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-   -   LM1875 sound better than LM3886?? (http://www.diyaudio.com/forums/chip-amps/176608-lm1875-sound-better-than-lm3886.html)

jamal 4th November 2010 02:24 AM

LM1875 sound better than LM3886??
 
hi, The LM1875 wtih lower THD sound better than LM3886 according to my taste. I try to parralle 2 LM1875 but did'nt work fine. can LM1875 work in parralle............thanks

abraxalito 4th November 2010 02:40 AM

Certainly it can. I don't have direct experience with the LM1875 but I have made both the LM1876 and the TDA2030 work well in parallel. They're jolly similar to the LM1875. What circuit did you use that didn't work?

jamal 4th November 2010 04:12 AM

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

abraxalito 4th November 2010 06:02 AM

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 4th November 2010 10:00 AM

Using amps in parallel to deliver more current is like trying to do a 5m pole vault with 5 poles at 1 meter each. Use an amplifier which can deliver more than your required current.

abraxalito 4th November 2010 10:08 AM

Do please explain why?

Omega_Void 4th November 2010 12:55 PM

@ 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. :)

AndrewT 4th November 2010 01:05 PM

"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.

jamal 4th November 2010 01:06 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.

Quote:

Originally Posted by abraxalito (Post 2353833)
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?


Omega_Void 4th November 2010 01:15 PM

Not to dissuade you from the project but...

Quote:

Originally Posted by jamal (Post 2354089)
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.


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