The DC Filter was designed to eliminate DC background noise known as DC offset.
Germany (December 14, 2011) -- Lehle Gitarrentechnik has announced the new DC Filter. The Lehle DC Filter is designed to clean analog signals of DC voltage. Audio signals with a DC offset can cause unpleasant switching noise. Line signals as well as high-impedance signals will be cleaned - without any coloration of the sound. The Lehle DC Filter is made in stereo and can filter mono signals as well as stereo signals, even balanced signals are no problem for this little helper. The Lehle DC Filter has a passive design, so it will not need a power supply.
A DC offset can occur in various places in an analog signal path. Most common points are outputs of active circuits like acoustic guitar or bass preamps, output sockets of effect processors, or input sockets of tube amplifiers. This DC offset can be measured easily with a simple voltmeter, which has two test leads, usually one is red and the other is black. Touch the signal ground with the black probe and the signal with the red one. Change red for black in case the voltmeter shows a minus figure (-). While the system is powered up but without playing a note the DC value should not be higher than 0.1 V. A higher voltage can result in a very loud switching noise.
The DC socket of the DC Filter is connected to the output of your FX unit or preamp, respectively the input of your amp. The 2nd socket - 0DC - is connected to the next unit in the previous signal path, which usually is a switcher. The Lehle DC Filter is plugged into the signal path with the DC socket towards the unit that causes the DC offset. Lehle suggests trying various positions in your setup if you are not sure about the source of the DC offset.
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