Blackstar UNITY Pro Bass U500, U250 amps and U250ACT Active cab review

Since its humble beginnings in a garden shed 13 years ago, Blackstar has really stamped its mark on the market. 

Back then, a group of ex-Marshall employees and band-mates decided to start with a clean sheet and build the best guitar amps they could. Right from the off, they were a big hit with rock and metal players - a glance through the list of endorsees reveals a definite slant to the distorted end of the spectrum. Now, Blackstar has released a range of bass combos, and given the nature of the company’s success so far, they should at least deliver on the rock and metal front. But will they be versatile enough for the rest of us? 

There are five new combos in the Blackstar Unity range. The U30, 60 and 120 have single 8”, 10” and 12” drivers respectively, and a slightly simplified analogue preamp. The two bigger amps we’re featuring here, the U250 and U500, also share preamp and control panel architecture. Even with a few more features, the layout looks clear and logical. 

On the left is the pad switch, input and gain stage. This section is analogue, but from here onward everything is digital. Next comes a selector switch with three voice options: Classic, Modern and Flat. At the other end of the preamp you can select one of three different amp Response settings: Linear, 6L6 and 6550. These two functions used together are at the heart of what these amps are about; in effect they allow a range of amp modelling. 

They also reveal a lot about the designers’ goals for the Unity series. The three Response settings emulate different power amp types. Linear offers the tight, accurate and bright response of a modern digital amp. The 6L6 and 6550 settings are influenced by the more organic characteristics of valve amps, and sound warm and tight. The 6L6 has a natural compression - like an old Fender Bassman or Ampeg B15 - while the open and dynamic 6550 sounds more like a big Mesa or SVT head. 

After the three-way Voice selector, there’s another switch with which you can select one of three distortions: OD, Distortion or Fuzz. When you’ve selected the type of distortion you want you can blend it into your clean signal with the Drive control. The cool thing here is that whichever combination of Voice and Response you choose, the Drive function will adapt to suit, so for instance the Overdrive on the 6550 Response setting is an authentic digital representation of the tone of a big old valve head being pushed hard.
Next in line is the three-band EQ with semi-parametric mid, and after that a three-way selector switch offering Octave - down, up or a blend of both - and Chorus effects, which can be adjusted from the back panel. After the Response control, which we’ve already covered, there’s a compressor with its own control and on/off switch, and finally the master volume and status LED. 

A glance at the back panel reveals that everything needed is present, including an input for the supplied double footswitch. This activates the distortion and FX circuit, or you can also use the optional FS12 footswitch, which gives greater functionality. There’s a stereo line in, USB and XLR outputs with optional cab simulation, level control and ground lift, Headphone, series FX loop, level controls for the Chorus and a control for blending between Octave up, down, or both. Lastly, like all the amps in the Unity range, there’s an XLR link for hooking up the U250ACT active monitor. 

Apart from the output, the most obvious difference between the U250 and U500 amps is the speaker configuration; the 250 has a single 4 ohm 15” driver, whereas the 500 ups the ante with two 8 ohm tens. These are Eminence Opus drivers designed specifically for the larger Blackstar Unity amps. Both combos are made from dense MDF and covered in tough, grained black vinyl. 

We think they look great - smart and purposeful. They’re also pretty compact given their speaker configurations. The difference in power will make a difference to the available headroom of course, but the 250 watt, single 15 should be warmer and fatter, which should suit the 6L6 and 6550 Response settings perfectly. 

Let’s turn to the Unity Pro Bass U250ACT. More and more manufacturers are producing powered cabs for bass, either to use as an extension cab that won’t alter the output or upset the impedance of a combo, or for use on their own with a stompbox preamp or pedalboard. One of the great things about the 250 watt Unity 250ACT cab is that its 15” driver means that it’s particularly suited to being used with the smaller combos, which may struggle to reproduce lower frequencies. 

In use it works brilliantly, and linked to the Unity 500, with its two 10” speakers, it adds not just volume and headroom but also a richness and natural warmth that you just couldn’t get by EQ-tweaking alone. Plugged into the Unity 250 combo, you get more of the same - a glorious full-fat bass sound with double the headroom and volume - and as a bonus, a slight lift in the low end due to proximity bass coupling. The expansion possibilities don’t end there; because the Unity 250 has an XLR Thru socket, you could link as many of them together as you want. 

Our initial question was “Are these amps versatile?” Well, after using them for a couple of weeks for gigs and rehearsals, our answer is a definitive yes. Although these aren’t modelling amps per se, in use the Response function in conjunction with the Voice options gives you so much choice. Want a bright and clean accurate tone with tons of headroom? Set the Voice option to Modern and the Response control to Linear, and there you have it. Perhaps you need a Jamerson-like soul groove with an old Fender and a bit of grit? You’ll want to set the Voice option to Classic and the Response control to 6L6. Dial in a little overdrive and a touch of compression and, without touching the EQ, you’re rewarded with a gorgeous vintage bass tone. 

As a stand-alone backline amp, the Unity 500 has everything you could possibly need in terms of power, accuracy, features and tone. Used in conjunction with the supplied footswitch, you have a versatile and powerful amp with which you can tailor your sound to pretty much anything you need - vintage, modern or virtually anything between. Hook up the U250ACT cab and you have a full-range rig that will deliver enough volume for any gigging situation. 

In many ways the Unity 250 has a more distinct character. It’s certainly not short of a clean, crisp top end, even without any HF tweeter or compression driver, but the inherently smooth, warm nature of the single 15” speaker still shines through. It’s surprisingly loud, too, although most of the action on the master volume happens in the first two thirds of its range, after which things get a bit gnarly. Despite that, for me this is the star of the range. 

Given its growing fanbase, Blackstar could easily have produced a range of bass amps that concentrated solely on producing bass tones for rock and metal players. The fact that it has created bass combos that will suit a whole range of players is to its credit.