The Headcase Stax thread

[spritzer]

I don't think Warwick are doing so hot these days... 

I snapped this in Selfridges on Oxfordstreet yesterday and I might have been tempted as an insane collector if I didn't already own one of those piece of shit amps.  Well that and it sounds like shit... there is that issue too. 

Edited November 29, 2024 by spritzer

[mikeymad]

65% off?! - they must have low overhead.... 

[spritzer]

That's what I was thinking, the margins must be insane on these as its a store not really known for any good deals.  

Now I'm thinking if I did a deep dive on this earlier in the year when I got a set dirt cheap... or I just sent all of that to Kevin?    Well first off input, bunch of parts here USB xmos, A/D etc:

All of this leads to a pair of ESS 9028 dacs:

Not the best picture but that looks a lot like filtering to try and make up for the utterly retarded driver design:

Finally output stage... yeah this is pretty dire.  Remember this thing is 4k$... 

Now how does this thing actually work?  The clue is those two gray caps and the wires going to the headphone plug.  450V B+ on  a single rail so shall we say a maximum voltage swing of ~840Vppss and the bias is clearly 2000V.  The bias is superimposed on the audio signal after the output caps and then we have the grounded shield, that's it.  These are even simpler than what Koss were doing in the 60's where the back stator on the ESP6 (and 7, 8 and 9) are grounded but otherwise normal electrostatics. 

[Craig Sawyers]

I had a pair of ESP6's in the mid 70's. Those were the self energized ones with a transformer in each earcup? I remember that they were not light. Sounded good as I recall, but listening time was limited by the head crushing weight and the sweaty fluid filled earcups.

[spritzer]

Yup, transformer in each cut and weight is close to 1kg.  I rebuilt one 15 years ago and recently got the urge to mass with one again.  700V bias (well cut off so probably lower in practice) and I'm going to put new earpads and a headband on them. 

[lupoal]

Hi everybody,

I have a 300 Limited and, unfortunately, I stumbled upon the problem of the very poor quality arch... despite the fact that I used it gently at one point, already on the head, the arch broke in two (I put a photo here)

I made a repair with harmonic steel lamina and two-component structural adhesive and it seemed to be fine...but it snapped again right next to the lamina edge... the plastic that Satx uses for this detail really sucks

now I inquired for a replacement part, Stax no longer sells only the arch but now obliges to buy the whole assembly... the problem is that the original one mounted on the 300 Limited has proven (you can find several examples on the net and confirmations on Facebook among Stax owners) to be very bad, to improve quality at "normal" level it would then be necessary to switch to the Arch Ass'y MK2 which however costs, here in Italy, 380.00 euro! (these Stax people must be completely crazy to ask for such a price)

now, I would like if possible to avoid being sodomized by Stax forcing the purchase of a replacement at great expense to fix a serious quality problem of which they cannot be unaware...

does anyone have any suggestions? some say one could cannibalize arch and pavilion attachments from another headphone (of another brand) that has mechanical compatibility (with slight DIY adaptation)...does anyone have experience with this? Any idea? Every idea is welcome... I do hate the possibility to pay more then 300 euros for that

thanks in advance for the help

[Timb5881]

Same place mine broke.  I also tried to repair them with h a plastic welder, but alas to no avail.  So I ordered a new L700 mk2 arc and it arrived the other day.  Much better fit and is a more robust design.

[Timb5881]

PS try eBay and see what prices you can on that.

[lupoal]

12 hours ago, Timb5881 said:

PS try eBay and see what prices you can on that.

thks

yes, I've already searched in ebay... almost all potential supplier are form Japan and is roughly  190 - 200 euros + shipment + VAT + custom fee... the final cost is not far from 300 euros that is damn crazy expensive for a piece of hardware like that

[spritzer]

Gotta love Edifer making worse parts at three times what they used to cost.  Still that price in Italy is just a ripoff, the arc from Stax directly in Japan is 6600Yen which is about 50$.  

Edited December 27, 2024 by spritzer
Typo

[lupoal]

thank you 🙂, I am “investigating” the possibility of getting a new arc from Japan (not the shitty 300 one), in the meantime I would like to ask....

