I am selling an Audio Logic 24 MXL “Magnetic Interstage Vacuum Tube Audio Processor” with Tube Research Labs upgrades for $800 plus shipping and any payment service fees. I had the 2 included Electro-Harmonix 6922 EH tubes cryo treated by Dave Elledge at PI Audio, after which I treated their contacts with Caig Pro Gold, along with the fuse and all external connectors on the DAC. You can find the specs and most of the content from the manual here:
I bought the DAC in 2007 from the original owner, who had it modified in Oct of 2006 by Paul Weitzel of Tube Research Labs. I have the letter from Paul listing the cost of the upgrades at $800, though it doesn’t list details. (I believe the DAC listed for $4500 in 2006.) Based on my inspection, aside from damping some of the internal components, the primary modification was to add a direct (single ended) output in addition to the original tube driven (single ended) output. For reference:
TRL modded AudioLogic 24 MXL, original tubed output: 1.56V TRL modded AudioLogic 24 MXL, TRL added direct output: 0.78V
If you look at the photo of the rear of the unit, the direct output is on top, and the original tube output is on the bottom. I regularly used both outputs, and would switch as the mood or recording dictated.
My audio journey has been bumpier than I’d prefer, so despite owning it since 2007, the DAC hasn’t seen much play time, and I was never able to develop a high-res library with which to take advantage of its 24-bit / 96 kHz capabilities. Since converting to a fully balanced, active system driven by a Mac Mini several years ago, the 24MXL has sat safely tucked away in a closet of my pet-free, smoke-free home. I just hooked it up again recently to ensure that everything was working, and it sounds as good as ever.
The only functional issue that I ever noticed was that the left LED was occasionally slow to come to full brightness. (There are 2 blue LEDs inside the unit, one on each side, that light up when the DAC comes out of stand-by mode upon sensing a signal on any input. See photo below.) I thus asked Wayne Waananen, formerly of Bolder Cable, to look the unit over and he confirmed the proper voltages and gave it a clean bill of health. I can’t find any cosmetic issues of note, though I have tried to take detailed photos to help back that up. (The thin metal plaque added to the back by TRL to acknowledge their mods is pulling away a bit, but I didn’t want to re-affix it in case the new owner wants to remove it instead.) I'm happy to supply additional photos if desired.
I have the original box and manual (3 double sided pages stapled together, though fairly detailed). No power cord came with the unit, though I can scare up a generic hospital-grade cord if needed. (It would have to ship separately.)
For what it’s worth, I am every bit as impressed by this DAC today as when I first received it. If I thought I could ever put together a second single ended system in a location that had the space, I’d keep it. Please let me know if you have any questions.