RJM Rack Gizmo Audio Loop and Function Switcher

RJM Music Technology raised the bar for audio loopers and function switchers when they released the RG-16 back in 2007. We weren’t the only players enamored by it, and the device has since found its way into the guts of many professional guitar rigs thanks to a fantastic blend of pro features and simple operation.

The Rack Gizmo is an evolutionary upgrade to the RG-16 that takes a great product and finds a few ways to make it even better. Before we jump into the upgraded feature set, though, we’ll recap what the Rack Gizmo does, for players who don’t yet own such a device:

Category Value Rating
Features 20% 4 Stars
Usability 25% 4 Stars
Sound 25% 4 Stars
Documentation & Support 10% 4 Stars
Price 20% 2.5 Stars
OVERALL RATING = 3.7, which earns it a WIHO Award! 
3.6 stars or better: Outstanding, WIHO Award
3 stars or better: Worth considering
2 stars or better: Suited to specific needs
1 star or less: Not recommended

By now, many guitarists are familiar with audio loop switchers. Rather than string a bunch of pedals into each other (which can easily kill your tone, especially if your prized boutique pedals are non-buffered), audio loop switchers isolate pedals from your signal chain and only pass audio through them while in use. This shouldn’t be confused with “looper” pedals that are used for recording sampled audio passages for you to play along with.

Function switchers, on the other hand, don’t pass audio data, but rather are used to replace the functions of your amplifier’s dedicated footswitch controls. Some amps provide multiple ¼” input jacks for control via external switching system, while others rely on proprietary multi-pin connectors for control. What we loved about the original RG-16 was that rather than rely on a tangle of multiple ¼” cables for switching functions, RJM Music Technology produces custom cables that match the proprietary interfaces on most popular amps (and they make custom cables when needed, too).

Like its predecessor, the Rack Gizmo is both an audio loop switcher and a function switcher, and with support for up to eight audio loops and eight function switches, it can control extremely complex rigs and operate advanced, multi-channel guitar amps with ease. You can even use it for switching between multiple amps!

Subtle refinements to the product have made the Rack Gizmo even better than its predecessor. The most notable differences: support for stereo effects, and the incorporation of RJM’s noise-eliminating Click Stopper technology, first introduced in the Effect Gizmo product (we have a review of the smaller Mini Effect Gizmo here).

If you’re ready to tame a collection of effects (pedals and/or rack gear) and a multi-channel amp, and put everything neatly under MIDI control from a foot controller, the RJM Rack Gizmo makes it a breeze to accomplish this seemingly complex task.


At a quick glance, you would be hard-pressed to tell the Rack Gizmo apart from an RG-16 save for the cool blue LEDs instead of red, and the addition of a 6-pin XLR jack on the unit’s face. (You can read our review of the original RG-16 here.)

The Rack Gizmo has eight audio loops. The first four are grouped in series, so you don’t have to install short jumper cables between loops as you do with many other looping products. The latter four are isolated, which enables them to be used for additional purposes besides switching effects in and out of your signal path (more on this when we discuss function switching) — switching among multiple amps being the obvious alternate use.

New in the Rack Gizmo, audio loops 5-8 are now wired for mono or stereo operation. Just use standard TRS/stereo cables, or if your outboard gear has separate Left/Right jacks, use familiar insert cables that are ¼” stereo at one end and dual mono jacks at the other. You can optionally custom order the Rack Gizmo with all eight loops wired for stereo if needed, too.

The eight function switches are accessed via proprietary cables specific to different amplifiers. With two DIN-8 connectors and the right cables from RJM Music Technology, you can control up to two amps from a single MIDI foot controller. Both jacks work in unison, so this feature is best suited to rigs with backup/standby amps at the ready. No need to re-cable anything if your primary amp blows a tube during the performance.

Controlling your audio loops and function switches requires a MIDI foot controller, and the MIDI IN jack is a DIN-7 connector that provides phantom power to footswitches capable of benefiting from this. On the face of the Rack Gizmo, though, is something new — a 6-pin XLR MIDI interface! Using this interface, present on the latest generation of RJM’s Mastermind MIDI foot controller (and planned for their upcoming Mastermind GT), a single cable provides power and MIDI via a rugged XLR cable (albeit a special one with more pins than your 3-pin microphone cable). If you have an original Mastermind foot controller, RJM will be manufacturing custom cables to take advantage of the front-mounted 6-pin connector.

