Review: Blue Tube, a tube-based pre-amp

by Mark Longo

Following are facts and some subjective impressions about the Blue Tube pre-amp from Tubeworks, which I have owned and used with my Hammond-Suzuki XB-2 and PRO-3 for many months. My impressions of the Blue Tube unit were formed from using it in gigging situations at unreinforced volume levels in mostly small and medium sized club venues.


The Blue Tube pre-amp is a single space rackmount device for use in the signal chain between your organ (or guitar, bass, etc) and an amplifier. The unit routes your input signal through a 12AX7 vacuum tube and provides front panel controls for volume, tone, drive, and tube bias. The Blue Tube output signal is then sent to your amplifier, mixer, effects boxes, etc.

The purpose of using such a device is to make your organ's tone warmer, fatter, and punchier, and I feel that the Blue Tube accomplishes this purpose. My XB-2 and PRO-3 combination simply sounds bigger and more present with the Blue Tube unit and my organ punches through the stage mix better than ever before, giving my XB-2 a more meaty, solid tone.

When overdriven, the Blue Tube yields a pleasantly warm harmonic distortion. This is not the full throated growl of an overdriven Leslie 122, but it's a great improvement over any solid state overdrive effect in existence.


The Blue Tube was not very widely available when I bought mine in early 1996. I mail ordered my rackmount unit through Manny's in New York for $240 US plus shipping. Availability may improve as the popularity of tube effects in general is rising. There was also a stomp box version of the unit available for about $100 less, but I chose the rackmount version for reasons described below.

Physical Description

The Blue Tube unit I chose fits into a full width single rack space with a depth dimension typical of effects units. It has medium sized control knobs on the front of the unit which are spaced far enough apart to be easily accessed.

There is a large green "power on" LED and a red active LED that is illuminated whenever the unit is not in bypass mode. The unit is medium blue in color with yellow lettering which stands out in your rack. Input, output, and footswitch jacks are located in the back, the power switch is in front, and an internal power supply is used (no hated wall wart!). The unit runs cool in my rack and needs no special ventilation or placement.

There is also a stomp box version of the Blue tube available for about 40% less money. I chose the rackmount unit for convenience of setup (no wall wart to deal with), and because with an expression pedal, piano damper pedal, and PRO-3 speed control at my feet, the floor around my rig is crowded enough already. Also, the stomp box unit did not appear to have a "contour" control in the pictures I saw of it, and this has turned out to be an important control for me. (see below).

The Blue Tube is manufactured in the USA.

Signal Routing

You run a line out of the organ (or module), into the Blue Tube unit, then out of the Blue Tube and into your amp, mixer, Leslie simulator, etc. If you're using effect boxes, try experimenting by putting the Blue Tube in different places in the signal chain. My signal routing looks like this:

XB-2 -> Lexicon Alex -> Blue Tube -> PRO-3 -> mixer -> amp -> speaker

I find that the PRO-3 sounds good when fed a hot input signal, so I run the Blue Tube master on 10 and place it immediately before the PRO-3 in the signal chain. On the other hand, I found that my Lexicon reverb unit prefers a weaker input signal (it was apparently designed to work well with a guitar input level), so I put it first in the signal chain. I could just as easily have turned down the Blue Tube master and run it into the Lexicon (the Blue Tube has both line and instrument output level jacks) but I wanted to feed the PRO-3 something hot. Your results will probably be different, so experiment and above all let your ears be your guide.

The Blue Tube is a mono effect. If you are using a Leslie simulator in stereo and want to preserve the stereo image, you'll need to route the organ signal into the Blue Tube before it goes to the Leslie simulator or mixer.

The Blue Tube has separate input jacks for either an instrument level (for plugging in a Fender Rhodes, guitar, effects loop, etc) or a line level (for plugging in an organ module, mixer output, synth, etc). It also has separate instrument and line level output jacks, so use the line level for driving a mixing board or good quality effects box, and the instrument level for an effect or amp that's expecting that a guitar will be plugged directly in. With these input and output options and master volume for controlling the output level, the Blue Tube has enough versatility to be useful in a wide variety of settings.


BOOST SWITCH: Increases the amount of gain to the tube by 10dB. The switch is overridden when a footswitch is connected to the boost jack on the back of the unit. The idea is that you can drive the tube hard for a solo using the boost switch for increased volume and distortion, then turn the switch off after the solo to fade back into the mix. This feature seems intended for guitarists as I simply boost my input level via the expression pedal for the same effect.

BYPASS SWITCH: Switches the Blue Tube in and out of the effects chain. This can also be controlled using a footswitch plugged into the bypass jack on the unit back. Again, this seems to be more useful for guitarists.

