The Headcase Stax thread

[jamesmking]

6 hours ago, Jon L said:

At the other side, LTA rep posted this info:

"Frequency response (8-ohm load): 6Hz to 60kHz, +0, -.5dB
Input impedance: 47k
Electrostatic Headphone Output: 5 pin Stax interface, 580V bias

One additional bit of info that's not on the page is the output voltage, which is limited to 410Vrms on the Z10e. STAX themselves recommends that "maximum output with 470 Vr.m.s. or below for any amplifier driving STAX headphone in order to avoid damages to sound elements."

"there are no transformers. The electrostatic signal comes straight off the tube, and due to ZOTL's unique topology, the tubes run natively at 750V, for a 1500V peak to peak (each channel has two tubes, one is for the bottom half of the signal and one for the top half, so the full voltage swing is both added together). The ectrostatic headphone output is live all the time, because we didn't want to degrade the audio signal with a switch."

T2 frequency response is at least that good

so it's confirmed to be running class AB....

7K is an awful lot of money that's shop built blue hawaii se with a really nice potentiometer and 0.1% 15ppm resistors. Or two modern full T2s if you go DIY... so its up against the best of the best.

1. does it have interstage coupling caps (bad for sound)?

2. is the signal path cap free?

3. is it using constant current sources? if so where?

4. does it have a 5M ohm resistor on the bias to protect the headphones.

5. does it have 5.1K resistors on the outputs to protect the stax headphones?

6. how quiet are the power supplies?

7. is the B+ delayed on startup?

As a speaker amplifier it's interesting, as a stax amp I am not convinced.

Edited October 27, 2020 by jamesmking

[Paul160672]

Anyone listened to the Heddphone compared to the stax?

[EtherealCereal]

Hello, I'm new here.

I recently acquired a nice looking (and complete) pair of Realistic HP-100s (re-badged Stax SR-3, from what I understand), and upon cracking open the energizer I'm finding things aren't quite as nice as they would seem.  When I'd first begun to listen to them, the left channel was nearly dead and the right channel was quiet.  I quickly discovered the issue with that, this 3.3ohm ptc that had, at some point, swollen to the point of beginning to crack:

The cracked one was registering 265 ohms.  No wonder one side was nearly dead!  So, I purchased some replacements from Mouser. 3.3ohm ptc, just like the schematic called for.  I soldered them into place, and as I begun to ease the volume knob up, I started to smell burning.  Turns out this was happening:

 

Apologies for it being blurry, but it started to arc across points C1 and 3 on this top circuit board.  Naturally, I removed the headphones the first time this happened.  This is a screenshot of the video I took to recreate the issue, and there was nothing hooked to the headphone output when I took this.

[spritzer]

Shorting due to the flux becoming conductive over the years? 

[EtherealCereal]

 

17 hours ago, spritzer said:

Shorting due to the flux becoming conductive over the years? 

I don't know.  I tried to remove as much flux as I could, I wiped that spot down and I sprayed it with electronics cleaner and it still shorts out.  It's not just the left channel, either.  The right channel is doing the same.

In any case, I removed the resistors and cleaned the through-holes, and after I removed the resistors from the circuit the shorting ceased.

 

EDIT: (Blow the picture up, it's large)

[Orb]

Hello all,

I just picked up a functional Stax SRM-T1 that I’ll upgrade with new caps and Jim Lin’s CCS upgrade pretty soon.  My preamp has balanced outputs, and I was wondering if it makes sense for me to do an XLR balanced input conversion to the SRM-T1, given that the T1 uses virtually the same PCB as the XLR-equipped SRM-T1S.  I have the T1 schematic, but I’ve not been able to locate one for the T1S nor details on how the input circuit differs between these two amps.  

Is the sonic benefit from using a balanced input more trouble than it’s worth?  Would the XLR mod be straightforward to do?  I’m experienced with electronics work.

Thank you very much for any suggestions!

[spritzer]

The XLR mod doesn't change anything really, if there is a sonic improvement it really depends on the source if the different outputs are handled differently.  The XLR just doubles the input voltage (though that is not set in stone either). 

To do the mod, just remove the resistor which grounds the gate of one half of the input fet and copy what's on the other gate. 

[Orb]

Understand, thank you for the quick response!  The mod looks reasonable, I would just need to find a quad volume pot of the same value that fits mechanically (but preserving variable L-R balance may not be practical, not an issue in my case).

