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This article was originally published in issue #32
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Need more channels? Want a better sound with a little tube magic? Andi Picker checks out a very effective proposition from PreSonus.
I’ve reviewed a number of audio interfaces for Guitar Interactive (including a couple of PreSonus units in issues 23 and 30); they all have at least one microphone pre-amp, and they are all plenty good enough for making serious recordings, so what’s the point of a stand-alone pre-amp?
Well, sometimes you just need more microphones, and sometimes you fancy a change of scenery. Whichever situation you’re in, so long as you have some way to get signal from an external pre-amp into your recorder (typically, you’ll want some spare line-in sockets on your audio interface) then you can plug-in and play.
The PreSonus Bluetube DP V2 is a half rack sized tube pre-amp with a metal case and the familiar PreSonus blue fascia, in this case dominated by a pair of back-lit VU meters. The input (mic/instrument combi-sockets) and output (balanced XLR, unbalanced ¼” jack - you can use both at the same time) sockets are on the back panel along with the 12V input for the external power supply, leaving the front panel for all the fun bits. You don’t get an option to fit rack-ears, so if you want to rack the Bluetube you’ll need to use a rack-tray (there’s a threaded hole in the bottom of the case and you get a screw to fix it).
Each of the two channels has backlit buttons to select 48v phantom power (on the XLR only, not on the instrument/jack part of the input), polarity invert, -20dB pad and an 80Hz low-cut filter, along with its VU meter, a finely stepped Gain knob (with a clip LED) and a Tube Drive knob with built-in on/off switch. There’s no power switch on the unit, but there is an in-line one on the power cable.
Now this isn’t a tube pre in the classic sense; the onboard 12AX7 tube isn’t the main amplifier, and it isn’t running at its full 200-300 V plate Voltage (a quick Google search suggests around 48V, which is higher than the typical 30V used in many “Starved Plate” designs). In the good old days tube pres were designed to run as cleanly as possible with as much headroom as could be designed-in; here the heavy lifting is done by the discrete, solid state, class A, high headroom XMAX pre-amp and the tube drive can be added gradually to sweeten the sound.
Logic says “start gradually”, so, like most people probably will, I turned the Tube Drive all the way up just to see what it does. With the drive on maximum, the sound is noticeably saturated, and I lost a very happy hour or so playing my Strat plugged into the instrument input and then recorded direct (I can see the Bluetube getting a lot of use for recording clean-but-big guitars, and I’d have quite liked to have an instrument input on the front panel).
Reducing the Tube Drive produces a range of gritty-to-sweet sounds that can work really well on vocals and miked electric guitars, and the lower settings are rather subtle and just seem to make things sound a bit bigger. Interestingly, the 1/3 rack sized single channel version of the Bluetube doesn’t have the switch on the Tube Drive control; you can turn it down but not off (I really didn’t miss it that much because the minimum setting is, as it should be, somewhere between subtle and unnoticeable.
There are many far (far) more expensive tube pre-amps available (including some from PreSonus themselves) and no doubt you can get a more refined sound from some of them. That said, I was pleasantly surprised by how good the Bluetube sounds; I think I expected the Tube Drive to be a bit like a distortion effect, but it’s actually a lot more gentle and useful than that. The XMAX pres work very well if you just need a couple of additional clean mic inputs, and that Tube Drive does a lovely job of adding flavour to taste. (...speaking of taste, there’s a recipe for Jambalaya in the back of the Owner’s Manual!)
Overall then, this is a cost-effective option to add a couple of additional channels of mic pres to your recording rig, with the added benefit of getting a useful range of new sound-flavours in the same box.