A question about the input of amplifier designs.
Most amp circuits I see on this board have on the input: a parallel resistor to ground, a series capacitor and a series resistor in some configuration.
The series capacitor is there to block DC.
The parallel resistor, as I understand it, allows a small current to flow from the signal source, which some output stages require to work properly.
I have never been able to figure out the purpose of the series resistor. Anyone care to enlighten me?
Most amp circuits I see on this board have on the input: a parallel resistor to ground, a series capacitor and a series resistor in some configuration.
The series capacitor is there to block DC.
The parallel resistor, as I understand it, allows a small current to flow from the signal source, which some output stages require to work properly.
I have never been able to figure out the purpose of the series resistor. Anyone care to enlighten me?
preiter said:A question about the input of amplifier designs.
Most amp circuits I see on this board have on the input: a parallel resistor to ground, a series capacitor and a series resistor in some configuration.
The series capacitor is there to block DC.
The parallel resistor, as I understand it, allows a small current to flow from the signal source, which some output stages require to work properly.
I have never been able to figure out the purpose of the series resistor. Anyone care to enlighten me?
as far as i know :
The parallel resistor stops high gain oscillation when you unplug the source.
The Series resistors increases impedence a little bit
and the series/parallel configeration as a whole creates a devider.
the cap across the input stops rf getting into the input from cables etc
the in series cap blocks dc.
Hi,
there are commonly two filters on the input to an amp.
A low pass and a high pass.
The high pass usually comes first. series capacitor followed by cap to ground. The -3db frequency of this filter is F=1 / [ 2 Pi R C ]
it is usually set between 1Hz and 10Hz.
The low pass filter usually follows, it is a series resistor followed by a capacitor to ground. F-3 is usually set between 40kHz and 300kHz
There is somtimes a resistor to ground from the input terminal to reference the input end of the capacitor to ground and help prevent a DC voltage building up on it if it is left unconnected. This resistor is usually about 10 times the input impedance of the amplifier.
there are commonly two filters on the input to an amp.
A low pass and a high pass.
The high pass usually comes first. series capacitor followed by cap to ground. The -3db frequency of this filter is F=1 / [ 2 Pi R C ]
it is usually set between 1Hz and 10Hz.
The low pass filter usually follows, it is a series resistor followed by a capacitor to ground. F-3 is usually set between 40kHz and 300kHz
There is somtimes a resistor to ground from the input terminal to reference the input end of the capacitor to ground and help prevent a DC voltage building up on it if it is left unconnected. This resistor is usually about 10 times the input impedance of the amplifier.
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