I'm about to build a gainclone, and I don't have that cap ( encircled in the schematic), so could I use the caps in the picture, 100V, 2.2 microF?
I do have 10 microF caps, but their only 25 Volts rated, so they might blow up if I apply +- 30 V to the circuit right?
/Christian
I do have 10 microF caps, but their only 25 Volts rated, so they might blow up if I apply +- 30 V to the circuit right?
/Christian
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One may also point out that in case of errors in the circuitry
the output may in the worst case have a DC voltage equal
to one of the rail voltages, which will also be the voltage over
the capacitor. The capacitor is not rated for this situation. On
the other hand, there are probably more serious things to
worry about than en exploding capacitor in that case. As
somebody else pointed out, however, if it is a polarized
electrolytic cap. even a few volts DC on the output may
kill it. However, this situation should not arise either in a
working amplifier.
the output may in the worst case have a DC voltage equal
to one of the rail voltages, which will also be the voltage over
the capacitor. The capacitor is not rated for this situation. On
the other hand, there are probably more serious things to
worry about than en exploding capacitor in that case. As
somebody else pointed out, however, if it is a polarized
electrolytic cap. even a few volts DC on the output may
kill it. However, this situation should not arise either in a
working amplifier.
The explosive capacitor...
In that case the capacitor will see a diference of potencial between his ratings 25 volts and the rail (30 volts) of 5 volts...
this 5 volts across the 1k Ohm resistor can have a maximal current of 5 mA...so the cap will not explode...
But of course to use a 35 volts or more rated capacitor doesn't hurt!!
That i don't understand...why a few DC volts in a polarised electrolitc capacitor.... can kill it???
In that case the capacitor will see a diference of potencial between his ratings 25 volts and the rail (30 volts) of 5 volts...
this 5 volts across the 1k Ohm resistor can have a maximal current of 5 mA...so the cap will not explode...
But of course to use a 35 volts or more rated capacitor doesn't hurt!!
That i don't understand...why a few DC volts in a polarised electrolitc capacitor.... can kill it???
Re: The explosive capacitor...
I don't what strange theory you are applying here? If you have
30V DC at the output, you will get 30V DC over the capacitor.
You are right, however, that the resistors will limit the current
so it will take some time before the capacitor is charged to
30V. It is also true that 30V will probably not be enough to
make a 25V capacitor explode, but if it is an electrolytic it doesn't
hurt to be on the safe side.
If the DC has wrong polarity with respect to the capacitor.
Tube_Dude said:
In that case the capacitor will see a diference of potencial between his ratings 25 volts and the rail (30 volts) of 5 volts...
this 5 volts across the 1k Ohm resistor can have a maximal current of 5 mA...so the cap will not explode...
I don't what strange theory you are applying here? If you have
30V DC at the output, you will get 30V DC over the capacitor.
You are right, however, that the resistors will limit the current
so it will take some time before the capacitor is charged to
30V. It is also true that 30V will probably not be enough to
make a 25V capacitor explode, but if it is an electrolytic it doesn't
hurt to be on the safe side.
That a don't understand...why a few DC volts in a polarised electrolitc capacitor.... can kill it???
If the DC has wrong polarity with respect to the capacitor.
The voltage ...or the current...
But what cause a capacitor destruction is the current across it and the consequent eating of the dielectric...in the case of reverse biased with 30 volts DC at the output...the reverse current will be +- 1,5mA ...(30V across 21K)...not much!
The voltage rating of a capacitor must not be exceded expecialy when conected to a voltage source...because this will cause a high DC current thru the capacitor that will heat it...but when the capacitor is feed with a resistor...this ratings become less stringent...expecialy the danger of explosion of the capacitor!!!
But as i have said...use a 35 volts if that gives better sleep...
But what cause a capacitor destruction is the current across it and the consequent eating of the dielectric...in the case of reverse biased with 30 volts DC at the output...the reverse current will be +- 1,5mA ...(30V across 21K)...not much!
The voltage rating of a capacitor must not be exceded expecialy when conected to a voltage source...because this will cause a high DC current thru the capacitor that will heat it...but when the capacitor is feed with a resistor...this ratings become less stringent...expecialy the danger of explosion of the capacitor!!!
But as i have said...use a 35 volts if that gives better sleep...
Re: The voltage ...or the current...
