Easy bridge

[carlosfm]

Re-reading 😱 the LM4780 datasheet I found this.
S'easy. 😀

 

[Dxvideo]

So do you think if we make two parallels in a bridge (BPA) can we get 200 x 4 = 800W (%10 THD) for 4ohms?

I cannot decide, should I use quad LM3886 or two LM4780 for my 300W (or more) gainclone... I already draw a PCB for quad LM3886 but still I am not sure that I will realise it or not!

What do you recomend to me?

One more question;
There are two BPA200 circuit on National's site. One of them is that. The other is which in the BPA200's reference book. There are two diferences between them. First is the input resistors, the second is the inv amps (-) pin to gnd... Which one I must cohice?

Thanx

 

[peranders]

The resistors are for reducing the input bias offsets, caused by unequal input bias currents. You can omit the resistors if you don't have any big problems with output offset voltage.

 

[carlosfm]

Dxvideo,

You'll find much more difficult to make a PCB for the LM4780.
The pinout is really mad.

I would do it with the LM3886, it has also the advantage of better heat transfer, spreading the chips through the heatsink.

 

[tschrama]

Dxvideo, You'll find much more difficult to make a PCB for the LM4780.
The pinout is really mad.

I would do it with the LM3886, it has also the advantage of better heat transfer, spreading the chips through the heatsink.

I don't agree on the pinout.. it's really simple to make an bridge amp with the LM4780. Just build two on veroboard, very easy layout. A PCB shouldn't be more difficult.

I do agree with the heat issue. Those chips get pretty warm when idle, at a 1/4 of the rating they will dissipate so much they will get very, very hot .. too small a surface...

About the power issue: 4 LM4780 or 8 LM3886 will likely be able to drive the 4 ohm load in bridge mode (with a BIG powersupply that is) but the max Vssuply is around 30 a 40Volt, = 60 a 80Volt pp = 42 a 56 Volt rms in to 4 Ohm equals 784 Watt rms... probbably a bit less due to output resistor losses and headroom needed for the chips.. but still 784 Watt ..pffff

that's 196 Watt dissipation for each of 4 LM4780.. NO WAY ehhh .... aha.. 70% efficientie.. so only 60 watt dissipation?

or

98 Watt total power gives 30 watt dissipation for each of 8 LM3886 ... still alot ... am I right?

hmmm you'll need a large heatsink

just my 2cts,

Thijs

 

[carlosfm]

I don't agree on the pinout.. it's really simple to make an bridge amp with the LM4780. Just build two on veroboard, very easy layout. A PCB shouldn't be more difficult.
Thijs

I made my LM4780 on veroboard.
A simple stereo version, no bridge, no parallel.
But a PCB for the LM4780 would have to be double sided, and it would become expensive.
For a guy that is building this for the first time I would recommend the LM3886.

Oh and I really think that the National engineer that decided on the LM4780's pinout is really crazy or had a bad day.😱 😀

 

[Luke]

Hi Carlos,

I have tried a few gainclones , but allways preffered the LM3875 sound.
How does the 4780 sound in comparison?

 

[carlosfm]

Hi Carlos,

I have tried a few gainclones , but allways preffered the LM3875 sound.
How does the 4780 sound in comparison?

I cannot make a direct comparison.
The other GCs I made (LM3875, LM3886, OPA548) were all IGCs.
This time I tried NIGC, with LM4780.
The sound is smooth, detailed and dynamic, it really drives difficult speakers better than the LM3875.

 

[Luke]

thanks Carlos,

I think Ill try it one 🙂

 

[Dxvideo]

So I can use LM3886 x 4 for my GC... But I still wonder what is that circuits effective power output for 4ohms. And does 2 x 350VA EI type transformer enough that circuit?