SR-404LE, SR-404 Signature, and SR-Lambda Pro

When I first started learning about Stax headphones, I was always confused on how people would talk of the different headphone models like the SR-202, SR-303, and SR-404 as “lambdas”, while at the same time you have the SR-Lambda and the SR-Lambda Pro headphones which directly uses the “lambda” name in their model type. It’s important to realize that the name “lambda” is used for all Stax headphones that shares the Lambda frame, starting from the SR-Lambda, all the way to the current SR-404 flagship and the SR-404LE.

The SR-Lambda that we reviewed a while ago is the first lambda design headphone created by Stax in 1979, which Stax later replaced by the SR-Lambda Pro model. The Pro model requires a higher bias voltage of 580 volts, compared to the 230 volts normal bias non-Pro models. (It is important to note that the Pro and non-Pro models are non-interchangeable. The non-Pro models come with 6 pins on their plugs, so you won’t make the mistake of plugging them into Pro amplifiers which comes with only 5 pin connectors. The connectors simply won’t fit. However, you can accidentally plug in a 5-pin Pro model into a non-Pro amplifier. The resulting sound will be very low in volume, and it’s not recommended because damage may occur when you try to turn up the volume excessively. Anyway all the Lambda headphones that we’ll be comparing here are Pro models.)

After a few model revisions, the current lambda that’s offered by Stax is the SR-202, SR-303, and the SR-404. And in the spirit of celebrating Stax’s 30th anniversary of the Lambda design, Stax released a Limited Edition SR-404, dubbed the SR-404LE headphones with a sound that’s noticeably different than the regular SR-404 Signature. Aside from the black paint finishing an the SR-404 Limited and 30th Anniversary emblem found on the SR-404LE, the non cosmetic changes of the SR-404LE includes a new copper-silver hybrid cable, as well as real sheep leather earpads. As quoted from the press release:

The core cable makes use of highly reputed 6N Cu high-purity soft copper cable (diameter of 0.14 x 3) with six silver-plated soft copper wires (diameter of 0.08 x 9) set around the core cable.

Although Stax did not mention any changes in the driver, we are still highly suspicious if the driver on the SR-404LE is the same to that on the SR-404 Signature. The sound difference between the two models are quite evident, and it’s hard to imagine that they were contributed by just the new cable and the the real leather pads. Anyway, the introduction of the SR-404LE has been met with enthusiasm among the headphone crowd. Most people thought that the Limited Edition version sounds noticeably different, and overall, is an improved version of the SR-404 Signature. Stax only produced 1,000 SR-404LEs, and seeing how production has been ended on these headphones, it may be fairly difficult to source out new units. Rumor has it that almost all of the 1,000 pieces have been sold, with only a few left worldwide. Good thing that rumors also say that Stax will soon introduce the updated SR-404 Mk2 which may have a similar sound to the SR-404LE, though the Mk2 may not come with the real leather pads.

SR-404 Limited Edition Badge in Gold Lettering

Holding the SR-404LE in your hand, you can feel that this is one serious Lambda, and definitely on a different class than the other Lambdas. The black color finishing looks much better than the drab looking SR-404 Signature. And though the cables of the SR-404 Signature and the SR-404LE are wider than the other Lambda models, I can’t help but noticing that the SR-404LE cable is significantly heavier on my hand than the SR-404 Signature and the SR-Lambda Pro cable. The gold printing on the cable and the housing of the SR-404LE gives a feeling of class, and its black finish looks blacker and glossier than the black finish of the SR-Lambda Pro. Overall, the cosmetic changes on the SR-404LE alone may warrant the higher price tag.

The rig that I’m using for this review is a fairly high end one, starting from the Neko D100 Dac that supplies a balanced analog signal to the Headamp KGSS Electrostatic Amplifier. Since I’m unfamiliar to the Neko D100 DAC, I tried hooking up the Grace m902 DAC to the KGSS, via RCA connection, and it’s very clear, that the Neko is in a superior class than the DAC on the Grace m902. The Neko had a superior three dimensional imaging, where the Grace m902 has little depth to the soundstage. I find the Neko to be a great sounding DAC with a relaxed sound that would complement the Lambdas well.

HeadAmp KGSS on Left, Neko D100 on Right

The KGSS Amplifer is huge. Enclosed in a single casing, it has a far bigger footprint than the average Hi-Fi gear. At the moment, the KGSS is probably ranked as the 2nd tier Electrostatic amplifier along with the Woo GES, and at $2,295, it is not a cheap amplifier. The KGSS has a separate volume control for the left and the right channel, and by utilizing stepped attenuators, channel imbalances found in the headphones can be easily remedied.

The KGSS is configured with a 5-pin Stax Pro Bias Connector, and Individual Left/Right Volume Controls.

Hi quality cables were used for the review. Zu Mother Power cable for the DAC, a Kimber PK10 Power cable for the KGSS, Transparent MLB XLR Interconnects, Stereovox Coax cable and a Trends UD10.1 USB-Coax converter, with the Apple MacPro and iTunes on the source end.

As usual, I used a combination of mainstream pop, alternative rock, classical, and reference jazz and classical recordings.

Now, let’s move on to sound impressions.