You are neglecting that the capacitor gets charged and the
voltage over it will raise to 30V eventually. The exception
would be if the leakage current is so big that the current
through the resistors cannot charge the capacitor to more
than the rated voltage (25V)., or if it breaks down before
reaching 30V. As far as I Know, a capacitor breaks down
when the internal voltage becomes too high, so you get sparks
between the plates, damaging the dielectricum. It thus has
nothing to do with charge currents.
Anyway, we are probably being overly theoretical here. A
25V capacitor is probably quite OK in practice, since it will
not take any high voltages under normal operation.
Tube_Dude said:
You are neglecting that the capacitor gets charged and the
voltage over it will raise to 30V eventually. The exception
would be if the leakage current is so big that the current
through the resistors cannot charge the capacitor to more
than the rated voltage (25V)., or if it breaks down before
reaching 30V. As far as I Know, a capacitor breaks down
when the internal voltage becomes too high, so you get sparks
between the plates, damaging the dielectricum. It thus has
nothing to do with charge currents.
Anyway, we are probably being overly theoretical here. A
25V capacitor is probably quite OK in practice, since it will
not take any high voltages under normal operation.
When the theorical meet....
I 100% agree with you.!!!
Anyway this is what i said i my first post...
Cheers!
PS: I have seen some japonese constructors even with +-45 volts rails use 25 Volts rated elect. capacitors in series with the lower arm resistor of the feedback voltage divider...maybe they are pushing their luck to far!!
I 100% agree with you.!!!
Anyway this is what i said i my first post...
Cheers!
PS: I have seen some japonese constructors even with +-45 volts rails use 25 Volts rated elect. capacitors in series with the lower arm resistor of the feedback voltage divider...maybe they are pushing their luck to far!!
Re: When the theorical meet....
No, I guess it is reasonable design practice. Under any normal
operation circumstances it is sufficient, and if something goes
terribly wrong, you will most likely end up with more important
components being damaged, perhaps even your speakers.
However, I guess my point was that when you build an amp
yourself and it is not yet tested, something may be wrong so
you actually get rail voltage over the capacitor. Most likely the
amp is not sealed within a box when testing it, so an exploding
electrolytic can be a nasty epxerience. That said, exploding
semiconductors can also be nasty and dangerous -- I have
experience of that. Wear protective glasses when working
with untested circuits.
PS: I have seen some japonese constructors even with +-45 volts rails use 25 Volts rated elect. capacitors in series with the lower arm resistor of the feedback voltage divider...maybe they are pushing their luck to far!!
No, I guess it is reasonable design practice. Under any normal
operation circumstances it is sufficient, and if something goes
terribly wrong, you will most likely end up with more important
components being damaged, perhaps even your speakers.
However, I guess my point was that when you build an amp
yourself and it is not yet tested, something may be wrong so
you actually get rail voltage over the capacitor. Most likely the
amp is not sealed within a box when testing it, so an exploding
electrolytic can be a nasty epxerience. That said, exploding
semiconductors can also be nasty and dangerous -- I have
experience of that.
Wear protective glasses when workingwith untested circuits.
when the theorical meet...reprise...
Of corse!!!
But try this...if you have a old 25 volt capacitor...connect it reverse biased to a your lab power supply set at 30 Volts DC via a 21 k resistor....you will see that the cap will not explode and doesn't even become warm...
Me to!!...and the worst of all is the smell!!!
Cheers
Of corse!!!
But try this...if you have a old 25 volt capacitor...connect it reverse biased to a your lab power supply set at 30 Volts DC via a 21 k resistor....you will see that the cap will not explode and doesn't even become warm...
Me to!!...and the worst of all is the smell!!!
Cheers
Ok,
so I went with the 25 Volt Caps anyway. But there's only one problem with these, they are polarized
I understand that I'm taking a slightly larger risk by using polarized caps, but will it affect the sound, and how? I've tested this configuration and it seems to work juste fine.
Here is what the modules look like, I'm building a 5 channel amp with these.
/Chris
so I went with the 25 Volt Caps anyway. But there's only one problem with these, they are polarized
I understand that I'm taking a slightly larger risk by using polarized caps, but will it affect the sound, and how? I've tested this configuration and it seems to work juste fine.
Here is what the modules look like, I'm building a 5 channel amp with these.
/Chris
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