Hi and welcome to Arturia forums.
Arturias ARP 2600 version unfortunately does'nt have the possibility to route audio into the Preamp internally.
Internally you can try to route audio thru the Envelope Follower. Just be sure to have the Amount slider above 0. Perhaps you shall have it at 0.1.
This will make it possible to get some results.
Exsperiment with filter types and settings and see which results you can get. That's the best you can do this way.
If you have a DAW where you can route audio into instrument plugins, then perhaps you also can route the plugins own audio back to create feedback using the plugins Preamp that work with external incomming audio.
But unfortunately Arturias ARP 2600 version also does'nt have the preamp Gain range parameter. So to get that effect, you perhaps need to and can do that in your DAW before routing the audio back. But i don't know.
I have no idea if this will work and how the result will be, as i have'nt tried it. I can't route audio to instrument plugins in my DAW.