I have already replaced the trimmers in the 006Ts with multiturns that allow me to have a blasphemy-free adjustment (but still not very stable), on FB an enthusiast from Bulgaria, Velin Tourmakov, the same who suggested me the model of potentiometer to use (thank you! 🙂), also told me that he got a significant improvement by changing the factory diode bridge with one made with schotky diodes... what do you think?

I put here a picture where you can see both the pots and schotkies mounted on a pcb I think made a US... hard to find 😕

edit: found! here is the pcb... well, there is the pcb... https://partsconnexion.com/discrete-bridge-rectifier-pcb-type-1-axial-style/

[jamesmking]

4 hours ago, lupoal said:

thank you 🙂, I am “investigating” the possibility of getting a new arc from Japan (not the shitty 300 one), in the meantime I would like to ask....

I have already replaced the trimmers in the 006Ts with multiturns that allow me to have a blasphemy-free adjustment (but still not very stable), on FB an enthusiast from Bulgaria, Velin Tourmakov, the same who suggested me the model of potentiometer to use (thank you! 🙂), also told me that he got a significant improvement by changing the factory diode bridge with one made with schotky diodes... what do you think?

I put here a picture where you can see both the pots and schotkies mounted on a pcb I think made a US... hard to find 😕

edit: found! here is the pcb... well, there is the pcb... https://partsconnexion.com/discrete-bridge-rectifier-pcb-type-1-axial-style/

the problems with the stax srm006t is that like the srm007 it has too many design compromises that massively effect the sound.

1. its high voltages are not well regulated

2. it uses resistors as a anode load for the valves which reduces current drive and efficiency rather than using a constant current source. (the srm007t is exactly the same design but parallels up the values to get a bit more drive but its still not fixing the problem and costs twice as much)

3. it uses values which don't have much current drive or are that high voltage. Most of the good designs use far more powerful values such as EL34 running at conservative currents (for what they can do) rather than running tubes design for pre amps really hard.

The result of this poor bass, poor dynamics, mushy and in general, a sound that, as you turn the volume up the bass gets more soggy but not that much louder. The drive situation gets far worse if you use a difficult to drive headphone like the sr007 (I tried this and you cant get even close to the performance the 007s can provide with a well designed energizer. 

Replacing a silicon diode bridge with Schottky diodes might give you a bit less switching noise and slightly lower voltage loss but its not addressing the major design issues.

If you really want to upgrade the energizer get the anode resistors replaced with a constant current source. This massively increases the drive and addresses some of the poor design of the energizer.

 

If you are in to diy electronics and want to build your own energizer there are a variety of energizers so much better than the srm006 or srm007.

one of the simple and fairly cheap options, with better valves and fully regulated high voltage power supplies is the alpha centauri from http://www.high-amp.de. Its relatively simple to build and walks over and kicks in the head the srm006t. I am speaking from experience here. I started with a 006 and built the centauri. The published design still uses resistors for the anode load but the website does offer pre built constant current sources for it. Unfortunately the schematics and the pcb files are not available for the constant current sources.

Next come the energizers with constant current anode sources, fully regulated high voltages and beefy output valves:

The blue hawai, it will cost more to build than the alpha centauri, is bigger and more complex but sounds even better

At the apex of stax energizers is the diy T2. The original one uses transistors which are no longer available and so getting non fake transistors for it is not easy or cheap. The design has been updated to use more modern transistors. I built the mostly modern version which has a mix of old and current production transistors. It big, complex and fairly expensive to build but the performance is fantastic. I replaced by blue hawaii with it and never went back. There is also a mini T2 which is a simplified version using modern transistors and smd (surface mount components). Its not as good as the full T2 but I think its better than the blue hawaii.

if you want something that is fairly simple and will warm up a room on cold nights then there is the megatron. I never got around to finishing my build but its one of the more simple designs.

There are many more diy designs out there and in this forum. But the bottom line is if you want a realy good energizer for your Stax headphones, Stax does not sell one and most of the other commercial designs are almost equally as bad (and in some cases worse).

P.S.

the offset or balance DC voltages being a few volts out or drifting around by a few volts is not going to effect the sound or reliability. Remember the headphones are designed to take 100s of volts, 5V or 10V of DC offset or DC balance is nothing to them.

