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The Stax Thread III

Discussion in 'High-end Audio Forum' started by currawong, Aug 20, 2013.
  1. walakalulu
    As the extension cable is silver plated copper I would guess that an increased length may add to high frequency uplift.
  2. Jones Bob
    Using any STAX cable extension adds capacitance to the load the amp sees. Depends on the amp and available output current, whether there will be an audible HF roll off when using one. Generally speaking there will be a slight change (degradation?) in SQ when using one, especially with the lower powered STAX amps. Applies to either the silver plated or plain copper version.
    Last edited: Jan 4, 2019
    GarageBoy likes this.
  3. PointyFox
  4. 336881
    If headphone cables are anything like speaker cables the cable itself should act like a resistor. Why you want your speaker cables the same length. It should be a degradation but who knows.
    GarageBoy likes this.
  5. PointyFox
    How does length, resistance, load compare?
    Last edited: Jan 4, 2019
  6. azabu
    I'm running a BHSE and don't hear any degradation at all, just a nice uplift in tone from the silver-plated copper cable. I have experienced degradation when using iem adapters, nothing too drastic but noticeable.
  7. Jones Bob
    With a BHSE, there is enough power to drive the additional capacitance of the extension cable. You might not notice much of a degradation with that setup. I believe I can with my now sold SR-007 MK2 and current SR-009s though. Or at least I enjoy them more without the extension cable in the signal path.

    Just asking: How do you know its the SRE-925S silver plated cable that is responsible for your observation? Have you compared it to the SRE-725 plain copper version? I’m far from being a wire agnostic, as after a lot of experimentation, I settled on using custom Neotech silver/gold alloy solid core wire for my signal wires. Even replaced the internal wire in my GG from the PCB to STAX jack with it. That was one area that did not make much SQ difference.
  8. JimL11
    Might be due to differences in amplification. This was at a local meet, there weren't a lot of people there so it was relatively quiet. I used a BHSE for the 009, but I plugged the Utopias into a Gilmore Lite MkI with LPS. Yes, I know, a HUGE difference in amp cost, but that was what I had to listen through. Reportedly the Utopias are relatively insensitive to amp choice, and I believe that the Gilmore Lite is considered a relatively bass-light amp. Same source for both amps (Mojo Audio Mystique V2 plus DAC). On classical (specifically Elgar's Cello Concerto by du Pre, the Utopias did sound a bit confused compared with my 007 MkII, which I prefer to the 009s.
    HoloSpice likes this.
  9. JimL11
    Electrostatic headphone cable requirements are NOT anything like speaker cables. Speakers generally have an nominal impedance of 4-8 ohms and a real impedance of 2-30 ohms or more (the Quad ESL runs between 35 ohms and 2 ohms of the audio spectrum, and at high frequencies somewhat resembles a 2 uf capacitor. Speaker amps have an output impedance of a fraction of an ohm, and may rise somewhat at the highest audio frequencies - this is especially true of transformer tube amps. Thy often have to deliver several amps on musical peaks along with tens of volts. So, speaker amps are moderately high voltages, high currents (by comparison)

    Dynamic and planar headphones generally have an impedance between 10/s to 100's of ohms, Dynamic headphones commonly have a bass peak which may be two or more times the nominal impedance, while planar headphones are generally pretty flat across the audio frequency spectrum. Dynamic and planar amps usually have to deliver less than 1 amp and a few volts. The least efficient planar headphones will deliver 120 dB with 17 volts RMS or less, sufficient to cause permanent hearing damage within a minute.So, non- electrostatic headphone amps, relatively low voltages and moderate currents.

    Electrostatic headphones have a largely capacitative impedance which is broadly similar to a capacitor of around 100 pf, give or take. Impedance is very high - the Stax SR-007, for example, is specified as having and impedance of 170 kilohms at 10 kHz. This means that at 100 Hz, its impedance should be around 17 megohms. Electrostatic amplifiers can produce 100s of volts, but usually have to deliver peak currents of 5-10 milliamps, or thereabouts. So, electrostatic headphone amps, very high voltages, very low currents.

    Every cable (speaker, headphone, interconnect) has a combination of resistive, capacitative and inductive components. This is due to the physics of paired conductors and is inescapable. Increasing the distance between two parallel wires increases their inductance be decreases their capacitance.

