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Hello, Big project and where to start?
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Old 18th August 2011, 05:32 PM   #1
Zaaphod is offline Zaaphod  United States
diyAudio Member
Join Date: Aug 2011
Location: Florida
Default Hello, Big project and where to start?

Hello everyone,

Wow this forum is just HUGE! I've been on it browsing around for a few weeks and it's just amazing. Let me introduce myself, and what I am hoping to accomplish, and perhaps someone could point me in the right direction.

I have a degree in electronics engineering, so I'm not a complete noob, however most of my actual experience over the last 20 years has been with digital electronics, microcontrolers, motion control, and things like that. In the projects I have worked on, I have done a bit with various transistors, mostly in switching applications. I have done some work with op-amps and such in analog applications as well, but not for audio use, so sound quality was never an issue

My Project:
I am currently building a new house, doing all trades by myself, so I'm literally building it. I have got to the interior wiring, and it became obvious that if I wanted to include central audio system, the time to work it all out would be now, so I can figure out what kind of wire I want to run, and get it installed while it's extremely easy to do, since I haven't installed any drywall yet. I have no mortgage for my new house, I pay for materials as I need them, so when I am done I will just own it, that does put me on a budget.. that and the fact that I simply love electronics, and that I want this to work a little differently than commercially available systems I wish to make this a DIY project.

What I would like to do, is have my computer playing MP3s, and instead of running it into a gigantic amplifier, send a line level signal all over the house, and use much smaller speakers in every room. I have done the big AMP thing, and it just doesn't suit my tastes.. you have to have it too loud in the room it is in to even hear it across the house, and from upstairs all you hear is the bass line. I would rather have it at a much lower volume, that is fairly constant as you move from room to room. I would like to extend this past the house, and onto the patio, and even out into the yard, over to my workshop.. etc.. everywhere I would like to be. I have tested this idea in a previous house, by putting cheap amplified speakers in several rooms of the house and just running shielded cable to them all, and while it sounded 'OK' needing much improvement, it did prove to me that I liked the multiple small sound environment over the large blast in one room approach.

So Here I am, trying to pull together the details of this project, and still wondering if it's really practical as I see it. Here is where my thinking has brought me thus far.

The area I wish to cover in sound is quite large, most of 5 Acres on a lot that is 660 feet x 330 feet. While I will not cover every square foot of it, I will have walkways that wind around and go to different areas. I would want this to work along those pathways, as well as in whatever structures or gardens are along the way. I am thinking that with that much distance, the expense of the wire alone becomes an issue... it's simply not that practical to make 2 runs of 10Ga outdoor rated, direct burial speaker wire all over the place. So I'm thinking I could run outdoor rated CAT5 cable a lot less expensively, and by converting my line out to a balanced signal with a differential transmitter, it should provide good quality. I am thinking I could use multiple differential receivers on the same line. So that would take care of signal distribution, and now I would need a whole lot of little amplifiers. This is where I need some help. I'm not looking for a ton of power to each speaker, however it would be nice if power could be available should I want it. the main concern is how to build inexpensive amps that sound reasonably good.. it doesn't have to be the most amazing sound ever, it just has to be clean and as distortion free as practical.

I've been thinking about chip amps, and it seems like the LM3876 is a favorite, however it's kind of expensive if I'm going to want 100 of them, and I don't think I need that much power. I am wondering if I could just put a power transistor, or mosfet of something in the feedback loop of my differential receiver circuit. Does anyone have a recommendation for some kind of small amplifier. I don't think I would need more that 30W. Cost effectiveness is the main issue, it could be a chip amplifier, or discrete semiconductors, I don't I'll use tubes. I did notice that the LM3876 works over quite a large supply range of 20v - 94v I suppose many other amplifiers can work over a large power supply range as well, this would be nice because I could build little power supplies, and if later I wanted more power in certain areas, all I would need to do is replace the power supply with a larger one. and that brings me to the next area of concern.....

Power Supplies:
this biggest area that I am lost in is the power supply for my amps. I've seen a lot of your posts here about various amplifiers with a lot of photos, but not really many details on the power supply. Many of the 'Power Supply' schematics and projects only show the rectifier and regulator section, and just have AC in... but no details on what kind of transformer to use. It seems like there is a lot of use of toroid transformers... are these something you all wind yourselves? How do I go about calculating what the power supply current should be? I have seen some power supplies that are just a transformer of some configuration, going to a rectifier of some configuration, and charge up some really big capacitors, and thats it. Do I need any more than that? are there other types of power supplies that would sound better, perhaps some kind of voltage regulation? and are there some that would be more inexpensive to build? I would think that for DIY everyone would like transformers, because they are isolated from the line voltage, but I've noticed that most commercial electronics have almost all gone to small switching power supplies, the driving force probably being they are cheaper to build, so I am wondering if there are DIY solutions for small switching power supplies.

