Some veteran digital-gear manufacturers have only recently ventured into mobile apps, or have yet to do so. But Positive Grid flipped that equation around: They started out with inexpensive yet full-featured amp and effect modelers for iOS. (I raved about their early products when I reviewed them three years ago.) Since then the company has launched other iOS tools, software plug-ins for desktop DAWs, and now, two hardware versions of their amp modelers: BIAS Head, which can sit atop a speaker cabinet, and BIAS Rack, a near-identical device in a two-rack-space format. It’s an amp modeler and a 600-watt solid-state power amp. You can connect directly to recording and PA inputs, or disable cabinet modeling via a front-panel switch and plug into any guitar cab.

BIAS products were conceived to play well together. You can devise sounds on a phone or tablet, refine them on the studio computer, and then transfer them to BIAS Head or Rack for gigs. You can also download free sounds from a vast online user library.

BIAS Rack offers such forward-thinking features as a wireless audio receiver and Bluetooth for use with Positive Grid’s wireless switching hardware (sold separately). There are dual XLR and 1/4" outputs, two expression-control inputs, a mono effects loop, and MIDI in, out, and through jacks.

When it comes to mimicking Dual Rectos and Diezels, BIAS is among the best.

Mix-and-Match Models
BIAS amp models are derived from a sequence of modeled components—everything from tubes and transformers to tone stacks and cabinets. You can freely mix and match—a fun and creative process. The lower row of knobs includes analog-style tone and gain controls, while top-row knobs let you select amp types/topologies and manage presets. It’s a lucid interface that’s easy and fun to use.

BIAS Rack organizes its models into five categories: clean, glassy, blues, crunch, and metal. You can save five programs for each amp type, which means 25 models on tap without connecting to another device. Another knob defines the number of virtual tube stages, from one to five.

BIAS Rack is designed to work in tandem with Positive Grid software—specifically, the desktop version of BIAS Amp, which sells for $159 but is included with a BIAS Rack purchase. You must connect to a computer running BIAS Amp to access deep editing functions, the vast online library of free user-generated amp models, and the amp-matching feature. I had very different experiences using BIAS Rack on its own, and in tandem with BIAS Amp software. (More on the latter in a bit.)

Metal Maven
Positive Grid products are especially popular among metal players, and it’s easy to hear why. They excel at punishing high-gain tones. When it comes to mimicking Dual Rectos and Diezels, BIAS is among the best. But the clean and moderately overdriven sounds are also impressive. They’re detailed, spectrally accurate, and dynamically responsive.

You can definitely create, edit, and store sounds solely via Rack’s front panel, never connecting to a computer. One caveat, though: BIAS Rack’s knobs lack the light rings that some rival products use to indicate the controls’ current settings. When you load a new sound, the knobs no longer display what you’re hearing. The instant you touch a knob, the sound updates to the current knob position, but it’s often impossible to discern your current settings by sight.

If your plan is to use BIAS Rack without a computer connection, all is good. Just connect to a cabinet, audition presets, fiddle with a few parameters, and you’ll be creating cool custom sounds before you know it.

But if you want to connect the hardware to a computer for deeper editing, online library access, and amp matching, things get … problematic.


Excellent modeled tones. Lucid control layout. Large (and free) cloud-based tone library. Designing custom amps is a blast.

Incomplete documentation. Multiple software issues. Amp Match failed to perform.


Ease of Use:




Positive Grid BIAS Rack Amp Match Power Amplifier

The Match Game
To match amps, you set the sound of BIAS Rack as closely as possible to the target amp, mike up your analog amp, and then record the sounds of your model and your amp into BIAS Amp. Based on the comparison, the software applies an EQ curve to the model, capturing the character of your cabinet and speaker. (It’s like the Match EQ function in some DAWs.) This creates a snapshot of a particular amp at a particular setting, but everything still gets routed through BIAS’s simulated amps and tone stacks, so you’re not duplicating the target amp’s controls or the way the amp interacts with other gear. (I’m not singling out BIAS Rack here—other amp-matching products use a similar process.) Once you’ve made your match in software, you save it as a preset and load it into the hardware.

That’s how it works in theory, anyway. But I spent four frustrating days grappling with the software (with help from several Positive Grid product specialists) and never managed to make amp-matching work.

Communication Breakdown
Sadly, the amp-match problems aren’t the only software issue. After the initial software installation, BIAS Rack sounded, well, lousy. The models were inaccurate and unresponsive, with nasty-sounding resonant peaks. It wasn’t until a Positive Grid specialist suggested removing and reinstalling the software that I realized how damn good BIAS Rack actually sounds.

But even after reinstallation, BIAS Amp was difficult to work with, at least when connected to BIAS Rack via USB. The software is extremely crash-prone. Some menus literally appear and disappear between restarts. The help popups reference nonexistent controls. Some of the UI design is counter-intuitive. All these issues are compounded by the fact that BIAS Rack has no proper manual. The product website has a FAQ-style collection of topics, but these omit such crucial functions as amp matching.

The Verdict
BIAS Rack has enormous promise (especially in the context of Positive Grid’s powerful software, hardware, and cloud-based ecosystem), but it’s currently hobbled by poorly performing software, which can block access to key functions. (Positive Grid CEO Calvin Abel says, “We are aware our current Amp Match user interface experience is not ideal,” adding that the company will release improved software in the very near future.) I have no doubt that the BIAS Rack software experience can be great, so stay tuned for that promised update.