When I reviewed the LaChapell Audio 583S mk2 tube preamp [Tape Op #104], I learned that it is a fantastic mic preamp with lots of tone and personality, and it is the only 500-series preamp that I know of that provides a full 250 V to its 12AX7 tube. The 500TDI is a 500-series tube DI inspired by the 583S mk2, born out of a need for a great DI. The 500TDI generates a mic-level output signal, ready to be fed into a 583S mk2, or any other preamp of your choosing. Conveniently, my review unit arrived a couple days prior to a tracking session with The Beat Connection here in Seattle, and I immediately noted that this DI module is every bit as robust and well-built as its preamp sibling.
The front panel of the 500TDI is dominated by two large, brushed aluminum knobs, one labeled "Tube Drive" for setting input level, and another for output level. They both turn detented pots that feel great in the hand. There are two 1/4'' jacks, held captive with metal nuts. The high-Z Input jack is suitable for any instrument-level source, active or passive, while the Thru jack can be used either as an output to feed an amp, or as a low-Z input for additional variance in tone. A high-pass filter is engaged by a metal toggle that feels solid. Interestingly, the HPF, which is implemented after the first gain stage, has its −3 dB point at 65 Hz when Tube Drive is at maximum, but it shifts semi-proportionately with the level of Tube Drive. A small bar assists in the insertion and removal of the module — which may sound inconsequential, but I am often surprised by how challenging it can be to pull a module out of a 500-series frame when there is nothing to grab other than a control knob. Inside is a 12DW7 tube operating at 250 V.
The 500TDI is capable of producing a nice, pristine output signal, and there are many situations where that is what you need for the job. But the real fun starts with cranking on Tube Drive. Harmonic saturation is a result of increasing the input level, and it is quite effective in bringing flat sources to life and making them stand out in a mix.
Through the 500TDI, a vintage Rickenbacker bass with flat wound strings sounded very focused, with every bit of note you could hope for. The lows were meaty, and there was plenty of articulation in the mids and highs. When I plugged in my trusty old P-Bass, the 500TDI delivered all the character of the bass, and I was able to accentuate some of the growl with Tube Drive cranked up a bit. The low end was never tubby, but it was extended and robust. On guitar, Tube Drive could be tweaked for grit; and when driven harder, the 500TDI offered some degree of tube compression, which sounded great. We also used the 500TDI to record a Moog Sub Phatty. Not only were we able to capture all the super-low character of the synth, but we were also able to add in a little hair to give it some definition.
As classy as the LaChapell 500TDI looks, when pushed, it is capable of some superbly aggressive tones, but that's not to say it cannot play nice as well. Having a tube DI in your arsenal is like having another color in the paintbox, and with the option of driving the tube, it's like getting the big box of Crayolas with the sharpener on the side.