[Reticuli2]

Anyone know the max input these are supposed to be taking with no added distortion due to overloading?

 

[livewire]

1.21 Jigawatts.

 
Are you talking signal input? I've had sources as high as 5 volts.
I suppose you could call Koss. They might know.
 
If you are talking input to the phones themselves, then -
 
A little bit of kentucky windage here:
 
Standard bias is 600 VDC. I've read that they can be boosted safely to ~620 VDC.
 
Standard rail voltage is +/- 600 VDC. (Koss E90 amp)
 
I run mine on my KGSSHV at 450 VDC. The ESP-950 seems to beg for more.
I've cranked mine to three o'clock. (ear bleeding levels - see my avi) Never gone up all the way.
The KGSSHV can be built to output 500 VDC. I'm guessing the ESP-950 would be OK with that.
At this point in time, there are only two 500V KGSSHV amps built.
Nothing concrete has been reported yet - other than "they sound good".
 
So the standard disclaimer applies: HV + HV = BS! (high voltage + high volume = blown stats!)
Who knows? Could happen....
 
Edit: changed voltages to reflect correct values, per the Koss manual.
 

 

[FrankCooter]

 
Quote:

 
 
So the standard disclaimer applies: HV + HV = BS! (high voltage + high volume = blown stats!)
Who knows? Could happen....
 

I inadvertantly put 700Vrms across my ESP-950's. The drivers didn't survive. I sent them back to Koss. I was honest about what happened and offered to pay for replacements. They wouldn't take my money and replaced the drivers with no charge. Great for a DIY test bed!
 
 

 

[milosz]

Quote:

 

I inadvertantly put 700Vrms across my ESP-950's. The drivers didn't survive. I sent them back to Koss. I was honest about what happened and offered to pay for replacements. They wouldn't take my money and replaced the drivers with no charge. Great for a DIY test bed!
 
 

I'll bet they've never seen THAT before! I bet your blown drivers are pinned to some engineer's cubicle wall.  
 
Good to know that the Koss folks over there in Milwaukee mean business when they say "Lifetime Warranty."  Wonder if Stax would replace my SR-007's if I blew them out on some giant stat amp....?
 
I guess I know what 'phones I'll be using the  first time I try out my DIY T2 when I'm done building it.....  
 

 

[spritzer]

The stock bias on the E90 is +600 and the rails are +/-600V, not +/-400V.  Most electrostatic transducer have Vmax=bias*2 so 1200VP-P in this case.  700VRMS (2000VP-P) would certainly be enough to kill them.... 

 

[Reticuli2]

So the drivers are not actually tweeters in larger speakers, as I'd read somewhere?
 
I was talking about source into for the E90.  I can't exactly test it with 1khz signals and TrueRTA.

 

[Mr.Sneis]

I had about an hour or so with the esp/950 with stock amp and I thought it was OK -- definitely on the bright side and lacking some detail from memory.  Didn't pair it with any Stax amps though.  Anyone know how to quickly/cleanly convert the plug? Build an adapter?

 

[dagothur]

 
Quote:

 Anyone know how to quickly/cleanly convert the plug? Build an adapter?

  Scissors and really strong duct tape.  That should do the trick.
 
 

 

[n3rdling]

livewire can probably go into more detail, but you basically take the Koss extension cable, lop off the female end and replace it with a female Stax compatible plug.

 

[livewire]

Quote:

livewire can probably go into more detail, but you basically take the Koss extension cable, lop off the male end and replace it with a male Stax compatible plug.

FIFY!

 
The Stax compatible male plug is a mil-spec Amphenol part, available from Newark Electronics.
I believe that it is listed as a microphone connector, I dont have the part number handy at the moment.
Price varies from ~$20 to $36 depending where you buy it. I believe Newark is cheaper.
The Amphenol part is the chrome plug on the right. Click pic for better detail.
 
A few minor mods are required. This is a six pin connector, similar to the regular bias Stax plug. 
However, most will want to use the Stax Pro Bias five pin version to mate with their amps.
The center pin can be removed by breaking it off with needle nose pliers
(bend it back and forth gently - so as not to crack the surrounding plastic)
Use a dremel tool to grind off any remaining material. I dont recommend a drill, but if careful it too will work.
 
Toss the set screw and the threaded nose ring in the trash.
Before soldering the wires, assemble the connector tailpiece assembly onto the cable.
After soldering the wires, glue the plastic pin base flush with the edge of the chrome housing
in order to make the pins protrude further. Use epoxy for this.
Then back-fill the cable side with hot melt glue to act as a strain relief.
Epoxy can also be used here, but the result will be "more permanent"
not allowing disassembly if repair to the internal connections are needed.
Inspect and test all soldered connections before gluing.
 

 
 
 

 

[Reticuli2]

BTW, the Koss specs/manual pdf on their site, which oddly wasn't in the box, says the nominal input is 1Vrms.  But I don't know if that has anything to do with max input.  If there's an opamp input stage, then I assume it has some kind of max input.  1Vrms might just be what it's rated at to get full unclipped output with the volume pot all the way open... not sure.  I left a message with the Koss engineer's voice mail about this and my hum issue.  My unit is pretty imbalanced if you leave the dual pots centered.  I have to put the smaller one higher than the larger outer one.  I also notice the 100hz range is further to the left than the rest of this spectrum and moves with ear flipping (ensures it's not my ears).  So you have to kind of average it out, with the majority of response range slightly to the right, and 80-120hz area slightly to the left.  I'm wondering if running inputs into the front and the back at the same time (which I did accidentally when testing it during the first hour it was here) damaged something, causing the mild hum RF pickup issue on the right channel and the volume/frequency imbalance between channels.

 

[n3rdling]

Oops.  Yes obviously the male side, I don't know what I was thinking.

 

[koonhua90]

Is there analog RCA input on the stock amp? Or is it just a 3.5mm jack input?

 

[livewire]

Yes, both.

 

[Anaxilus]

Quote:

Oops.  Yes obviously the male side, I don't know what I was thinking.

We know what you were thinking!