Stax SR-007 Omega II electrostatic headphones Page 2
The SRM-007t tubed headphone driver looks similar to the SRM-717, but with more venting on the top of its chassis. Just above the center point of where each of the four tubes are socketed in the chassis, exhaust holes on the top cover swirl around a punched-out bulge in the metalwork. Damn cute.
The SRM-007t's front panel is almost the same as the 717's. An additional push-switch on the 007t lights on impact, as it were, and two input switches select said input. There are three outputs—two Pro Only five-pin sockets with 580V polarizing voltage, the third a six-pin "Normal" type with a 230V voltage. And you've got that same superior dual-ganged, four-level volume pot.
The 007t's rear panel is a bit more populated than the 717's. There are a pair of switch-selectable XLR and single-ended inputs, paralleled, marked Input 1. Next to that, Input 2 is arranged like a tape loop: L/R In and Out on RCAs, with a sturdy ground terminal beneath. Once again, a graphic on the rear panel illustrates the pin-2-negative "standard"; both headphone amplifiers will invert polarity when driven by source components wired with pin 2 of their XLRs "hot."
The SRM-007t is a direct-drive system with no transformers between the amplifier and the Earspeakers, for "stable and high-quality sound." A simple two-stage design uses dual FETs in the initial stage, and, in the second stage, the 6FQ7 dual-triodes, which have a "high dielectric strength." This achieves, in Stax's opinion, "the best, clearest, and most natural sound." Because it's DC-coupled, the SRM-007t has no output caps, which are "unfavorable to sound quality," says Stax.
The SRM-007t is designed for "ideal driving" of the Omega II Earspeakers, but even Stax admits that their solid-state and tubed units sound different: "Vacuum tubes in the output stage of the SRM-007t provide transparent and clear sound different from that of solid-state drivers." The four dual-triode 6FQ7/6CG7 tubes are "highly reliable" and "registible against high pressure," whatever that means, and are used in parallel in the output stage for low impedance and greater transparency in the high frequencies.
Setup & tweaking
The casual setup I used with the Cary CAD-300SEI/Sennheiser HD600 combo wasn't going to cut it for critical listening with the high-resolution Stax devices.
The Cary sits on the top shelf of a good-looking BDI Ventura three-glass-shelf stand located behind our Corian-topped desk. The only real "problem" are the glass shelves, which are rather thin at 3/16". So the big'n'heavy transformed Cary, despite its own substantial rubber feet, was suspended on a trio of extra-large AudioPrism Iso-Bearings.
The only other tweaks being used with the Cary when the Stax system arrived were choices in power cord and interconnect. I'd found long-term happiness with the Cary with a Golden Sound Navigator power cord with gold-plated silver wire and black mesh cover. Interconnects changed over time, but I was never really happy with what I achieved in that department—nothing too thick and unwieldy, please! There's only so much room...
Preparing for the review, I took out the Rotel 971 CD player I usually run on the middle shelf and replaced it with the Linn CD12, no footers. (All of Scotland looks at you aghast when you mention footers of any kind. "Our equipment is designed to sit on a flat shelf," sniffed Linn's Man in America, Brian Morris.) The CD12 was a good bet for this comparison—it has two sets of analog outputs! Switching between the Stax headphone amps simply required unplugging the SR-007 headphone from one amp, plugging it into the other, and matching the volume. Naturally, I spent some time with the Linn into my reference headphone setup to familiarize myself with that combo's sound. Yummy.
To power the two Stax amps, first I dragged the PS Audio Power Plant P300 (mit fan) and MultiWave upgrade out of our main system—I did the upgrades here with all ten of my own thumbs—and dropped it behind my writing chair near the headphone amp stand. Yeah, I got a writin' chair too. Had it for quite some time, actually (he sniffed too!). It's the now-popular Herman Miller Aeron Chair. I pop my keyboard on a Scooter, also by Herman Miller.
Both the Stax amps' power cords dove into sockets on the rear of the P300 with Synergistic Research Resolution Mk.II Master Couplers with angled connectors at the IEC end, making hookup easier regarding space. A third socket on the P300 was taken up by the generic Belden-like cord Linn delivers with the CD12. (Linn claims that their space-age power supply is immune to power-cord type, and that it actually functions as a line-enhancer, as its switch-mode supply doesn't pull down and notch the AC sinewave or dump garbage back into the line the way traditional big amps do.)