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Old 30th November 2007, 09:57 AM   #1
Puffin is offline Puffin  United Kingdom
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Default Decibel Dungeon Gainclone

NuuK. I have put together an LM3886 as per your circuit (the only change being OR22, for which I used a 1R WW res as it was all I had.

I don't appear to have any output (yet seem to read -5v DC offset ?)

I have put together a power supply to run it with. the DC +V and
-V is 47.3V.

I am getting the following readings :-

Pin 1 - 3 37.3
Pin 1 - 4 40.3
Pin 1 - 7 32.2
Pin 1 - 8 34.6
Pin 1 - 9 36.3
Pin 1 - 10 32.2

By the way I am getting a strange reading from the PS, +V and OV = 32.5, -V and OV = 15V

Any help you can give would be appreciated.
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Old 30th November 2007, 11:17 AM   #2
Puffin is offline Puffin  United Kingdom
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Don't know if photos will help

http://i73.photobucket.com/albums/i2...nsex/chip2.jpg

http://i73.photobucket.com/albums/i2...onsex/chip.jpg
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Old 30th November 2007, 12:27 PM   #3
Nuuk is offline Nuuk  United Kingdom
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First off, are your rails +/-47v or +/-37v?
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Old 30th November 2007, 12:35 PM   #4
Sherman is offline Sherman  United States
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I believe he is saying his V+ rail is 32.5V and his V- rail is -15V for a total difference of 47.5V. Definitely something odd happening there.
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Old 30th November 2007, 01:14 PM   #5
Nuuk is offline Nuuk  United Kingdom
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I reckon you have a short somewhere! Disconnect the PSU from the chip and measure it again to make sure it is correct.

Then check for shorts.

The chip isn't insulated from the heatsink is it?

Check for any shorts.

Are you using a muting cap?
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Old 30th November 2007, 01:27 PM   #6
Puffin is offline Puffin  United Kingdom
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It is insulated. I have attached th 100uf cap to pin 8
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Old 30th November 2007, 02:50 PM   #7
Nuuk is offline Nuuk  United Kingdom
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And how about the PSU voltages when it is not attached to the chip?
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Old 30th November 2007, 02:57 PM   #8
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Hello Puffin, i can see no V- connection to pin 4..?The neg side of that 1000uf cap connects to 4 as well, with the pos side to ground..
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Old 30th November 2007, 03:04 PM   #9
Nuuk is offline Nuuk  United Kingdom
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I wondered about that as well, but if the neg rail isn't connected, he should be getting the full rail voltage on the output!
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Old 30th November 2007, 03:47 PM   #10
Puffin is offline Puffin  United Kingdom
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NuuK. Voltage with chip disconnected +v and -v = 60.6, +v and Ov =32.8, -v and Ov = 27.8

With chip connected +v and -v is 47.1, +v and Ov is 32.10 , -v and Ov is -15v
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