more knowledge about whats available and what works good, can give me some advise.

There are 3 problems that I am trying to overcome. Usually fixing one will bring out another. They are:
1. Input Voltage Requirements.
2. Power Output.
3. Physical PCB Size.

It would be nice if the amp could run off USB power (5V) and still produce enough power to power book-shelf size speakers. I don't think that is possible (is it?), so I figure I will probably end up with a 12V DC input (8 AA or AAA batterys be best/cheapest?). Charging the batterys off USB while the speakers are not running would be a nice bonus though. Or maybe power off USB up to a certain point, then if it requires more power use the batterys? Or charge batterys if it can, otherwise use the batterys as the power source?

The PCB would have to fit in a small speaker enclosure. So would the batteries. I could possibly go with two mono amps to help save a bit of space in one enclosure (but then I would either have to have a second set of batterys in the other speaker enclosure, or run a wire just to power the other amp from the batterys in the first enclosure). I am thinking that may be best anyway so the volume of air in each enclosure will stay the same.

I would also like to build a custom sub with a small 6.5" or 8" car sub and would eventually need an amp to power that too, but right now I am just trying to get good wireless stereo sound from a small pair of book-shelf size speakers.

I see the TDA1521 is a pretty good powered amp IC? But it requires AC, how spendy is it in wattage to go from DC to AC? Are there any other IC's that I should be looking at? I would like to do as much custom work as possible to save money. If the number of components is small enough, maybe even skip using a PCB and just kind of wire all the leads together and stuff it in the box to save some money, although I would love to show off some high quality work.
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Old 10th November 2008, 05:39 PM   #2
AndrewT is offline AndrewT  Scotland
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Join Date: Jul 2004
Location: Scottish Borders
Forget any cheap car speakers, they are all too inefficient to run off batteries or USB power.
Try to find a full range driver that does not need a crossover (saves wasted power) and also aim for 8ohm ~>96dB/W/m.
Up close this may be loud enough to monitor what is happening from a low voltage power supply.

Do you realise that the Laptop batteries will last for an even shorter time if they are asked to power a pair of external amplifiers?

What about headphones for Laptop use?
regards Andrew T.
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Old 10th November 2008, 07:50 PM   #3
jdraughn is offline jdraughn  United States
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The laptop itself is plugged in so it's not an issue of running the notebook battery's dead, and I don't like to use headphones because I can't hear any other part of the enviroment around me (phone ringing, people calling my name out, ect...).
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Old 10th November 2008, 08:00 PM   #4
Buckapound is offline Buckapound  United States
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Location: Chicago, IL
Check out the Tripath class D amps like those based on the 2020 or 2024 chips. These offer very clean and detailed sound, high efficiency and low cost. There are boards on eBay, and kits from sources like 41hz.com (Look at the Amp6).

You can run them off low-cost 12v switching power supplies, or off of sealed lead-acid batteries or other types, of course. Loads of information over in the Class D forum. Come on in, the water's fine.

Good luck with the project.

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Old 10th November 2008, 08:03 PM   #5
AndrewT is offline AndrewT  Scotland
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if you have mains power available, then use mains power for your amplifier.
regards Andrew T.
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Old 10th November 2008, 08:13 PM   #6
mikejennens is offline mikejennens  United States
This speaker DIY thing, it's pretty addicting!
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Need an amp for computer speakers.
Check out Audiosector.com. Small amps and Peter Daniel (the designer of the amp and he runs a thread about the amp) might be able to help you customize this to what you need.
Jolida SJ502A, Squeezebox Touch, Paul Carmody's Sunflowers, Jeff Bagby's Continuums; Planet 10 HiFi's MarkAudio A 7.3 Frugalhorns and MarkAudio CHP-70s, Nola Brio Clones with a Voxel Sub and a bunch of others...
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Old 10th November 2008, 08:50 PM   #7
Redshift187 is offline Redshift187  Canada
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You can only draw about 100mA off USB. Can't run much of an amp with that.
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Old 10th November 2008, 09:31 PM   #8
pacificblue is offline pacificblue  Germany
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Default Re: Need an amp for computer speakers.

Originally posted by jdraughn
I see the TDA1521 is a pretty good powered amp IC? But it requires AC, how spendy is it in wattage to go from DC to AC?
No chipamp requires AC. The TDA1521 requires a split power supply. If you want to use a single supply or batteries it is easier to look for dedicated car audio ICs (e. g. TDA2003 for mono or TDA2004 for stereo). Of course you can buy something of similar quality cheap and ready made, e. g. like this. No 300 W of course, but 2 x 17 W into 4 Ohm or 2 x 8 W into 8 Ohm. You will find similar amps with different names at different prices everywhere. Don't pay more than 10 to 15 $ or for it, it is not worth more. But you won't be able to DIY anything similar at that price, if you count all components, connectors and the case.

Or use one of the class D amps from 41Hz. Higher price, better sound, more efficient for battery use.

What are the power supply requirements of that Bluetooth stereo receiver? Can it run off the same voltage as the amp?
If you've always done it like that, then it's probably wrong. (Henry Ford)
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Old 11th November 2008, 01:36 AM   #9
e_fortier is offline e_fortier  Canada
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Need an amp for computer speakers.
Default You need open type headphone

The headphone you are refering too or that you probably tried must of been closed type. If you need to hear what is going on around you is an open type headphone.

An inexpensive and very good sounding headphone are the Koss KSC-75, the sound is similar to Grado SR-60 and for a fraction of the price.

Another one is the Senn PX-100, works great and you remain alert with the surrounding.

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Old 11th November 2008, 03:04 AM   #10
jdraughn is offline jdraughn  United States
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Thanks for all the advice, you guys are awesome. I am going to do some more research with what you guys have told me.

As a guinie pig I took a cheap pair of powered computer speakers that I bought from a thrift store and used the built in amp module to power one of my 4x6" speakers and it sounded much, much better then the original 2" full range speaker. Even though it wasin't very effecient, it was actually louder and had much better highs. Lows actually wasin't really any different that I could hear, but that is probably because of some kind of built in high pass xover in the amp module. (they were in a temporary enclosure to at least seperate the back wave from the front wave).

The power amp ic in those cheapy computer speakers ($2.99 by the way is a Toshiba TA8207K. Only puts out like 4 watts at 10% THD. Pretty bad, but it actually sounds pretty damn good for what it is! Makes me pretty excited to get a 10 or 15 watt amp going (with good sound quality, not no 10% THD crap).

Thanks again, I don't think I have ever had that many helpful replies in one of my forum posts anywhere, ever!

BTW. The head phones I have are Shure in ear kind not the best but at $100.00, they sound pretty good. I could go with an open ear kind of head phones, and I probably will look at going with a good pair pretty soon, because half the time im at work im in quite enviroment with others and need to keep my music to myself. The other half the time im by myself in a noisy enviroment, but still need to hear the phone or someone knocking on a door (they are both secured areas with cameras and require badges just to get into the rooms, let alone the buildings).
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