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Old 7th November 2012, 06:01 AM   #1
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Default what happens if DC blocking capacitors is removed

what happens if we take out the dc blocking capacitor since i really dont want to spend on the Mundorf but would like to take off the input cap but what happens if we remove it the dc enters into the amp and blows up?
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Old 7th November 2012, 06:08 AM   #2
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You can leave it if you are sure there is no DC present at the output...
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Old 7th November 2012, 06:29 AM   #3
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The input cap is part of a high-pass filter. Removing it extends the input response to DC. The DC will enter the amp and be amplified.
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Old 7th November 2012, 11:49 AM   #4
AndrewT is offline AndrewT  Scotland
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Yes, the DC gets through to the load.

And the non blocking of DC at the input opens up the input to errors that affect the input offset current and input offset voltage of the amplifier, i.e. the amp will not work as intended by the designer.

If you don't know this then you should not be considering this modification.
You are behaving like a foolish child, who has no appreciation of danger and takes risks because they have no previous experience to fall back on. The not so foolish child listens to their parents.
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Old 7th November 2012, 02:39 PM   #5
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I agree Andrew thank you for the input as i didnt knew thought to take out the capacitor and see how it behaves but eventually it needs experience which i dont have now if somebody asks me the same question i have the answer thank you...
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Old 7th November 2012, 04:39 PM   #6
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The learning process can be painful to experienced onlookers, as in electronics it often results in damaged and destroyed components. Still, if I had never messed anything up, I wouldn't know what I know today.
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Old 7th November 2012, 04:51 PM   #7
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Quote:
Originally Posted by AndrewT View Post
Yes, the DC gets through to the load.

And the non blocking of DC at the input opens up the input to errors that affect the input offset current and input offset voltage of the amplifier, i.e. the amp will not work as intended by the designer.

If you don't know this then you should not be considering this modification.
You are behaving like a foolish child, who has no appreciation of danger and takes risks because they have no previous experience to fall back on. The not so foolish child listens to their parents.
Yes Andrew, I am of the school of thought that extending response to DC is quite foolish, and I do not understand the panacea surrounding it.

I think it is equally foolish to elimate the capacitor from the feedback network. Doing so will cause DC offset with "real world" signals (not test signals).

Oh those evil capacitors. I cannot stress enough that a properly designed circuit will not exhibit degraded performance with the inclusion of these two capacitors.
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Old 7th November 2012, 05:19 PM   #8
sreten is online now sreten  United Kingdom
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Hi,

You can leave out the input capacitor as long as you
are sure the output driving it has a coupling capacitor.

(The same applies in reverse for omitting output caps.)

rgds, sreten.
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Old 7th November 2012, 06:03 PM   #9
Mihkus is offline Mihkus  Estonia
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What? you will have very loud mains noise in ur woovhers.
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Old 7th November 2012, 06:21 PM   #10
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I agree that working without a DC blocking cap is not advised.

The other thing, you didn't say which amp design you are working with. If it is one of the MyRef series, then the collected wisdom is that removing the cap also hurts bass response due to an interaction with the 318 opamp. Other designs, the interaction won't be a problem.

If you don't want to spring for the Mundorf in question, then look around for other, less expensive alternatives. Try one of the cheap Russian caps. Depending on the value needed, you could try a Sprague Orange Drop or any number of metalized polypro caps.
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