Other builders of rig infrastructure products are also offering this interface, but as there’s no universal standard for it, everyone wires their pins differently. Fortunately, RJM Music Technology is a custom shop, and as such, you can always custom order an XLR MIDI cable that supports your equipment.

Up to 256 programs can be saved in the Rack Gizmo’s internal memory. This is a great feature as some audio looping products lack internal user memory and instead rely on your MIDI foot controller’s memory for different configurations/setups (i.e. which loops are active when you select a preset). If you’re wary of programming MIDI foot controllers, or you want to use a compact controller that lacks flexible programming options, saving configurations in the Rack Gizmo is the simplest approach available.

There are both buffered and non-buffered inputs for the audio signal. If you make use of the buffered input, then there is also a tuner output to take advantage of, but this side-chain is bypassed in the non-buffered audio path.

A new feature in the Rack Gizmo is the addition of RJM Music Technology’s Click Stopper technology. Because relays are used for switching loops in and out of the signal path — optimal for an overall low-noise design, switching some pedals in and out might generate unwanted pops or clicks, though how noticeable these pops can be will vary based on your pedals and your amp. The Click Stopper technology mutes the individual loop output quickly during the switching process to remove the offending noise, and it’s recommended for use with the effects running into the front end of your amp (not your effects loop). We were impressed with this technology in the RJM Effect Gizmo, but historically, we never had any pop/click noise issues with the RG-16 (which lacked this feature).

On the function switching side of the Rack Gizmo, up to eight amp functions can be controlled. RJM makes a wide range of custom cables for numerous popular pro amps from builders including (among numerous others): Bad Cat, Blackstar, Bogner, Egnater, EVH, Fuchs, Marshall, Mesa/Boogie, Peavey, Soldano.

If your amp isn’t on the custom cable list, don’t fear. Audio loops five through eight can be used alternately as ¼” switch jacks for any amp that supports standard audio cable connections for channel and function switching – both Normally Closed and Normally Open modes are supported. Of course you don’t have to give up any of these jacks in most cases, as RJM makes cables that run from the dedicated amp control DIN-8 connectors to standard ¼” plugs, too. Or, you can always have RJM Music Technology build you a custom cable.

Function switches can be operated in either latching or momentary modes of operation.

The Rack Gizmo responds to both MIDI Program Change (PC) and Continuous Controller (CC) messages depending on the action being performed. PC messages select from 256 saved configurations, while CC messages can be used to turn individual switches On and Off.

A series of sixteen buttons and corresponding LEDs run across the front panel of the Rack Gizmo corresponding to the eight function switches and eight audio loops. Along with an Input jack (duplicated on the rear), the 6-pin XLR MIDI jack, and a Write button for saving settings, that’s it for controls.

If you’re looking to tame a collection of single-channel amps, the Rack Gizmo can be used as a virtual channel switcher. Just connect the Sends from each channel to the inputs of multiple amps to switch between them. Odds are that you’ll still have loops left over for a few pedals, too!

Another subtle feature improvement in the Rack Gizmo: the power supply and power input jack were relocated to the left side of the unit’s rear vs. the RG-16’s right-hand power jack. Anyone wiring custom rigs will welcome this improvement as we always try to run power cables down one side of the rack and audio down the other to best reduce crosstalk from electrical wiring.

The only thing missing? Ideally, we would have loved to see power provided for pedals in the audio loops, but given the complexity of isolated power solutions, it’s unlikely that such a solution could fit into this 1U rack device.


The Rack Gizmo made it a breeze to control our amp features and pedal/rack effects loops remotely via a MIDI foot controller, with no programming required. Here’s a detailed look at the process for setting up our rig:

Basic Functions
We tested the Rack Gizmo with an ENGL Powerball II head and a random assortment of pedals and effects. The Powerball II is a four-channel amp, and it features three sets of ¼” input jacks for controlling an assortment of features remotely: jack one controls Channel 1-4 selection, jack two controls Volume A or Volume B, and a Mid Boost, and jack three turns the effects loop On/Off and the noise gate On/Off.

