i started doing this with a borrowed Ibanez DM 1000 (rackmount) digital delay, back when i couldn’t afford any gear. the raw signal can be tremendous-sounding, ear-piercing, industrial, sometimes beautiful and delicate, but hard to control. reading about toshimaru nakamura (no-input mixer) in WIRE magazine most likely put the idea in my head, and i eventually acquired a second delay, along with a cheap tapco mixer, for live wrangling. i often resorted to it because i was a lousy guitar player. like @oot said, it’s sort of a cheap way to get modular-like sounds. again, echoing @rvense’s statements, it definitely can sound like a VCO- tonal, sustained, burp-y, stuttery, and wild … it’s fairly easy to control the pitch, though the pots’ range are so tight/narrow that it’s hard to dial in a gradual range, or have any real measured, linear control of the pitch.
i made several recordings of it, some early experiments, and then some later on. the original DM 1000 is now missing most of its knobs, after two decades of misuse, or proper use
https://miscellaneousfrankums.bandcamp.com/track/larmn - here i sampled the delay feedback with an akai s20 to several banks/triggers and further altered the pitches using the sampler. i just sort of freestyled (lazily) with the trigger buttons, then added a spare recording i’d made of an outdoor alarm to it. it’s pretty loose/aimless. the s20’s input died soon after making this, after sampling a lot of delay feedback. i’m not sure if it’s because the signal is so hot, or what.
https://miscellaneousfrankums.bandcamp.com/track/open-field-francis - this is a crude melody/sketch. the delay time (mSec) pot is detented- i just turned it back and forth, 2-3 notches, to get a sort of melody going. i doubled up the recording briefly, during the “lead guitar” part, and added a bass line using the green (es1?) synth in logic pro 9.
https://miscellaneousfrankums.bandcamp.com/track/live-feedback-for-cj - this is one of the last things i did with the 2 delay/mixer setup. i sent a recording of a live improvisation, where i played each delay independently (simultaneously) thru the mixer, amplified in a small tiled room, to a friend living in Boulder, Co. he processed it further, and added what sounds like mbv or gate (NZ) -like, soft electric guitar drone/distortion. then i recorded another episode of the same setup, in the same room, using the ‘remix’ for reference/pitch. i tried playing a mic’d clarinet thru an mxr blue box pedal, along with the sustained feedback, but i didn’t last long. i added the subsequent live recording to the “remix”, and it sounded agreeable, pitch-wise. the feedback sounded quite clean and pronounced during the last recording episode.
i’m sorry for the excessive share, here. it’s possible to ‘play’ an amplifier like this, too