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LM1875 Amp in the works: Need help with power supply.

post #1 of 6
1/18/11 at 4:23pm
Thread Starter 

It's been a while since I've been on Head-Fi. I just finished my LM386 battery amp...and it's pretty cool, but I think I'm capable of much more. I'm trying to get all the parts together for an LM1875 amp. I'm hoping to couple that with a HiVi full range driver.

 

Because of it's wide input voltage range, I don't think I'm going to make it a regulated supply, as I don't think there are any linear regulators that can handle that much current. So, I'll use some high power diodes with a couple capacitors...

 

Is this acceptable? Or should it be regulated?

 

In regards to the transformer: If the max output of the LM1875 is theoretically 20W, then would a transformer with 24V output at 1.0A, be sufficient? (24x1 = 24W???)

 

 

I'm a bit confused on this part.

 

Thanks in advance.

 

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post #2 of 6
1/19/11 at 9:52am
Thread Starter 

Anyone? No?

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post #3 of 6
1/19/11 at 10:21am

 

There is tons of info on the LM1875 GainClone chip.

You don't need a regulated supply for this.

The transformer should be rated MUCH higher, about 50VA should be OK for each channel.

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post #4 of 6
1/23/11 at 4:35pm
Thread Starter 

Thanks. I haven't had acess to a computer in a couple of days so sorry for such a delayed response. Are my transformer calculations wrong? It should be able to put out ~25W, and with the chip speced up to ~20W, shoulnd't it be okay? What is the rationale behind more VA? Less heat? Thanks alot.

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post #5 of 6
1/23/11 at 5:35pm

The chip is not 100% efficient.

20 watts out = probably twice than in (check the data sheet).

You will want a transformer rated at least 50% higher than

that to keep the heat build up to a safe level. If you don't listen

at high levels or for a long time you might get away with a

smaller transformer but it wouldn't be reliable for heavy use.

 

Quote:
Originally Posted by TheLaw View Post

Thanks. I haven't had acess to a computer in a couple of days so sorry for such a delayed response. Are my transformer calculations wrong? It should be able to put out ~25W, and with the chip speced up to ~20W, shoulnd't it be okay? What is the rationale behind more VA? Less heat? Thanks alot.

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post #6 of 6
1/23/11 at 5:39pm
Thread Starter 

Oh duh. I've known that from my knowledge of PC power supplies....Thanks, that clears it up.

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