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Old 7th May 2012, 02:14 AM   #1
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Default 1000 Watt LM3886 Or TDA?

Hello everyone!

I am a bit curious as to how to get high power out of some LM3886 or TDA chips. I am looking into buying a 1600 watt 8 ohm sub woofer and was wondering how i can put around 1000 watts into this. I was looking at using a lot of LM3886 chips/kits. I ran across the BPA200 schematic and was wondering if something like this would work. Bascially 2 x 4 LM3886's in parallel and then bridged. Would 2 x 8 LM3886's in parallel then bridged add more power? Or would that just split up the load?

Thanks in advance!
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Old 7th May 2012, 03:35 AM   #2
gootee is offline gootee  United States
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There are some basic power equations that impose some limits.

Power to a load R will be P = VČ/R which is equivalent to P = IČR.

Those expressions are valid for DC and for RMS AC.

We can also solve them for voltage and current:

V = √(P R) and I = √(P/R)

So, for 1000 Watts into 8 Ohms, V = 89.44 Volts RMS

V peak = (√2)(V rms) = 126.5 Volts peak

That's more voltage than the chipamps can handle.

The only way to get that much power with a lower voltage would be to lower the R value.
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Old 7th May 2012, 11:27 AM   #3
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Quote:
Originally Posted by gootee View Post
There are some basic power equations that impose some limits.

Power to a load R will be P = VČ/R which is equivalent to P = IČR.

Those expressions are valid for DC and for RMS AC.

We can also solve them for voltage and current:

V = √(P R) and I = √(P/R)

So, for 1000 Watts into 8 Ohms, V = 89.44 Volts RMS

V peak = (√2)(V rms) = 126.5 Volts peak

That's more voltage than the chipamps can handle.

The only way to get that much power with a lower voltage would be to lower the R value.
Wow thanks for the great information! I guess it looks like im either gonna have to find a 4 ohm sub or wire two of these in parallel. I can't even think of a chip amp that's capable of putting out 100 volts. I know the lm3886 is capable of about 40 volts... but does anyone know how many volts bridged? I guess I would only be able to achieve 500 or so watts at around 40 or 50 volts with the lm3886. Anyone have any other amp suggestions?

Thanks!
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Old 7th May 2012, 11:33 AM   #4
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Bridging the 50W LM3886 may develop about 200W in Bridge Mode.

I posted an article at Maplin Sub-Woofer Project which explains the maths behind bridging amplifier modules.

You'll need to drill down to Post #4

Last edited by KatieandDad; 7th May 2012 at 11:36 AM.
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Old 7th May 2012, 12:06 PM   #5
AndrewT is offline AndrewT  Scotland
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Bridging allows one pair of amplifiers to deliver double the power into double the load impedance.

If you start with a pair of 68W chipamps and bridge them, the maximum you can get is 2*68W into your new load. Note that two 68W chipamps can deliver 68W+68W into two loads. That is exactly the same maximum power output as for the bridged arrangement.

If you parallel chipamps, you can drive a load to twice the current. This allows one to halve the load impedance for approximately double the power. But that doubling of power cannot actually be achieved. The lower the load impedance, the worse that loss from theoretical becomes.

Let's take a 68W 3886 running at near maximum supply voltage.
It will deliver 68 into 8r0.
Bridge a pair of them and you get 136W into 16r0.

Now take 4chips and parallel & bridge them.
You can now drive half that 16ohm impedance, i.e. 8r0 and get nearly double that 136W. 250W might be achievable. 4 chips in BPA200 arrangement to get a maximum of 250W into 8r0. These cannot be used to drive a 4r0 load any higher than than that same 250W maximum !!!

That 4chip could be increased to 8chip in a BPA400 arrangement and could drive a 4r0 load from near maximum supply rails. Expect 450W into 4r0 as a sensible maximum power capability


Far simpler to pick up an lme49811 and use that to run on +-90V supply rails for big power delivery.
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Last edited by AndrewT; 7th May 2012 at 12:08 PM.
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Old 7th May 2012, 12:08 PM   #6
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That doesn't compute with the article that I posted above.

Their maths shows that you can get 4 x the power of a single amplifier module.

If their maths is wrong then I will eat my words.
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Last edited by KatieandDad; 7th May 2012 at 12:16 PM.
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Old 7th May 2012, 12:23 PM   #7
AndrewT is offline AndrewT  Scotland
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Their assumptions are wrong.
That invalidates the maths.
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Old 7th May 2012, 12:31 PM   #8
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Sounds like 49811 is what I need. It seems as though the max I can get out of a 3886 is around 400 watts. Using the bpa200. Is it possible to bridge two 3886s, then bridge another 2 and then bridge the outputs from the two bridged sets?
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Old 7th May 2012, 12:32 PM   #9
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by binsky3333 View Post
........... It seems as though the max I can get out of a 3886 is around 400 watts............
No, max is ~68W
Quote:
Is it possible to bridge two 3886s, then bridge another 2
No, I explained the options by referring to the BPAx00 arrangements.
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Old 7th May 2012, 12:39 PM   #10
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400 Watts is certainly pushing the limits of any assumptions in the maths.

150W in bridge mode is certainly possible.

More can be achieved into lower impedance loads with paralled LM3886s.

But why would you want to go down that route with easilly available Class D amps that can do 600W.
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