It seems that audiophile-quality 8×2 stereo mixers looking for a home always seem to find one here at my studio! Since the early 1970s, I have purchased several such units, and have never seen the need for a larger board, since I do mainly classical and acoustic jazz recording sessions. And yet, although I own many tube mics and preamps, I have never had the opportunity to audition a tube mixer any more sophisticated than my extremely basic vintage Ampex MX-10 4×2 unit.
Product PointsApplications: Studio, project studio
Key Features: 8×2 mixer featuring hybrid amplifier structure with electronically-balanced input amplifiers, vacuum tube triode second stage and summing amps, and balanced, floating solid state monitor and main output amps. Flexible design features comprehensive monitoring and insert facilities, four-band EQ, and two mono aux sends and stereo returns. Optional 96 kHz, 24-bit ADC outputs in various stereo formats.
Contact: TL Audio/Sennheiser USA at 860-434-9190, Web Site.
Early in the summer, a TL Audio M-3 Tubetracker ($3,530) arrived at Studio Dufay in a shipping carton nearly the size of a refrigerator. This baby is heavy, and its center of gravity is nowhere near its physical center! The specs list its weight as 18 kg (40 pounds), but it feels much heavier than that due to the layout and distribution of its internal parts. Its (2RU) separate power supply resembles a large stereo mic preamp, in size.
This huge (10 rack-units high) mixer has every feature I have ever seen in an audiophile 8×2 mixer, and then some!
Looking at the rear panel, one sees eight XLR mic inputs, two more XLRs for line output, and three sets of eight 1/4-inch connectors for line input, insert, and direct output. It is really nice to have separate direct outputs (switchable to -10 or +4 dB levels) in addition to the typical TRS in/out insertion points; thank you, TL Audio! There are also pairs of 1/4-inch jacks for monitor and aux outputs, and for two sets of effects returns; there is also a pair of TRS jacks for a two-track return. Most of these 1/4inch jacks have -10/+4 dB pushbuttons associated with them. There are also DB15 input and output connectors for linking multiple units. Across the bottom of the rear panel are various sets of recessed channel, link, meter, and stereo output level calibration trimpots.
The upper left-hand corner of the rear panel features a 4-inch rectangular opening that can either be covered by a plate or, in the case of my review unit, fitted with a stereo ADC option card. Mine had several parallel digital outputs (AES/EBU, S/PDIF and TOSLink), as well as a BNC jack for word clock input, and a switch for selecting external or internal clock. On the front panel, one can select any common sampling frequency between 44.1 kHz and 96 kHz, and bit depths (dithered, of course) of 16, 20, and 24 bits.
The front panel has eight identical channel strips, and then a double-width master and monitor section. Each input channel features – from top to bottom – a gain pot (16 to 60 dB for mic, -20 to +20 dB for line), four pushbuttons for selecting line/mic, polarity, a 90 Hz, 12 dB/octave high-pass filter and EQ on/off. Below these are six EQ knobs – HF and LF shelving level, and upper and lower midrange variably swept frequency, and level. The EQ shelves are at 80 Hz and 12 kHz, while the range of frequencies selectable for the peaking circuits runs between 50 Hz to 2 kHz on the LM band, and between 500 Hz to 18 kHz on the HM band. The Q is fixed at 0.7, and all bands have ±15 dB level controls.
Below the EQ controls are level controls for the two mono aux sends, each with a PFL (mono solo) switch. Further down are a channel pan pot, mute and PFL switches for each channel, a scribble strip, a pair of LEDs showing the attainment of a particular peak level, and a “drive” light, indicating attainment of a specific place in the mixer’s gain scenario between the first (solid state) and second (triode vacuum tube) stages. Learning how to read these two LEDs enables the engineer to creatively use the characteristic saturation sound available only with slightly overdriven tube preamp circuits.
Mixing to the stereo buss is done via the aforementioned pan control and a 100mm fader, which is located at the bottom of each input strip.
Over on the output and monitoring strip located to the right, one first notices the pair of large illuminated moving coil VU meters (each with a peak LED beneath it), which follow the monitor output – which normally follows the stereo output. However, one can also monitor the two-track return inputs. Any PFL (mono solo) signal automatically overrides the monitor output. Directly below the meters is a single horizontal set of LEDs that correspond to the digital output level, and two controls for the unit’s stereo digital output’s sample rate and bit depth.
There are also master level controls for the two aux outputs (with PFL switches), and separate level and balance controls for the two effects returns (also with PFL switches). Below all this lies the master 100mm fader, and a 1/4-inch headphone jack, which drove my Sony, AKG, and Sennheiser headphones to appropriately high levels.
