Should it be enough !? Heatsink + Supply !

[-_nando-_]

Hi everyone !


I'll make an amp with four LM3886, using Parallel + Bridge configuration. My idea is parallel two, and two... Then I'll have two pairs, and bridge it!

With this big heatsink, and two 2x 5A 24V (10A 24+24v) supply, will it work happy!? The Load will be 8 Ohms ! After retification, the supply will be 33+33v, no problems?


Any tips to make it !?


I don't know yet how to do this parallel + bridge, but I'll start searching right now, if you can help me, I'll be glad !


Pictures bellow !



Thankkkssssssss !

[-_nando-_]

How could I forget!?

How many watts will this thing deliver? 33 + 33v, two pairs (each pair is two 3886 paralleled) bridged @ 8 Ohms!


Thanks again !

[-_nando-_]

40 views and no answer eheh... Why?

Well, I'm reading AN-1192 datasheet, any sugestions?!


Bridged circuits and paralleled ones I found a lot here in the forum, so, I don't need this answer (but will be very nice to have some...)... But I need to know, if this heatsink and supply is okay... Heatsink I think it is more than sufficient But supply worries me, 33+33v worries me too when driving a bridged circuit.


Thanks !

[jaudio]

-_nando-_ That is more than enough heatsink. You cut 2 four inch pieces(fin running Vertically not horizontally). The power supply VA is on the low side,so you wont get full power because the supply voltage will sag. To get an estimate of the output power goto www.the12.com and use the calculators. I would uses 24volt for the power voltage

After you read the datasheet,it should be a breeze

By the way that is a h*ll of a heatsink!!!

[Bazukaz]

Hi,
The heat sink should be okay. The larger - the better , there will never be too large a heat sink.
Note that insulator thickness is also important; for example , if you use insulator with thermal resistance of 0,6C/W , at 30W dissipation from each IC , the temperature on chips will be 0,6*30 = 18 degs celsius higher than at heat sink.
But , for bridge paralell version and 8 ohm loads , power dissipation should not be an issue.

[-_nando-_]

Thanks for the feedback !

The Heatsink is more than enough like I was thinking heheh


I don't know how many VAs is this supply... 2x 5A 24v = 10A 48V supply, and it can deliver 480W. I read the datasheet, and each CI should dissipate 40W, so 160W of total dissipation. My objective is achieve 200W of power in 8Ohms load, so if I get it, will be 360W of consuption from the 480W supply! I think its more than enough too.

Am I wrong? I don't have much knowledge about this !


Other doubt is about the voltage. 24 * 1,41 is 33V, is it too much? I don't think it is, because of the heatsink and the parallel + bridge configuration, are 4 3886s to drive one speaker, but I can be wrong !


I've read all that datasheet:

http://www.national.com/appinfo/audi...ation_Note.pdf

Everything is much more clear now, but the only doubt about the circuit design, is if I realy need the SERVO amplifier, or if it just will cost more and don't worth the implementation.

Sorry about all these questions, but as I said, I don't have that much knowledge... So, just two more !

Which opamp shoud be fine to use as input buffer and servo amplifier? Opa2134 can be used? And NE5532? I have them here. I know they're dual opamps, but as I already have it here, I'll use it!




Thank you !

[jaudio]

The two transformers Va is (5*24)*2=240VA. On the datasheet they use a 385VA transformers that is 30volts * 12.833amps.

With 24volt transformer and your heatsink dissipation is not a problem in the least.

I would use the OPA2134 it is a fet opamp,like the 411.

Go thru the datasheet one more time,it should clearup something for you. I have to read it about four times


Your transformers have 4 secordary wire is it 24+24?

[-_nando-_]

No, the transformes aren't center tapped, that's why I bought two !

I bought two, because I can have regulated supply with LM338 you know? But I was wrong when I bought it, because voltage isn't high enought to use regulators (at least more 5v will be necessary), so 338 is OUT, and I'll just use big caps, snubbers, and a good retification bridge, and the Supply is done ! Without 338 I'll have less dissipation too, so "more" heatsink to LMs...


OPA2134 as Imput buffer right?


What about the SERVO amplifier? Is it necessary to my objective? If I use this, NE5532 is ok?

And the most important, that I forgot, how does it sound? Sounds almost like a single 3886? I'm worried about quality... I need quality, not thaaat much, but I need it! If it don't have quality, it's more easy go to a Solid State design...



Thanks again !

[jaudio]

Ok

So it (24*5)*2=Va

Use OPA2134 as input buffer

It not absolutely nesserary,you can always match resistors to .1% and leave out the servo. Some say 1% will do but I have not tried, I used .1% resistors.

My amp sounds pretty good. It doesnt quite sound the same as a single LM3886

I cant tell if it is easier than go discrete. My just really getting into discrete components myself.

[-_nando-_]

About the sound, the best way to know it, is building and listening !

I'll just left the project if you said that the sound is horrible eheheheh !


Only doubt remains, my 240VA supply is enough to get 200W in 8Ohms? If it isn't, how many W will I get!?


Any tips and suggestions will be very welcome !