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cwteoh 24th April 2004 01:27 AM

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?

Will 24th April 2004 08:11 AM

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. ;)

cwteoh 27th April 2004 12:50 AM

2 Attachment(s)
I am using 4 x 10CTQ140 as PSU Bridge with 2 x 10000uF before Vout, Toronoid Transformer 18v-0v-18v 6A

skyraider 27th April 2004 01:27 AM

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..

RFScheer 27th April 2004 01:38 AM

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?


cwteoh 27th April 2004 01:40 AM

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.

RFScheer 27th April 2004 01:44 AM

What are the components?
How about listing the component types.


skyraider 27th April 2004 01:45 AM

try taking out r32, c36, and c38

cwteoh 27th April 2004 02:00 AM

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?

jackinnj 27th April 2004 03:10 AM

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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