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The saga continues...

All seemed fine today until I turned off the amp & pulled the plug from the jack. The hum rose quickly in level & changed in timbre. It then disappeared as the plug left the jack. I could not hear any residual hum in the earspeakers after that. It seems to be an amp issue, for sure. Is it failing?

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Hello, i am new here and since the Mafia reside here... i'm gonna ask for a help to the Padrino or some of his associates....

I recently bought a sra-12s that needs some love (a recap, a pot cleaning and an adding of a pro bias out), i got a discount on the original asking price and i got gifted a pair of stax sigma Normal bias ("because i don't know what to do with them if i sell the amplifier").

The Sigma are really ok, the drivers are ok, they simply need a cleaning AND a new damping because the original glass wool dampening have been removed.

My question is:

What can i use for remake the dampening? (I llan to use quilt batting, is that ok?)

What shape the dampening should have? (Should i cover all the planes except the driver one, am i right?)

And there seems to be a pair of resistor attached to the cable connecting the driver, are they normal?

Thank you very much.


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44 minutes ago, spritzer said:

Those are actually silistors and I'd remove them at this point.  They don't age well and at 30+ years old... jut them off. 

The damping is on all sides of the housing and needs to be very dense or it won't work at all. 

Thank you very much, i'll remove them and try with something dense.


By the way in my sra12s i have a +640V rail on the PS that feeds the amplifer board. Using that 640v point and a 2 resistors voltage divider to create the pro bias voltage is the normal way to do that? Ir therebis a better way?

Thank you very much and sorry for the newbie requests...

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Hello, while i wait for some parts for restoring my sra12s i made some new earpads for my sigmas.

I also made the internal dampening. Following the advice of Spritzer i used the most dense material i could find.

By pure luck the material and quantities i used seems to be ok. The soundstage seems here, definitely the best of the headphones i own. The bass is present and clear so i am pretty happy of the final result.

I decided to substitute the earpads because i don't feel comfortable  using earpads that have been used by someone else for 30 years...

I decided to not use a spare pair of lambda earpads because of the different shape of the lower back part.

I made them in leather following the procedure Stax (or their supplier) probably used.

I used an embroidery machine to sew the ear oval on the reverse side of fabrics, then i reversed the fabrics.

With the fabrics now on the right side i added some low heigh memory foam cutted a couple of mm smaller than the finished earpad.

Now i used the embroidery machine to close the earpads. Cutted the excess leather and here they are.

They are a bit bigger than the original ones and are less stuffed, nothing dramatical but i will remade them the next time i have time to use the embroidery machine.

The same method can be used to make them with a sewing machine for the oval and an overlock machine using 3 threads and a short lenght stitch.





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  • 2 weeks later...

The SRM-1/Mk-2 has been played everyday for two weeks, and I am very pleased with it. Definitely a more solid sound than that of the SRM-252S. I need to get ready to do the recapping. I am considering replacing that weird & frustrating volume control with a Goldpoint 47-position attenuator, however, I do not know whether it will fit.

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So I had the 009S for a bit but I went and got the modern 007A instead, wow.... Even though in its current state its underdriven (353X) It absolutely smokes every other Stax can I've heard or owned. Way better than the 009S and 009 and a meaningful step up from the L700. I just have to get a proper amp now (haha)

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3 hours ago, Spychedelic Whale said:

What is the serial number, from what I understand the one to get now a days is the sz3? 

Spritzer may need to barge in on this one but as far as I can tell the SZ2/SZ3 turns out to not mean much. Seems to me that the SZ3 are the modern black international ones while the SZ2 can be any of the Japanese silver ones. Mine is an SZ2 007A (silver japanese) but the serial is 23XX and its brand new so most definitely the 007A 2.9.

On 2/27/2019 at 7:24 PM, Mach3 said:

Is your 007A port modded?

And it was. I port modded it after one song. The lower mid-bass emphasis and the one note bass tone made it really annoying. I actually was going to leave it unmodded for a bit to become "accustomed" to the stock sound so to speak. But that mid-bass was to shitty for me to leave it stock.

Edited by Hi-Fi-Anatomia
Elaboration and further detailing
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I came across a video on YouTube on fitting very different, muff-style pads to the 207, using adhesive sheets & printed adaptor plates. Worthwhile? I would expect the sound to be quite different after that mod. On my 207 pair, the pad profile appears to be angled. I’m considering using 507 pads because they are leather. Those seems to be flat. Would I alter the sound significantly by using the 507 pads?

Those adaptor plates feature ports. Do they really make a difference in the bass response? I’m very satisfied with bass reproduction as they are. Does it become muddy or boomy due to the ports? I don’t understand how they work since the drivers are completely “open”. What’s being vented?

Edited by Sisterray
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Porting the front volume of a headphone shifts the bass response upwards, more midbass less subbass. The extent to which it is affected depends on port size. As for what is being vented you have the front volume (facing your ear) and the back volume (facing outwards). For the sake of bass extension only the front volume needs to be closed, which is why open headphones can have good bass extension, in other words the back of the drivers are completely "open" as you state it but the front of the driver is sealed to your head with the pads.

I can't answer your question about the 507 pads, but I'm sure someone else can chime in/have experience.

Personally I would not vent the front volume, 507 pads seem like a much better bet.

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