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Old 27th January 2013, 12:17 PM   #31
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Ah ok, thanks!

I will start with just a wire and see how much current is drawn. Then I'll (try to) calculate the resistor needed.

Thank you so much for the much needed help!

Kind regards,
Sjoerd
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Old 27th January 2013, 01:08 PM   #32
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Did the work and all is dandy :-)

The DC offset is going crazy (back and forth) but no big problems whatsoever....

Question: If you have say +- 30mV DC offset.... what can you do about that?

Kind regards!
Sjoerd
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Old 27th January 2013, 02:10 PM   #33
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When measuring the offset ensure that you have a shrting plug at the INPUT of the amplifier.
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Old 27th January 2013, 02:13 PM   #34
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Just as a starting point, once the amplifiers are stable and you can measure the DC current being drawn from the power supply.

You might be looking to drop approximately 1V across the X3 and X4 resistor.

If the two amps are drawing a combined current of say 3A.

R = E / I.........so R would be 1 / 3 Ohms = 0R33

P = I ^^2 x R.......so it would need to be at least 3W ...... 5W would be better.
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Old 27th January 2013, 02:46 PM   #35
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Quote:
Originally Posted by KatieandDad View Post
When measuring the offset ensure that you have a shrting plug at the INPUT of the amplifier.
That should read SHORTING plug .
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Old 27th January 2013, 02:50 PM   #36
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The plug results in a DC offset of 0.3mv... thats good I guess... but when I take the plug off, the voltage goes to 3 vdc.... normal?
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Old 27th January 2013, 02:52 PM   #37
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That's normal. With a floating input you will get fluctuating output.


If the DC offset is only 0.3mV with the shorting plug then you are ready to carry on.
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Old 27th January 2013, 02:55 PM   #38
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Ok, thanks!

I think it's time to connect some speakers :-)
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Old 27th January 2013, 02:56 PM   #39
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Always try some cheap spare ones first time....
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Old 27th January 2013, 02:57 PM   #40
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Haha, good point!

I'll do that.... I'll let you know how it turns out :-)
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