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Can my SET tube speaker amp power HE6/Stax?

post #1 of 14
Thread Starter 

I've got a pretty nice speaker setup, but I'd like to integrate headphones into the chain without buying dedicated components.

 

As such, I'd like to use headphones that can use speaker amps, such as the HE6 or the Stax.

 

My speaker amp is a 845 tube based SET tube amp, the Cary 805C.

(Link is to the AE version, but C is pretty much the same)

http://caryaudio.com/products/classic/CAD805AE.html

 

The speaker amp has a switch that I can set between 4-16ohms depending on the impedance of the speaker I'm using, along with corresponding speaker posts for the particular ohm setting.

 

Would I be able to use either a Stax SR007 w/ WEE or a HE6 with this speaker amp?  I know the HE6 is a 50 ohm impedance, which is way higher than the highest ohm setting on my amp.  If either one does work, what ohm setting shall I set it to?  4, 6, 8, 12, or 16?  Or is it a case of, any setting is good and I just try to see which one sounds best?  Most interested in if a SR007 w/ WEE pairing is electronically compatible.

 

Thanks!

post #2 of 14

STAX are out because you will need a high DC bias voltage to even start to operate them.  They are different technology than Orthos which are dynamic headphones with an extremely thin diaphragm and a wide area voice coil.  STAX are of course electrostatic headphones that require upwards of 500 volts to properly drive and consist of an even thinner diaphragm ( several microns thin ) and magnetic plates that push / pull the diaphragm back and forth.

 

What you need to know about your amp is how much power it can drive into a specific load.  The spec. will look like 250mW @ 16 Ohms.  Most people consider a good operating power for the HE-6 to be around 300mW to 500mW.  The HE-6 is a 50 Ohm resistive load rated at 84dB sensitivity.  Considering you want the volume knob smack in the middle of its range equating to 500mW of output you will want an amp that can deliver 1.0 watts of power.

 

The headphone sensitivity is a number that represents how loud the headphone will get when supplied 1.0mW of power.  In general for every 3dB the spec is below 100dB you need to double the power needed.  For example the HE-6 is rated at 84dB @ 1mW.  Subtracting 84dB from 100dB gives 16dB.  Dividing 16dB by 3 shows how many times we need to double the power to get the 100dB of volume.  Taking 16dB / 3 = about 5.3.  That means we need to double the 1mW of power about 5.3 times to achieve 100dB of loudness using the HE-6.  What does that equate to for us?  The original sensitivity spec. was recorded at 1mW so we double that 5.3 times ( call it 5 ) to get how much power is needed to sustain 100dB with the HE-6. 1*2*2*2*2*2 = 32mW.  That means you will need a minimum of 32mW of output power from an amp to achieve 100dB of loudness.  Taking into account dynamic range adds on average 15dB so we backtrack and rework the math.

 

Dynamic Range Calcs:

100dB ( loud listening levels ) + 15dB ( dynamic range of music ) = 115dB

115dB - 84dB ( HE-6 sensitivity) = 31dB

31 / 3 = about 10

Doubling the 1mW sensitivity rating 10 times yields 1024

You may need up to 1034mW or 1.03 Watts of power to get the full dynamic range for any type of music.  This is why so many people recommend a higher power amp for Orthodynamic headphones.  They typically have low sensitivities.

 

Give us the rating for your amp, the one you plan on driving the headphones with, and we can crank out the math.  You should be able to do this yourself with the above example.

post #3 of 14

Actually, with a Woo Wee connected to your 845 amp, you should be able to power Stax 007.  845 tube usually produces about 20 watts, even for 007 that should be enough, but you might want to try it out first since the 007 has a reputation for low efficiency.

post #4 of 14

Honestly, and I'm well aware that this is not the best way to go about it, I've never really paid any heed to the technical requirements.  Just plug em in and slowly turn up the volume.  The STAX I'm seriously doubting will work but I drove HD650, LCD-2, AKG K701, K340, Denon AHD700, and quite a few more off my speaker amp.  They are all mono blocks, but for comparison mine go from 5 watts, 10 watts, and 30.  All tubed.  Never had any issues.  The Denons exhibited some hiss due to their sensitivity but everything else worked great.  That Cary, I've owned one, will sound better than any headphone amp.  You'll prob have some decent hiss as 50 watts is waaay more than you need for headphones, but the music will sound great.  You could always build a 1/4 jack converter with a couple resistors so your amp sees its regular load while the headphones see their load.  In other words, you amp will see an 8 ohm load while your headphones will see 300 ohms or whatever they need and the excess is just dumped through a resistor.  No harm done and does away with the hiss, just need to figure out the right resistance values.  

