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Old 6th December 2010, 05:11 PM   #1
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Default Re-visiting this site

Apparently I joined this site about 7 years ago right after high school... Anyway I once again have some time to invest in this particular direction of my hobbies. I have a few things that I would like to work on over the next few months and I'm sure it will seem like a lot to take on but for now I am not sure which forum I should start in. One thing to keep in mind is I don't have a lot of time to search the internet like I did right out of high school so I am looking more for direction so that my time can be mostly spent on learning and then applying what I've learned.

Ok so the idea started with rebuilding my computer to become my one stop shop for computing and entertainment seeing as how I will most likely be moving back in with my dad in about 6 months so I can start college again. I've done away with my stereo receiver and large floor standing speakers. What I would like to have is a nice but realistic 5.1 setup that will work well in a large bedroom yet not beat down the house. Initially I was going to purchase PC speakers but now I would like to build them which lead me to think about building the amps for them also. The end goal is to build a custom PC case that will house the computer and the speaker associated parts while being a reasonable size.

I'm not sure how much power I need but seeing pre-made speakers on Newegg shows anywhere from 10-75 watts rms on the satellites and 30-100 watts on the sub. I'm also not going for extremely high end sound or quality, I would rather take the $200-$400 that would be spent on a decent surround sound set up and use that money to build my own that would hopefully be a bit better.

Initially I am thinking that the fronts should be 3 ways for about 35 watts rms, center should be either a 3 way or a 2 way with less focus on the bass/mid bass and around 25 watts, the rears should be 2 ways at about 25 watts and the sub should be 6"-8" at 35-75 watts.

Am I way off point with that thought process or does that sound about right to get where I want to go? I want a relatively small system that is easy to move yet provides a decently full sound. Thanks in advance.
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Old 9th December 2010, 12:48 PM   #2
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Welcome to the forum. I did fine with 35 W/channel stereo amp for thirty years, although as it was a tube rig it didn't exactly fit the USAF traveling lifestyle. >98 DB @ 1 W speakers (a standard specification method of pro-quality speakers) can make this amount of power produce quite lifelike sound. Packing that much in a computer chassis seems entirely doable with Chip amps (see that forum) although you may want more power supply than +- 12 available from the PC supply. See Audiopower.it for a nice 400W switcher units with useful audio voltages. That sort of thing would be discussed on the amplifier power supply forum.
I think 3 way speakers are a bit flashy when the job can be done well with a horn +woofer, however there are as many speaker designs are there are hobbiests, it seems. Stop by a pro music shop with a full frequency CD and audit some Peavey SP2's or the equivalent JBL or Mackie horn + 15" speaker, to know what you are up against when you are building your own.
Have fun.
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Last edited by indianajo; 9th December 2010 at 12:53 PM.
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Old 11th December 2010, 09:16 AM   #3
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Thanks for the reply! I do agree that a 3 way design is quite possibly over designing the system for what I want to do. If I remember correctly isn't a 100% increase in power to the speakers equal to a 3db gain?

I guess where I'm still a bit lost is the power supply and amp side of things. I think I still remember enough that I can find my way to the information I need to design and build the speakers and refine them.

In terms of the power supply I would prefer designing it and building it myself for at least the sake of experience but what in your opinion would be the best type of PSU to use? You mentioned chip amps with regard to size, do you have any sites that explain the functional differences between PSU types with strengths and weaknesses?

Also I'm guessing the amp part of this is a little less of a choice as compared to a PSU, would you say a class D style amp would be appropriate? Again do you know of a good place that explains the major functional differences between amp types and their best suited applications?

