2 LM3886 BTL advice

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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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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.
 
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 .
 
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.
 
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.
 
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
 
Hi Tom,
Maybe you are right..
Sub is two Alpha 15A in H frame, so they give about 95 db (with what you call room gain, I prefer say "walls effect" because listening room is not a amp).
If I connect TA2020 , it does not work, TDA 2050 (17/0/17 volts) it does not work too. No bass magnitude, no bass dynamic, flat sound.
If I use mosfet amp (190 watts, weight 18 kg), it's works.
Tell me why ?
Thank's in advance.
Phil.
 
Contrary to other advice, I say "go ahead and build it" (the dual, parallel, integrated-chip amplifier)

ONE important thing though - it'll be critical to shim the gain of each half to be quite similar and symmetric. LOOK AT the PA-100 diagram. Note that there are 3 resistors in parallel (cheaper than buying a big wire-wound resistor) on the output of each chip-amp. These are called "current steering" resistors, since they work to decouple the load from the output of each opamp a bit. 3 resistors each, at 1/2 ohm is 1/6 ohm per stage. Two of those in parallel (the two stages), and you're now at 1/12th effective ohm of series resistance to your subwoofer speaker.

Since "ohms is ohms" and P = I²R ... with no squaring or other "power" fiddling with the R, then if R = R1 + R2, you can also say that P = I²R1 + I²R2 = P1 + P2, etc. Which is to say, power delivered will be shared by the impedances in series, in proportion to their values.

Therefore, for a nominally 4 ohm subwoofer, and a 1/12th ohm series current-steering resistor network, 2% of the output power goes to heat the resistors instead of powering the load. And, given our memory of decibels ( dB = 10log10( pA / pB ) ) then

dB = 10 log10( (1 - 0.02) / 1.00 )
dB = 0.088

So, you'll be losing a completely inaudible 0.1 dB (close) of sonic energy. Seems like a good trade-off.

NOTE though - all this assumes that you use precision resistors for R3, R4, R8 and R9 at the least. You'll probably want precision resistors for R2 and R7 as well. These are the resistor values that set gain for each half of the parallel circuit.

GoatGuy
 
Products_ORION


The problem with an open baffle is that it is very inefficient at low frequencies. So you need a lot of power for a sub. Try one of those drivers in an enclosure to hear what is being lost at low frequencies.

One amp per driver and an active or dsp filter to boost the sub bass is what I would go for. You could place the amps and filters close to the speakers.
 
Hi Mark,
Linkwitz use two driver with low Qts, so they need a boost and bass drop compensation..
In my cas I use Alpha15A with hight Qts, 1,26 in OB and near 1,5 in H frame.
The predict with MJ King sofware (at listening position 3,5 m) :

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The mesurement :

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Where did you see I need a boost ?
Phil.
 
Nice looking build. I had checked them out before posting.

I am convinced you know more about your speakers than I do.
I just don't see how they can output 20 Hz. The driver has a Fs of 41Hz, placed in an open baffle that acts as a high pass filter.

Even if you don't need the baffle compensation, I would still use an active or DSP filter and one amp per driver. This configuration simplifies the amp design with all the advantages of active filters.
 
I do not try 20 hz or 30 hz, cause cone displacement is 1,25 mm at 30 hz for only 1 watt.
Cone displacement is the big problem with OB at very low frequencies.

Class D ?
I knaw several chipamp, but I never heard class D amp, in doubt I prefer what I know.. Maybe I wrong.
Phil.
 
ONE important thing though - it'll be critical to shim the gain of each half to be quite similar and symmetric.

Yep! These days 0.1 % tolerance resistors are only slightly more expensive than dirt. Don't bother matching your own resistors. Just buy the 0.1 % resistors and use them in the few critical spots in the circuit. You only need two precision resistors per amp channel if I recall correctly.

~Tom
 
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