Edited January 10 by jamesmking

[Pars]

1 hour ago, lupoal said:

thank you 🙂, I am “investigating” the possibility of getting a new arc from Japan (not the shitty 300 one), in the meantime I would like to ask....

I have already replaced the trimmers in the 006Ts with multiturns that allow me to have a blasphemy-free adjustment (but still not very stable), on FB an enthusiast from Bulgaria, Velin Tourmakov, the same who suggested me the model of potentiometer to use (thank you! 🙂), also told me that he got a significant improvement by changing the factory diode bridge with one made with schotky diodes... what do you think?

I put here a picture where you can see both the pots and schotkies mounted on a pcb I think made a US... hard to find 😕

edit: found! here is the pcb... well, there is the pcb... https://partsconnexion.com/discrete-bridge-rectifier-pcb-type-1-axial-style/

I did a board like this years ago for 31DQ10 shottkys (or anything in an axial package) that I've used on most of the GRLV PSUs I've built, etc. I attached the gerbers for this board if you want to have some made for yourself. I would prbably do these in 2oz copper instead of 1oz. Here is a screenshot from JLCPCB's gerber viewer on their site:

 

Bridge.zip

[JoaMat]

6 hours ago, jamesmking said:

if you want something that is fairly simple and will warm up a room on cold nights then there is the megatron. I never got around to finishing my build but its one of the more simple designs.

I’ve made a solid state CCS for Megatron to replace the top EL34. Seems to work all right. I think a modified Megatron with solid state CCS will simplify the building of Megatron considerably.

[lupoal]

23 hours ago, Pars said:

I did a board like this years ago for 31DQ10 shottkys (or anything in an axial package) that I've used on most of the GRLV PSUs I've built, etc. I attached the gerbers for this board if you want to have some made for yourself. I would prbably do these in 2oz copper instead of 1oz. Here is a screenshot from JLCPCB's gerber viewer on their site:

 

Bridge.zip 9.91 kB · 2 downloads

do thank you!

[MLA]

On 1/11/2025 at 2:05 AM, JoaMat said:

I’ve made a solid state CCS for Megatron to replace the top EL34. Seems to work all right. I think a modified Megatron with solid state CCS will simplify the building of Megatron considerably.

These are really nice; drop in replacement for the EL34s in the current source positions. Just plug it into the tube socket and then spend some time comparing tube to solid state CCS sound.

Joachim was kind enough to provide four of these for a Megatron we're experimenting with in Gothenburg. The current source itself is really nice and in comparison to the EL34's, might have an edge when it comes to transient reproduction (completely subjective opinion of course).  

Edited Sunday at 05:50 PM by MLA

[kevin gilmore]

great idea.  but there had better be a tail to ground the heatsink. otherwise not safe.

[JoaMat]

The heat sink is not grounded and the two Gothenburgers has been warned. Those drop in devices are only for testing purpose and should be handled as most dangerous - able to kill you. Absolutely no children or pets around.

Edited Sunday at 08:22 PM by JoaMat

[MLA]

^ What he said. Live transistor tab and risk of considerable voltage on heat sink, so for testing only and to be treated as an open lid amplifier.

The original question for this testing was whether Joachim's latest current source can match the EL34 in performance sonically.

After quite a few  hours of listening, my conclusion would be yes;  a Megatron modified with this solid state CCS is a really great amp (just as the regular Megatron is, btw). Designing a pcb for it where the CCSs can be mounted inside the chassi on proper heat sinks would be a great next step. Let's see if we can convince Joachim to take this on... .      

[kevin gilmore]

since pin 6 of the tube is a no connect, you can modify the amplifier and tie the 4 pin 6's to chassis ground.

then in the adapter, pin 6 to the heatsink.

[kevin gilmore]

will look into the megatron boards and see if the mods are easy. likely they are.

[JoaMat]

Thank you.

For daily use heat sink certainly needs to be grounded. We also need some cover for the transistor tab and leads, which otherwise are exposed for any 5-year engineer. I think it’s solvable.

Better also an isolated mosfet... if available?

 

[kevin gilmore]

12 volt filament version with pin 6 grounded.

for existing boards modification is easy. solder short wire from pin 6 to the ground pin on the .1uf 630v cap nearest to that tube.

megatron12vcs - CADCAM.ZIP

Edited Monday at 01:53 PM by kevin gilmore