Thanks again!
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Old 12th December 2010, 06:35 PM   #4
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wikipedia decibel article says a doubling in power is 3 decibels. I had a 3 way speaker system when I was 20 but later found 2 way systems that sound better to me. Depends on the design. I test with high keys solo piano hits, and low bass drum hits, both difficult for amps & speakers to do. My 2 ways weigh 98 lb, so they are not tiny, but they sound great. The company has replaced them with some weighing 80 lb. They will produce 126 db at 300W, but I listen to them at about 1W (101 db @ 1m) where the datasheet says they produce less distortion, anyway. Not a lot of consumer products come with a chart of harmonic distortion versus frequency at two different wattage levels, plus the standard frequency vs power chart.
Chip amps produce 30 W pretty well. The clearest chip amp article I have read is Worlds ugliest chipamp. I don't reccomend his construction methods, but I like the clear schematic. I don't own one, but am thinking if building a 3 channel version for my tube amp organ to save 150 lb and 2 amps @ 120 VAC. Plus replace some bad contact tube sockets. I build on perf board I make myself by drilling lots of holes in glass reinforced boards I got 12/dollar. The board gives some support to the solder joints to keep them from breaking.
The audiopower.it power supply at 2 lb produces +-55V and fits the traveling lifestyle. If you built one yourself, it would howl like a dog into everything at 87 KHZ. They spent a lot of time reducing the emited noise to something like 90 db down. I can't find the thread but the description is at www.audiopower.it/# I don't know anybody that use them but somebody said they were in a commercial product as a subcomponent. You could fit it in the spare space in a PC tower case, in a suitable steel box to keep the noise down.
The next best thing is printer wall transformers selling for $2 at charity resale shops. +32V @ 4 A. They come in both transformer versions and switcher versions, I don't know if the switcher versions howl or not. But they are not made for audio. Two of these could make a 35W supplly easily, using conventional capacitors and LM320 regulators. This is clunky for an airman that travels a lot, however. You could also buy a 65V CT conventional transformer and make a conventional supply, but it would weigh 8-10 lb and not fit in the computer case, and produce a lot of heat.
I don't know anything about class D amps except they are too hard for me to scratch build with a DVM, a 10 Mhz scope, perf board and a soldering iron. There is a whole thread about them here. You have access to better equipment at the airbase hobby shop. I'm doing tube amps, straight transistor amps with commercial power supply, tube and op amp preamps, suitably low tech for me.
Have fun.
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Last edited by indianajo; 12th December 2010 at 06:53 PM.
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Old 12th December 2010, 11:32 PM   #5
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I'm guessing you saw my location as VAFB, unfortunately that isn't up to date and that was where my dad was stationed so I don't have access to those resources anymore. I'm looking into the chip amps like you suggested although I'm not finding any direct information for beginners with regards to concepts and then to designing.

For now I have a basic idea of what I want the end result to be but I'm having difficulty finding the information I need to figure out which path is the most appropriate. Forums are always a bit discouraging since they have so much information yet it's almost entirely useless unless you have either a ton of time to search through it all, have someone to guide you through it or even more rare is to find a forum that consolidates the good usable information into an organized set of threads.

Is there anyone you know that knows a good amount about chip amps that might be willing to provide some guidance?
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Old 13th December 2010, 12:09 AM   #6
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[QUOTE=meltmanbob;2396323
Is there anyone you know that knows a good amount about chip amps that might be willing to provide some guidance?[/QUOTE]
Just click on world's ugliest chipamp link above in blue, and read that. Has nice, clear schematics short text, mostly a gag article but it works and electrical design seems standard. Copy the schematics, with better construction, I intend to. You can Private Message the guy by clicking his name if you want to ask questions. He knows a lot more about chip amps than I do- I'm just laying in the power supplies for my project. There are a thousand different ones, you just have to pick one you understand, buy parts & tools, go.
Good texts for beginners wanting more organized information are available at the local community college. I got my obsolete text for $2 at Goodwill, the problems are obsolete. "Electronic Devices, the electron flow version" by Thomas Floyd. Good discussion of power supply basics, how to use a meter, how transistors work, etc. Boy Scout merit badge handbook is useful for beginners, and more organized than a forum.
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