Tubey or not tubey? That is the question you can answer with the help of these affordable preamps!
PreSonus have updated their BlueTube DP range of half-rack valve microphone preamplifiers, the result being the two products reviewed here: the BlueTube DP V2 and the TubePre V2. The mic input stage, common to both devices, is based on the company's Class-A XMAX preamp circuit, and the user is offered the ability to 'dial in' the desired amount of valve warmth, or, of course, to use only solid-state circuitry.
I'll start with the BlueTube DP V2. Like earlier incarnations, this two-channel preamp can accommodate high-impedance instrument or mic-level signals and it now offers a maximum overall gain of 80dB, so it can also double as an instrument DI box. Both balanced XLR and unbalanced quarter-inch outputs are provided, with 'combi' sockets handling the balanced mic (XLR) and unbalanced (jack) instrument inputs. Some cosmetic changes are also evident, such as the curvaceous housing, while power comes from an included 12V DC, 1A, 'line lump' universal-voltage power supply.
Although the manual provides no figure for the actual operating voltage for the 12AX7, PreSonus tell me that it runs at 48V, which, despite being rather less than the 300 or so volts you'd expect to measure on more traditional valve circuits, is more than is found on many competing designs. In my experience, many such low-voltage tube preamps impart a softer sound when they're pushed into distortion, although this may be more to do with such units being designed to add this sort of character than to the tube operating voltage itself.
All the usual preamp features are present: there's switchable 48V phantom power, an 80Hz high-pass filter, a -20 dB pad and a polarity-invert switch, all with attractive blue buttons which light up when engaged. There are separate controls for overall gain and for the amount of 'tube drive', and an integral switch bypasses the tube drive when the knob is in its fully anti-clockwise position. Circular, illuminated VU level meters and associated clip LEDs complete the picture.
On a technical level, the solid-state path offers a THD + noise figure of better than 0.005 percent (unweighted), although when the tube kicks in, the distortion can be anything up to 30 percent. Again, that's not a bad thing, as the purpose of the tube here is to impart musically pleasing distortions! The signal-to-noise ratio is specified as better than 95dB, and on a subjective level is similar to what you'd expect from a decent analogue console preamp.
The single channel, third-rack width TubePre V2 follows a similar design, the main difference being that the tube can't be switched out of circuit — although at minimum drive settings it has to be said that the signal passes through pretty cleanly. It has the same control setup as the BlueTube DP V2 and boasts a dual-servo gain stage, with no coupling capacitors. Presonus claim that the tube saturation sound is much improved over the previous version.
Space isn't as tight as on the two-channel unit, and this allows the inputs to be presented on separate unbalanced quarter-inch (instrument) and balanced XLRs for the mic input, rather than sharing combi sockets. There's no sonic advantage to that, but it does allow you to leave different gear plugged in, which can be useful in some situations. Again, there's a choice of unbalanced quarter-inch or balanced XLR line-level outputs, and there's the same cute round meter plus clip LED to keep an eye on the levels. Both units have a 20Hz to 20kHz frequency range, which is flat to within better than one third of a decibel.
Taking the BlueTube DP V2 first, with the valve stage bypassed the result is a clean, quiet sound that is, quite frankly, not very different from that obtained from any other capable preamp or console input stage. That's not a put-down, by any means: it's just that when the design aim is for low distortion and low noise with a flat frequency response, the results are bound to converge. Switch the Tube Drive on, and at the start of the control's travel there's very little change — maybe just a hint more flattery, but nothing dramatic. Turn it up, and although the overall output level stays pretty much constant, the sound becomes more solid and thicker but without losing clarity at the high end. This middle area of the control is nicely flattering to vocals and instruments alike. As you approach the upper end of the control's travel, the sound takes on a noticeably saturated quality, but, importantly, it's very usable, without too much roughness added in the high frequencies. It's the kind of timbre a rap vocalist might enjoy, but can also add useful weight to electric guitars, basses, and even snare drums.
As you might expect, the TubePre V2 behaves in pretty much the same way as one channel of the BlueTube DP V2 in its Tube Drive mode, and again ranges from subjectively clean to noticeably saturated, with plenty of musically useful options in between. It's clean enough at the minimum drive setting that I didn't miss the absent tube-bypass mode.
In a studio situation, where you typically have a decent level coming from a close mic, both these preamps are capable of delivering the goods in style, and they both provide the added bonus of variable tube 'flavouring'. If you need more gain, as you might for a low-output, passive ribbon microphone, you may be justified in spending more money on a dedicated preamp — although, having said that, adding something like a Cloud Mics Cloud Lifter gain booster (reviewed in SOS November 2011) to these preamps gives great results with such ribbon mics.
Given their very affordable prices, these two units turned out to be surprisingly versatile, and while throwing a lot more money at a preamp may deliver a more esoteric level of performance, there are far weaker links in a typical project studio chain to worry about first.
When it comes to preamps that offer the choice of 'with and without' tube flavouring, the choice is pretty limited, and even more so at this end of the price range. While the more well-heeled might look at something like the Universal Audio Twinfinity, the budget conscious might be better directed to the Studio Projects VTB1 we reviewed in SOS July 2011, or some of ART's more affordable tube hybrid offerings where the degree of tube coloration is adjustable.