What should be the optimim level of Input Signal to a LM3886 based amplifier

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How the input level signal to a gain clone amplifier is selected for the optimum use of its power?

Is this way correct -
Considering a gain of 21 (the Reference schematic given by NS in LM4780 datasheet, 1+(20/1)) for LM3886 or LM4780, and if the chip is operating at +30-30 volts. Load is 8ohm, so for power of 50 watts,
the output voltage swing is = sqrt(power*ohm) = 20 volts, and
hence input voltage level = 20 volts/gain = ~1 volt.

is it correct?
i have just finished a 3-way active filter based on this circuit,

3 Way filter

But when i connect it to my LM4780 amplifier, the sound output was quite low even at full volume :confused:

Can anyone please suggest how to raise the sound level,
( do i have to add a gain before or after the 3-way filter so that LM4780 chip gets enough input level signal).
 
Hi,
firstly, +-30V won't allow 20Vac at the output.
20Vac=28.3Vpk.
loss through the chipamp ~4V.
droop of the PSU on full power ~5V.
PSU voltage ~28.3+4+5 ~=+-37.3Vdc, not +-30Vdc.

for full power you need 20Vac as stated.
Input for full power = 20/21=950mVac.
most CD players put out a maximum of around 2Vac.
usually this is attenuated by at least -6dB and often by -30dB and we still consider it loud enough.

If you cannot get sufficient volume then something is wrong.
Look first at your speakers. Do they suit a chipamp?
 
If I bypass the 3-way filter circuit, i am getting the normal sound reproduction as it should be. I am using a My PC sound card output as source.

I have made the 3-way filter exactly as in the article(using opa4134 opamp), now i am facing this reduced output problem. All the filters in that article are at unity gain, so dues a gain stage is required at output or input).
 
here is the filter schematic
and the link for filter design - 3-way crossover

and i am using DANITY 6" 8ohm woofers, 3" mid and tweeter with it, these are runningexcellent with LM4780 with out the filter, BUT with filter the sound level is decreasing.
 

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Well from you tell us, it sounds like the problem is in the filter. And a possibility is that you have made a mistake somewhere and are filtering too much of the signal, or the wrong frequencies.

So check that out first. I know from experience it is very easy to make a mistake with filter circuits.
 
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