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Old 9th March 2013, 09:57 PM   #1
tony Ma is offline tony Ma  United States
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Default Capacitor value

Dear All,

Sorry for a newbee questions

I like to know what you guys think with this "upgrade" scenario

Let's just say originally the Tube Pre-AMP has a 1UF capacitor

Can we substitute with some thing close to the original value such as .82UF ?

Is there any sound different?

I knew that the voltage must be the same

Let me know your insight guys

tks
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Old 9th March 2013, 10:57 PM   #2
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Do you know the function of the cap? Smooting, coupling, powersupply, etc.

The value of a cap always depends on the surrounding circuitry. Let's assume it's a coupling cap. Combined with the impedance of the next stage, you get a high pass filter with a certain frequency. For example, if the next stage has a impedance of 10k ohm, the -3dB frequency will be 16 hertz. With a .82uF cap, the -3dB point will be 19 hertz. Just 3 hertz. But with a 1k ohm impedance, it's 159 vs 194 hertz. A 35 hertz difference. You might detect a small change in frequency response in the sound of the preamp, but not anything world chaning in my opinion.

If it's a cap e.g. tuned to prevent high frequency oscilations somewhere in the preamp, or part of the EQ network, the change might be more significant though.

Last edited by funk1980; 9th March 2013 at 11:00 PM.
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Old 10th March 2013, 12:35 PM   #3
DF96 is offline DF96  England
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The voltage does not have to be the same. It has to be sufficient, under all normal and most fault conditions.

The value depends on exactly how the cap is used in the circuit, whether it sets a rolloff, whether it is within a negative feedback loop etc. A 20% change is unlikely to make much difference.
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