So that is what I am trying to do, and what some of my questions are. I would love to get some feedback on the entire project... am I even approaching the idea of central audio the right way? I would like to keep the cost down on each amplifier and power supply, however even if it ends up that the total of all the little amps and power supplies would cost more than a really big amp, I would still prefer to do it with a lot of little ones, because I do not have to build them all at once. I can build a few and get some of the system working, and over the next few years, build more and expand more until I have sound everywhere I want it. having some results at a low cost and expanding over time would be the ideal way for me to create the system that I would eventually like to end up with.
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Old 18th August 2011, 06:44 PM   #2
nad is offline nad  United Kingdom
diyAudio Member
Join Date: Oct 2009
Hi Zaaphod, that's one hell of a large project, great idea too. Best of luck.
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Old 18th August 2011, 07:07 PM   #3
east electronics is offline east electronics  Greece
diyAudio Member
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Join Date: Jan 2006
Location: Athens GREECE
Welcome to the forum !

your approach is not bad .... but there is too many things versus too many other things ...Not all of the things you need can be diyed ... you are going to run in to various trouble if everything is not designed properly .

here is a few highlights ...

---UTP idea to distribute line level signal is a good idea but quality baloons or transformers might come expensive .

--- Line level shilded cable will not work ... it is obvious that no matter how good evntually it will pick up something .

--- design and use of active speakers amplified inside with 3886 or similar is not a bad idea but will also cost and also need to be designed properly

---design and use of active speakers amplified inside with 3886 will also require wiring of electrical power for each and every speaker that ... for a big ammount of speakers will obviously increase the cost of material and labour respectively .

--- power supply is critical for audio amps but for your application will not require space technology or Marsian material ...simple things will work just fine ...more or less as you described it trafo/bridge/caps /decoupling will be just fine ....

alternative !!!

Welcome to the 100v technology !!!!

the 100v systems work in hotels hospitals banks and generally when a lot of relativelly small speakers is needed all of them conected on one source ...

--use only one amplifier
--use Utp cables
--you may use tampers that will allow level setting for each speaker individually
--you may buy speakers that allready feature 100 v feeds
--in one and only pair of utp you may drive almost as many speakers as you like
--in the other pairs you may also drive other programs of music and select from localy
--you may also drive infrared signals back to the source of the music making able to control the source from distance

the only disavantage will be that the sound will never be high end
still if good quality trafos are used expect it to sound at least hifi
choise of speakers will also have some to do with quality and obviously all the above (S) versus cost ...

I think that if you use a pen and a paper to make a sum you will find it the most effective solution that will also not include a load of risky diy .

obviously before ordering 560 pcs of LM 3886 you need to remember one that you are an amature and two chips blow far too easy !!!

( in Greece now is 36 degrees and its 10 in the night .....economics are terrible so i hope i am allowed from time to time to make a joke with the amature thing.... other than that chips blow far to easy and sound bad to my taste .)

kind regards
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Old 18th August 2011, 11:08 PM   #4
Zaaphod is offline Zaaphod  United States
diyAudio Member
Join Date: Aug 2011
Location: Florida
Thanks for the input Sakis,

The 100V system you mentioned sounds interesting. I will have to investigate this to see what it is all about. Do they have these systems in stereo? I am wanting to strategically place left and right channel speakers so one is constantly getting stereo effect as they are moving around. I agree I need to figure this out what the most cost effective method would be. it all comes down to cost vs performance really.

For my Cat5 runs, I plan on using a DRV134 to provide the differential output, and for the receivers either an INA137, or perhaps my own op-amp based buffer, which I think will be less expensive than INA137s. I am wondering if I could somehow integrate the the receiver and amp into one thing, and perhaps either come up with an amp that uses the differential signal, or a differential receiver with some kind of power stage in it's feedback loop.

Just doing some simple cost estimates, I think I can make the receiver / amplifier section for a reasonable cost.. the one thing I am still in the air about however is power supplies. If I'm going to use the transformer/bridge/capacitor method, where do I get the transformer, and how much is that going to cost? It seems I will likely need either a power supply with 4 outputs, +15 / -15 for my op amps, and +35 / -35 for my amplifier.. or is there a way I can regulate my +35 / -35 down to +15 / -15.. after all my op amps won't draw very much current at all. I don't know if I can just stick 35V into an LM7815 / LM7915 to regulate it down to 15V, that seems kind of high. Perhaps I need to simplify things and just get some resistors and Zener Diodes. In any case, I think the biggest expense of the power supply will be the transformer, and capacitors.
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