LM1875 sound better than LM3886?? - Page 2 - diyAudio
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Old 4th November 2010, 01:20 PM   #11
jamal is offline jamal  Singapore
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I am using JBL 4 ohms 2 way speaker. driving a 8 ohm Dyanaco also the amps get hot. feedback resister is only 22k. no PCB board just christmas assembly.
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Old 4th November 2010, 01:40 PM   #12
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Does the heatsink take a long time to heat up when in use? If so that indicates poor thermal coupling from the chip to the heatsink.

I used a rather thick sil-pad on my first LM1875, and it took maybe an hour for the heatsink to get warm at constant listening levels. And it did get very warm, even at moderate SPL. Cranking up the volume caused the protection to cut in. Switching to a thinner sil-pad solved that, and the heatsink and chip stabilised much quicker, and at a much lower temperature. Protection doesn't kick in when I crank it now.

If the heatsink is coming up to temperature quickly (and assuming it's large enough) the problem is something else, oscillation being the top suspect.
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Old 4th November 2010, 02:11 PM   #13
jamal is offline jamal  Singapore
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the heat is coming slowly. if there is a problem the LM1875 will cut off. I ON the amp without a heatsink and the protection did kick in.
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Old 4th November 2010, 03:37 PM   #14
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Quote:
Originally Posted by jamal View Post
I ON the amp without a heatsink and the protection did kick in.
Probably better not to do that. If the protection doesn't kick in fast enough you could damage the chip.

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Originally Posted by jamal View Post
the heat is coming slowly.
Seems like you need better thermal coupling from chip to heatsink, then.

If you're using mica and thermal paste, don't use lots of paste. Cover the mating surfaces fully, but with the thinnest layer you can.

If you're using a sil-pad, make sure it's very thin. And remember different makes and types will have different performance for the same thickness.

Make sure the chip is screwed down tight -- but not too tight or the body of the chip may get levered up and not make good contact.

Maybe consider getting one of those clips which press down on the body of the chip, although I've not found them necessary.

It should run cooler once you've got better thermal conductivity. If the heatsink warms up quickly and it's still too hot... well, worry about that if it happens.

Hope it goes well.
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Old 4th November 2010, 04:21 PM   #15
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Quote:
Originally Posted by AndrewT View Post
"Use an amplifier which can deliver more than your required current."
"Do please explain why?"
No Andrew, my question was directed at the pole vaulting 'analogy', not the other statement. But anyway, since you're here...

Quote:
chipamps are designed to drive higher impedance, higher efficiency loads.
Chipamps are fine for (effective) loads of 4R and higher. Below that, they're a very poor choice unless paralleled.

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All the BPA versions are simply a ploy to sell more chipamps for a duty for which they were never designed.
Do please share with the assembled company how you know this for sure?
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Old 4th November 2010, 04:35 PM   #16
jamal is offline jamal  Singapore
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I am using sil. pad .I think a bigger heat sink and a fan will help. .
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Old 4th November 2010, 05:50 PM   #17
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Quote:
Originally Posted by jamal View Post
........... btw I prefer the LM1875 cause the sound quality is so much better than the LM3886 and TDA7294 ...............
I find the LM1875 has better impact on transients than the other chips. It does sound very good but other circuits have better mid range and more 'transparent' HF than the 1875. It's a very hard choice between circuits. I haven't yet come across one ( within my budget or accessible for audition ) that would have all of the above ( including good LF performance).
Most fall short in some area and picking one that suits our requirement can be quite difficult. Have you seen the number of people who change numerous amplifiers over time . Surely if they had found THE greatest amp they wouldn't need to change any more ..........or at least as often!
I keep going back to my 1875 more often that I thought I would. Pity that it so low powered. But it doesn' t really matter too much. It goes pretty loud for me. I only miss the power when we are having a party or having a music and booze session !
That needs SPL !
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Old 4th November 2010, 07:31 PM   #18
jamal is offline jamal  Singapore
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LM1875 got a tight bass and it really punch out the bass also the treble is sharp. btw my reference amplifier is Mission Cyrus 1. so any amp I come across will be compared to my reference. the LM1875 it is very cheap $1 for 1pcs. recently I bought 10pcs and blow up a few:d
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Old 4th November 2010, 11:51 PM   #19
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Its a good price for the LM1875 - what's your source? There are definitely fakes about, a friend sent me a link to pics of TDA2030As (which are even cheaper) re-badged as LMs. Here in China an (apparently genuine) LM1875 goes for a little over $1 but TDA2050s are less than half that. A local place sells 'recycled' chips cheaper, they're more likely to be genuine ones I reckon.
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Old 5th November 2010, 12:35 AM   #20
jamal is offline jamal  Singapore
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hi Abraxalito, I bought the LM1875 from a wholesaler. but another shop selling it for $4.50. both look alike and sound alike. hmm TDA2030A relabel as LM1875??? interesting,
what will they think of next.
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