> anybody tried a LM4780? think it could possibly sound good like a 3875?
Sure looks to me like a dual LM3886, with maybe some small 20KHz difference in bias or stray coupling.
Also looks to me like it may not really be out yet. There may be one production run for sampling, and they may not make any more unless somebody places a Big Order.
That is a lot of pins and they are VERY close together (0.040"). And this thing will need a HEAVY heatsink base to pass 125 Watts of dissipation. It almost makes more sense to use two LM3886. Easier to wire, and you don't have all that heat coming down in one place.
As a PA amp: it works great up to a point. Start paralleling speakers down to low-Z, and the Overture amps will clip and shut-down where a good PA amp will huff and puff and keep putting out most of rated power or more. You can't beat dozens of devices.
Sure looks to me like a dual LM3886, with maybe some small 20KHz difference in bias or stray coupling.
Also looks to me like it may not really be out yet. There may be one production run for sampling, and they may not make any more unless somebody places a Big Order.
That is a lot of pins and they are VERY close together (0.040"). And this thing will need a HEAVY heatsink base to pass 125 Watts of dissipation. It almost makes more sense to use two LM3886. Easier to wire, and you don't have all that heat coming down in one place.
As a PA amp: it works great up to a point. Start paralleling speakers down to low-Z, and the Overture amps will clip and shut-down where a good PA amp will huff and puff and keep putting out most of rated power or more. You can't beat dozens of devices.
li_gangyi said:
unfortunately the stereo 50 and 60W chips have too many pins to fit in a veroboard/breadboard with a standard track pitch even if you bend the pins significantly (not recommended)
see here
http://oc4free.scalded.net/amplifier/amp3.html
Please
I got some samples from national of the 4780's. It has been a real pain wiring it up. The pins are smaller and a lighter gauge that one would expect. I carefully clipped all of the NC pins off and then very carefully bent them to plug into a more usually spaced protoboard.
Results? Not sure yet as I just got it playing. I would not want to go through doing it again. SO if someone builds a bog-standard PCB for these, I will buy 4 of them.
I got some samples from national of the 4780's. It has been a real pain wiring it up. The pins are smaller and a lighter gauge that one would expect. I carefully clipped all of the NC pins off and then very carefully bent them to plug into a more usually spaced protoboard.
Results? Not sure yet as I just got it playing. I would not want to go through doing it again. SO if someone builds a bog-standard PCB for these, I will buy 4 of them.
Got the LM4780:s, designed the PCB, and i have almost all parts soldered on the board.
I had to ask a friend in Canada to order the samples, because it was impossible to get the samples direct to Finland...
The package is nonstandard (as far as i know). Hopefully "mt200" type mica washer can be used.
My LM4780 page is here:
http://hepso.dna.fi/misc/LM4780/lm4780_amplifier.html
Picture, showing the board in real life:
http://hepso.dna.fi/misc/LM4780/lm4780.jpg
I had to ask a friend in Canada to order the samples, because it was impossible to get the samples direct to Finland...
The package is nonstandard (as far as i know). Hopefully "mt200" type mica washer can be used.
My LM4780 page is here:
http://hepso.dna.fi/misc/LM4780/lm4780_amplifier.html
Picture, showing the board in real life:
http://hepso.dna.fi/misc/LM4780/lm4780.jpg
I don't like inverted mode after i realised that it causes problems when doing loopback testing - ground current error is duplicated in inverted mode vs. canceled in non-inverted mode (assuming unity gain).
Anyway, it is rather easy to modify the board for inverted mode. All you need is sharp knife to cut some tracks.
Anyway, it is rather easy to modify the board for inverted mode. All you need is sharp knife to cut some tracks.
I built an amp using the LM4766T. The sound is very good out of it. I am running it in bridged mode, delivering 160W RMS into 8-ohms. It would be nice to run 4-ohms, but it cannot run it (Believe me, I tried on a 4-ohm sub). I would stick to the 3886, though. Remember, power doesn't relate to loudness or quality. The 3886 will work great for your application as a PA Amp
Well, my LM4780 PCB amp is now working. Had to change ground traces a little, to get rid of hum. Now it works as well as my dual LM3886 amp. No case yet...
http://hepso.dna.fi/misc/lm4780/lm4780_amplifier.html
http://hepso.dna.fi/misc/lm4780/lm4780_amplifier.html
For sound quality i can only refer to the RMAA results (done with my USB DAC/ADC). I could hear some hum in the first version when listening with my Sennheiser HD280 closed headphones connected to the headphone connector, but after some changes in the ground traces the hum is now just barely hearable. It sounds perfect to me. I have engineer attitude, i trust the measurements more than my feelings about it. The reference card is probably better with shorter traces, but i think this one is good enough. The PCB can be done even with hand drawn dalo-pen (or Edding permanent marker) technique (which i used in the prototype).
LM4780 PCB
In continuation to my earlier posts here is the double sided LM4780 PCB (not actual size) layout.
I will take out the completed boards from the amplifier cabinet, take a photograph, scan it and post here soon.
1.) star ground.
2.) absolutely no hum.
3.) 4.8X2.7 inches.
4.) designed to include interference suppressing components.
5.) no jumpers.
6.) can also be used as per National Semi application circuit.
7.) can be used for parallal operation(not bridge though).
8.)bypass capacitors very close to power supply pins avoiding oscillation.
9.) High current capable power traces.
10.) Signal traces away from power and high current traces.
Green: Bottom Layer.
Red: Top layer.
Mahendra Reddy
In continuation to my earlier posts here is the double sided LM4780 PCB (not actual size) layout.
I will take out the completed boards from the amplifier cabinet, take a photograph, scan it and post here soon.
1.) star ground.
2.) absolutely no hum.
3.) 4.8X2.7 inches.
4.) designed to include interference suppressing components.
5.) no jumpers.
6.) can also be used as per National Semi application circuit.
7.) can be used for parallal operation(not bridge though).
8.)bypass capacitors very close to power supply pins avoiding oscillation.
9.) High current capable power traces.
10.) Signal traces away from power and high current traces.
Green: Bottom Layer.
Red: Top layer.
Mahendra Reddy
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