post #5 of 14
Peek into any of the power threads for the 6s. They will sound great, issue is have you enough power to get all they can provide. They exhibit the same traits of their Maggie linage. They eat most amps without remorse. Wuwhere is using a couple of tube amps on his 6s. Most are running SS amps of various wattage from 50-500 watts without resistors. Just be responsible with the volume control and you'll be surprised at how well these perform with some power. The soundstage opens and firms up positioning, impact and deep bass come alive, they do scale with quality components.
Edited by Happy Camper - 9/26/12 at 8:28pm
post #6 of 14
Quote:
Originally Posted by NA Blur View Post

STAX are out because you will need a high DC bias voltage to even start to operate them.  They are different technology than Orthos which are dynamic headphones with an extremely thin diaphragm and a wide area voice coil.  STAX are of course electrostatic headphones that require upwards of 500 volts to properly drive and consist of an even thinner diaphragm ( several microns thin ) and magnetic plates that push / pull the diaphragm back and forth.

 

Remember that most older Stax systems were bundled with an SRD-series "energizer" that amounts to a transformer box meant to accept speaker-level input. That's how you get the high voltages needed for electrostatics out of a speaker amp, and that's how I'm driving my SR-Lambda right now.

 

Most of them are Normal bias-era setups, though. Pro bias SRD-7s do exist (SRD-7 Professional, SRD-7 Mk2), but tend to be priced around $250 to $300, which is very close to SRM-1/Mk2 Pro territory ($300-400).

post #7 of 14
I'd just go with something like the WEE or one of the STAX transformer boxes and be done with it for the STAX/stats in general. Regarding the HE-6 or similar, HiFiMan has the HE-Adapter that will accomplish the same thing for dynamic and isodynamic headphones (you can build one at home alternately) - contact the mfgr and make sure connecting -VE together won't blow the amp up, otherwise you gotta run the dynamics via balanced drive. With the STAX transformer couplers that usually isn't a problem (TMK they're all differential).

colin,

If you add resistors, the amp will not "see" lower resistance - you'd need a transformer to accomplish what you're describing. The hiss isn't due to "silly output power" either, it's due to the low Znom + high Zsource + high sensitivity, you're picking up noise. Throwing resistors on the line (like the HE-Adapter) will likely eliminate that noise as well. smily_headphones1.gif
post #8 of 14
Quote:
Originally Posted by obobskivich View Post
colin,
If you add resistors, the amp will not "see" lower resistance - you'd need a transformer to accomplish what you're describing. The hiss isn't due to "silly output power" either, it's due to the low Znom + high Zsource + high sensitivity, you're picking up noise. Throwing resistors on the line (like the HE-Adapter) will likely eliminate that noise as well. smily_headphones1.gif

 

Ahh I see, a while back I had a friend of mine (i'm no engineer as I think we've all realized by my last post tongue_smile.gif) build me something to that effect.  Looked like a headphone jack with a few sand resistors strapped to it.  I thought he had described its function as allowing both the amp and the heaphones to see their respective loads and dump the rest.  It's been a while tho, I'll see if I can grab a schematic from him this weekend if you're at all interested.  For all I know I could be describing jet propulsion by this point and the schematic is for a flashlight.  

post #9 of 14

The specs are vague but 50 W into 8 ohms would be 20 Vrms and 2.5 A. This is plenty for the HE6, which needs 2-3 V and 50 or so mA of current to get to 105 dB. It doesn't say the gain but if it's for speakers it'll be high enough for the HE-6 (maybe even too high, might be noisy).

 

You should have no problems attaching HE6 to any of the speaker outs, it has plenty of voltage and current. Also, why would you add resistors when 50 ohms is already more than a speaker load?

post #10 of 14
I was of the assumption that the resistors in circuit were for protection of the amp, not the headphone.
post #11 of 14
Quote:
Originally Posted by joeyjojo View Post

The specs are vague but 50 W into 8 ohms would be 20 Vrms and 2.5 A. This is plenty for the HE6, which needs 2-3 V and 50 or so mA of current to get to 105 dB. It doesn't say the gain but if it's for speakers it'll be high enough for the HE-6 (maybe even too high, might be noisy).

 

You should have no problems attaching HE6 to any of the speaker outs, it has plenty of voltage and current. Also, why would you add resistors when 50 ohms is already more than a speaker load?

 

From this FAQ http://www.geofex.com/tubeampfaq/taffram.htm.

