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Old 31st July 2011, 02:19 AM   #11
gootee is offline gootee  United States
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OK. You need to be using the schematic for the "single supply" version of an LM1875 amplifier circuit.

Go to National Semiconductor | High-performance Analog and download the datasheet for the LM1875. The circuit you posted is the dual-supply one, from page 1. The circuit you need is the single-supply one, from page 2 (at least in my version of the datasheet).

Note that C1 and probably C5 should be film caps, polypropylene. Also, connect the 0.1uF and 100uF decoupling caps as close to the chip's power pins as you can.

You could increase the values of the C1 1.0uF cap and the 100uF cap, if you wanted to.

Tom

Last edited by gootee; 31st July 2011 at 02:30 AM.
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Old 1st August 2011, 05:46 PM   #12
johnr66 is offline johnr66  United States
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Also note that with a single 15 volt supply, the maximum clean power into an 8 Ohm load would be 2 watts or less.
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Old 2nd August 2011, 04:48 PM   #13
AndrewT is offline AndrewT  Scotland
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One might be able to squeeze another 1.6dB out of 15Vdc, i.e. ~2.9W into 8r0 (6.8Vpk, 13.6Vpp, 850mApk).
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Old 2nd August 2011, 11:33 PM   #14
johnr66 is offline johnr66  United States
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Quote:
Originally Posted by AndrewT View Post
One might be able to squeeze another 1.6dB out of 15Vdc, i.e. ~2.9W into 8r0 (6.8Vpk, 13.6Vpp, 850mApk).
With a TDA2003 he probably could, but the LM1875 just won't "swing" that. The TDA2050 has a bit more output swing at a given Vs, but these higher supply voltage "Hifi" chips weren't designed with optimized output swing in mind.
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Old 3rd August 2011, 12:38 AM   #15
infinia is offline infinia  United States
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yup you need at least double the supply for any reasonable output.
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Old 5th August 2011, 05:40 PM   #16
Havoxx is offline Havoxx  United States
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Ah, I appreciate everyones help . I uh, made the mistake of buying a grab-bag of resistors so I'm spending my day Iding and organizing them . but I did get ~2000 of em for about 7 bucks
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Old 5th August 2011, 07:31 PM   #17
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learn to buy resistors in strips of 100 minimum when you need a new value, they work out to less than a cent each that way sometimes.
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Old 9th August 2011, 04:57 AM   #18
Havoxx is offline Havoxx  United States
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Ok, about the power supply, I'm trying to buy one online, what in the world should I look for? I was going to find a 12 - 12v supply, but what is it called? Or is it the toroid?
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Old 9th August 2011, 12:39 PM   #19
hurtz is offline hurtz  Germany
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Toroids are the preferred choice in power-supplys due to their high output power and little magnetic radiation.

First you should decide how much output power you want. So look at Page 3 on the datasheet. Lets assume 20W, thats around +-22V

One page forward look at the power dissipation vs. output power. At 20W with +-22V we get a disipation at around 15W

As a last step we want to decide which heat sink to use. We know we dissipate 15W at maximum power, and given a really hot summer day on which we incidently have a party we look at 40C ambient temperature. The 5C/K won't do since it will drop just below 15W at 40C. 2C/K is plenty so 3C/K will work, 4C/K might also.

Now back to the power supply, the chipamp wants 15W heat + 20W output power. so you need at least 35W or 35VA output power. be safe and add ~30% for loss in the various components so above 45VA is a safe choice.

The voltage of the toroidal: after rectification and filtering you get: (initial AC Voltage) * (square root(2)) = (DC Voltage)

We want +-22V DC so thats: around 16V AC.

So the toroidal you want is 2 * 16V AC @ 45VA or something like that.

keep in mind that you need a PSU for rectification and such..

cheers
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Old 9th August 2011, 02:07 PM   #20
Havoxx is offline Havoxx  United States
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Ah ok, I thought that's how you read em but I wasn't sure, being self-taught is a bit difficult .
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