    For speakers, because speaker impedances are low, low resistance is very important, inductance may or may not be important (it can be significant for electrostatic speakers because it is highest at the highest audio frequencies, where electrostatic speaker impedances are lowest, whereas most dynamic speaker impedances tend to rise at the highest frequencies due to the inductance of the tweeter voice coil, which offsets the rise of the cable due to its inductance), and capacitance is not that important except if it causes amp instability and oscillation (bad). For example, 10 feet of 18 gauge zip cord, has about 280 pf of capacitance. OTOH, 10 feet of Polk cable, which was an early "super" cable, had a capacitance of around 5000 pf, which was enough to cause oscillation in some amplifiers of the time.

    For Dynamic and planar headphones, low resistance is relatively important, inductance is unimportant because it is generally negligible compared to headphone impedance for any audio frequency, and capacitance only matters if it causes amp instability. Given the impedances, voltage and current demands, the wire diameters in headphone cables are similar to those of interconnect cables. Belden cable specifies that 26 gauge wire can carry more than1 amp of current with less than a 10 degree centigrade rise in temperature of the wire.

    For electrostatic headphones, resistance and inductance are unimportant because both are negligible for typical cable lengths compared to the impedance of the headphone itself, but capacitance is very important, because excess capacitance requires more current drive with increasing frequency. If the extension cable has 100 pf of capacitance, which is a typical amount for a standard interconnect cable 1 meter in length, for example, that doubles the amount of current that the amp has to deliver to produce the same signal at the headphones. So a 100 pf extension cable is equivalent to connecting a second headphone to the amplifier.

    So, the primary requirement for an extension cable for electrostatic headphones is very low capacitance. I find it noteworthy that Stax and Koss, who individually have more experience designing and building electrostatic headphones, than all the other companies currently marketing electrostatic headphones put together, both came up with a similar flat, parallel wire cable whereas on their earlier phones, they both used round cables. Perhaps they know something the other companies don't.
    Last edited: Jan 5, 2019
    gepardcv, jgazal, Zoide and 5 others like this.
  10. azabu
    The SR-007 Mk2 uses copper for the headphone cable, so it's just a matter of plugging in the SRE-925 SPC extension cable for a simple AB test. The extension cable is just a small and inexpensive tweak to lift the treble and bring it closer to the 009 series *cough*. At this stage, I'm more than pleased with my system and will probably get a Mutec Ref 10 instead of picking up a 009S.
  11. walakalulu
    Given the circuit requirements of energisers, are they more susceptible to mains cable variations than standard headphone amps? This seems to be my experience.
  12. popof94
    Hi all, I leave in Paris and just bough here from a reputable member a STAX SRM600 in 117VA. I want it rewired in 220VA. I saw some post from 2012 about that but I can’t open the old link. Anybody can help me? Many thanks jm
  13. JimL11
    Try contacting spritzer at Mjolnir Audio. I remember he posted instructions on doing a voltage conversion several years ago. The T1 series had a voltage converter built in but I don't know if the SRM600 did.

    Also, I seem to remember hearing of some issues with the plate output resistors blowing up. If you want to improve its performance further, you can modify the amp by replacing the plate output resistors with my constant current mod. People who have done the mod in the T1 series (which has essentially the same design except for the output tube and plate resistor values) report tighter bass, more extended highs, and better detail.
    Last edited: Jan 5, 2019
    popof94 likes this.
  14. popof94
    Done, contacted spritzer and Kevin Gilmore and both have explained how to rewire from 117V to 240V. However I am a little bit afraid because spritzer told me that the amplifier has already been rewired from 100V to 117V an If something fails there...then it would destroy the amp.
  15. JimL11
    If that is a concern, you can always get a 240V to 120V step down transformer to drop your AC from 240V to 120V. Just plug the step-down transformer into your wall socket, and the amp into the step-down transformer. The amp uses 52 watts so any transformer rated for higher wattage than that should be OK.

    If you are interested in the constant current mod, I published an article on it in AudioXpress July 2017. I believe back issues are available for $9 US plus postage. If you have any questions feel free to PM me.
    Last edited: Jan 5, 2019
    azabu likes this.

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