MIDI is great when it comes to controlling or accessing MIDI instruments, sequencers or what have you, but it is less helpful when you want to incorporate non‑MIDI equipment into your system. Analogue synth users can get around this to some extent by using CV‑MIDI converters, but what if you want to switch a non‑MIDI effects unit in or out of circuit, or even use MIDI to turn on your studio's coffee machine at the end of a track? (Actually, the switches are only rated up to 125 volts, but if you really did want to control a mains‑operated device, it would be a simple matter to use the RP93 to switch an external, larger relay.) More practical uses are amplifier channel switching, footswitch inputs on keyboards, and the switching of devices connected to the effects loop of an amplifier or mixer.
One answer is to use a device such as the Rolls RP93 MIDI switcher, which uses MIDI program changes to access eight switch functions, four of which are straight on/off switches and four of which are designed to control effects loop devices. Switching is accomplished using relays so there's no signal degradation.
The 1U, rack‑mounting RP93 has 12 switch buttons on the front panel for programming; a non‑volatile memory system ensures that programs aren't lost when the power is switched off. The eight switch‑related buttons have amber status LEDs, and there's a three‑digit LED readout for use when programming. Occupying the rear panel are 14 jacks — four for the straight switches, four pairs for the effects loop device Ins and Outs (connected as a series chain), and overall effects In and Out jacks for connection to the Send/Return sockets on the external device. MIDI In and Thru jacks are provided, and power is via a captive mains lead. Pins 1 & 3 of the MIDI In socket, normally unused, carry a 12V power supply feed, which may be used to power other devices, such as a Rolls MIDI controller pedal.
Programming is a simple matter of entering Learn mode, by pressing and holding the Up and Down buttons simultaneously (for at least five seconds), stepping to the required Program number, and then setting up the switch combinations as desired. Once this has been done, the switch settings may be saved. The MIDI channel may also be set from 1‑16, Omni or Off. As shipped, the unit comes programmed with a set of default programs, which may be recalled later if desired. To exit Learn mode, the Up and Down buttons are again pressed and held, and any unsaved changes will be lost at this point.
Simple though the device is, I feel it fills a niche — and the more you think about it, the more uses you can dream up for it. For example, you could use the switches to switch between channels on your mixer to provide rudimentary mix automation, or to switch the feed to an effect processor to bring it in and out under MIDI control. The effects loop switches can be used to chain together four (mono) effects devices or pedals, providing independent In/Out control for each of them, or the simple switch contacts could be used to operate non‑MIDI studio gear such as tape echo footswitches, tape machine remote starts or amplifier reverb switches.
While not everybody will need MIDI control over switches, those who do will welcome the Rolls RP93 and the possibilities that it provides. No doubt it was conceived with guitar players in mind, but it has a wealth of practical uses in the studio. Now if only they'd made the effects audio path stereo! Paul White