A custom cable from RJM connected the Rack Gizmo’s dedicated amp/footswitch interface at one end to a set of three ¼” TRS jacks for our ENGL amp at the other.

We had a mix of rack effects and pedals in our rig that we wanted to control via the MIDI foot controller: a TC Electronic G-Major 2, Eventide Space, and a variety of other effect pedals (all installed on a shelf in our effects rack).

Controlling our amp was a simple affair. Before adding a MIDI foot controller to the mix, simply pressing the function switches on the front panel of the Rack Gizmo activated the appropriate settings on our amp, and a corresponding LED above the switches indicated which ones were enabled. Buttons one and two in various combinations switched between our amp channels, and the other buttons controlled the other features mentioned above. Switches 7 and 8 had no use with this amp.

Previously, we had used the RG-16 with a Mesa/Boogie Road King II, and that amp took advantage of all eight switches for various functions replacing the enormous King Controller footswitch that ships with that amp.

We placed a few pedals in the first four loops of the Rack Gizmo, and ran the Click stopper output from those loops to the front of our amp. We placed our G-Major 2 and Space effects in isolated loops (5 and 6) and ran those effects through our amp’s serial effects loop. For added benefit, we also ran the output of those time-based effects into an RJM Mini Line Mixer so that bypassing the loops wouldn’t chop off our delay repeats and reverb tails (see our review of the MLM to learn more). As with selecting amp functions, enabling any of the audio loops was as simple as hitting the corresponding button on the front panel of the Rack Gizmo.

We appreciated the convenient placement of the In and Out connections to the Click Stopper circuit – after the connections for the four series loops, and before the separate loops 5-8. The intention here is obviously to make connections nice and tidy for pedals in the first four loops utilizing Click Stopper technology, and rack gear in the latter four loops without it. But if you’ve just got a ton of pedals to tame and could care less about rack-mounted signal processors, you can still patch the Click Stopper circuit into your signal chain after all eight loops have been connected to pedals.

  • The guitar signal passes from the front panel jack, through the buffer, then through the first 4 audio loops, through the Click Stopper circuit and into the amp’s input.
  • The last four loops are inserted into the amp’s effects loop. These can be either pedals or rack units.
  • The Rack Gizmo controls channel switching on the amp using one of the function switching jacks.

Now for the real fun — controlling the rig from our MIDI foot controller.
MIDI and Programming
[Before reading this next section you should have a basic understanding of MIDI foot controllers, otherwise much of this may sound like rocket science. If you need a primer on the topic, check out our in-depth tutorial on MIDI foot controllers here.]

First, we needed to connect our foot controller to the Rack Gizmo. Our Mark L FC-25 lacked a 7-pin DIN MIDI connector — they have their own proprietary 6-pin XLR MIDI interface for Mark L hardware products. But rather than relying on an optional 9V power supply, it was easy enough to order a custom cable from RJM to take advantage of the XLR MIDI interface.

Next, we connected the MIDI Out from our Rack Gizmo to the MIDI In of the TC Electronic G-Major 2, and its MIDI Thru to the MIDI In of our Eventide Space pedal, and away we went with configuring our setup.

The programming interface was extremely simple. To create a configuration (program, patch, preset, etc.) in the Rack Gizmo, all we had to do was the following:

1. Step on a preset switch on our FC-25 foot controller for whatever preset we planned to create.
2. On the Rack Gizmo, push the appropriate switch buttons to select our amp settings and activate specific audio loops for the desired tone.
3. Press and hold the Write button for one second, after which all the lights blink on the face of the Rack Gizmo, confirming that settings have been saved.

We set up a numerous presets, matching our clean and heavy amp channels to various effects in our rig. After saving a few different configurations, anytime we stepped on the footswitch for preset 01, one configuration of amp settings and effects was selected, while stepping on preset 02 would pick an entirely different configuration. It couldn’t have functioned more easily!

