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The Headcase Stax thread


thrice
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I can stitch you up with a three layers deep laceration, but I have no clue how to add resistors to an amp.

Probably the easiest way is to add the 5.1 megohm resistors (needs to be rated for 500 volts) at the headphone socket, between the socket and the wires going to the socket from the amp board.  

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I can't get over the looks of the new Orpheus package. Like really? Marble enclosure for the amplifier with a built in DAC, an array of tubes on right side and a black shoe box with lid on left side that is a headphone case.....did some 10 year old design this at SennheiserHQ?

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Probably the easiest way is to add the 5.1 megohm resistors (needs to be rated for 500 volts) at the headphone socket, between the socket and the wires going to the socket from the amp board.  

I wouldn't know which wire to choose for adding the resistor.  I'm really ignorant about this stuff.  I can solder wires for a TRS headphone jack or to a pair of speaker leads on the back of a speaker driver, and that's it.

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I wouldn't know which wire to choose for adding the resistor.  I'm really ignorant about this stuff.  I can solder wires for a TRS headphone jack or to a pair of speaker leads on the back of a speaker driver, and that's it.

It's really pretty simple.  You need to identify which pin(s) in the socket is (are) the bias pin.  For the Pro socket, it's just one pin, for the normal bias it's the same pin plus the center pin.  If you have a voltmeter, just connect one lead to ground and probe the other pins one at a time.  The amp output pins should all be close to zero whereas the bias pin will be a few hundred volts, so there shouldn't be any issue with identifying which is which.  Note that the actual value of the voltage doesn't matter, it won't be accurate anyway, but there should be a clear difference between close to 0 volts and a few hundred volts.  You can do this test with the box closed for safety.

 

Note which pin is the bias pin.  Then turn off the amp, unplug it,wait for the power supply to discharge, and open the box.  You solder a 5.1 megohm/500 volt rated resistor between every pin and its connecting wire EXCEPT for the bias pin - that should be 4 resistors.  Actually it won't hurt if you solder a 5.1 megohm resistor to the bias pin since it doesn't carry any current, but it isn't necessary.  Just make sure they don't touch each other - if you want to put some heat shrink around them so the connections aren't exposed that's fine.  That's it.

 

 

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It's really pretty simple.  You need to identify which pin(s) in the socket is (are) the bias pin.  For the Pro socket, it's just one pin, for the normal bias it's the same pin plus the center pin.  If you have a voltmeter, just connect one lead to ground and probe the other pins one at a time.  The amp output pins should all be close to zero whereas the bias pin will be a few hundred volts, so there shouldn't be any issue with identifying which is which.  Note that the actual value of the voltage doesn't matter, it won't be accurate anyway, but there should be a clear difference between close to 0 volts and a few hundred volts.  You can do this test with the box closed for safety.

 

Note which pin is the bias pin.  Then turn off the amp, unplug it,wait for the power supply to discharge, and open the box.  You solder a 5.1 megohm/500 volt rated resistor between every pin and its connecting wire EXCEPT for the bias pin - that should be 4 resistors.  Actually it won't hurt if you solder a 5.1 megohm resistor to the bias pin since it doesn't carry any current, but it isn't necessary.  Just make sure they don't touch each other - if you want to put some heat shrink around them so the connections aren't exposed that's fine.  That's it.

 

 

Okay, that does make it sound easier.  But is it worth it to resurrect the eXStatA hybrid amp if I still have an HEV-70 pro bias amp, a Stax SRD-7 Pro, and a Stax SRD-7SB to drive all my staxen (SR-5NB Gold Ed, SR-Lambda, SR-LNS, and Baby Orpheus)?  I'm not counting the Woo WEE that's for sale, which I only like with the LNS (or 007 before I sold them).

