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Electrostatic Amplifiers Voltage ratings

Discussion in 'High-end Audio Forum' started by kevin gilmore, Nov 28, 2011.
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  1. kevin gilmore
    I get asked about this fairly often, there are a number of different ways of measuring the voltages
    so here in one place is all the amps i know about, and all are rated the same.  The voltage is
    peak to peak voltage measured from one stator to the other stator.
     
    For solid state amplifiers, the output voltage is usually very close to the power supply rails.
    For OTL tube amplifiers, the Rp of the output tube(s) usually takes about 60 volts off of the
    maximum voltage swing, for Stax made amplifiers the negative power supply is increased to
    compensate for this. These are theoretical maximums, in practice the voltage swing will be less.
     
    There is of course more to these amplifiers than just the voltage ratings, Slew rate into a
    capactive load is also very important, i will be measuring some of these amplifiers and will
    add slew rate at a later time.
     
    3000 volts peak to peak stator to stator (+/-750 power supplies)
    KG TOGTE
     
    2400 volts peak to peak stator to stator (+/-600 power supplies)
    koss esp950
     
    2300 volts peak to peak stator to stator (+/-575 power supplies)
    KG’s new Silicon Carbide jfet based space heater.
     
    2000 volts peak to peak stator to stator  (+/-500 power supplies)
    Stax T2, DIY T2, KGSSHV (ixys parts)
     
    1800 volts peak to peak stator to stator (+/-450 power supplies)
    KGSSHV (sanyo parts)
    craig has said his new electra amp does 1800 volts, power supply unknown
    Ergo Jecklin
     
    1600 volts peak to peak stator to stator (+/-400 power supplies)
    BH, BHSE, singlepower ES1,ESX (after being modified to remove the 100V offset)
    Cavalli Audio Liquid Lightning
     
    1400 volts peak to peak stator to stator  (+/-350 power supplies)
    KGSS,Stax T1,T1s,T1W,313,323,717,727,sra-14s,srm-1 mk2,srm-monitor
    woo audio wes
     
    1300 volts peak to peak  stator to stator
    stax sra-10s/12s
     
    1200 volts peak to peak (+/-300 power supplies, and +600 capacitively coupled)
    KG tube #1,aristaeus,HEV70,HEV90,RSA A10,srm300,Exstata
    Egmont,Cirolan,SRM-1,srm-3,woo audio ges,srm310
     
    1100 volts peak to peak stator to stator
    stax sra-3s
    stax srm-001 (when the batterys are at full power)
     
    1000 volts peak to peak (+/-260 volt power supplies)
    Rudistor Egmont
     
    960 volts peak to peak stator to stator
    Stax srmXh, srm212
     
    540 volts peak to peak stator to stator
    Very early HEV70  (+525 volt power supply and tubes biased at 390 volts)
     
     
    More added later
     
     
    edited 5/3/12 for clarity and fixed srmXh,srm212
    added a couple of others
     
  2. TMoney
    Thanks for posting this, KG.
     
  3. chinsettawong
    Thanks a lot, Kelvin.  :)
     
    Wachara C.
     
  4. gurubhai
    Thanks a lot.
    Looking forward for the Slew Rate measurements too. :)
     
  5. kiertijai
    Thanks so much Kevin
    How much does the voltage swing influence the performance of the electrostatic
    amplifier?  Are there any other factors?
     
  6. spritzer
    When my email starts working again then KG will have an updated list to post.  [​IMG]
     
    It's should also be noted that while voltage swing is important, it is only one aspect of an amplifiers performance.  It also says nothing about the load tolerance of the amp or how far into Class A the output stage is biased. 
     
    While most of these amps will never see anything close to their full voltage swing in normal use, they have enough voltage on tap to destroy the electrostatic transducers.  Some are more sensitive than others (Stax normal bias, Sennheiser HE90) but this is a real issue given enough input voltage and high enough gain. 
     
  7. FrankCooter
    Not that it really matters, but I'm curious why you chose peak to peak  rather than rms output voltage. Stax uses rms in their product descriptions. Seems this has caused a good deal of confusion here in the past.
     
    Appreciate the info and look forward to your slew rate measurements. I'm also curious about the current levels in the output stages of the amps.
     
  8. spritzer
    Well peak-to-peak has become a bit of an industry standard in the DIY world with only Stax using RMS.  Still it is easy enough to convert, RMS*1.41*2 to get the P-P value.  The SRM-300(310) is listed at 350VRMS so that would be roughly 1000V P-P.  Stax always post conservative specs plus these are measured, not simply derived from the rail voltages (in this case +600V regulated). 
     
  9. kevin gilmore
    Here are some of the output stage currents. Remember that every single amplifier has balanced outputs, so
    there are actually 4 output stages. The new eddiecurrent thing probably has output transformers, so its different.
     
    kgss  8.3 ma x 4
    kgsshv 5.5ma x 4  (you can turn it up if you have lots of heatsink)
    T2 14ma x 4
    ES1/ESX  8.5ma x 4  (when its modified to work correctly) (if you change out the plate resistors with current sources, up to 20ma x 4)
    kg tube amp #1, aristaeus and hev90  6.3 ma x 4
    kg silicon carbide space heater  50ma x 4
    koss es950  1ma x 4
    BH,BHSE  18ma x 4
     
    most of the other stax tube amps are about 7.5 ma x 4
    srm313,srm323  5.5ma x 4
    srm717,srm727 6.6ma x 4
     
     
     
    The rest i will have to look up later.
     
  10. bcg27
    Whoa, the KGSCSH is a beast - higher output voltage than T2 and 3.5 times the output stage current?!!
     
  11. jcx
    depending on the devices used output bias current may be largley used just charging/discharging the semi device output C - easily as much or more C than the ES headphone (ES headphone + cable C is ~100 pF)
     
    and larger current as substantially more dangerous - 50 mA is above the tetanous threshold for AC, near the DC threshold for women = when the muscle contractions are so severe you can't let go
     
     
  12. bcg27
    I assume he is using one of the semisouth SiC jfets
     
  13. kevin gilmore
    Technology is driven by demand these days, not the other way around.
    The silicon carbide devices are very new, and designed for use in
    huge solar panel arrays. The devices are designed for up to 25 amps
    and just happen to be good for 1200+ volts. I doubt that lower
    current devices with a much more narrow channel and much lower
    capacitance will ever show up because there is no need for them.
    Great for guys like Nelson Pass whose monster power amps are going
    to love these things. For electrostatic amps, 400 watts of standing
    power is a bit over the top.  You won't see me releasing a circuit
    board for this unit. Besides which the energy storage of the power
    supply is over 2000 joules.
     
  14. FrankCooter


     
    Quote:

    I'm a little bit surprised by the relatively low currents here and would think that they would dramatically  impact slew rate in a negative manner.  What kind of slew rates are considered acceptable? If slew rate equals 2piFVp/1000000, and you use 20kHz and 500Vp as your target points,SR equals 68V per microsecond.  Current should equal SRxC. The SR009 has a capacitance of 110pf. Using this value, looks like you need  a minimum of about 7mA. in the output stage. Of course I'm just "parroting" (or 'misparroting") Broskie here.
     
    On a purely subjective level,using the very basic Egmont circuit, increased output stage current levels seem to correlate to a higher sound quality.
     
     
  15. Tadj
    Thanks KG, interesting information and useful information,
     
    I am going to put the parts together for (your) KGSSHV but I thinks the silicon carbine part might not available commercially in Thailand as yet! any suggestion?
     
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