LM3886 in parallel

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Hi

I was using only one of my 2.1 DIY amp to push my subwoofer, since the Onkyo receiver was doing all the work, bu the I found out that I can use 2 LM3886 in parallel to push my subwoofer, duplicating the power.

Theorically now, I am using 100w instead of the 50w, but what is the benefit of this? I didn't notice any difference in the sound at all. The only difference is that now they are a little bit warmer than before ( maybe becouse of the 2 amps working, duh!).

I was expecting that the sub was going to be a little more louder, but it is just the same volume.
 
Doubling the power should ideally only give you a 3dB difference in maximum output level. Depending on the speaker etc. you'll probably get a little less than 3dB which, due to the logarithmic nature of human hearing, is only a barely perceptible difference. Again, we're talking about _maximum output level, which you may or may not ever reach during regular listening - possibly only during loud bass drum hits or explosions in movies.

-j
 
Hi,
if you have a chipamp delivering a maximum output of 60W into 8ohms, then it is effectively driving the speaker with a 21.9Vac signal (~31Vpk).
Putting two of these chipamps in parallel gives the same drive voltage to the speaker, i.e. 31Vpk.
The amps try to deliver equal current to the speaker load, so each amp effectively deliver half the current that a single chipamp would do.
The parallel chipamps driving a 16ohm load (what each of the parallels sees as a load) will probably achieve a maximum output of ~32Vpk (+0.3dB).
If you can hear that increase of 0.3dB you will be doing very well.

Don't even think about bridging the chipamps.
Each chipamp in the bridged pair will see an effective load of half the speaker impedance.
A 60W into 8ohm amplifier will see a 4ohm load and try to send that maximum signal of 31Vpk into the 4ohm load. It will shut down repeatedly due to over current and over temperature.
It might just about manage 28Vpk on a transient. That is equivalent to ~56Vpk into your 8ohm speaker. About 200W into 8ohm.
You are going rapidly into melt down.
You will need to redesign the amplifier to allow it to be bridged.
Just to put you off a bit more all these chipamps are crippled by the very limited peak current they can deliver and this gets worse as the chips heat up.
 
LM3886 in parallel needs high precision

Theoretically now, I am using 100w instead of the 50w, but what is the benefit of this? I didn't notice any difference in the sound at all. The only difference is that now they are a little bit warmer than before ( maybe because of the 2 amps working, duh!).
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The reasons for paralleling is the presumed ability to drive a 4 ohm speaker with same rail voltages of an 8 ohm, IF the gains are perfectly matched. If not then the mismatched voltages produced will create circulating currents in the amp chips causing heat and inefficiencies. Tiny voltage mismatches can produce huge currents across the small output ballast resistors (typ 0.1 ohm). Probably best to tweak the final gains to within 0.1% or less. The initial tolerance build up using 4x 1% resistors is not good enough. The circulating currents may be the cause of your running hotter. Parallel operation s/b really done by extra precision and not for newbies to achieve the 3dB power gain.

circulating currents with 0.1%
Ipk =0.1%*30V /(2*0.1)=1.5A still high
 
Denis.BR said:

I was expecting that the sub was going to be a little more louder, but it is just the same volume.

Unless you boost the power supply voltage to max for 8 ohms
And drop your speaker impedance, it will be the same maybe worse (Vgains matched?). If you just add another sub in parallel you can see the most gain in volume and power.
 
Hi,
chipamps were designed and sold as a cheap way to power the internal speakers of cheap audio, be it a radio or a TV or a computer screen.
It was discovered, after the event, that tweaking the circuits surrounding the chipamps could allow more than adequate audio performance to be extracted from these "designed to be cheap to assemble" offerings.
Since then higher quality better protected versions have been released to power upper market cheap audio products.

Expecting High Fidelity from these chipamps is not a matter of course. It takes great care and attention to detail to allow good quality sound to come out of these chipamps, but even so they are crippled by their specification for their original duty.
I think that this shows well in the peak current output from these products.
This can never be overcome. National as a major producer of these "improved" chipamps does no credit to itself by hiding how low the peak current limits can fall during elevated temperature operation.

Paralleling is just one example of a bad way to try to extract high currents into low impedance loadings from an unsuitable chipamp.
Just accept that these things are designed for higher impedance loads and nothing else.
 
helo guys out der,,its my frst time here in this furom..i get interested in building lm3886--PA100.I BUILD ONLY ONE CHIP,,since i dnt hve yet available power supply,i made a temporary PS with 2 ampere 12v center tapped transformer,den it gves me a filtered output almost 34vdc...i impressed wen i tested the suond is good...den i get confused when i measured at the output--speaker terminal.it gves me 16vdc???is it normal hving this votages in speaker terminal???.since it says there that must be DC OFFSET NEAR TO ZERO.PLS HELP ME....but sound is good

by the way im not fluent in english coz its not my mother tougue;)
pls pardon my grammar....tnx




DARREN of PHILIPPINES:)
 
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