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Class D Switching Power Amplifiers and Power D/A conversion

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Old 26th January 2011, 02:19 PM   #1
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Default Need a cheap amp, and my brains about to explode, help!

So I have been wanting to put together my own 2.1 speaker system for my computer for the longest time. I always thought that for a just a little more than a premium set of computer speakers you could do something really great. So I got a 10" 100w powered polk audio sub, and a pair of polk audio T15 book shelf speakers. Now I know this might have been a stupid idea, but I thought that I might be able to power the speakers using the sub's built in amp, but it turns out the the connections on the amp are just pass through. I think they do separate out the base, but they do not power the the book self speakers. So I need a 2 channel amp. I don't want to buy a $100 cheap receiver because then I would be way over my budget, and my argument, for a few more bucks you could have this, would be ruined. So I want to do this as cheap as possible, but it also can't be that difficult.

So the speakers that I need to amplify are 20-100 watt 8ohm. When I was testing out the speakers, I used an old computer speaker amp, that has 6 watts per channel, and it actually sounded pretty good.

At first I was thinking about getting a already put together TA2020 amp off ebay, which is 12 amps per channel. But then I saw the TK2050, and thought that it better matched the speakers 20-100 watt rating.

This is what I'm thinking of doing. Get a Sure 4x100W @ 4 Ohm TK2050 Class-D Audio Amplifier Board, and power it with old computer power supplies, i have a bunch of them lying around, and put it in a wooden box or something along those lines. Probably line it with aluminum foil to block electromagnetic interference. I guess I could also use an old computer case. I have a few extra. I had a whole bunch, but I gave most away when I moved.

So my main questions are, is this the way to go?

Can I use computer power supplies, and would I need to use 2 in parallel?

I have been on the internet looking at this stuff all night, about 8 hours. My eye balls feel like they are going to fall out, and my brain is fried. I can't think anymore. I'm going to take a nap. Sorry if this is way to long of a post. Thanks for any help.
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Old 26th January 2011, 07:58 PM   #2
gooki is offline gooki  New Zealand
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First off don't get the Sure 4x100W as you don't need a four channel amp. The 2x100 will do.

Since this is near field listening you shouldn't need much power at all. I'd just settle on one of the cheap 2x20 watt tripath amps, all built ready to go.

Last edited by gooki; 26th January 2011 at 08:06 PM.
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Old 26th January 2011, 08:55 PM   #3
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GR20 KIT TA2020 T-Amp Stereo Amplifier 20W*2+Power+Line - eBay (item 350403961907 end time Feb-10-11 21:45:04 PST)

I mean it. You will be surprised, i compared it to some amplifiers around 300-500 Usd and it was not loosing at all, so if you donīt need to play it very loud, you can be very happy with this, and the price makes you smile
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Old 26th January 2011, 09:32 PM   #4
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I'll third that. Those little TriPath's are great, and even if you decide at some later date to get a larger amp, there are lots of things you can use it for. But it's important to know that to go twice as loud, you need ten times the wattage. 10-20 watts is all you'll probably need--all most people listen to most of the time, I'd bet. Speaker wattage ratings don't mean what a speaker needs, it's what a speaker can handle, max.

--Buckapound
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Old 27th January 2011, 05:13 AM   #5
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Yeah they did do really well with that computer speaker amp that only ran 6 watts, and that would be a lot less trouble.

I do like loud music sometimes, and doesn't the quality start to degrade after about half volume?

The reason I was going to get the Sure 4x100W was because the 2 channel has a small fan. Would rather have passive cooling, and the price isn't much different from the 2 channel.

I was looking at the wattage of the higher end computer speakers, and the wattage rating was surprising

M -audio speakers run 20-10w per speaker and has the biggest drivers
Corsair 56w
logitech 62-35w
creative labs 6-7w
ALTEC LANSING 33 Watts @ 4 ohms

They really vary between manufacturers. It kind of makes me ask myself if some of these are really running the wattage that they claim. The m-audio is a 2 speaker system without a sub, i wonder if it needs a higher wattage to produce base?

Honestly even at 6 watts the speakers sound plenty loud, and an out of the box ready solution would be nice, but I am a bit of a perfectionist, and It would be nice to have something more comparable to the major manufacturers. I kind of wanted to try and get other people, that normally just buy computer speakers, interested in doing the same thing. Of course when I've mentioned this idea in the past on computer hardware forums, no one had any interest in it.

