The Headcase Stax thread

[purk]

It hasn't shipped yet which is good for me. 

Is the Carbon's bass a bit too much for the SR007 MKI given that you said it is more robust down there compared to the BHSE?  Is it a better match to the SR009 or SR007?  Thanks.

[mwl168]

but this one is kind of fun and majorly ugly

 

http://page11.auctions.yahoo.co.jp/jp/auction/n145221931

 

It's a used item and not refundable. 

 

Wonder what's the key for? Ignition?

Edited June 12, 2015 by mwl168

[spritzer]

Self-destruct.... 

[wink]

 

lets see,

 

1) plate resistors, bad

2) ac coupling to the output tubes (average)

3) voltages too low for those output tubes,bad

4) opamp front end, very bad

 

etc. and the price...

 

go buid a srx2. way cheaper, way better

 

 

But, but,  but     aw! c'mon   it's German engineering at it's best.

 

Must be at least as good as the Luminaire & Verto when it's boxed and burnt up in........... 

[JimL]

A few more comments on this wonder of German engineering:

 

1)  If I'm reading the Bing translation correctly, with 140 watts in it's producing 1000 V peak-to-peak out, which is about the same as the Stax SRM007tII that draws only 55 watts from the wall - and has a better all discrete transistor front end.

 

2)  The plate resistors are only 26.5k, which is a lower value than almost any other stat headphone amp out there.  The designer probably did it to have enough current running through the output tubes, but almost all that current goes to driving the plate resistors to get some voltage swing, which is probably the reason the thing wastes so much power.

 

3)  LF351 op amps - really?  Those were designed in the 1990s and have an open loop frequency response that rolls off above about 12 Hz -not kiloHertz, Hertz.  There are way better op amps now, although I don't know what the current hot op amp is.

 

4)  Love the ultra-fi pot metal RCA input sockets

Edited June 13, 2015 by JimL

[DefQon]

OK, so, who's up for this little beauty...?

 

http://www.ebay.com/itm/Audio-Valve-Board-PCB-Electrostatic-Headphone-Kopfhorer-Verstarker-Amplifier-DIY-/261924370799?pt=LH_DefaultDomain_77&hash=item3cfbe8b96f

 

Must be a reeeeeel bargain.

 

You're a bit far behind wink:

 

[JimL]

DefQon said:

 

"You're a bit far behind wink:

 

"

 

Wow, it's deja vu all over again!  

Edited June 14, 2015 by JimL

[wink]

Yep, nothing like repetitive reinforcement.......  

[DefQon]

Wonder how it sounds. Looks simple enough for a quick p2p build. Wonder if it can be improved.

[spritzer]

It can be improved but why bother, just build a KGST. 

[JimL]

Sure it can be improved.

 

Substitute a state of the art discrete solid state front end for the IC op amps, add current source loads to the output stage - and you end up with the KGST.

 

Or,

 

Substitute a good high gain tube front end ifor the IC op amps, add current source loads and acurrent source cathode sink for the output stage - and you end up with the SRX Plus.

 

Any questions? 

[DefQon]

In that case fuck that haha. Have my KGST boards on the way to me so no point if thats the case.

[spritzer]

If you want to try and fix anything...then there is this:

 

 

Jecklin Float amp....  Epic clusterfuck. 

Edited June 15, 2015 by spritzer

[kevin gilmore]

srpp, yikes. but that can be fixed in a few seconds.

 

perfect for the circlotron power supply

 

so i'm assuming the top tubes have seperate filament windings for all 4 tubes?

Edited June 15, 2015 by kevin gilmore

[spritzer]

SRPP with a 300V tube...   

[kevin gilmore]

another mikhail at work

[spritzer]

We should do a layout for this.  Well that and the B10.  SRPP magic or something like that... 

[wink]

http://valvewizard2.webs.com/SRPP_Blencowe.pdf

[DefQon]

Kgst boards came. So small compared to my new and old kgsshv offboards.

[JimL]

So, re SRPP and stat headphones:

 

As both John Broskie at TubeCAD and Merlin Blencowe in the AudioXpress articles referenced above have pointed out, SRPP as a push-pull design can be optimized only for a specific fixed resistor load.  An electrostatic headphone is, of course, anything but that.  

 

However, there is a work-around of sorts.  That is, if we use a load resistor that is significantly lower than the lowest impedance of the stat headphone, say 40 kilohms, the combined load is mostly the load resistor over the audible spectrum, so the SRPP just needs to be designed to be optimum for that load resistor.  

 

Of course this "solution" does nothing to address the other problems of SRPP for this application, such as low voltage swing, the need for separate filament windings for each top tube, and the fact that you are literally designing an amplifier to drive the load resistors rather than the headphones.  Don't misunderstand me, if this circuit is like an ugly man with a hunchback and a hairy mole, I'm saying..... we can remove the mole.  Or as Joe E. Brown says to Jack Lemmon at the end of "Some Like it Hot.", "Well, nobody's perfect."

Edited June 17, 2015 by JimL

[nopants]

you're selling your omegas birgir? I remember years ago I read something about how the omegas are prone to head/reliability issues. Is this a factor still? Can we hook these up to all the modern amplifiers without them melting down on us?

[spritzer]

One of my Omegas...    The SR-Omega was an amazingly ambitious design but some of it was just badly done.  The aluminum housing is just a skin for a poly carbonate body inside which everything is attached to.  As we all know, metal screws into tapped plastic is always a sound plan...    Other than that they seem to hold up well but spare parts are becoming scarce.  From what I gather there are no more spare earpads but the foam from the 007 pads can be modified to fit the Omega skin. There should be some arcs left but Lambdas could always be scavenged to keep the Omegas going. 

 

So the bottom line is that they will be fine when plugged into modern amps.  I'm using it right now from the Carbon so it doesn't get any more more modern than that. 

 

In other news I was just sent some Sennheiser Unipolar 2000 and 2002 units so expect a thread on them soon. 

[nopants]

do you like them out of your carbon? Did you do anything special like goop in order to foolproof some of the implementation shortcomings?

 

I've always been interested but they're so damn elusive. I feel like a dumbass for not having picked up j-pak's pair. Maybe if I'm able to offload some amps and your pair isn't sold yet I'll pull the trigger. 

[spritzer]

I did recoat the diaphragms and replaced the bias connect with something sturdier which I fabricated out of silver wire.  As they age the bias seems to drift on some of them by a tiny margin.  I have no doubt that this is tied to sunlight or rather the drivers being exposed at some point to direct sunlight.  Some will drift from time to by a tiny margin by 0.5dB or something like that, just a slight change but I recoat to try and prevent that.  The bias connect used by Stax was the biggest afterthought I've ever seen, this tiny metal clip which slots into the bias contact and is pushed onto the brass rings that hold the diaphragm.  I soldered this connection to the cable entry and then push fit to the diaphragm. 

 

They do sound stunning off the Carbon.  From day one the Omega has needed power more than any of the other Stax phones and the Carbon gives it so effortlessly.  With the BHSE they will always have that extra bass edge, a slight coloration if you will, but here the bass is leaner but more natural.  It will hit even harder though... 

Edited July 5, 2015 by spritzer

[sorenb]

007 ...anybody having any experience repairing a cable that has a loose connection just before the molded plastic strain relief piece?

not talking about buying a spare unless someone knows where to get it a an reasonable price?