Investigation into possible mods for the Stax SR-404

[moray james]

What kind of adhesive did you use to mount the elements? Was it hard? If so a softer adhesive (when curred) might help to damp the structure a little. Just a thought.

[spritzer]

I used polyurethane so not excessively hard like epoxy but very strong. I'm thinking about adding a layer of the paper material to the back to the drivers and see if it makes a positive difference.

[Tachikoma]

The Lambda Sigs have never struck me as being shrill so there might be something else at play here. I'm very sensitive to exaggerated HF response and even with my sole use of silver wire they have never presented like that. That's about 10-15 sets in total so have you checked that the set still has the stock drivers? There are plenty of them out there with SR-404 drivers...

My Lambda Pro with 404 drivers was really midrangey and not shrill at all, so I'd expect these to be more mellow if the drivers were replaced. Wasn't the 1um film notorious for being shrill-sounding? Maybe the SRM-X Pro is just a crappy amp >_>

Anyway, I found that I only needed a half of the tissue paper I used before to tame the midrange etch to tolerable levels. A double-layered piece of tissue paper took away too much of the bass for my liking.

[wrecked_porsche]

The Lambda Sig, shrill? Etch? nah. Edgy, exciting and energetic is what I'd call them.

It be mah favourite headphones. Been driving them outta the T1 and 717, been loving every second of it. I even ditched the O2mk1 in favor of the Lambda Sig.

Birgir, thanks for the pics, I've seen and touched that kinda material somewhere some time back but I can't, for the life of me, remember right now where I saw it.

Don't wanna mess with mah L. Sig sound though. If I were to mess with it, I'd wanna bring out a little extra separation and texture in the bass region. If you find a way to do that on the 404, let me know, I might try it on the Lambda Sig.

[spritzer]

Given a good nights sleep the change from using tape to permanent glue isn't so bad and mostly the fault of me jacking up the volume too much. Any damping scheme will be dependent of the intended volume setting since it changes the sheer amount of air the drivers are shifting.

My Lambda Pro with 404 drivers was really midrangey and not shrill at all, so I'd expect these to be more mellow if the drivers were replaced. Wasn't the 1um film notorious for being shrill-sounding? Maybe the SRM-X Pro is just a crappy amp >_>

Now that makes more sense. The thinner diaphragm needs more power to behave as it lacks mass to damp it self. Put those phones on the budget amps and it isn't pretty...

Anyway, I found that I only needed a half of the tissue paper I used before to tame the midrange etch to tolerable levels. A double-layered piece of tissue paper took away too much of the bass for my liking.

You need to damp the back as well to get the bass back but I'm struggling to get back some of the presence in the upper bass/lower midrange. Foam might be the ideal material here but I don't have any of the good open cell stuff.

The Lambda Sig, shrill? Etch? nah. Edgy, exciting and energetic is what I'd call them.

It be mah favourite headphones. Been driving them outta the T1 and 717, been loving every second of it. I even ditched the O2mk1 in favor of the Lambda Sig.

Birgir, thanks for the pics, I've seen and touched that kinda material somewhere some time back but I can't, for the life of me, remember right now where I saw it.

Don't wanna mess with mah L. Sig sound though. If I were to mess with it, I'd wanna bring out a little extra separation and texture in the bass region. If you find a way to do that on the 404, let me know, I might try it on the Lambda Sig.

Nobody will ever accuse the L-Sigs of being dull that's for sure. It will be hard to give them more separation since they are diffused by nature and the bass is also hard to fix.

[Tachikoma]

You need to damp the back as well to get the bass back but I'm struggling to get back some of the presence in the upper bass/lower midrange. Foam might be the ideal material here but I don't have any of the good open cell stuff.

I didn't really "damp" mine properly though - I just stuffed a little tissue between my ears and the drivers. The bass is very much present with the amount of damping I'm using.

Now that makes more sense. The thinner diaphragm needs more power to behave as it lacks mass to damp it self. Put those phones on the budget amps and it isn't pretty...

No BHSEs here Do you think one of Stax's hybrid amps will cut it? Or perhaps the Poor Man?

The Lambda Sig, shrill? Etch? nah. Edgy, exciting and energetic is what I'd call them.

It be mah favourite headphones. Been driving them outta the T1 and 717, been loving every second of it. I even ditched the O2mk1 in favor of the Lambda Sig.

Even without the etch, the lambda sig sound still isn't really my thing. I much prefer the "round-driver" based Staxen, and the SR-5NB (RIP) was my "go-to" headphone when I'm looking for a little excitement.

Birgir, thanks for the pics, I've seen and touched that kinda material somewhere some time back but I can't, for the life of me, remember right now where I saw it.

It looks like the filter material used in air-conditioners.

[deepak]

Birgir, nice work with the mods!

I can see where you're coming from when you say that the soundstage gets a bit smaller when the upper midrange coloration is lessened. In my experience headphones which project a larger "soundstage" is based in large on two things:

a) driver distance from the ears

emphasis on upper mids

and

c) (lesser extent) angling drivers away from the ear

[spritzer]

For a great Stax amp on the cheap there is really only the 717 but the Warthog (PoorMan) could have what it takes. Time will only tell...

[wrecked_porsche]

Indeed. Many people have wanted to buy my 717, but I ain't letting it outta me sight.

Its a really, really nice amp.

[spritzer]

Here are the pictures I promised I would upload yesterday. Anyway here are the earpads with the front damping material. I take one sheet of the damping paper, break it in half and then iron in nice and flat. The dustcover is upside down in all of these pictures and should have the plastic rings facing towards the ears.

In the second picture you can see the "pocket" which is on the new Lambda pads. This makes installing the damping sheets far easier and has allowed me to use only minimal amount of double sided adhesive to secure the pads for testing.

Next up are the drivers permanently mounted to the baffles with polyurethane glue. If somebody reading this is crazy enough to do this, please use as little of the stuff as you can and let it cure for 12+ hours.

The drivers are wired and ready to go in the second pic. The Lambda drivers are always wired in phase (the wire with the stripe on it is connected to the front stator) but this isn't the rule with all Stax headphones. Some of the SR-1,3 and 5 units were wired out of phase and the Sigmas are all wired out of phase.

Here is the back damping layer. This felt is called craft felt by the ortho crowd, is 1005 polyester and of lowish density. The part numbers can be found in the massive ortho thread over on HF but I'm sure most types of felt would give an acceptable result and the same goes for medium density foam.

Finally here are all the parts need for assembly (minus the screws and the glue for the earpads).

I'll probably try a few different materials for damping the backwave but I'm rather happy with how this configuration sounds. I've accomplished what I set out to do, tame the damn midrange peak. Now when damping one can't have his cake and eat it too and when damping the midrange there will be consequences elsewhere. The top end is dulled a bit (a good thing to my ears) and the bass isn't as quick as it is on the stock cans. There is also a hint of edginess from time to time but I can live with it.

[faust3d]

Great guide. Why didn't you cover the entire back and sides of the cups?

[spritzer]

I did it to let the bass breath just a bit. The housing presses the felt close to the drivers at the back and there is a 4mm or so gap to the front of the headphones.

[faust3d]

I finally tried the paper in front of my SR-303 drivers, don't like it that much as the HF energy seems to go down a lot with this mod. I also had the foam behind it so that might not be an ideal configuration.

[spritzer]

You know I likes my HF on the soft side (SR-007 Mk1 ) but the distance from the drivers could be an issue. The felt on the back of the drivers is needed though to even out the sound so that could be a factor as well.