Gaudeamos
New Head-Fier
- Joined
- Jun 5, 2013
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I've built a couple of CMoys with slightly different input stages from Chu Moy's design (written up in HeadWize: "A Pocket Headphone Amplifier"). For evaluation purposes I wanted a unity gain amplifier with an audio bypass switch. That allows me to easily compare the amp's output to the non-amplified source signal for a given pair of phones.
... So, I left the level-reducing resistor (R1) in addition to adding a 10K stereo pot for volume control. I recognized the topology as an (almost complete) passive band pass filter. All it was missing was an appropriate cap to ground following the attenuating resistor, which I thought might be a good idea to dunk any HF/RF noise picked up by the interconnect cable.
Then I came across another HeadWize article "Designing An Opamp Headphone Amplifier" where I read "Low and high pass filters can be cascaded at the input, so long as the resistor values of each filter are different by at least a factor of 10."
My question: why? I haven't found any such requirement anywhere else regarding passive filter circuits. Any insight would be appreciated.
... So, I left the level-reducing resistor (R1) in addition to adding a 10K stereo pot for volume control. I recognized the topology as an (almost complete) passive band pass filter. All it was missing was an appropriate cap to ground following the attenuating resistor, which I thought might be a good idea to dunk any HF/RF noise picked up by the interconnect cable.
Then I came across another HeadWize article "Designing An Opamp Headphone Amplifier" where I read "Low and high pass filters can be cascaded at the input, so long as the resistor values of each filter are different by at least a factor of 10."
My question: why? I haven't found any such requirement anywhere else regarding passive filter circuits. Any insight would be appreciated.
