anybody tried a LM4780?

[sayang001]

Will you sell these boards ?

 

[ashok]

Supplier?

Hi Mahendra,
From where did you pick up the LM4780 chip ? I am assuming it was picked up locally. I saw some LM3886 at a shop in Chennai. He wanted 650/- bucks for it .
What software did you use to make your pcb layout? Looks nice.
Thanks,
ashok.

Did you also build the LM3886 amp ? If so how does the sound of the 4780 compare with the 3886.

 

[mahenreddy]

Sayanq001,

I can sell these boards but I need to get them ordered with the film I have. The PCB manufacturer takes apprx 2 weeks to dliver.

It costs USD20 per board and minimum order quantity is 5. Postage(from India) extra.

Mahendra Reddy

 

[mahenreddy]

Ashok,

I bought them(LM4780) locally for Rs750/- each. If you want I can send you through courier. Let me know.

It sounds as good as LM38xx series if not better. Also it drives 4ohm - 8ohm loads unlike LM38xx.

LM3886 is also availabe here locally for Rs500/- each.

Mahendra Reddy

 

[carlosfm]

I tried it

Guys, my last GC was made with the LM4780.
I felt like trying it.

Let me say that the engineer that decided on the pinout of this chip was either drunk or in a bad mood.
Complete madness.

Before making the amp, after some thinking I made my own circuit this time.
No time yet to make a sketch and post here, sorry.
Anyway, here it goes:

Inverted LM4780 GC "a la Carlos" :

- LM6172 input op-amp (buffer)
- 2.2uf input cap, between the LM6172 and the input resistor.
- 1.2k RI (input resistor)
- 47k RF (feedback resistor)
- 1.2k resistors from NI input to the signal star gound.
- 2.7 ohm resistor from signal star ground to power star ground (this is important here).
- Join the two muting pins and connect a single 10k resistor to V-.

The sound?
Different for sure, but fantastic.
Anyway, I have an input op-amp, so I'm not testing in the same conditions.
The sound is dynamic, very detailed, and a little smoother on the treble (without loosing any detail) than the LM3875.
I would have a very hard time if I was to decide between the sound of my Pre and GC power amp and this integrated amp.
They are different, but they are both High-End.

In the end, I think I prefer the magic treble of the LM3875 (working with my pre), but this clearly is a question of taste.

 

[supereri]

Socket for the 4780

FYI the sockets for these chips are made by Loranger Part# 04555-271-6271. For 1-49 they are $40.50 ea and he told me that if I ordered 2500 he could sell the for $15 ea...LOL, not in this lifetime.

 

[SkinnyBoy]

It sounds as good as LM38xx series if not better. Also it drives 4ohm - 8ohm loads unlike LM38xx.

The LM38** chips will quite happily run 4 ohms..... I am not sure where people got the idea that they wouldn't....

 

[li_gangyi]

The LM3875 is not really good at 4 ohms...from my experience...

 

[carlosfm]

For 4 ohm speakers the LM3875 is not very good indeed.
The LM3886 is better for that, and the LM4780 too.
Check the datasheets.

 

[li_gangyi]

Yeah...means to say not all the 38xx series are suitable for 4 ohms load...

 

[carlosfm]

You can always parallel them.
But then, one single LM3886 has the same current output as two LM3875s in parallel.
The same for the LM4780.
Two LM3886s in parallel will drive almost everything.
Gotta test this one.

 

[li_gangyi]

So there's no real advantage going the 47xx series way?? other than having more pins...

 

[carlosfm]

So there's no real advantage going the 47xx series way?? other than having more pins...

Yes, the pinout is a real pain.
P-P is not practical here.

Some advantages of the LM4780 are:

- With only one transformer for the two channels, absolutely no noise with the volume at max.
- Exactly the same DC offset on both channels.
- You can make an amp even smaller.

I recommend the use of 2.200uf caps here (near the chip's pins) instead of 1000uf, this is a stereo chip, so you're feeding two channels.

 

[li_gangyi]

Ok...so that's all right...assuming I dun wanna parellel the 2 together...

 

[matjans]

lm3875 & 4ohm speakers

3875's can very well drive a 4 ohm load, if you lower the voltage somewhat.
I used 2x15 volt and 2x18 volt secondaries. Doesn't run hot or anything and sounds pretty nice. Liked the 15v psu better.

I'm currently using 3875 with 22V secondaries on an 8ohm load.

btw, anymore people using 4780s ? I'm interested in a few pbcs ...

edit: that is, in bridged mode

 

[li_gangyi]

I guess that will also be PCBs...instead of PBCs...

 

[matjans]

whoops, typo!

 

[li_gangyi]

hmmm...so any offers?? On the PCBs...

 

[theChris]

hmm, i'm also working on a PCB for the lm4780. mine will be milled at school, but i probably could make a standard etching overlay as well.

anyways, for the bias-current resistors, is there a need to give one to both channels or just use a common one?

 

[jackinnj]

Nat Semi's demo board

i cleaned up the perspective a bit -- here's their demo board: