A different Chipamp - LM4766

[JesseG]

Hey All:

I have been messing around with a different chip from National - the LM4766. This is a great little bit ofsilicon - stereo @ 40wpc, the usual National stuff like SpiKE, seems like a little brother to the 4780. BUT - it is only a 15 pin package, VERY easy to implement (7 Rs, 4Cs and that's it!).

Mine is built exactly from the National datasheet with 1,000uF PS caps, 20k metal film feedback Rs, 1k mf and 22uF to clamp feedback to ground and a dual 100K pot between the input and In+ in place of the 1K input R specified. The amp is absolutely silent with no input signal.

This one is running of a +/-32V PS and barely gets warm (nice BIG heatsink from an Intel Xeon processor) and makes the 92db/w bipoles play really quite loud, with the sound quality every bit as good as the 4780 so far as I can tell.

Here's some pix - whadd'a y'all think?


Inside view

Jess
Alert bay, BC

[JesseG]

Sorry 'bout the pix - this should work

[JesseG]

Now, the back panel



The Canon is the feed from the +/-32V PS.
The heat sink is, as I said above, from an older Intel Xeon CPU

[JesseG]

And the silly little box at work in my system

[Russ White]

Great work!!! The amps not bad either, but hey those are some nice speakers.

[JesseG]

I can't take credit for those - I just get to enjoy them. They are bipole transmission-lines designed by Dave Dlugos (Planet10) from Victoria, BC and built by Scott Dunn of Campbell River, BC.

They use CCS drivers and sound as good as they look.

[lineup]

Yes, a nice project and good work, JesseG.


I searched for some info of LM4766.
It is a Dual 2x40Watt and in same line of chips as LM4780 - The Overture.
Here is National product page: http://www.national.com/pf/LM/LM4766.html

General Description

The LM4766 is a stereo audio amplifier capable of delivering typically 40W per channel with the non-isolated "T" package and 30W per channel with the isolated "TF" package of continuous average output power into an 8 load with less than 0.1% (THD+N).

The performance of the LM4766, utilizing its Self Peak Instantaneous Temperature (°Ke) (SPiKe™) Protection Circuitry, places it in a class above discrete and hybrid amplifiers by providing an inherently, dynamically protected Safe Operating Area (SOA). SPiKe Protection means that these parts are safeguarded at the output against overvoltage, undervoltage, overloads, including thermal runaway and instantaneous temperature peaks.

Each amplifier within the LM4766 has an independent smooth transition fade-in/out mute that minimizes output pops. The IC's extremely low noise floor at 2µV and its extremely low THD+N value of 0.06% at the rated power make the LM4766 optimum for high-end stereo TVs or minicomponent systems.

Datasheet in PDF download: http://www.national.com/ds.cgi/LM/LM4766.pdf

[jleaman]

Originally posted by JesseG
I can't take credit for those - I just get to enjoy them. They are bipole transmission-lines designed by Dave Dlugos (Planet10) from Victoria, BC and built by Scott Dunn of Campbell River, BC.

They use CCS drivers and sound as good as they look.

I rmember listening to these. They are nice. How do you like them ?

[sangram]

Umm I have to differ, I've used the 4766 and they don't have the same type of sonic signature as the 4780, everything apart. They handily beat out most commercial amps I've heard though, and they sound good, but not as good as the 4780.

What I like about that chip is that P2P is as easy as pie, but that's about it. It makes an enjoyable experience but they don't have the same drive capability as the 4780s. The point is you're using FR125s, which are pretty easy to drive compared to some of the monsters we have to deal with down this side of the planet.

Therefore the first set I built came out a little thin in the lower registers - fast-paced and coherent, but not very solid and rounded. The same supply and (not very good) speakers when used with a 4780 just filled the bottom end in very nicely, and the heatsink (the same heatsink as the 4766) ran a couple of degrees cooler.

IMO it's just the lower current capability of the 4766 that leads to this. It's also a more economy oriented chip (but only slightly) so it has slightly lower channel separation figures, but on the datasheet it quotes slightly lower distortion figures.

I still have three of the chips lying around (one with all its compnents soldered on to its thin legs but without a heatsink) and do plan to implement them in a small full range system, where I think they'll shine.

[JesseG]

Hi Lineup: thanks for posting the tech stuff.

I rmember listening to these. They are nice. How do you like them ?

Hi jleaman - on ss amplification, they are very good. A little thin in the midband, byt very fast and detailed with phenomenal bass from the 4.5" CCS drivers.

In fact, they are why I built a chipamp. Driven by tubes (my 12AQ5 PP amp is my fave) they are very thin in the midband and not a pleasant experience.

Hello Sangram

Therefore the first set I built came out a little thin in the lower registers - fast-paced and coherent, but not very solid and rounded. The same supply and (not very good) speakers when used with a 4780 just filled the bottom end in very nicely, and the heatsink (the same heatsink as the 4766) ran a couple of degrees cooler.

I agree with your observations - this amp chip is not a replacement for the 4780 and less so for the bridged 4780 design. It is good for an application where one does not need big power. I come from using 10w of tube power so this little 30wpc is quite a step up and drives efficient speakers very well within its design parameters.

On your point about the 4766 being a bit less expensive that 4780 - yeah, but these chips are all so inexpensive that I don't think it matters much.

The 4766's biggest asset is the ability to build a clean, quiet amp using p-t-p wiring. I'm not into pcb layout, so have to obtain boards from elsewhere. I once tried to p-t-p a 4780 and failed 'cause the pins are so small and easily broken.

All in all, I am very pleased with my little project and will keep it around for a long time even after I return to using my beloved tube amp.

Jess