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The Headcase Stax thread


thrice

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The driver is rotated only along with the cable connector though right? If so, I'm thinking there should be a "correct" position for the driver. Right now I'm getting a very slight seal break under my cheekbones, so I'll probably rotate the pads just a bit to get a nice seal. This is pretty fun just messing around with the multitude of positioning factors on the O2. :) Right now I'm trying to decide if I'll keep the 717 or one of the T1's.

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The driver is rotated only along with the cable connector though right? If so, I'm thinking there should be a "correct" position for the driver. Right now I'm getting a very slight seal break under my cheekbones, so I'll probably rotate the pads just a bit to get a nice seal. This is pretty fun just messing around with the multitude of positioning factors on the O2. :) Right now I'm trying to decide if I'll keep the 717 or one of the T1's.

The driver is more or less perfectly symmetrical, so I would seriously doubt there is any "correct" orientation (but you probably still don't want the strain relief parallel to the ground).

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Omega II Mk1 = OMG, great phone.

With the 313 it sounded dry and lifeless but with the T1S it was very good(a surprise), it is leaps and bonds ahead of any Lambda in many areas, and I didn't find it sounding dark. I wouldn't say it easily worth the hefty extra cost though, at least not with a mediocre amp. And the fit was quite fiddly for me, I had to re-adjust it many times, maybe the Mk2 with the thicker pads would suit me better.

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The fit could have been due to worn pars (which you'll never see on the outside) or the arc's have been modified to fit the owner so they don't work for you.

Now for something different, I need some input. I have a SRD-7 Pro PCB all drawn up but I'd like to know if you thought it was a good idea to place jumper's on the PCB for the signal coming out of the transformers. All the input wiring is there but I'm not sure if Stax passed the output though the PCB too on the older models. A pic but it is much smaller then this to say the least, roughly 4*2.3".

spritzer-albums-stax-picture860-srdpro2.jpg

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Yes, the condition was not tip-top but the sound quality was. When I rotated the earpads, the outside ring with the cable always wanted to move so I had to hold it with the other hand, is that normal?

Yes, you can choose the pad orientation and cable input position to suit you best.

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Ok, will try tomorrow :) It looks much better in person, too. The Lambdas look very cheap in comparison. But I don't feel heartbroken for desperately wanting one, good job that I only have a T1S, because the SR-Lambda seems to be the optimal partner for it ;)

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Now for something different, I need some input. I have a SRD-7 Pro PCB all drawn up but I'd like to know if you thought it was a good idea to place jumper's on the PCB for the signal coming out of the transformers. All the input wiring is there but I'm not sure if Stax passed the output though the PCB too on the older models. A pic but it is much smaller then this to say the least, roughly 4*2.3".

Hi Birgir,

I am missing the input resistors (4R7?). I suppose they have an equalization function as well as presenting a better load to the connected amplifier and give some addition protection to the phones (thermistors) and your ears :)

And why not add a normal bias tap as well?

I have an SRD-7 (normal bias). If it helps for you to know how the transformer wires are connected in there, I can open it and have a look for you.

These adapters have an output capacitor across the bias output. Some amplifiers have that as well, but all later ones have a series resistor to the output. That gives some protection against short-circuits (burns in the membrane if the membrane touches a stator?) and makes it safer to touch.

In my SRA-12S, I added a capacitor across the output first, but later decided against it and added a series resistor (4M7) as well.

What is your opinion about this?

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Hi Birgir,

I am missing the input resistors (4R7?). I suppose they have an equalization function as well as presenting a better load to the connected amplifier and give some addition protection to the phones (thermistors) and your ears :)

I did indeed leave the protection devices off the board but this is essentially a niche design for modded transformer boxes so I'd assume the users know better then plug it into a 400W Krell amp and listen at full output. :P

And why not add a normal bias tap as well?

I have an SRD-7 (normal bias). If it helps for you to know how the transformer wires are connected in there, I can open it and have a look for you.

I have the schematic for the SRD-7 Mk2 bias supply as well (which has both outputs) but frankly there isn't much need for the NB output. You also just need two resistors to drop the bias voltage so it is easy enough to accomplish. I could fit that to the PCB though...

These adapters have an output capacitor across the bias output. Some amplifiers have that as well, but all later ones have a series resistor to the output. That gives some protection against short-circuits (burns in the membrane if the membrane touches a stator?) and makes it safer to touch.

In my SRA-12S, I added a capacitor across the output first, but later decided against it and added a series resistor (4M7) as well.

What is your opinion about this?

The 5M or so resistor is absolutely needed, not only for safety reasons but it also sets the constant charge mode of the diaphragm. I don't see how a cap across the bias line could work since the bias is DC and that can't pass through caps. :confused: I've at least never seen a cap in that position and even the oldest Stax schematic which I have at hand (Feb 1961 SRA-6S) shows a 5M ballast resistor.

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The 5M or so resistor is absolutely needed, not only for safety reasons but it also sets the constant charge mode of the diaphragm. I don't see how a cap across the bias line could work since the bias is DC and that can't pass through caps. :confused: I've at least never seen a cap in that position and even the oldest Stax schematic which I have at hand (Feb 1961 SRA-6S) shows a 5M ballast resistor.

The capacitor is across the bias (to ground) and not in series with the bias line, so I see no problem.

It will filter a little bit of the mains ripple, due to the resistor before the capacitor, but not much at this value. But the current consumption is very low, so the cap will stay charged and there will be very little ripple anyway.

As far as I know the following Staxes have a parallel output capacitor of 0.01uF (and no series resistor after that!):

* SRD-7

* SRD-7 mkII

* SRM-Xh

* SRM-X pro

* later versions of the SRA-12S

* your new pcb

There may be other types as well.

The series resistor does not really make a constant charge circuit, since the value (4.7 or 5 MOhm) is way too low for the capacitance of the phones (say less than 150 pF). The time constant is about 0.75 ms, so this is not active anymore below several hunderd Hz.

Thanks for your input on desirability of the series resistor. I fully agree that it is beneficial.

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Ahh now I understand what you are getting at. The cap will certainly do no harm and I suspect that Stax added them when they were having issues with ripple. I know Justin also added one in the amp chassis in the BHSE, probably to make up for the long wire from the bias supply and the close proximity to the filaments on the way.

All of the SRD-7's have a series resistor (I have the schematics for most of them) but it's been too long since I opened up the small Stax amps to be sure. The 313, 323, 717, 007t, T1, T1S all have them.

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