Sound quality: LM4780 vs LM3886

[Peter Daniel]

cool...that was going to be my original plan before i started to second-guess myself did you use it as a stereo amp, or parallel?

Only used them in parallel.

 

[enochRoot]

I had to enlarge some of the holes on my perfboard and bend the pins a little to get the chip to fit in properly.

Cutting off the NC pins helps. But on the smaller chips it may weaken the chip to board connection too much. So add some standoffs or something.

thanks! but you lost me on the last part. add standoffs how? and this is obviously not for the 4780, right? that has tons of pins

 

[carlosfm]

Like I said, I made an LM4780 amp on veroboard and didn't cut the NC pins.
You have to be patient to fit all the pins, space them gently.
A labour of care and love.

 

[thomas997]

thanks! but you lost me on the last part. add standoffs how? and this is obviously not for the 4780, right? that has tons of pins

When I am working on my amp I am a little worried about the pins from the chip to the perf board breaking. But this is just with the smaller chips, or if you have really heavy capacitors or something.

So the standoffs would go from the bottom of the case to the board to keep it steady.

4780 probably doesnt need this though.

 

[enochRoot]

oh...i got ya. i had thought you were talking about between the chip and the board somehow

 

[percy]

The LM3886 and LM4780 use the same silicon die, LMP3886AT. There are two of them in the LM4780. They should therefore sound almost identical.

Glenn,
The following information is from the national website -
Slew Rate GBP
LM3886 19V/us 3Mhz
LM4780 19V/us 8Mhz
LM3875 11V/us 8Mhz
LM1875 8V/us 5.5Mhz

The LM3886 has a gbp of only 3Mhz but your webpage suggests 8Mhz. Which one is correct ?

Also, if LM3886 and LM4780 are as similar as they are claimed to be then why the difference in gbp ?

 

[UrSv]

Glenn,
The following information is from the national website -
Slew Rate GBP
LM3886 19V/us 3Mhz
LM4780 19V/us 8Mhz
LM3875 11V/us 8Mhz
LM1875 8V/us 5.5Mhz

The LM3886 has a gbp of only 3Mhz but your webpage suggests 8Mhz. Which one is correct ?

Also, if LM3886 and LM4780 are as similar as they are claimed to be then why the difference in gbp ?

Where did you find that number for LM3886. My datasheet from National says 8 MHz.

 

[percy]

The parametric table at http://www.national.com/pf/LM/LM3886.html

 

[UrSv]

Well since they are the same die and the datasheet says 8 MHz I'd be inclined to believe the datasheet and suspect the parametric table might be inaccurate.

 

[w00t1985]

Isn't there also a differance of about 8 watts between the output of a 3886 and a single channel of the 4780? I'm pretty darn sure I read that in one of the data sheets, and will dig it up if required. The differance is minimal, and I believe the datasheet quoted about a .5 dB differance in output. But still, a differance

 

[carlosfm]

Isn't there also a differance of about 8 watts between the output of a 3886 and a single channel of the 4780? I'm pretty darn sure I read that in one of the data sheets, and will dig it up if required. The differance is minimal, and I believe the datasheet quoted about a .5 dB differance in output. But still, a differance

There's a very slight less power and also current comparing the LM4780 to the LM3886.
The reason is simple: with two channels in one chip it concentrates the heat on a "hot-spot" and has more difficulty in staying cool.
This is the only reason: heat dissipation.
I should say that the 4780 needs a good, and preferably thick heatsink, so that heat spreads away from the chip.