DRIVE CONTROL: Also can be thought of as a pre-amp volume control, it determines how much gain is provided by the pre-amp section. Setting the drive at 5 or below yields some tube warmth but with a clean output signal (no distortion). Increasing this control beyond 5 gradually adds more harmonic distortion. (see the section below on Sound).

CONTOUR CONTROL: Adjusts the amount of low frequencies driven into the tube. Some players prefer a fatter texture to their sound, while others prefer a more articulated "less muddy" contour. I find the effect of this control to be broader and more general than a simple bass control. When used with my XB-2 it increases punch and presence across the entire keyboard, but at the cost of a little boosted low end rumble. I run the contour control at about 7 and roll off some bass with the organ tone controls. Alternatively you could compensate by turning down the bass control on the Blue Tube itself, but I find that turning it down on my XB-2 sounds a little better.

As a separate note, I feel that the contour control lets me add some punch and presence to the organ in the overall sense. My personal opinion, considering the tone I like, is that a significant amount of the tone improvement I got by using the Blue Tube came by adjusting the contour control. Your preference may well be different, but note that the stomp box version of the Blue Tube doesn't have a contour control (at least I couldn't see one in the catalog picture I saw).

BIAS CONTROL: Quoting from the two page owners manual, "The bias control actually adjusts the amount of cathode bias voltage of the tube stages, thereby regulating the amount of plate current." Hogwash. I've played with this knob and I'm damned if I can hear that it does anything that couldn't just as well be my imagination. I turn it up just on general principle but I think this knob is marketing hype as well as a waste of front panel real estate. Maybe if I was a guitar player...

MASTER CONTROL: Sets the overall output level of the unit. It changes output volume without noticably altering the tone of the unit.

HI CONTROL: Shelving control for frequencies of 1500 Hz and up.

MID CONTROL: Adjusts mid-range frequencies. Center is 500-600 Hz.

LOW CONTROL: Shelving control for frequencies from 100 Hz down.


For most of us, the tone generated by a tube Leslie, such as a 122 or 147, is a critical part of the best loved classic Hammond tone. A well-founded criticism of Leslie simulators and organ clones are that they sound somewhat sterile and are without personality when compared to the classic B-3 and 122 rigs. This is a true statement and in spite of advertising hype to the contrary, the only thing that sounds like a B-3 and 122 is a B-3 and 122. Adding a simple one tube pre-amp to your clone rig doesn't change that fact.

The much loved sound of a great tube Leslie comes from many properly maintained components acting together as an orchestrated team. The full range of tonality from clean & creamy to full throated growling screaming banshee that a tube Leslie is capable of requires its full tube amplifier (including, but not limited to, the big 6550 power tubes), a carefully matched and balanced speaker and driver combination with specific, unusual, and complimentary frequency response characteristics, a properly operating crossover, a tuned bass resonator, and more. Not to mention a nicely tweaked B-3 in the hands of an expert player contributing the source material!

But for those of us who have chosen or are compelled to play an electronic approximation of the classic Hammond rig, a tube pre-amp such as the Blue Tube unit does help us get a more classic sound. The sonic improvement I heard when I first hooked up my Blue Tube unit in my living room was satisfying, but subtle. There was a nice warmth and a little more guts to the tone, but nothing that really grabbed me. But when I took it out to gig I was very impressed. When playing with other instruments my XB-2 took on a presence it had never had. My comping and pads had a more solid foundation that in the past, and my solos carried through the mix with authority.

Regarding the overdrive, when the signal fed to the Blue Tube's internal 12AX7 passes a certain threshold, you begin to hear growly tube distortion which, while it doesn't quite match the deep grinding distortion of a big tube Leslie, does sound good and imparts some of the classic overdriven Leslie to your sound. And it definitely beats the lame solid state overdrive sounds found in many modern organ modules and leslie simulators (notable exceptions are the Digitech RPM-1 and Motion Sound R3-147 which both use a 12AX7 tube circuit).

I set the drive control on my Blue Tube unit so that it's relatively clean when I'm playing with the expression pedal at intermediate levels but when I put the "pedal to the metal" the growl comes in.


I think the Blue Tube unit very noticeably improves the sound of Hammond clones by adding some tube warmth, depth, and punch. It also makes it possible (though not necessary) to add some of the desirable aspects of tube based overdrive to your sound. Considering the comparatively limited expense of the unit, I think adding such a device to your rig is a cost effective way to improve its sound.

The Blue Tube unit is simple yet versatile. Its mono patching scheme includes both line and instrument level input and output jacks allowing it to be used with a variety of instruments (try it with your electric piano) and signal routing schemes. It's controls are logically laid out, clearly labeled and have obvious purposes (except for the bias control) and footswitches can be used to bypass and boost/cut the unit during performance. The unit can be set up to deliver clean tube warmth or infinitely selectable overdrive that increases or decreases with input volume, just like with a real tube amp.

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