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Great, passive, tiny little DC offset filter box! The in's and out's can be confusing so I have them labeled with adhesive letters—happy to remove those if you prefer not to have them but I found them very convenient.Some external wear from having been mounted at one point, but the box functions perfectly. If you know Lehle stuff you know that every unit they built is made to last a lifetime. This thing will probably outlive us all.FROM THE USER GUIDE:The Lehle DC Filter will 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, i.e. 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 2 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. This is where the Lehle DC Filter can help!Connect the DC socket with the output of your FX unit or preamp, respectively the input of your amp. Connect the 2nd socket - 0DC - 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. Try various positions in your setup if you are not sure about the source of the DC offset, also try to swap the DC/0DC sockets. With a little patience you will find the best position with the lowest switching noise, this is where the Lehle DC Filter can work its magic.Warning: Do not use the Lehle DC Filter for speaker signals coming from an amplifier! The Lehle DC Filter is designed for line levels up to 22dBU.Technical dataWeight: 117 gLength: 7 cm (2.8”)Width: 3.7 cm (1.5”)Overall height: 3.1 cm (1.2”)Frequency response: 20 Hz - 100 kHzLoad impedance: 4.7 MOhmMax. level: 9.75 V RMS (ca. 22 dBU)