Simple Amp

[Christian]

Hi,
I'm new to audio electronics, and I am looking for a very simple power amp design, preferably with a chip-design, and not something complicated containing a lot of mosfets of transistors.

Doesn't have to be single-chip, can very well be briged, only I don't now how to bridge a non balanced amp.

Until now I have not found a amp-chip rated higher then about 80W, thats the LM3886, but I would like to build an amp rated higher then 500 W.


Since this is my first amp-project, any suggestions are very welcome.

Best Regards,
Christian V

 

[AudioFreak]

If you want that kind of power from chip amps, there are only a couple of options....

Have a look @ www.tripath.com for one possible choice.

 

[Dirk]

If you are completely new to amplifier building and DIY electronics in general, I would recommend something smaller than an amp rated over 500W. Voltages and currents involved are so high that you risk blowing up your investments (which are considerable for such a big amp) in microseconds.

Usually, chip amps do not come in very high power since only one device has to dissipate all the heat.

Regards,

Dirk

 

[hugobross]

If you're sure to build an amp of 500W as your first project; have a look at my previous thread, there's a link to the schematic and you can download the pcb too:


500W

Or, if you're patient enough I'm designing one at myself too, but I can't tell you when it's finished, tested and modified properly.

>> to Dirk: nice to meet someone here from Belgium too!!!

best regards,

Hugobross.

 

[paulb]

Another problem with chip amps is that they oscillate easily. Especially since this is your first amp project, I too recommend starting with something smaller. You'll learn a LOT on the first one.

 

[SemperFi]

A 500watt amp, that's simple? Ha ha, that's a good one. Not to be rude, but why not build an amp that sounds good, and not just for show-off?
That was kinda rude, but really, why do you want that much power? There are so many great simple amps out there but none with the power u mentioned. It's a shame to limit your options because of a rather ridiculous criteria.

 

[AudioFreak]

now i've got a little more time to write a reply I too will agree that while making a high power chip based amp is doable, there are many good reasons not to do it...... in no particular order........

1) 500W is a lot of power ... unless this is PA you absolutely dont need it

2) unless you have the right equipment, troubleshooting will be near impossible as osscillations usually occur @ very high frequencies in these amps...

3) quality is without a doubt better than quantity..... there are a number of simple projects or kits available that should pose little problem to the beginner...

 

[Christian]

Thanks for the pointers, I think I'll go with less output power.

I have done some experimenting with the LM3886 chip, but never put it together into an amp.

If there is anyone wo knows how to easily bridge this chip, I would be more than thankful. The schematic I use can be seen here http://www.fortunecity.com/tinpan/inutero/547/lm3886.html

I do not have a balanced input signal, so is it even possible?

Best Regards,
Christian V

 

[SteveG]

Christian,
National has an application note on their web site for the 3886 (search for BPA-200) that tells you how to use multiple chips in bridge and parallel modes to get 200 watts out of them. I would attach it, but it's too big.
I am with the others though... I think that it's best to start simple. It will probably sound better too. Try a Zen or something.
Steve

 

[Jamie F]

There are a number around, but this is the most thorough explanation of the issues I have seen:

http://www.national.com/appinfo/audio/files/BPA-200_Application_Note.pdf

It is also a scalable design.

Jamie

(It's also the one Steve refers to above)

 

[paulb]

Also see project 19 at:
www.sound.au.com

There are also articles there about bridging amps. Be careful, a bridged amp is effectively running into half of the load impedance: for example, an amp needs to be able to drive 4 ohm loads to be used in a bridged amp driving an 8 ohm load.

 

[AudioFreak]

one of the probs with the LM38xx based amps is even if you series/parallel them, they have a relatively low max voltage swing for high power amps unless you run into 4ohms or less then you need to put plenty of them in parallel to overcome the current limitting circuit

 

[paulb]

Yes, many have said those amps get ugly if the overcurrent protection kicks in. Don't push it too hard.

 

[AudioFreak]

those amps get ugly if the overcurrent protection kicks in

Now that must be the understatement of the month

 

[SteveG]

rethinking my previous post

I know that these things can get ugly if the spike overcurrent kicks in, but in rethinking my reasoning behind building something else, a couple points in favor of the chips come to mind, especially for someone new.
1. they are cheap! 5.23 each at digikey in 1-quantities, less for 10, I believe. You could afford to run eight of the suckers in parallel, for about $42!
2. the example design looks like it has minimal components, and would be extremely easy to build.

Sometimes I find myself falling into the trap that everything has to be bigger and better than... I have to remember what it was like to build something simple and get it to work. Hey, if you want to take the chip route, go for it! Let us all know how it works.
Steve

 

[tiroth]

Even $42 is a lot of money in outputs when you blow them all up at once. Perhaps you could build a couple discrete (still LM3886 based) amps, get them tested and working, then bridge them and build a couple more. You could be more amibitious and use 2 chips per output, ending up with 4 parallel per amp, without the same risk of mass destruction.

 

[AudioFreak]

if you parallel em you really need to use the servos as per the example.... LF411ACN or TL071 aint 2 bad for this cause all they do is form integrators but i'd use something a little better for the other opamps...

 

[JBL]

I'm not sure that this would be a good idea putting 8 chip in paralelle is not very a good thing.

The power will be limited by the voltage swing of the chip anyway. And it will not really stop the protect of the amp. speaker with low impedance are very reactive and cable impedance become more and more important. And the current balancing resistor after each chip are going to be somewath high if you d'ont want each amp driving eachother.

It would be alot simpler just to build a lorge mosfet amplifier than messing with eight chip in parallel.

 

[JBL]

Oh and if the speaker impedance is low each resistor in serie with the chip is going to dissipate alot of heat and it's alot of wasted energy

 

[djk]

If somebody in the USA can scan and post a schematic I can show you how to build a 500W amp, 800W peak, with only $20 worth of semiconductors. It uses the LM3886 as a driver and does not require a bunch of servos to balance out everything. At the voltage and current required the output stage has over 1.5KW of safe area and this design also has short circuit and thermal protection. I'm thinking this would be a very good match for a DIY subwoofer like the Shiva.