soundNERD said:
Hi soundNERD
The LM3886 is a low power version of LM3885 and comes included with the mute function.
As per the specs sheet, the LM3886 capable of delivering 68W of continuous average power to a 4 ohms load and 38W into 8 ohms with 0.1% THD+N
The LM3875 is capable of delivering 56W of continuous average power to an 8 ohms load with 0.1% THD+N.
http://www.national.com/ds.cgi/LM/LM3886.pdf
http://www.national.com/ds.cgi/LM/LM3875.pdf
So you are better off with a LM3875.
The pinouts of the 3886 and 3875 are a little different since LM3876 and 3886 incorporate the mute switch whereas lm 3875 doesn't. It is normally agreed that chips without mute are sonically better than chips including those. Well, don't look at me, i never said that
Pixo said:As per the specs sheet, the LM3886 capable of delivering 68W of continuous average power to a 4 ohms load and 38W into 8 ohms with 0.1% THD+N
The LM3875 is capable of delivering 56W of continuous average power to an 8 ohms load with 0.1% THD+N.
http://www.national.com/ds.cgi/LM/LM3886.pdf
http://www.national.com/ds.cgi/LM/LM3875.pdf
So you are better off with a LM3875.
On the surface this might be true, but a closer look at the sheets show a graph (Output power vs supply voltage) that puts the output for both at over 80W with 40V supplies. The limiting factor is the heat dissipation and the heat sink would have to be huge indeed. I think the telling stat is that peak for the '75 is 100W while the '86 will give instant peaks of 135W.
And while many people agree that chips without mute sound better, if you get to these very high levels, there is no protection for the '75. If anybody other than myself is handling the equipment, then I'll give up some sonics for an amp than can protect itself and/or the speakers.
ensen.
Thank You
Mika,
Thank you for this contribution. I know there are many interested which will enjoy trying the project. Looks like the stuffed PCB could be below $150 for 5 channels of HT. Combined with some TB satellites or something, this could be a potent package for a large group who don't have good HT access. I may well attempt doing my first PCB using your image for a project for a friend.
I used to work for Valmet in the US and have a few good friends who are Finns. If you're an F1 fan, I hope you get a good surprise at Japan.
Best Regards,
Sandy.
Mika,
Thank you for this contribution. I know there are many interested which will enjoy trying the project. Looks like the stuffed PCB could be below $150 for 5 channels of HT. Combined with some TB satellites or something, this could be a potent package for a large group who don't have good HT access. I may well attempt doing my first PCB using your image for a project for a friend.
I used to work for Valmet in the US and have a few good friends who are Finns. If you're an F1 fan, I hope you get a good surprise at Japan.
Best Regards,
Sandy.
Okay, now Im confused. Pixa says that the LM3875 sounds better and has more power, but then purplepeople says the LM3886 is better. So, which one really is better in terms of sound quality? Also, can the LM3875 drive 4-ohms? Would it run at 140wRMS into 4-ohms? Can it be bridged to drive a 4-ohm load at 280wRMS? If so, that is impressive power ratings. Final question: in bridged mode, which sounds better into 8-ohms, 3886 or 3875?
Thanks, Mike
Thanks, Mike
soundNERD said:
I did not say one is better, just that I am willing to give up sonics for durability. I have not heard a 3875-based amp, so I can only go by other opinions, which seems to point to the '75 sounding better. Even if that turns out to be true, I would prefer the '86 in a setting where others also use the equipment. In the privacy of my own office, I might choose the better sound, but in my living room, better just means longer lived.
ensen.soundNERD said:
Mike,
As far as bridging goes, I wouldn't recommend it.
The simple reason is, you feed an already amplified signal that has enough power to deliver 60W from the first amplifier into the second. The amplifiers may well be capable of 120W output with intermittent peak power output of 200W when bridged, provided you have adequate heatsinking. But you will get a lot of noise, and distortion will be higher than normal. This happens during the second amplification stage where feeding an amplified signal to the second amplifier will amplify the existing noise present in the waveform and induce some of its own.
Amplifiers are comfortable working with a low powered signal.
Moreover it is easy to drive a bridged amplifier into clipping and that's not what you would want. People always talk about how the signal from a CD player when passed into a preamplifier and then to an amplifier sends the amplifier into clipping easily whereas taking out the preamp from the signal path smoothens things out. The same thing happens with bridged amplifiers. Well, you can say that the preamp acted as a kind of "low powered bridged" amplifier
Most amplifiers when bridged, can drive a load not less than 8ohms since it presents 4ohms load for each amplifier. Taking it down to 4 ohms means each amplifier gets to drive a 2ohms load which is well below what most amplifiers are capable of. That might be serious trouble.