[spritzer]

It is pretty much impossible to find the split volume controls but the quad RK27 pots are out there and they are a drop in replacement.  You will need a new knob for it though. 

[Orb]

Great, will look for one, thanks!

[Hifilutin]

On 11/12/2020 at 10:05 AM, EtherealCereal said:

 

I don't know.  I tried to remove as much flux as I could, I wiped that spot down and I sprayed it with electronics cleaner and it still shorts out.  It's not just the left channel, either.  The right channel is doing the same.

In any case, I removed the resistors and cleaned the through-holes, and after I removed the resistors from the circuit the shorting ceased.

 

EDIT: (Blow the picture up, it's large)

I have a set of these that also do not work. Dug out my own adapter, Mine does not short out, but there is also no discernable difference between powered and unpowered functionality- as in the biasing circuit does not function whatsoever. I'll replace the capacitors here and get back with results. I doubt that the diodes are spent- they don't look cooked.
As an aside, here are some pictures of the boards. The board that handles the raw audio signal is totally covered in old flux. I pulled the ptc resistors for testing, they seem reasonably functional. I used similar resistors here to check against, seems both work more or less the same- as they should. Whomever put this together in factory did not clean the excess... I've done a quick little job (and left a bunch of cotton fragments that i'll remove with compressed air later) and pulled off the old flux. I don't see much difference in our two boards- anyone know why his circuit would attempt to jump an air gap between the 100pf capacitor and a 5.3kohm resistor? I can't imagine that crossing open air is the lower resistance pathway. Doesn't make much sense.

I included the schematic too for anyone else who is looking.

[Orb]

Studying the input circuit for the SRM-T1 (for future balanced input mod), came across what looks like a resistor in a neon bulb.  What is special about this part vs. using a conventional resistor?  Is this the same pair of parts that I’m pointed to in the attached input schematic?

Thanks!

 

[luvdunhill]

I assume it’s used for over voltage protection?

Here’s a good reference on the topic:

https://www.tiffe.de/roehren/neon.pdf

[dripf]

009 discontinued.

https://stax.co.jp/2020/11/09/sr009dis/

[Lord_Rexter]

Is STAX hinting us to get ready for new Omega 🤔

[velomane]

Maybe the 009S will now to be their TOTL can?

[spritzer]

The 009BK was always the TOTL unit so they might just be moving to that direction.  For me they were always the best 009's by a mile too

[Lord_Rexter]

Luckily I was able to manage to grab 009BK and now out of production 009 silver for me 😊

[Mach3]

According the the Edifier youtube clip. The Stax Japanese team will release the Omega successor when they are ready.

When are they ready: When they are ready

When will it be release: When they are ready

Edifier calls Stax japanese team, "What time frame you need for the new Omegas": We will let you know when we are ready

 

[hekoman]

I am attempting to repair a SRA-3S and I am having trouble trying to figure out the value of two of the caps on the first card. I can read on one of them that they are rated for 50V, but all other marking have been worn off. I tried looking online for pictures of the card, but I can't find any pictures online that are high enough resolution to read the values.

Any one that has one of these amps and can read the values on theirs would be greatly appreciated, Thanks!

[spritzer]

It's been too long since I've had one here to be but sure but here is the schematic:

[Hifilutin]

I've always wanted a SRA-3s, but never decided to bite that bullet. I don't have any way to convert to 100v anyways. Would like to hear impressions of the sound once you get it recapped.

[faust3d]

So I run out of Stax Sigma replacement earpads. Are replacements still obtainable?

[Mach3]

You should try contact vesper audio, they can custom make the earpad for them that uses much higher quality lamb skin, super soft and durable and memory foam. I've had a few custom design done from them for my ESP 950, thicker angled pads that offer better seal. Did the same for my 007 Mk1. 

[Pirx]

On 11/29/2020 at 5:07 AM, hekoman said:

I am attempting to repair a SRA-3S and I am having trouble trying to figure out the value of two of the caps on the first card. I can read on one of them that they are rated for 50V, but all other marking have been worn off. I tried looking online for pictures of the card, but I can't find any pictures online that are high enough resolution to read the values.

Any one that has one of these amps and can read the values on theirs would be greatly appreciated, Thanks!

I have one unit, that is not working, but I opened it and it is obvious that both caps are 220 nF/50 V and they are input caps.