I’ve had the Tubetracker here in my studio for nearly two months, and have used it just about every day. Everything that I could possibly send through it, I have. Thus, I have certain conclusions about its “sound” or, more specifically, its various “sounds.”
The easiest way to explain these conclusions is to begin by detailing what I call my “simple audiophile switching setup.” Take a great sounding source (for example, “Things I Miss the Most” or “Pixeleen” from the new analog-recorded Steely Dan CD, playback through the best DAC chain you have (in my case, an Audio Alchemy CD transport through a Weiss DAC-1 Mk. II converter – directly through a passive Coleman Audio MS8 switching box (PAR 4/00) to heavily modified McIntosh MI-200 industrial tube amplifiers, driving Manley Tannoy loudspeakers augmented by custom transmission line subwoofers.
What did I switch? Well, the direct output from the Weiss, and the various outputs from the Tubetracker. That is to say, I connected the TL Audio mixer’s direct outs, aux outs, main stereo buss outs, and monitor outs – so I could hear clearly which parts of the Tubetracker imparted the most coloration to the audio signal passing through it – and carefully matched the levels amongst them. TL Audio publishes a block diagram of the mixer’s circuitry and, by carefully studying it, one can easily map the number of various tube and solid state amplifiers through which the audio signal passes onto the listener’s subjective impressions. Sort of an “informed A/B” test.
Parenthetically, I also tested the Tubetracker’s mic preamps, but found them not as outstanding as the unit’s line level and EQ circuitry. Low-output ribbon mics, such as Royer or my AEA R-84, sounded very noisy and undistinguished, and picked up strange whistles (never-before experienced) in my studio. (Editors Note: TL Audio is aware of the problem and says that current production models have an improved preamp.)
Modern solid state microphones, such as my Gefell M-930s, sounded more or less as I expected, albeit with a bit of a solid state edginess, which I did not expect – since I’m so accustomed to hearing them through my various high end tube mic preamps. The Tubetracker’s mic stage is an electronically-balanced solid state one, so one should not expect much “tube magic” from it.
There were a few other surprises, but the Tubetracker’s obvious “winner,” sound-wise, was its direct outputs. And that’s a good thing! Through these, Donald Fagin’s voice stayed completely “in focus,” while the rest of the band was given a small “euphonic coloration” from the single triode tube stage and solid state buffer amps through which the signal passed. Thankfully, the Tubetracker’s design allows the most important part of its circuitry, in my opinion – its EQ – to be applied to the direct outs, so I can comfortably state that, for someone who simply wants to send eight tracks through something for EQ and “tube coloration,” the Tubetracker would be perfect!
The main stereo buss outs sounded almost as good as the direct outs, and the vocal still sounded fine. Their sound is big and “ballsy,” and the solid state outputs were able to drive any sort of cables or adapters I could muster from my basement milk crates. And when I used the Tubetracker’s digital ouputs, I was really pleasantly surprised that they sounded great, even at 44.1 kHz! If you own a Tubetracker, you’ll be hard pressed to justify the expense of an external ADC.
The aux outputs, for some reason, imparted a bit of softening and quite a little phasiness to the voice. According to the schematic, the main difference between the aux and main output circuitry lies in the fact that the main outputs include a triode gain stage before the solid state buffer amp, while the aux outputs have both solid state summing and output amplifiers. This slight degradation of the sound quality may or may not affect most users – depending on what they expect the aux outputs to drive. For example, an optical stereo buss compressor would change the sound much more than the aux outputs do and, thus, would swamp any of their slightly negative effects. On the other hand, if an engineer wanted to use the auxes to drive a separate recorder, or a super-duper audiophile-quality equalizer in insert mode like a Manley Massive Passive, the decision would be more difficult to make.
The monitor outputs imparted the most phasiness and softness to a center channel vocal but, after all, they are only monitor channels. My original Neil Muncy-designed Suburban Sound SS-III 8×2 mixer from 1971 (the small high-end mixer from those days) uses a pair of little Beyer transformers to isolate the PFL signals and then needs an extra +30 dB gain stage to get the level back up. That bit of elegant engineering compromises its sound quality much more than the TubeTracker’s monitor circuit does, so a little perspective here is indicated.
But where it counts, the sound quality of the TL Audio Tubetracker is unimpeachable and, at its asking price, it is quite a bargain, considering all that you get. I know of no other piece of mixing equipment that does as much, and sounds as good, overall, as TL Audio’s TubeTracker.