Want to build a 300 watt stereo power amp

AudioMike

Member
2010-07-15 1:01 pm
UK
Hi folks,

After having sucessuflly built a 2x30watt amp, I'm now interested in building a 300 watt Stereo power amp. I'd like to build a 2 x 150 watt (approx) circuits into a 19" rack type case.

Can this be done with say 2 x LM3886 chips on each circuit? If so, does anyone have or can recommend any schematics or PCBs.

Thanks in advance.
 

ChrisA

Member
2008-01-08 12:22 am
Hi folks,

After having sucessuflly built a 2x30watt amp, I'm now interested in building a 300 watt Stereo power amp. I'd like to build a 2 x 150 watt (approx) circuits into a 19" rack type case.

Can this be done with say 2 x LM3886 chips on each circuit? If so, does anyone have or can recommend any schematics or PCBs.

Thanks in advance.

First, Why 300W? How did you determine you need that much power? Maybe you don't. There are good resons for needing a big amp. I need one also but do make sure you have one of those reasons or you will just waste your money. In my case I happen to own a pair of hugely in-efficient and large 1970's vintage Infinity speakers. I'm working on a tube based design of about 100 WPC.

At 300W you are pretty much out of the "chip amp" range. But if you want something very much like a chip amp, in that all you do is add power, a chassis and connect it up then look at this
PM224 MOSFET Power Amplifier Module, High Voltage Power Amplifier
 
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First, Why 300W? How did you determine you need that much power? Maybe you don't. There are good resons for needing a big amp. I need one also but do make sure you have one of those reasons or you will just waste your money. In my case I happen to own a pair of hugely in-efficient and large 1970's vintage Infinity speakers. I'm working on a tube based design of about 100 WPC.

At 300W you are pretty much out of the "chip amp" range. But if you want something very much like a chip amp, in that all you do is add power, a chassis and connect it up then look at this
PM224 MOSFET Power Amplifier Module, High Voltage Power Amplifier

There are ways to get more power with chip-amps...you just have to know how to do it. Take a look:

http://www.national.com/an/AN/AN-1192.pdf

Scott
 
Hi,
try the "Lynx" amp by Jan Dupont. If for no other reason his build instructions from his website are excellent. Actually the best instructions that I have come across) It's a very powerful amp and there is a pcb group buy going on at the moment.

It's not a chip amp but check out the specifications and decide for yourself.
 

tryonziess

Member
2007-04-13 12:15 am
audio mike,
Having been successful with the low power chip amps you could try to build an amp with the lme498xx chips. they have very high voltage ratings and a member on this forum pansonaudio.com has some very nice kits available.
You will be getting your first try at a semi discrete setup and have a very nice amp when completed. National states these chips can be built to over 500 watts. This should put you in the power territory you want.
Just a note the Jeff Rowland chip amp running 6 lm3886 devices in bridge parallel was rated at 300 watts into 4 ohm loads. I have built this amp and can tell you it sounds very good but gets too hot when run hard on troublesome speakers. You can find pcb's for this Jeff Rowland clone here at diy audio. If you go to shine7.com you can read all about this clone.

Tad
 

ChrisA

Member
2008-01-08 12:22 am
There are ways to get more power with chip-amps...you just have to know how to do it. Take a look:

http://www.national.com/an/AN/AN-1192.pdf

Scott

Yes, I know a series/parallel setup would work for him. But for a 300W stereo amp he'd need a total of as many as ten chip amps. May as well use mosfets. But we don't know what he needs maybe he as an 8 ohm load or maybe 4 ohm, maybe 100WPC is OK?
 
Yes, I know a series/parallel setup would work for him. But for a 300W stereo amp he'd need a total of as many as ten chip amps. May as well use mosfets. But we don't know what he needs maybe he as an 8 ohm load or maybe 4 ohm, maybe 100WPC is OK?


He said 300W stereo, but then said 2x150..so I thought the BPA amp would work for him.

-Scott
 
DIY BPA300 6x LM3886 300W audio Amplifier

You need about 6 lm3886's to get 300W into 4 ohms.

3 in parralel bridged with 3 in parralel. with at least a 500VA transformer and about 40000uF per voltage rail.

DIY BPA300 6x LM3886 300W audio Amplifier

So for 300W stereo you would need 12 x lm3886's and 1kv 25 0 25 toroidal and a massive amount of filtering caps for all the current.

