LM3886 very quiet

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Hi,
the pre-amp questions are the clue.

The "system" gain must be designed to suit the duty.
What is the output of your guitar?
What load does the Guitar need to see?
What is the sensitivity of the speakers?
What signal do they need to see.
From what the Guitar sends out to what the speakers need to see, you can design the system gain.
 
I dont have a preamp. Its just the LM3886. The load on the guitar must be al least 1Mohm as far as i know. The sensitivity of the speakers is 88 dB/W/m. In the spec it says Rated power: 15W, Maximum power: 50W. BTW whats system gain and how can I design it. Also, I tried a guitar effect and it louder but it is still not as loud as what i imagine 50W would be. I have a 25W fender amp and its much louder than the LM3886.
Thanks
 
Thank you for all the replies. But even when I connect it to my computer its still not that loud. I also double checked all the components and they seem correct.
I'll guess and suggest that setting Rin to 1M0 and gain to 200times (+46dB) will allow a guitar to overload a 3886.
So all I have to do is change R3 with a 1M resistor.
Thanks
 

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no.
You have to find out what load the guitar expects to see.
You have to find out what signal level the guitar is capable of sending to that specfied load.
You have to determine the maximum signal you expect the speakers to need.
From there you can (or with our help) determine the system gain.
You have to make your self informed, before you can take decisions, otherwise it's all guesswork and where did that get you first off?
 
About 40 or 45 years ago I built a guitar preamp/effects for my younger rockstar wanabee brother. The guitar pickups were magnetic coils and the output was in millivolts depending on how hard he hit the strings or where the volume and tone controls on the guitar was set. Guess 1 to 100 millivolts max. To get 50 watts out you need 20 volts at the speakers.( 8 ohms) Therefore you need a gain of 200 to 20000 total. Your amplifier has a gain of around 33. Your preamp should have a gain of at least 100 with an input impedance of 1 megohm. But I am just guessing and my memory is foggy.
 
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I am not sure but I think the guitar expects a load of around 1-1.5M ohms since most guitar effects have and impud impendance of 1-1.5Mohms. The pickup signal should be around 100mV RMS. But i dont now anything about the speakers signal.

You need a preamp.
Assuming your guitar pickup outputs ~100mVrms, and your amp (as shown) has gain of 34, that is ~3.4Vrms on the output - max. That equates to 1.4 watts on an 8 ohm speaker.
Your preamp should have a gain around 6 to drive your amp to max output.
 
I'll guess and suggest that setting Rin to 1M0 and gain to 200times (+46dB) will allow a guitar to overload a 3886.

That's bad advice. The 3886 does not have sufficient GBP (gain bandwidth product) to be used with a gain of 200. The output will have substantially reduced high frequency output, and will be highly distorted (due to lack of left over open-loop gain to correct HF distortion).

It's ironic that you blast the OP for not being "self informed" and yet you offer the above uninformed advice.
 
I have a DOD 250 preamp/distortion and I measured the gain pot with a multimeter so that it was 120kOhms and by looking at the schematic i think that this should give me a gain of 6. So I connected it to the amp. But when I measure the voltage at the speakers its still only about 2-3 volts.
 
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It's doubtful that a pedal has an output gain of 6. IT may have internal gain of some large number but clipped at the output with diodes - that supplies the distortion.

It's not difficult to build a simple preamp for this. It can be battery powered, which is probably the best way to do it. One opamp, a couple of caps and a handful of resistors.
 
I'll guess and suggest that setting Rin to 1M0 and gain to 200times (+46dB) will allow a guitar to overload a 3886.

That's bad advice. The 3886 does not have sufficient GBP (gain bandwidth product) to be used with a gain of 200. The output will have substantially reduced high frequency output, and will be highly distorted (due to lack of left over open-loop gain to correct HF distortion).

It's ironic that you blast the OP for not being "self informed" and yet you offer the above uninformed advice.
compare what I actually posted with what you interpreted.
I did not suggest that as a good way.
I guessed that a Guitar could overload a chipamp by doing what I think might be the case.
That is not a build suggestion.
I told him elsewhere to find out and use the answers to determine the system gain required.

I don't play guitar but I do know that electric Guitarists love to have a box of tricks to shape the sound that comes from their finger/s. Back to that pre-amp.
 
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