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Chip Amps Amplifiers based on integrated circuits

Yet another LM3886 lacking bass thread.
Yet another LM3886 lacking bass thread.
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Old 8th November 2018, 09:13 PM   #1
isaiahb is online now isaiahb
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Default Yet another LM3886 lacking bass thread.


First time posting here, I know it's a well discussed territory over the years but after hours of reading older threads and trying out different solutions nothing seems to work for me so I thought I would ask for your opinions before throwing more money at it.

My problem is, like mentioned in the title, disappointing bass performance from my LM3886 based amp. Mids and highs I like a lot actually. But it's not just a they-are-louder-than-cheaper-amps issue. I played some pure sine waves through it and around A1-C2 (55hz to 65 hz) it gets real quite suddenly. When I turn the volume all the way up it sounds like there is a light distortion too. This test I did with my computer, both with its onboard soundcard and a USB- soundcard, which is my main sound source. But the lack of bass is also noticeable with my record player + OPA2134 based RIAA preamp.

Now, the amp itself. It's the most simple design, I tried to build it after BrianGT's recipe, since reading about that one made me interested in building it. It's on a different PCB but I used the same values. Here are a some points to mention which might be asked:

1. There is space for an input cap so I have a 2.2 uF Wima there (replacing this with a wire did not have an influence on the lack of bass).
2. After reading about more capacitence on the board, I soldered 470 uF paralel to 100 uF caps and this did not have any influence either.
3. I have 8 ohm speakers. First I used a 120VA 18VAC transformer. Replacing it with a 225VA 24VAC transformer made it not better, bass sounds weaker actually.
4. Zobel network is there but no thiele network.

5. On the power supply board, I omitted the snubber. It has the first 2.2k resistor and the .1 uF cap between the pins of 10.000 uF cap.
6. The heatsink (one per channel) is rated 1,8 K/W. The termal compund used is Arctic MX-4.

I would be really happy if anyone has any idea what might be the problem and shares it with me because the joy of it working after wiring it all up for the first time is slowly replaced by the frustration of it not sounding good.
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Old 8th November 2018, 10:51 PM   #2
JMFahey is offline JMFahey  Argentina
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That chipamp (like all others) is ruler flat from infrasonics to ultrasonics and anything in between, so if you are lacking Bass I wouldn´t blame it.

Check your speakers instead.
Design/make/service musical stuff in Buenos Aires, Argentina, since 1969.
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Old 8th November 2018, 11:34 PM   #3
isaiahb is online now isaiahb
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Well, the same speakers (Bose Syncom tested) have no problem with filling the room with bass with my 50 years old amplifier (Dual CV40) so I don't think the problem is with them.
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Old 9th November 2018, 01:25 AM   #4
farley is offline farley  United States
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Do you have a schematic of your amplifier that you can post here? I've not experienced a lack of bass in the LM3886 I built, but I haven't tested it to any degree other than listening to it.
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Old 9th November 2018, 02:12 AM   #5
adason is offline adason  United States
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I suggest to put 8 ohm dummy load at output, drive it with say 1 watt, measure fr response, distortion, phase...and post the results.
I use RightMark audio software, it's free.
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Old 9th November 2018, 02:21 AM   #6
MAAC0 is offline MAAC0  Portugal
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Are You driving the amp with a low impedance source ?
Don't use phones or mp3 players since most of them lack bass.
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Old 9th November 2018, 02:50 AM   #7
abraxalito is offline abraxalito  United Kingdom
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Subjective lack of bass isn't going to be shown in the FR, it'll be due to inadequate PSRR. Noisy bass is perceived as lack.
I know you think you understand what you thought I said but I'm not sure you realize that what you heard is not what I meant - Alan Greenspan
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Old 9th November 2018, 08:37 AM   #8
00940 is offline 00940  Belgium
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The old dual amps have a reputation for "generous" bass. You might be used to a boost in that region, something the lm3886 would not provide. Maybe a simple EQ is in order ?
All that is excessive is insignificant. Talleyrand
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Old 9th November 2018, 08:54 AM   #9
mjf is offline mjf  Austria
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......yes, these old amps often have a loudness network built in (e.g. on the volume pot) that gives you more bass (and treble)..........
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Old 9th November 2018, 08:57 AM   #10
maty tinman is offline maty tinman  Spain
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LM3886 works better with 8 Ohms nominal or higher.

With 4 ohms nominal speakers, better idea two chipamps by channel.
"Comment is free, but facts are sacred" - C. P. Scott
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