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Old 24th April 2004, 02:27 AM   #1
cwteoh is offline cwteoh  Malaysia
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Default Sound Quality of LM3875T

I just finish building my LM3875T Amp. Tested, but sound quality is very bad. Is that mean I need to add a preamp or a tune control in front of it?
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Old 24th April 2004, 09:11 AM   #2
Will is offline Will  Malaysia
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You need to be more specific bout ur problems.

Start with circuit - which config did you build
What PSU caps are used,
Tx configuration
And the sound Q you are hearing.
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Old 27th April 2004, 01:50 AM   #3
cwteoh is offline cwteoh  Malaysia
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I am using 4 x 10CTQ140 as PSU Bridge with 2 x 10000uF before Vout, Toronoid Transformer 18v-0v-18v 6A
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Old 27th April 2004, 02:27 AM   #4
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teoh,
you have to e specific about your problem, does it lacks bass, or does the sound cracks up, or distortion?
a picture of your work will help here..
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Old 27th April 2004, 02:38 AM   #5
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Default What's that feedback loop?

Your time constant on the feedback loop is 10 seconds for the top path and 0.1sec for the bottom. I'm no expert, but what's going on with that?

-Robert
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Old 27th April 2004, 02:40 AM   #6
cwteoh is offline cwteoh  Malaysia
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OK... The unit is not with me... With the above schematic I am very happy that I can't feel any distortion or cracks up. But I heard bass-less. I can't feel any bass came out from the speaker. If it do so, it sounds like a bang from "an empty box". It doesn't sound solid at the bass level.
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Old 27th April 2004, 02:44 AM   #7
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Default What are the components?

How about listing the component types.

-Robert
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Old 27th April 2004, 02:45 AM   #8
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try taking out r32, c36, and c38
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Old 27th April 2004, 03:00 AM   #9
cwteoh is offline cwteoh  Malaysia
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I started the circuit excatly like the application circuit in datasheet but it was lack of bass and has ringing on output when I increased the volume. The ringing problem was solved using zobel network at output but still lack of bass. I understand that this LM3875 has lower input impedance and does it mean that I need to add additional opamp stages to make it becomes high impedance?
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Old 27th April 2004, 04:10 AM   #10
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most likely you're overdriving the LM3875 -- go to the National Semiconductor website, pull down the "Overture Design" spreadsheet and determine the input voltage you need for max output (given load, power supply voltage etc.)
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