So, finally, if you want 140W getting pumped into your speakers, buil a single amplifier that's capable of 140W.
There are designs on the Net for amplifiers from 100W to 300W class AB's. What more do you need?
purplepeople said:
On the surface this might be true, but a closer look at the sheets show a graph (Output power vs supply voltage) that puts the output for both at over 80W with 40V supplies. The limiting factor is the heat dissipation and the heat sink would have to be huge indeed. I think the telling stat is that peak for the '75 is 100W while the '86 will give instant peaks of 135W.
And while many people agree that chips without mute sound better, if you get to these very high levels, there is no protection for the '75. If anybody other than myself is handling the equipment, then I'll give up some sonics for an amp than can protect itself and/or the speakers.
Jensen,
A little reiteration: The LM3875 can provide 100W peak power into 8ohms whereas LM3886 gives out 135W peak into 4ohms.
So the LM3886 should still be capable of 100W peak into 8ohms, although i am not sure if the LM3875 can be used at full power into 4ohms load without overheating it.
But i am sure there will be atleast one person who has done that. Maybe they can give us some insight?!
As for the graph of LM3886 you were referring to, i see you can get 80W+ into 4ohms with a rail voltage of 30V. But at the same supply voltage it barely crosses 40W into 8ohms. Although you can get 80W into 8ohms with a rail voltage of 40V, i don't find the ratings for 4ohms. i guess if you're using 40V rails and 4ohms load, you are in knee-deep $h!t!
If LM3886 is capable of 135W peak into 8ohms, do you thing these guys would have left that chip alone for this long? There are a whole bunch of power hungry freaks out there and they are the ones driving DIY to its limits and i see LM3875s referred to more often than LM3886s
Considering that most tweeters and midranges are rated for 8ohms and GCs make better amplifiers to drive speakers of this category, it makes sense to use an LM3875. And if you want the mute function with it, there is the LM3876! (This is gonna get Mike confused a whole lot)
I must say that this amplifier looks great! Very good job.
Your webpage was very informative, but is it possible for you to share your PCB file? My etching is not very good. Usualy they end up in the trash.
Keep up the excellent job!
PS: Where is the best place to buy the LM3875 chip?
HFosse
Your webpage was very informative, but is it possible for you to share your PCB file? My etching is not very good. Usualy they end up in the trash.
Keep up the excellent job!
PS: Where is the best place to buy the LM3875 chip?
HFosse
I think that i wont share all information of my digitally controlled 6-ch preamplifier, because im now busy with my final project in a school. I have now fully working prototype of 6-ch preamplifier. It consists volume control, level adjust (+/-8dB) for every channel, all adjustments are stored in EEPROM so you dont need adjust levels every startup and so on...So software is ready.
Hardware is PIC16F877A, 2x16 HD44780 LCD, CS3310 x 3, input buffers for all channels, power supply (+5V digital, +/-5V analog, +/-15V analog).
Im now working with remote controller and rotary encoder (as volume control). Next thing to do, is make some measurements, I hava allready measured bandwidth (1Hz - 270kHz -3dB) and some other basic things. It is very nice thing, that i cant see anymore processors oscillator frequency at output signal. Anyhow it isnt most important thing because processor is in SLEEP-mode when users isnt doing any adjustments.
Next thing to do, is measure Signal to noise ratio, anyone know how to do it on right way? And what measurements are important to do? My school have quite good equipments, as example EMC-laboratory.
Hardware is PIC16F877A, 2x16 HD44780 LCD, CS3310 x 3, input buffers for all channels, power supply (+5V digital, +/-5V analog, +/-15V analog).
Im now working with remote controller and rotary encoder (as volume control). Next thing to do, is make some measurements, I hava allready measured bandwidth (1Hz - 270kHz -3dB) and some other basic things. It is very nice thing, that i cant see anymore processors oscillator frequency at output signal. Anyhow it isnt most important thing because processor is in SLEEP-mode when users isnt doing any adjustments.
Next thing to do, is measure Signal to noise ratio, anyone know how to do it on right way? And what measurements are important to do? My school have quite good equipments, as example EMC-laboratory.
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