 

"... the thing you CAN do to hurt a tube output transformer is to put too high an ohmage load on it. If you open the outputs, the energy that gets stored in the magnetic core has nowhere to go if there is a sudden discontinuity in the drive, and acts like a discharging inductor. This can generate voltage spikes that can punch through the insulation inside the transformer and short the windings. I would not go above double the rated load on any tap. And NEVER open circuit the output of a tube amp - it can fry the transformer in a couple of ways.

 

Extended A: It's almost never low impedance that kills an OT, it's too high an impedance."

post #12 of 14

Good to know.

post #13 of 14
Quote:
Originally Posted by colinharding View Post

Ahh I see, a while back I had a friend of mine (i'm no engineer as I think we've all realized by my last post tongue_smile.gif ) build me something to that effect.  Looked like a headphone jack with a few sand resistors strapped to it.  I thought he had described its function as allowing both the amp and the heaphones to see their respective loads and dump the rest.  It's been a while tho, I'll see if I can grab a schematic from him this weekend if you're at all interested.  For all I know I could be describing jet propulsion by this point and the schematic is for a flashlight.  

I lol'd at the last line. smily_headphones1.gif

Basically what the resistors do is make the amp "see" a higher Z load (to use something I own and know about as an example, I've got a receiver that has Zout from the taps of some sub-1ohm value, and has 470R between that and the headphone jack), and knock down current and voltage (power) before it gets to the headphones. It makes both sides "safe" as long as the amplifier in question can handle what is attached to it. wuwhere's point is also worth noting - it really depends on what the OT can (or can't) do as to whether or not this will blow things up. You may need *additional* transformers beyond the OT, which is like the STAX box (which will only work with STAX and a few other headphones that can run on Pro Bias) - with a transformer the amplifier "sees" the load it wants to see (8R or whatever), and the headphone "sees" the source it wants to see (and with an ESP step-up, you have bias HV too).

There's a basic schematic for this kind of circuit available from Rod Elliot:
http://sound.westhost.com/project100.htm

But as he notes, the amplifier has to be able to have -VE connected. If it can't, you can run balanced (just put the resistors in and ignore the common GND, so you'll have like tap left +/- -> resistor -> headphone left +/- and repeat for right). I'd contact Cary for more information about whether or not the amplifier can run a circuit like this safely - they'll probably tell you right away if it's dangerous or unsupported (for warranty reasons or what have you).
Quote:
Originally Posted by Happy Camper View Post

I was of the assumption that the resistors in circuit were for protection of the amp, not the headphone.

Actually they protect both. They prevent the headphone from having too large of a signal sent into them, and the amplifier from blowing up the headphones and seeing a crossbar. It's more for the load's protection though, but they're entirely essential for connecting a dynamic or isodynamic headphone to many amplifiers (now in this scenario, the HE-6 might be fine hooking up straight-off the taps and running differential, and then just use the WEE or SRD-7 or whatever else for STAX and you'd be fine; the problem is you'd have to switch out wiring between the various configurations whenever you wanted to change up - a speaker selector might be worth looking into).
post #14 of 14
This thread makes my project on speaker tapping my HE400 through Jolida FX10, really looks like David vs Goliath...biggrin.gif:D OR am I in the wrong level here?....biggrin.gif:D:D

Should I be brave enough to proceed with my setup---loving the sound not blowing out my ortho--I would like to step it up to my antique Adcom GFA 7000 power amp. through GTP 600 preamp.....biggrin.gif:D:D:D:D:D:D;) Curiosity hopefully will not burn my system and blow out my ears...biggrin.gif:D:D:D:D

I will accept any suggestions and inputs, anyways. I have learned a lot since I joined head-fi.

Thank you in advance guys.
Cheers

My Jolida FX 10 tech specs:
Technical Specifications:
Maximum power Output: 12 W per channel at 8 ohms, 1KHz
Rated Output Power: 10 W per channel at 8 ohms, 26Hz to 50KHz
Frequency Response: (at 1 watt into 8 ohms) 17Hz to 37KHz + 1dB; 0dB at 1KHz
Bandwidth: 14Hz to 50KHz + 3dB; 0dB = 10 W 1KHz, 8 ohms
Distortion THD + N: Less than 1% at 10 W output, 39Hz to 10KHz, 8 ohms
Circuit Type: Ultra Linear, Class AB1
Input Impedance: = or < 100Kohms
Input Sensitivity: Max. 670 mV for 10 watt output at 1KHz
Output Impedance: 4 ohms and 8 ohms
Negative Feedback: Less than 3 dB
Signal & Noise Ratio S/N: 81dB below rated output from 10Hz to 200Khz
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