LM3886 Sounding too messy and less power than expected. - diyAudio
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Old 8th August 2006, 05:17 PM   #1
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Default LM3886 Sounding too messy and less power than expected.

Hi, I've built a power amp using LM3886. The sound is a bit too up front and less bass and power. I'm following the original circuit from National Semiconductor website. I would like to know is there any improvement could be made? One more thing, I would like to know is there any benefit if I parallel tow LM3886 together? Will it be sounding more control, more powerful and more bass? By the way, I'm feeding the LM3886 with +28vdc and -28vdc, will it be enough for 2 LM3886? I hope you guy can help me, thank you.
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Old 9th August 2006, 12:43 AM   #2
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How big are your rail caps?
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Old 9th August 2006, 01:14 AM   #3
Leolabs is offline Leolabs  Malaysia
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Quote:
The sound is a bit too up front and less bass and power.
Try to start from the power supply section.
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Old 9th August 2006, 03:41 AM   #4
bawang is offline bawang  Malaysia
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Try pushing the power input to +- 35V DC. Bigger caps, say 6,800uF for 2 channels. You can also try to parallel two LM3886s (ie PA100 configuration), which will push around 100W into 4 ohms. The power limit of around 50W into 8 ohms will remain, limited by power supply voltages. For more power into 8/4 ohms, try the BPA configuration. What is your speaker impedance?
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Old 9th August 2006, 09:58 AM   #5
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I'm using 8ohm speaker. I have already used 4 3300uF and 4 2200uF caps. I think I'll try to push the voltage up till around +-38vdc and see how is the sound quality. besides the +- voltage, is there any thing else that I can improve?
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Old 9th August 2006, 04:42 PM   #6
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By the way, you said that I should raise my voltages to +-38 vdc, but would it be too high especially when I use 4ohm speaker? I've read some article and were stated there +-28vdc is the best for LM3886, it is true?
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Old 9th August 2006, 05:05 PM   #7
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It's about thermals on your voltages rails and speaker impedance. For 4 ohm +/-28V is what National recommends. For 8 ohm it is +/-35V. You can run a little higher if running music since it is not as demanding as a sine wave. If you get a big heat sink and keep it cool enough you can run even higher. One amp I built have bridged channels using LM3886. They were fine with music but would over heat with sine waves after a few minutes. Probably not the best design but it was another fun project so not worried.

Caps will affect sound quality. Be sure the input cap is large enough in value to get good bass as well as the feedback cap (what National usually calls Ci) is also large enough. You can also parallel nice poly caps with these to help improve sound. Having enough rail capacitance will also help the bass, driving 4 ohms needs more than 8. Other ideas spread around these forums but those are the basic. If you have no DC from the source then you can remove both caps for best sound quality. Just be sure you know you don't have DC or it will get amplified to the load by the amount of gain you have, if Ci is removed. If Ci is there only unity DC gain.

-SL
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Old 9th August 2006, 11:26 PM   #8
lndm is offline lndm  Australia
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Could it be that the chip is offering more damping on the bass than the amp you normally listen with? Temporarily connect a small (1/2 ohm or so) resistor in series with the speaker and see if this moves toward the bass you want.
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Old 10th August 2006, 12:24 AM   #9
bawang is offline bawang  Malaysia
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Oops..... someone beat me to it.... The support from guys in this forum is great. Any progress? I'm in the midst of completing the PA100 configuration. Still have ground loop problems to iron out.
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Old 10th August 2006, 04:51 PM   #10
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Today I've found another transformer with 25v-0v-25v AC and +-38vdc. I've connected it to my LM3886 power amp and the result is the bass is tight and lower bass is more crontrol, but the same problem is still there, upper bass is still less than what I've expected. And 1 more thing is the LM3886 is quite hot, without any input signal, the heatsink temperature is around 43c, 5c more than the previous transformer. Is it normal? I also have changed the Cl cap from 22uF to 33uF. I think I'll add more e-cap and see what is the result.
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