I built mine for an overkill mono subwoofer (80hz and lower) duty. Can't think that i will ever in my life need 300W stereo except if I become a public speaker which I won't because I don't do speeches.
 

tryonziess

Member
2007-04-13 12:15 am
The problem you will face with a high power chip amp is getting rid of the heat. There just is not enough surface area on the National transistors to transfer the heat to the heatsink. You also lose most of your long term reliability.
The LM3886 chips are prone to hum when subjected to numerous pcb tracks and external wires. You will need quite a few, they are not cheap, which complicates the trace layout and wiring.
Do you have your mind firmly set on using integrated chips? If not, there are several PROVEN and debugged layouts here on this forum. Quasi, for one has several good mosfet and bjt designs which are scalable to almost any sane power level. You could also build a very nice Leach amp. These will last a long long time.

Tad
 
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There just is not enough surface area on the National transistors to transfer the heat to the heatsink.


I disagree with that. or at least i'd like to change your sentence too

"If you go out of the maximum bounds of the datasheet of the lm3886 There just is not enough surface area on the National transistors to transfer the heat to the heatsink."

if you stay within the maximum voltage and load conditions set out by the manufacturer it all works fine for years.

maximums
a)
1 x lm3886 at +-35Vdc can drive 50W rms into an 8 ohm load , do not laod it with 6 ohm or 4 ohm or lower at +-35Vdc , look at the datasheet to see how big your heatsink should be

b)
1 x lm3886 at +-28Vdc can drive 68W rms into a 4 ohm ,do not load with 3 or lower ohm. look at the datasheet to see how big your heatsink should be.

c)
2 x lm3886 in parralel at +-35Vdc into 4ohms can drive 100W (each lm3886 "sees" 8ohm)
heatsink needs to be twice the size than situation in a.

d)
2 x lm3886 in bridge mode at +-28Vdc can drive 100W in to 8 ohm (eac lm3886 "sees" 4ohm load)
you will need double the heatsink size than situation in b.

if you need a higher power amplifier and you stick to within design rules for each chip you should have no issues.

Just do the math cost wise. at a certain stage it gets cheaper to rather use solid state.

I like bridging two chipamps for 8 ohms to get 100W with a 22V 0 22V toroidal and 50V rectifier capacitors much more than play with 44 0 44 AC and 80V capacitors.
 
I like bridging two chipamps for 8 ohms to get 100W with a 22V 0 22V toroidal and 50V rectifier capacitors much more than play with 44 0 44 AC and 80V capacitors.
I much prefer 35+35Vac transformer with 63Vdc smoothing caps to give a 110W to 120W into 8r0 amplifier. You don't need 80V caps and you don't need 44+44Vac for 100W.
I would expect >200W into 8r0 from 44+44Vac.
 

star882

Member
2007-03-19 8:41 pm
The problem you will face with a high power chip amp is getting rid of the heat. There just is not enough surface area on the National transistors to transfer the heat to the heatsink.
The TI chip I linked to is quite small, yet easily handles a lot of power. It's all about making proper use of your transistors.

For obvious reasons, discrete MOSFETs will easily outperform any integrated solution as far as power goes. And discrete IGBTs outperform MOSFETs. (IGBTs are used in motor drives for EVs, some rated to handle over half a megawatt!)
 

ChrisA

Member
2008-01-08 12:22 am
The problem you will face with a high power chip amp is getting rid of the heat. There just is not enough surface area on the National transistors to transfer the heat to the heatsink. You also lose most of your long term reliability.

That can't be true. Each time you add one more chip to the amp that chips comes in it's own case which has it's own surface area. It scales perfectly.

T
he LM3886 chips are prone to hum when subjected to numerous pcb tracks and external wires. You will need quite a few, they are not cheap, which complicates the trace layout and wiring.

Yes much of the advantage of a chip amp is lost when you need to put 10 of them in the same chassis. Now you have long leads and the wiring is no longer simple. This is why I pointed out that MOSFET PCB uo near the top of this thread. Likely something like that is the best way to go.

But really before you run off and build something think about the sound you want. Amps all have their own sound. Decide on that first, then build the design that sounds the way you like. I'm working on a large tube based amp now just because that is what I want not because it is simple or cheap. The entire purpose of any amp is so you can listen to music with it. So let the desired sound select the design.
 
The LM3886 chips are prone to hum when subjected to numerous pcb tracks and external wires. You will need quite a few, they are not cheap, which complicates the trace layout and wiring.

Tad

I am not really agree here. On the contrary. The LM3886 do have a (like a good opamp) very good CMNR. That said, I archived dead silent result with many LM3886's in one chassis, but all wired truth balanced differential wiring to each chip. In this setup, the LM3886 are even easier to wire up on a PCB with very good results then discrete designs.

In general any design need good lay out considerations for good result, no matter if it are chips, tubes or transistors.

With kind regards,
Bas