I just hooked up the Arp and like it so far. My plan is to integrate it with my existing setup that's based around the Retrokits RK-006. I think this is a very flexible partner for the Arp, allowing control over many MIDI devices and the RK is rock solid in my experience. I have it set up in mode 1 (basically a simple MIDI thru setup, where the RK duplicates incoming MIDI to all its out ports).
My plan is to use the MIDI host capability of the RK (I've connected a powered USB hub to it). This works well with other MIDI devices, e.g. I can use my Digitone Keys to play notes via USB and the RK passes them through to other MIDI devices connected to the out ports as expected.
When I connect the Arp to the RK with the same USB-B cable as I used for the Digitone, it powers up and I see the lights of the RK blink when I press play, signifying it's receiving data from the Arp, but I can't get my devices to play anything the Arp is supposedly transmitting. If I hook up the Arp via regular MIDI, either via the RK or directly into the unit, it plays back as expected. I also tried powering the Arp separately and connect to the RK with a the other Arp USB port (type A, both ends) cable but that doesn't work either.
Any thoughts as to what I can do to get it to work? Or is the USB on the Arp only designed to work with a computer, as the manual states "supports MIDI over USB to connect to software sound generators, VSTs and DAWs."