The Stax Thread III

[ESL-1]

That was Lil Knight and he stole over $20k from commissions/chassis work for DIY T2/HV

Thanks for backstory and warning. Sounds like a real bad one.

Willing to give a 2 hour head start but he must do it barefoot in rough terrain..

I think a battle cry of “NO MERCY” might be quite appropriate.

Always sorry to hear about such Low Life’s.

 

[gammi]

These kinds of questions are probably better suited on headcase since not many here are DIYers
That said - I'm kind of perplexed why you'd go through the trouble of completing a transformer box when you don't have the expertise and are risking far more by damaging your relatively much more expensive headphones.

1) You're being very presumptuous about my expertise. I happen to be a computer engineer with a minor in electrical engineering.
2) You're also being presumptuous about the research I put into this. SRD-7 and SRD-7 MK2 both have capacitors on the bias output just like my DIY circuit. One would assume STAX themselves wouldn't build a damaging circuit and having these capacitors is safe. My question was not about the circuit but rather operating procedure.
3) It's fun to take risks. Same reason I race my car in spite of having no on-track insurance and risking about two HE-1's worth of damages

I've attached the circuits for both the SRD-7 and SRD-7 MK2. May they be helpful to someone.
Edit: I attached a post from spritzer backing me up here that the bias is always on for the official STAX transformer boxes, just like my DIY.

 

[kevin gilmore]

both of those stax transformer boxes pre-date current stax headphones by more than 35 years.
its not a good idea to have a capacitor on the bias output after the 4.7M resistor. plugging headphones in when that capacitor is already charged can put holes in the diaphram. all stax amps newer than 1995 do not have this capacitor.

having the bias always on is a really good idea.

measuring the voltage after the output resistor is going to give you the wrong number unless you have a VTVM

 

[gammi]

Thanks. Yeah, I'm gonna remove the second cap (the one after the resistors) to be safe. Surprising even the newer MK2 box has the capacitor on the output. The fact STAX themselves did it (apparently not anymore) made me think the impedance of the headphones themselves was enough to prevent a sharp discharge.

measuring the voltage after the output resistor is going to give you the wrong number unless you have a VTVM

This is only true if I measure after the Mohm resistors, because the current is so low that the multimeter draws down the reading whereas the VTVM's high impedance probe doesn't, correct? I was able to get a stable reading on the capacitor output, but perhaps even though stable, it was low?

 

[gammi]

Well the cliche "hearing things I've never heard before" is happening. Listening on my Lambda and I heard a burp for the first time at 6:43 on Over Now (Unplugged) by Alice In Chains lol

 

[Kiats]

After some time away from the Lambda NB, decided to take it out for a spin this evening. Gosh! I have forgotten how much I do enjoy it!

 

[KDS315]

Got a STAX SRA-14S complete with all boards incl. that ultra rare ECC-1 for electrostatic systems. The 7th ever built one.

Came with a SIGMA NB and after a quick test, I was thrilled how good this amp really is!!

 

[alota]

Got a STAX SRA-14S complete with all boards incl. that ultra rare ECC-1 for electrostatic systems. The 7th ever built one.

Came with a SIGMA NB and after a quick test, I was thrilled how good this amp really is!!

Nice. It is all solide state?

 

[KDS315]

Noce. It is all solide state?

Yes, all solid state

 

[Kiats]

Got a STAX SRA-14S complete with all boards incl. that ultra rare ECC-1 for electrostatic systems. The 7th ever built one.

Came with a SIGMA NB and after a quick test, I was thrilled how good this amp really is!!

Looks good! How is the Sigma NB driven off it? Man... Now that you brought up the Sigma NB, let me bring up mine for a listen later today, once I am done with the Lambda NB.

 

[KDS315]

That SIGMA NB is driven very well, especially with Rock & Pop!

 

[Kiats]

That SIGMA NB is driven very well, especially with Rock & Pop!

I can imagine! The Sigmas should come with a warning label that they prefer driving power.

 

[KDS315]

Hi hi, indeed, and that SRA-14S certainly has that...saw your FB postings, too

 

[Kiats]

Hi hi, indeed, and that SRA-14S certainly has that...saw your FB postings, too

Indeed! I am fortunate that Mjolnir Audio sent me one of their Octave v4 which uses the chassis of the SRM1 only with a more neutral sound and more driving power to the earspeakers. @spritzer kindly made sure that one of the Stax sockets was for normal bias Stax. I have been enjoying the Octave v4 ever since then.

 

[KDS315]

Just a bummer that OCTAVE 4 is not with symmetric XLR inputs ... nice small amp for the desk. But for that I have my symmetrical ANTARES with SRPP modification