single-supply LM3875 design not working :( - diyAudio
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Old 28th May 2009, 06:31 PM   #1
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Default single-supply LM3875 design not working :(

Good morning, everyone---

I've designed two versions of a single-supply powered 3875TF setup, and have had no luck getting the chip to output sound.

The power supply outputs a DC voltage when AC is applied to it, with little if any AC at the outputs (haven't looked at the signal with a scope though, so take that as you wish).

Here is a picture of the reference design for a single-supply setup:

Click the image to open in full size.

I've used this same setup with two exceptions:

-didn't use any of the optional/starred parts
-I used a 56k resistor in place of the 75k resistor because I had one around

Cap values are as stated in the reference design, with a Cs value of 100uF

Here are a few pics of my implementation, power supply first:

Click the image to open in full size.

Click the image to open in full size.

Click the image to open in full size.

I'd appreciate any help you guys can provide! Thanks again.
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Old 28th May 2009, 06:59 PM   #2
mjf is offline mjf  Austria
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hello.
have you left away ci,rsn,csn?
this can cause some problems.
greetings....................
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Old 29th May 2009, 12:49 PM   #3
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Default Re: single-supply LM3875 design not working :(

Quote:
Originally posted by strykerhorse
The power supply outputs a DC voltage when AC is applied to it,
How much DC? The LM3875 needs > 20 V single supply.

Could you post photos, where the important parts are not hidden in the shade? And maybe a bottom view as well to see, if all connections are in the right place?
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Old 29th May 2009, 06:45 PM   #4
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Default Re: Re: single-supply LM3875 design not working :(

Quote:
Originally posted by pacificblue

How much DC? The LM3875 needs > 20 V single supply.
I'm giving it ~45V DC. I'll get more pics up for you momentarily....
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Old 30th May 2009, 04:06 PM   #5
bbp is offline bbp  China
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check pin 1 and 4, there is a voltage = your PSU
check pin 7, pin 8 , pin 3half voltage of PSU
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