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The Stax Thread III

Discussion in 'High-end Audio Forum' started by currawong, Aug 20, 2013.
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  1. kevin gilmore
    Joamat is running one at 500V supplies with hand selected parts

    Probably not a great idea

    If you use an alternate version of the current source with 4686a you can go to 600v
  2. JimL11

    Yes, it's true that you don't need as much voltage running a choke as a resistor or constant current source, but as I pointed out, the power part of music lies in the 50-300 Hz range, and the impedance of a choke is relatively low at those frequencies.  The largest commercial choke I have seen is 200H, but even if we assume a 400H choke, its impedance at those frequencies is 125 kilohms to 750 kilohms.  If we assume a 200H chokem the impedance drops to 62 to 380 kilhoms.  This sounds high, but remember that the impedance of the headphone at those frequencies is 3.9 megohms to 460 kilohms (actually somewhat lower due to the fact it makes sound).  So with a relatively low choke impedance combined with a very high headphone impedance, guess where the bulk of the signal current is going to go - burned up in the choke rather than used to drive the headphones.  This means that the output device has to produce much more signal current for the same output voltage, which means more distortion.  All this assumes a perfect choke, but real chokes have resonances, leakage capacitance etc., and realistically, pretty much never have a reactance greater than 1 megohm.
    On the other hand, a good cascode MOSFET current source has a measured impedance of over 150 megohms, so essentially none of the signal current is wasted driving it.  You trade off the greater DC efficiency of a choke compared to a constant current source, for much worse AC efficiency, and much greater cost.
    Now, chokes definitely have their place if you can afford the cost.  But the output stage of an electrostatic headphone amp is not the optimum location IMHO.
    arnaud and Sko0byDoo like this.
  3. JimL11

    At the time it was designed, pretty much all headphones rolled off below about 40-50 Hz.  Mercedes wanted a headphone that went down to below 20 Hz, and they asked Stax to design one for them.
  4. JimL11

    In terms of sheer output, assuming no differences in sound quality, going from 400 volts to 450 volts buys you 1 dB increase in level prior to clipping.  Going from 400 volts to 500 volts buys you 2 dB.
  5. Ampeezy
    Not much worth then for going higher in voltage, as I have ample headroom, and I also assume It will turn into a toaster. I don't get how people have carbons that run cool.
    Also beyond clipping, there must be some sonic advantages otherwise why would some try to build the circlotron? I dont much about it, but I always thought It was more like a KGSSUHV ( Kevin Gilmore Solid State Ultra High Voltage) lol.
  6. Whitigir
    Carbon runs hot....it is not cool
  7. hpeter
    Recalculated my setup, it looks like this at 100Vrms out. (LL1660 36mA 2:2,25+2,25 center tap)
    Below <20Hz cannot hear much; >30Hz is fine. So far in music i have not noticed deficiency, during tone sweep it was noticeable. Kind of a can´t-turn-off subsonics filter, hmm

    Back to the discussion, i read some thread where people measured gyrators, it seems parasitic capacitances in mosfet does reduce it´s properties. Mostly the Cdg does the harm. Ideally a gyrator which would be AC shielded from circuit; could maintain it´s performance even at treble frequencies; bass seems unharmed
  8. Ampeezy
  9. kevin gilmore
    nothing I have ever built including the t2 and the megatron get as hot as a krell fpb600
    hot is a relative term. if you can hold onto it for 5 seconds it is not too hot. (does not apply to the tubes themselves)
  10. yates7592

    My headinclouds build Carbon runs warm at most, never hot.
  11. Whitigir

    The transistors are all running very hot, and if your chassis doesn't get that hot, it means the heat dissipation from your transistors is not efficient enough. My transistors run upto 56-60 C and while my chassis runs upto 46-47 C easily, it will remains stable for hours on end and that is hot.
  12. yates7592
    Or the heat sinks on my chassis are more efficient? All I know is it sounds amazing, and like you the best quality bass I've ever heard in a set of headphones.
  13. Ampeezy
    Which headphones do you have??
    Also, that krell amp is a monstrosity
  14. Whitigir

    True :) and yea, the Carbon + 009 is magically amazing in the bass department, given that I love quality Bass
  15. Feilong4
    I've been occasionally listening to my Stax system for a few weeks now, but I have ultimately decided that the electrostatic sound presentation just isn't for me.
    I'm sorry in advance for advertising, but if anyone is interested I'm selling my system here on the Sale forums.
    Link to it here: http://www.head-fi.org/t/842331/stax-setup-sr-407-srm-300-310-wooden-stax-stand-stax-dust-cover-us-transformer-shipping-included-trade-for-hd800-andromeda-etc
    I feel my listing will be much appreciated if I let peeps here know.
    Comes with:
    - SR-407 Earspeakers
    - SRM-300/310 Driver Unit
    - Transformer
    - Wooden Stax Stand
    - Stax Dust Cover
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