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Old 9th June 2014, 08:41 AM   #1
Philfr is offline Philfr  France
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Default 2 LM3886 parallel advice

Hi all,
Need to build a new LM3886 amp for subwoofer, load is near 3 Ohm, power needed about 100 watt..
What do you think about that :
http://www.audiophonics.fr/images2/4...6_LM3886_1.jpg
http://www.audiophonics.fr/images2/4...6_LM3886_2.jpg
What is the manufacturer?
Don't find schematic, only a same (I think) but with 3 LM's :
http://www.audiophonics.fr/images2/4..._Schematic.jpg
Thank's in advance.
Phil.

Last edited by Philfr; 9th June 2014 at 11:59 AM. Reason: title
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Old 9th June 2014, 09:30 AM   #2
AndrewT is offline AndrewT  Scotland
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BTL?
is that a bridged configuration?

If so, then a bridged pair of amplifiers sees a load impedance of half the load connected to the output.

i.e. connect a 3ohms speaker and each half of the bridge sees a 1.5ohms load.
Your need to DESIGN each amplifier to drive a 1.5ohms load.
This is NOT chipamp territory.
You are in the wrong section. Try solid state.

If you are looking for a parallel implementation, then look at National's advice in their PA100 & PA150 amplifiers.

If you don't understand the difference between bridged and parallel, then you should not consider building any multiple chipamp topology.
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Last edited by AndrewT; 9th June 2014 at 09:34 AM.
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Old 9th June 2014, 11:06 AM   #3
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you need a parlell kit, not a bridged kit.
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Old 9th June 2014, 11:57 AM   #4
Philfr is offline Philfr  France
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Hi,
Thank's, and sorry for mistake, yes I meant parallel like this :
PA100 DIY 2x LM3886 in parallel gainclone audio amplifier
So, do you know this kit :
http://www.audiophonics.fr/images2/4...6_LM3886_1.jpg
Or a another good kit ?
Phil.
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Old 9th June 2014, 12:19 PM   #5
AndrewT is offline AndrewT  Scotland
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The input impedance of Audio phonics is R1||R4||R10||R8, i.e. 10k||10k||10k||47k = 3k11
Is your Source able to drive that?
What bass response do you need?
The Input filter has an RC of just 6.8ms,
whereas for extended bass response most Builders would adopt somewhere in the range 50ms to 150ms.

I don't recommend any of the multi-chipamp implementations to any Beginners. They have too many problems that require knowledge to debug. That's why we have here, lot's of enquiries about broken amplifiers.
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Old 9th June 2014, 12:24 PM   #6
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Then, What would be a simple, (beginner) , way for building a amp to drive a subwoofer worth of 100 watts power(sub max power is 150 watts).
The amp needs to be simple in design and build for a noob and the components easily procurable at the same time it needs to be cheap .
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Old 9th June 2014, 12:48 PM   #7
AndrewT is offline AndrewT  Scotland
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Settle for 60W into 8ohms and learn how to build that properly.
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Old 9th June 2014, 01:06 PM   #8
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and most probably that will drive Your sub enough.
even if the sticker says 100 or 150 watts or be it.. 15 megakillogigaterra watts it may not handle more than say.. 30.
depends on the box, and the freqvency range.
most probably a ingle lm3886 will be able to drive it.
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Old 9th June 2014, 04:51 PM   #9
Philfr is offline Philfr  France
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Thank's all..
Andrew, you're right, maybe I should be building (as I know) a simple LM3886 with a good power supply..
68 watt is enough in most cases.
Any recommendations for a subwoofer working from 20 hz to 200 hz ?
And especially about power supply..
Phil.
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Old 11th June 2014, 04:41 PM   #10
tomchr is offline tomchr  United States
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Is this for home use or are you trying to start a night club?

If for home use, I recommend that you get an SPL app for your phone and measure how much SPL you actually want. Then do the math on how much power is needed.

I generally find that much above 85 dB SPL at the listening position makes my ears ring to the point where I can't fall asleep, so I tend to not crank it that loud very often. With my 87 dB efficient speakers about 2 m away from the listening position, it only requires about 1 W per channel to reach this SPL. This does not include room gain (5~6 dB typical), so the actual power needed is around 250 mW per channel. Heck, you can do that with a LME49600 buffer IC...

If you really want to rock the house off its foundation, I suggest looking at some of the more efficient drivers, such as the Selenium (now JBL, apparently) pro drivers. With a 96 dB efficient driver, you could reach 120 dB SPL with a 25 W amp under listening conditions similar to mine. That's enough to cause permanent hearing damage...

Power supply advice? Well. Now that we've figured out that it only takes a few hundred mW, the power supply question should be pretty straight forward to answer: Keep the ripple voltage reasonable, use a good local reservoir cap on the PCB by the chip amp, get the decoupling right.

~Tom
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