LM1875 sound better than LM3886??

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jamal

Member
2010-09-20 1:53 pm
I used standard circuit from the datasheet. in fact the cicuit were hijaak from LM3886 application. when I parralle the LM1875 ,the output drop to low. I mean the sound was not loud as a single chip. also there was click sound every 3 second. I intend to parralle 3 LM1875. any help
 
Do you mean the (infamous) AN-1192 application note from National? It sounds like you did not have the gains matched closely enough - this is the biggest trouble when paralleling. Simply using 1% resistors in the gain network (as AN-1192 says may be used) is not nearly good enough - they need to be matched to at least 0.1%.

I can share the schematic I have for 8 TDA2030s paralleled and bridged if you like?
 
@ Ratza
Using amps in parallel to deliver more power (into a given load) would be like trying to do a 5m pole vault with 5 poles at 1 meter each.

To drive a load too heavy for one LM1875, increasing current capability by parallel amps is valid. And a better option if a higher current amp means higher THD. Noise performance should improve also, since the output signal would be correlated, but the noise isn't, I think.

@Jamal
As Abraxalito says, it's necessary to use closely-matched gains, or one amp ends up driving current into the other. Rod Elliott mentions this in his chip amp project notes.

The clicking sound you're hearing is possibly due to the protection circuit operating in the overworked chip. Hopefully that'll keep the smoke in until you get the gains matched. :)
 
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"Use an amplifier which can deliver more than your required current."
"Do please explain why?"
Hi,
chipamps are designed to drive higher impedance, higher efficiency loads.
All the BPA versions are simply a ploy to sell more chipamps for a duty for which they were never designed.
If you need to see technical confirmation then look at the current capability designed into a cold chipamp and then try to find from National's data what the designed in current capability becomes when as hot as their design guide says you can run them at.
 
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jamal

Member
2010-09-20 1:53 pm
hi abraxalito, thanks for sharing your circuit are you going to send to me;). btw I prefer the LM1875 cause the sound quality is so much better than the LM3886 and TDA7294 which I have built before. sorry guys no offend please
the LM1875 amp is going to be in my bed room so high power is not a issue.
but is running very hot at normal listening .
I intend to buit paralle LM1875 as a next project. seeking help here.

Do you mean the (infamous) AN-1192 application note from National? It sounds like you did not have the gains matched closely enough - this is the biggest trouble when paralleling. Simply using 1% resistors in the gain network (as AN-1192 says may be used) is not nearly good enough - they need to be matched to at least 0.1%.

I can share the schematic I have for 8 TDA2030s paralleled and bridged if you like?
 
Not to dissuade you from the project but...

the LM1875 amp is going to be in my bed room so high power is not a issue.
but is running very hot at normal listening .

Unless your speakers are very inefficient, that shouldn't be the case. My LM1875s run very cool.

I'd think yours may be oscillating, or perhaps has not enough thermal conductivity between chip and heatsink.
 
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.
 
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. :ill:

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. :)
 
"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...

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.

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?
 

ashok

Member
2002-06-06 4:43 am
3RS
........... 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 !
 

jamal

Member
2010-09-20 1:53 pm
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
 
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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