LM4651/LM4652 class D amps

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lawbadman

lawbadman

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Joined 2003
#1
Hello all,

It seems that these chips have been mentioned a few times but topics came to no real conclusion, so now I will have a go at it.

I want to build a few LM4651/LM4652 class D amps based on the audio application diagram in the datasheet (page 24 and 25). Can someone make the PCBs for me, or know were I can get PCBs made in the US for a good price, and done within a week or so?

Also I was thinking that I could just use perf board since the circuit is not very complicated, but I am a bit worried since high frequency is involved. So is it ok to use perf board or not?

Any suggestion is welcome.

http://www.national.com/pf/LM/LM4651.html
http://www.national.com/appinfo/audio/0,1819,968,00.html


Thanks
Lawrence
 
#2
Wouldn't it be much simpeler to use the Philips TDA8920? It is also available in a 23-pin, single row DIP style packaging and requires very little external components. Furthermore the BTL configuration will deliver up to 150-watts, enough for most applications I'd say. Oh, and in the spirit of DIY I suggest you also attempt designing a PCB yourself, else you're really taking the Y out of DIY.

Best regards,

Sander Sassen
http://www.hardwareanalysis.com
 
#3
Hi SSassen,

The TDA8920 was at the top of my list of amp to choose from, but I cant find any online store that sells it. If you know of any let me know.

My problem is that I need PCBs by next week and I have no experience with PCB design, plus the amp is class D with crazy high frequencies so it might be a bit difficult for my first try, and I have no scope.

But if you know of any other good high power (very important), inexpensive class D amps let me know.

I was thinking about just going with a regular LM4780 but I really dont want to be bothered with getting rid of all the heat it produces, since I would use 4 chips (parallel each chip), for PA and subwoofer use, thats why I want class D.



Thanks
Lawrence
 
#4
Use the example PCB from the datasheet.

It works nicely if you have access to a laser printer, or some other DIY method. I just did it a couple weeks ago.

Only thing you have to worry about is connecting the top and bottom layers. I soldered all components on both sides of the board, and used copper wire where there is no component lead.

Im still working on a power supply and pre-amp for it, so I cant tell you the final result.

So far it works, little hiss noise from the speaker. I could drop the output cutoff to take care of that.
 
#5
The gerber files and all the info you would need to have someone make boards for you is found here: http://www.national.com/appinfo/audio/0,1819,968,00.html

These chips can be difficult to work so be warned. You might want to go to this page: http://www.national.com/appinfo/audio/ and try out the Class D Design Guide to see if what you want is even possible. The Overture Design guide will help you with that LM4780.

The LM46521/52 full range design is only really good for about 100W. If you have a very stiff power supply you might be able to run higher. The biggest weakness of the LM4651/52 chipset is that it only has an abs max of 44V (+/-22V).

-SL
 
#11
Hi,

Sorry 🙂

You appeared to be asking for a completed layout and not PCB design tips for class D purposes.

I don't think you'll pick up many tips from seeing a completed layout though.

There's one post by Bruno Putzey made some time ago which goes into detail about how to make a good layout... If I knew the thread or had the link ...... hey I found it.

http://www.diyaudio.com/forums/showthread.php?postid=469427#post469427

Tripath also has a few application notes that give a tip on layout here and there, but I'll let you find those.

If in your travels you happen to come across any other good articles on that topic please post them.

Regards,
Chris
 
#19
Chris,
Thanks,
I will surely post if i come across someting good in Class D, thou i think Class D has very great potential as sub woofer application, and i have tried to make Amp with 4651/2 with single sided PCB, it just did not work.
I would go in for original PCB design given by national. So a i thought little more power is better and handy sometimes for small party operation that is the reason i was thinking of using 2 4652's in parallel.
 
#20
Hi,

You could try a dual layer PCB and use the component side as a ground plane.

I understand making PCB's does take many revisions and is costly.

Super efficient speakers are great for a class D DIYer, makes it more worthwhile playing with low powered designs.

What do you find unappealing about the typical module format?

It's the cheapest way to get clean high grade power, maybe not as fun though.

Regards
Chris
 
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