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Okay, that does make it sound easier.  But is it worth it to resurrect the eXStatA hybrid amp if I still have an HEV-70 pro bias amp, a Stax SRD-7 Pro, and a Stax SRD-7SB to drive all my staxen (SR-5NB Gold Ed, SR-Lambda, SR-LNS, and Baby Orpheus)?  I'm not counting the Woo WEE that's for sale, which I only like with the LNS (or 007 before I sold them).

Well, that's an altogether different question.  Both Birgir and Dr. Gilmore have documented the shortcomings of the eXstatA design - the solid state version measures worse than the Stax SRM-323, and the hybrid version takes 6S4A tubes, which are excellent output devices, and uses them in an intermediate stage, seemingly for no other reason than to say there are tubes in the design.  Let me just add that the output "current source" is based on a circuit topology that Walt Jung, a well known solid state engineer, gave as an example of what NOT to use (AudioXpress issue 4, 2007), because it just isn't a very good current source..  

 

On the other hand, Dr. Gilmore posted in the HEV70 query thread in the amplification section of Head-Case on Mrach 7, 2006, that, "I have 2 of them.  Never had a problem with either. They sound like crap but that is a different issue." And in his original article on his all triode direct drive tube amp design he said of the HV60/HEV70, "The solid state drive amplifier is horrible.  Headphones themselves are excellent."

 

You might be better off selling the hybrid eXstatA and putting the funds towards a better amp, either a used Stax or one of Dr. Gilmore's designs.  If you can buy or build a Stax to Sennheiser cable adapter you can use it to drive your Sennheiser stat phones as well (or, use the SRD-7 pro with a cable adapter for the same purpose).

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Well, that's an altogether different question.  Both Birgir and Dr. Gilmore have documented the shortcomings of the eXstatA design - the solid state version measures worse than the Stax SRM-323, and the hybrid version takes 6S4A tubes, which are excellent output devices, and uses them in an intermediate stage, seemingly for no other reason than to say there are tubes in the design.  Let me just add that the output "current source" is based on a circuit topology that Walt Jung, a well known solid state engineer, gave as an example of what NOT to use (AudioXpress issue 4, 2007), because it just isn't a very good current source..  

 

On the other hand, Dr. Gilmore posted in the HEV70 query thread in the amplification section of Head-Case on Mrach 7, 2006, that, "I have 2 of them.  Never had a problem with either. They sound like crap but that is a different issue." And in his original article on his all triode direct drive tube amp design he said of the HV60/HEV70, "The solid state drive amplifier is horrible.  Headphones themselves are excellent."

 

You might be better off selling the hybrid eXstatA and putting the funds towards a better amp, either a used Stax or one of Dr. Gilmore's designs.  If you can buy or build a Stax to Sennheiser cable adapter you can use it to drive your Sennheiser stat phones as well (or, use the SRD-7 pro with a cable adapter for the same purpose).

My HE-60 cable was converted into a 6" pigtail with a Stax 5-pin jack on the end, and the headphone cable has a 5-pin Stax plug on it, so I can use a Stax phone on the HEV70 and the HE-60 on a stax amp.  HEV-70 sounds a lot like my old Solid State eXStatA, which I didn't think was as good as the Hybrid while it was working.  

The HE-60 sound better with the HEV-70 than they did with any of my previous three SRM-1 Mk2 Pro amps or the Woo WEE (painful).  The Eddie Current ZDT 8-watt amp into the SRD-7 Pro is a little better, but the HEV-70 has more micro-detail while the SRD-7 Pro sounds more refined and punchier with better imaging.  I guess I'll just install the new amp boards in the eXStatA and sell it, unless I can sell it as a kit and let the buyer install the boards. 

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I believe they are called split rivets. 

Finally installed this despite it still having some PSU issues. 

zUDF4aDh.jpg

It faces an up hill battle against the Carbon that used to sit there.

 You might've mentioned this before Birgir, but I've not come across it if you have, which is how does your KGSSHV Carbon compare to your DIY T2 [ which BTW looks very nice ] driving the 009's ?

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