The corsair speakers claim 232 watts of power provided by six Class D amplifiers Bi-amplified, two-way satellites for clear, detailed reproduction. How do you Bi-amplify? is that something that could be done with the Sure 4x100W?

I have to get ready for work. Thanks for all the replies so far.
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Old 27th January 2011, 07:08 AM   #6
gooki is offline gooki  New Zealand
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In your budget the speakers will be the quality limiting component. Just grab a reliable well made tripath amp and call it a day.
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Old 27th January 2011, 07:25 AM   #7
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Biamping is when you run seperate amps for the woofers and the tweeters. Generally if you want good Biamp you will be running an active crossover setup. Also the speakers need to be configured for biamping, by having 2 sets of power inputs that usually do not have any passive cross over installed. (Though biamping can be down with passive crossovers instead of active I think). Your speakers are not configured for biamping and would take some surgery to setup in this manner.

Your speakers have a listed 89dB efficiency therefore at 1meter when supplied with 1 watt they will produce 89dB. Since your sitting at your computer the speakers are more than likely going to be within 1meter of your ear.

Now on top of this every doubling of power offers an extra 3dB of volume gain. Max output on the amp is 12watts @ 8ohms. Even if you ran it at only 4 watts, the speakers would (theoretically) be producing 95dB of sound @ 1meter distance. 95db of volume is actually recommended for a maximum of 4 hrs exposure per day as it will start to cause permanent damage to your hearing. Check out the following:

Decibel (Loudness) Comparison Chart

There is a reason that for years and years audiophiles were perfectly happy with tubes amps that only produced a small amount of wattage. You don't need a lot if you have high efficiency speakers (not that 89db is highly efficient).

This is also the reason that most AV Receivers run with -db volume. How many people want to listen to a movie at the same volume as your average nightclub (100-110db)?.

Addressing the quality degrading after half volume the most likely cause is speaker problems from over excursion/distortion etc. This will be unlikely if the polk website recommends anything under 100watts power. Unless you trying and run more than 100watts.Or the amp clips out because it is trying to force more power through than it is being supplied with from it's rails. This will depend on how loud your trying to force the speakers to play.

Computer systems will list what the maximum power the amps will provide, not what you actually listen too.

After seeing this amp I am seriously considering it for my main L + R Channel speakers, I live in an apartment and will never run them flat out. They also have an efficiency of approx 95+db to begin with. Even taking into account peaks in the music (cymbal crashes etc) this amp would provide HEAPS of power for me.

Bigger amp is going to give you more head room for musical dynamics and allow you to play louder over all.

How loud do you want to play your music?
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Old 27th January 2011, 08:06 AM   #8
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Okay, I'll shop around on ebay, and get a TA2020, and might try a TK2050 in the future just for fun.

Just for curiosity sake, and possible future reference. running the Sure 4x100W TK2050 off a computer PSU? I got a couple dell power supplies 250w i think the 12v rail is 16a, would I need to use both PSU's or would one do it? I know that it can run at 12v, but it seems like 24v is preferred.

I had the box designed in my head already. wooden box with 2 yateloon 80mm on both sides, 4 total running on 5 volt. No sides just 80mm fans, that way I don't have to cut holes. The air would enter the left side and exit the right. Take the PSU's out of their cases, mount the sure board on the left and the PSU(s) on the right. I wonder if the PSU would create electromagnetic interference with the sure board, probably have to put some wire mesh between the 2, and line the wood box with aluminum foil
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Old 27th January 2011, 10:23 AM   #9
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sounds good. I am currently trying to track down a 2.1 DAC lol. I'm starting to think I should just sell my CDA-254 and buy a receiver.
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Old 27th January 2011, 10:43 AM   #10
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Yeah I just have a reciever in my living room, with a HTPC using a cmedia 8768 based card. They only cost $20-$30, and with this open source driver cmediadrivers - Project Hosting on Google Code it gives true digital passthrough. But only in Windows, which sucks since I'll be switching to Linux at some point. Mine sounds good, only problem is no equilizer, and some songs need some adjustment. I probably should get a separate eq box at some point.

Hows the CDA-254? 250w per channel, wow! You powering a big sub or something?
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