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Old 3rd September 2012, 11:14 AM   #1
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is 160VA transformer is ok to power 5.1 channel amplifier of LM1875
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Old 3rd September 2012, 11:20 AM   #2
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can i use four diode (1n5401) as rectifier and four 2200mfd capacitors as smoother in 18-0-18 , 160VA transformer for dual 24V power supply ???
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Old 3rd September 2012, 09:45 PM   #3
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Mr. Ranjit Raj,

What's actually going on in your mind? Is it some college/training project or you want to build it as your hobby? Do you want it as a very low budget project compromising with sound quality or vice-versa? Do you have speakers for your project (5.1)? Do you have a cabinet to store your project components inside which has a 5.1 speaker outlets? (I don't think you will get it easily at your place). Please, elaborate about your project. Don't buy anything before you are sure off. Is it your first project? And, why 5.1? Do you have any collection of original 5.1 recordings with you? If not then building 5.1 is of no use. Rear channels will be almost silent all the time.

No one can help you until your intentions and plans are clear and elaborated.

Thanks.

Last edited by noddy55; 3rd September 2012 at 10:04 PM.
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Old 4th September 2012, 11:54 AM   #4
AndrewT is offline AndrewT  Scotland
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There is some good advice in there.
I too recommend you build a single channel using a single chipamp.

That is the first step.
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regards Andrew T.
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Old 5th September 2012, 01:19 PM   #5
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what is wrong with a 5.1 amp? or 7.1 for that matter?
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Old 5th September 2012, 02:26 PM   #6
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complexity, if the OP is not experienced it will lead to .. well nothing.
K.I.S.S.
we supposedly know what that means. And probably if its a first build, it should be kept in mind.
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Old 5th September 2012, 03:39 PM   #7
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hi,
Mr Noddy55,
Thank you for giving me attention.This is my hobby and this my 2nd project.I want to build a 5.1 channel audio amplifier with using either LM1875 or TDA2050 IC .But i have no idea about PSU and i have no such circuit . I have not great but good collection of 5.1 channel movies and songs. Cabinet and electronic parts is not a problem for me , these things are easily available in my city.
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Old 5th September 2012, 10:44 PM   #8
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Hi,
Please, give some more info and let us see if anyone can help you :

1. What was your first project? Were you 100% satisfied with you first build? Is it still working?
2. What model and make of DVD player you have, that you are going to attach with your 5.1 project?
3. Do you have any working stereo amplifier with you? What make and model? I mean what audio setup currently you use to listen music and your movies?
4. What make or model of speakers you currently have or these are also the part of your 5.1 project?
5. Have you heard 5.1 setup before? Where? And, what you like the most special about it?
6. Can you describe me a little about each speaker in 5.1 setup?
7. Do you know about surround sound? If we compare surround sound with 5.1 setup, which one of them will thrill your senses more? This one is really important.

Thanks.
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Old 6th September 2012, 12:01 AM   #9
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OK, lemmie try to provide some information that might be useful for you. It seems that the other posters in this thread have some other agendas in mind...

So, you want to build a 5.1 ch power amp using LM1875 and want to figure out what kind of power supply you will need. Let's start with the potential output of the LM1875 and work backwards, shall we? These will be back of the envelope calculatoins at best, but still usable for your purpose.

5.1 ch = 6 channels total. The IC can deliver around 20W output power to the load (the speaker). The IC also dissipates heat, which is power that you deliver to the IC, but is lost. The amount of dissipated power varies depending on several things, which I will not get in to here, but judging by the data sheet a typical amount might be 20W of dissipated power (30W max) per IC. So far we need 50W of power per IC, times 6 ICs, equals 300W. This would not typically be required for music signals, but I assume you will use most of the modest power the LM1875 can deliver, so I am assuming the worst case scenario here.

Now let's talk about the power supply. You want to deliver + and - DC of around 24V to each chip amp IC. What size transformer do you need? Typically you want the transformer to have AT LEAST the same power rating as what is required from it, so 300W. Now, how much capacitance do you need in your power supply? One quick and dirty rule of thumb that can be used is 2000uF per amp that the PS will deliver. How many amps will the PS deliver? Just use Ohms law V=IR. I will assume that you are using an 8 ohm load (that is the recommended load for the LM1875), and V = 48V. So, I = 48/8 or about 5.5A. So, you should use a minimum of 11,000uF of capacitance per rail, that is one 10k uF cap between + and ground and another between - and ground. Using twice that much would not be overkill. These should be electrolytic caps, with a voltage rating of 50V or more (35V is a bit too low). Finally, you will need a bridge rectifier - just use one of the 25A rated ones, with at least 400 PIV and you should be all set. I assume (and hope) that you know how to wire this all together, where to put fuses, etc...

Finally, you need to find a heatsink that can dissipate the heat that these guys will generate. The heat sink should never get so hot that you can't keep your hand pressed against it for at least 10 seconds.

If you only have 160VA 18-0-18V transformers available to you, these are OK but you will need to build two separate power supplies (split the capacitance equally between them) and power 3 channels from each one.

-Charlie
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Old 6th September 2012, 12:25 AM   #10
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5.5A on one LM1875?? with +/-24V supply that is 264W. and 48V on the output? not likely.
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