My newest hobby is listening to / restoring / tinkering with Stax headphones. Stax has been making electrostatic headphones since the early 1960's, and they still make them today. I became interested in these headphones after being involved with Acoustat direct-drive electrostatic loudspeakers. The Stax are also directly driven electrostatic speakers, just scaled down to a size just small enough to strap to one's head. "Earspeakers," as Stax calls them… which is more appropriate given their size. Below I am modeling the ever-so-fashionable Sigma "Earspeaker." These are very rare, and were only ran in small quantities. The idea with these units is to mount the drivers ahead of and perpendicular to the ears in order to make the soundstage (or "headstage" as head-fiers call it) more realistic. Nevermind the logistic issues of strapping shoebox-sized enclosures to the sides of the listener's head! This technique does work, and the sound from these things is nothing short of amazing. There was an updated Sigma model, called the "Sigma Pro," which is even more rare. These had a higher bias charge. You can update the older units with drivers from other high-bias Stax earspeakers, such as the Lambda Pro and the 202/303/404 series. However, many people who love the sound of the originals claim that the updated models loose some of the "magic" in the midrange and headstage. I have no plans to update mine!



So how are these driven? Many folks use a step-up transformer from the speaker outputs of their conventional amplifier to drive these. Or, Stax and some aftermarket companies have created amplifiers that will directly put out the voltage swing required for these headphones. They need somewhere on the order of 800 volts peak-to-peak to sound their best. I am working on a tube-based DIY amplifier to drive these, but for now I use Stax's own SRM1 MKII direct drive amplifier. It sounds quite good, but I usually prefer the tone quality of tube-based equipment. There will be much more to follow on this unit as I build it. For now, here is a picture of my Stax electronics:



The item underneath the SRM1 MKII above is the incredibly hard-to-find ED-1 Equalizer made for Stax's other popular headphone of the period, the Lambda Pro. I have two of these headphones (sorry no pictures of them on my mug!). The ED-1 was designed to make the headstage sound more "out of the head" with the Lambda Pro Earspeakers. All I can say is I like what it does most of the time. With some pop recordings it can make the performer sound a bit distant. The verdict is still out on whether or not I will keep this unit.


Restoration Projects


Stax earspeakers are incredibly reliable, and will last a lifetime with the proper care. However, after a couple decades of use and storage, the earpads and especially the protective foam over the drivers will become cracked and start flaking. Replacements are still available from Audiocubes2, Yamasinc, etc. Below are some pictures of my Sigma earpad replacement. As you can see, they are attached to the enclosures with two-sided tape. The Sigma pads are unique in that they have an inverted "cup" that is made from the protective foam instead of a straight piece of foam found in the Lambdas. Anyway, the procedure is to simply pull off the old earpads, clean the surface with alcohol, apply the two-sided tape, and apply the new pads, being careful to face the inverted foam cup towards the drivers. The pictures below should make things a bit more clear. Oh, and these need to be protected from dust. I keep mine in a leather box I found at Target.



This procedure is much the same as the Sigmas, except for the fact that the protective foam layer is just straight across the earpads. Also, care must be taken to position the earpads properly, as there is a thicker section towards the bottom and towards the back of the head. The pictures below show this asymmetric layout. The driver enclosure shown below is the left side (note the solid white line on the wire - the right side has a dashed white line). Also note that to remove the driver in a Lambda earspeaker, the earpad must be removed. The screws to hold the driver plate are located beneath the adhesive tape. You can see them in the pictures below.



The headbands on Stax gear sometimes become worn. For the Lambda series earspeakers, you can install bands from the newer models with some modification. For the Sigma earspeakers, it is best to find an NOS replacement. The original headbands for the Lambdas will work as well. The new headbands are a bit difficult to retrofit to the Sigmas because the pin receivers in the sides of the enclosures are not as easily removed as in the Lambda procedure below. For the Sigmas, you would need to drill out the receivers for the new style headbands to work. It could be done, but I chose to put the new style headbands on my Lambdas instead, using the mint condition headbands from those to replace the ailing headband on my Sigmas. I'll stop the rambling text here and move on to the pictures in just a minute…

Anyway, as you can see below, the original headband uses a small metal pin and a metal receiver that is glued into the sides of the earspeaker enclosure. Fortunately, the new style headband sort of mimics this geometry… the only difference being that the new headband is all plastic and works without a receiver. Because of this, you need to remove the metal receivers from the sides of your enclosures. Use pliers and tightly grab the receivers. You want to very gently wiggle these back and forth until the glue fails. Take your time and you will be successful. Do not rush this process or you may break your enclosures! Once you remove all four receivers, you can assemble the earspeakers with the new headband.


You can purchase new headbands from Audiocubes2 or Yamasinc for the models 202, 303, and 404. Since the original Lambda Pros were all black, you probably want either the 202 "Basic" headband (which is black) or the 303 "Classic" headband (which is gray). I would avoid the 404 headband for use with the black Lambda Pro drivers because those headbands are brown. Anyway, I restored both of my Lambda pros, using a 202 headband on one and a 303 headband on the other. The pictures below show why I feel the 303 "Classic" headband is superior… it has a plastic form sewn into the headrest. This helps keep the form of the headrest. The 202 "Basic" band only has a piece of fabric there, so it does not stay formed into an arc as well. The headsprings, aside from their color, are the same.


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