Q. How can I record from my pedal's headphone output?
3.5mm Mono to Stereo Adapter, 2 Pack 3.5mm 1/8" Mono Male Plug to 3.5mm 1/8" TRS Stereo Female Jack for Radio, Headphone
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adapter - how to wire a mono audio signal to a 3.5 TRS stereo jack - Electrical Engineering Stack Exchange
Simple Way to Convert Stereo to Mono : 5 Steps (with Pictures) - Instructables
How to...Connecting stereo outputs to mono input
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Headphone Amp Amplifier 4 Channels Metal Stereo Audio Mono,Mini Splitter 4X Quarter Inch Balanced Output and TRS ts Audio Input
Why are two 1 kΩ resistors used for this additive stereo to mono conversion? (For audio inputs to an amplifier) - Electrical Engineering Stack Exchange
Stereo to mono adapter | Electronics Forums
Headphone Amplifier with 3 Input Mute Audio Mixer Function Power Adapter,4 Channels Mono/Stereo Switch Audio Amplifier Mini Earphone Splitter 1/4" & 1/8" TRS Headphones Output and AV Input
operational amplifier - How could I build a headphone stereo to mono converter? - Electrical Engineering Stack Exchange