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Old 16th June 2010, 02:21 AM   #1
jstan is offline jstan  United States
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Default Lifeless Sound at Modest Volume

I built a LM3875 amp based on the premium kit from audio sector which I'm using to drive a pair of Tannoy R1's. At higher volumes the system sounds beautiful, but at modest volumes the music has no life: other ways to describe it would be to say that the sound lacks energy or isn't dynamic. The Tannoy R1's are relatively inefficient speakers (87db), which I understand can be a problem for LM3875 based amps. I'm considering a couple possible solutions, but being pretty inexperienced in the diy hifi world, I wanted to get some opinions. I've considered building a preamp to increase gain and I'm considering modifying the amp by increasing the ps capacitance and adding a snubber. Would either of these help or do you guys have other ideas? Thanks.
-Jeff
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Old 16th June 2010, 03:09 AM   #2
adason is offline adason  United States
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sounds like you need loudness volume control
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Old 16th June 2010, 05:11 AM   #3
lgreen is offline lgreen  United States
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My own view is that the speakers are too inefficient for an LM3875 to succeed. You need a lot more power and control. Of course some opinions will differ but you asked so there it is.
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Old 16th June 2010, 06:16 AM   #4
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Quote:
Originally Posted by jstan View Post
I built a LM3875 amp based on the premium kit from audio sector which I'm using to drive a pair of Tannoy R1's. At higher volumes the system sounds beautiful, but at modest volumes the music has no life: other ways to describe it would be to say that the sound lacks energy or isn't dynamic.
As Audio Sector are kind enough to show a PCB layout on their website I'd say the problem you've got is that their layout is poor. They're using ground fill rather than star earthing. Whenever I find a design with such the sound tends to be harsh and lifeless, just as you're describing.

One very obvious problem is that the high current ground paths to the reservoir caps aren't separated from the audio signal ground. If you're handy with a craft knife you can probably fix this but its not much fun hacking grooves in the copper. The results will be worth it though
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Old 16th June 2010, 09:13 AM   #5
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my 2cents

many ,many other people have built this same amp and are happy with it.

difference between yours and other peoples are the loudspeakers.

Have you tried a differenct set of speakers and see what the difference is?
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Old 16th June 2010, 06:18 PM   #6
jstan is offline jstan  United States
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I too suspect the problem is the inefficient speakers. Unfortunately, the only other speakers I have are also inefficient (90bd Tannoy Saturns), so I have no "compatible" with which to test the amp. Do you guys think that a 3886 based amp would do better?

Abraxalito, I don't think that the problem is the ground, because the setup doesn't sound harsh at all, there are just no dynamics at lower volumes (it's almost the opposite of harsh).

Adason, what do you mean by a loudness volume conrol?

Thanks again for all the input.
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Old 16th June 2010, 09:32 PM   #7
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How much capacitance do you have per rail, and are you willing to increase it as a test?
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Old 16th June 2010, 09:47 PM   #8
jstan is offline jstan  United States
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Right now, there's 1500uf per rail (actually on the voltage pins of the chip, only 10uf per rail in the ps) which seems very low to me. I was thinking of adding 10,000uf per rail plus a snubber to the ps, but don't have the parts on hand and don't want to spend the money if people who know more than me think it won't solve the problem. Tyler, I take it that you think this would help?
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Old 16th June 2010, 09:59 PM   #9
tinitus is offline tinitus  Europe
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It could be due to your speakers lacking the finer resolution
Usually seems more apparent at low levels
But it aint so easy to achieve
And has nothing to do with money, or power
Its about balance

Some say big speakers cant play well at low levels
And it would kind of make sense, somehow
If it wasnt for the fact that I use 15" woofers, in a 3way dipole
And they are just fine at low level(SPL)
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Old 16th June 2010, 10:23 PM   #10
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What are you using for volume control? Is it digital by any chance?
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