Our actual settings for use involved a bit more work that had nothing to do with the Rack Gizmo. For example, we set up a MIDI Map in our G-Major 2 so that receiving a program change (PC) message for preset 01 actually called up User Preset #32, a PC message for preset 02 called up User Preset #12, etc. This has nothing to do with the ease with which we configured our Rack Gizmo to response to commands from the Mark L foot controller.

There’s a lot more you can do with the Rack Gizmo, and we weren’t ready to call it quits just yet. Because the switches can each respond to MIDI CC messages, we next configured our FC-25 foot controller to directly access some function switches and loops.

Referring to the list of CC values assigned by default to the audio loops and function switches in the Rack Gizmo, it was simple to assign instant-access switches on our MIDI foot controller to those values. So even though we could configure our set list with specific combinations of amp sounds and various effects, when it was time to just jam and develop new music, we could freely change amp channels and turn pedals On/Off as if they were all just stomp boxes on the floor.


The Rack Gizmo improves upon the RG-16 thanks to its Click Stopper technology, but is otherwise as transparent as its predecessor. Using the CS Output, there was no perceived noise from the relays engaging/disengaging on various pedals in our effects loop. To recap, the technology works by introducing a very slight mute at the onset of the switching, but it happens so quickly that our high-gain lovers never noticed any sort of a delay, similar to using a studio-grade noise gate.

When running the output through the non-CS output, we could (in some scenarios) hear a subtle click from the relay switching, but it was actually much quieter than expected, and typically only noticeable when we had the amp set to a very high-gain tone and we weren’t playing anything at the moment. While playing and changing audio loops at the same time, we never noticed the sound of the relay switching, so you’ve got a choice of either “very good” or “great” output depending on your requirements.

The only scenario in which the relay switching was noticeable was in the fully passive configuration of the Rack Gizmo — using the non-buffered input with non-CS output. And in this scenario, we only noticed the switching noise with a few front-of-amp pedals. When we switched to the CS Out, but still using the non-buffered input, the relay switching noise was eliminated. In real-world use, we happen to prefer buffered inputs, so unless you’re a vintage tone purist, there’s nothing at all to worry about. In fact, if you’re a vintage tone purist, we have to wonder why you’ve got so many effects that you need a Rack Gizmo in the first place!

Documentation and Product Support

The User’s Manual for the Rack Gizmo is on par with other RJM Music Technology documentation, which is to say excellent as usual. It got us up and running in a matter of minutes, and numerous illustrations are provided to demonstrate the various ways you might implement the Rack Gizmo on its own as well as with a line mixer. Details on the MIDI operations and programming of the unit were all clearly explained.

The “stock” cable for our Road King II came with documentation that detailed which function switches controlled which features on the amp, and it also contained quick setup information for configuring the RG-16 to work with our amp. Our custom ENGL cable didn’t have any specific instructions, but with three footswitch jacks to control, it only took 30 seconds of experimenting to figure out which jack controlled which function. RJM thoughtfully color-coded the three plug ends, so we placed some matching colored stickers on the back of our amp head above its control jacks to make sure even an assistant could get our wiring straight.


The RJM Music Technology Rack Gizmo can be purchased direct for $799 (pre-order discounts available at the time of this writing), which is $150 more expensive than the RG-16 it replaces. It’s a fair price given the advanced functionality of the unit, but not quite the steal it used to be. Support for a wide range of popular amps with custom cables (instead of relying on multiple ¼” cable runs) enhances the product’s appeal for players who like to keep things streamlined in their rigs.

The custom cables for specific amps tend to average $49-52, and really, you should just consider this a required part of your purchase unless your intention is to use the Rack Gizmo for multi-amp switching instead of its use in replacing a complex dedicated amp foot controller. If you have an amp that can’t be controlled from one of the existing cables, builder Ron Menelli will be happy to create a new one for you. Just tell him, “Hey, those MusicPlayers.com guys said you’d make me a cable…”

Contact Information

RJM Music Technology

Evaluation Short-List
  • Mark L Custom B-16
  • Sound Sculpture Switchblade
  • Voodoo Lab GCX
  • Rocktron PatchMate Loop 8
  • Rhodes B/8 Blender

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