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Kung

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Posts posted by Kung

  1. 34 minutes ago, justin said:

    Has anyone heard from mikhail or rudistor lately? Possibly a collaborative effort?

    Don't know if it's true, the rumor from the dealer of rudistor in Shanghai said that the designer passed away a few years ago🙄, and they still have some unsold rudi amps in stock...

  2. From warwick official website, I think their aperio has a high voltage bias (1800Vdc) driver, which is much higher than the 1350Vdc of their lower models. it means that the output voltage of the amplifier no longer needs to be as high as the traditional electrostatic system, therefore does not require too much power and heat dissipation.


    In addition, for the built-in amplifier of HE1, I guess it may be the cool-mosfet version with reduced gain of the hev70 vas since Sennheiser applied for a patent(DE4329991A1) similar to the design of the HE1 in 1993. I heard HE1 once at the exhibition, and I also think that the potentiometer should be set to the position of about 2-3 o’clock to get loud enough, indicating the input sensitivity voltage can be a bit high based on the two-stage amplifier's gain setting being too low...🤷‍♂️

    • Thanks 2
  3. 5 hours ago, Timb5881 said:

    Based on measurements only, and Topping products usually measure very well.

    Yep, ASR's evaluation is just based entirely on measurements...

    My source told me that topping has also designed a discrete component version of electrostatic amp to drive estats directly, ap show that its specs far exceed any known electrostatic amps, and it will be on the market sometime in the future. . .🤷‍♂️

    • Thanks 1
  4. ::)Ray samuels the old friend of stax mafia just released a new amplifier B-21, the electrostatic part claimed 1800Vpp voltage swing with 200mA continuous current output performance just shocked me. . . Reminds me of the horribly weak output performance of the A10 he designed before, this new amp is also questionable...

     

    B21.jpg

    B211.jpg

    • Like 1
  5. From topping's previous amplifier products, the EHA5 normal amplifier section is likely to be a composite amplifier, just like the amplifiers of jds atom and benchmark things. The common practice is to combine a precision opamp1 with a higher idle current opamp2 which has a specified closed-loop gain. opamp2 is placed inside the feedback loop of opamp1, which is the "feed forward technology" claimed by some manufacturers. In fact, it introduces a huge amount of feedback, the distortion test is usually lower than what the manufacturer's specs , but I don't know whether it can drive the transformer to output such low distortion though...never tried before 😟

  6. 31 minutes ago, kevin gilmore said:

    is that supposed to be a choke load for the 300b?

    whats with the extra shunt rc filters?

    have no idea, since no more detailed schematics were provided,the most likely one is that the plate is connected to the transformer, the center tap of the secondary winding is grounded ,then it can output signal with opposite phases to headphones ::)

  7. 12 hours ago, rod said:

    @Kung, impressive work, looks quite time consuming to do in both carrying  out the repair  and sourcing materials , was it just to do a repair on a faulty pair you had or are you maybe thinking of doing this for others as well?

    Just to repair my own headphones, cause I have not only hifiman cans but also several other old estats of Stax and Sennheiser.
    it will be more reassuring to play with these old stuffs if I can do some repairs myself.:)

  8. On 6/5/2022 at 1:44 AM, qqiao said:

    https://i.imgur.com/Dz9hxo6.png

    I found the schematic fo 007, the bias circuit should be similar as t1, actually I don't fully understand how it can get 580v voltage, the output from the transformer only provides 270v, it looks like a half wave rectifier circuit.

    According to your 007t schematic, if the transformer outputs 270VAC, the voltage doubler will give you about 360+VDC bias.

    If the transformer outputs 435VAC, you will have a standard 580VDC pro bias.

    because there is no voltage regulator, the turn ratio of  transformer will be conservative for wider range of voltage fluctuation. ::)

  9. On 6/2/2022 at 2:13 AM, spritzer said:

    Great work and Stax had endless issues with the SR-Omega... same as Sennheiser with the glass stators. 

    It is likely that the #80 mesh is not easy to make a stator by hand, which leads to the failure of the omega driver, and the driver housing made by resin at that time was not as strong as later 007 009 though. There are some DIY estats such as Perun and Phenomenon in Russia, they use much lower number size copper mesh as stator. I have owned a pair of perun, the stators are made of about #10 copper mesh,  the mesh itself is very strong actually, and is glued to the PCB holder with structural adhesive.

    As for the glass stator of the HE90, the glass is indeed rigid, However, as a stator, it does not play the role in the Sennheiser advertisement at all. The only thing I can expect is that the glass is chemically stable and not easy to be corroded or oxidized, and Manufacturing microporous glass plate is extremely expensive which also leads to the insane price of the HE90... Unfortunately, Sennheiser is now not planning to stop, they use even more expensive ceramic based PCB stator on HE1.😦

    • Like 5
  10. Updating more DIY mesh stators. 

     

    Glue the brass holder to the copper sieve with ERGO 5500 or 5900

    IMG_2767.thumb.JPG.ab5c3faf1d6b944bd3e5c2da3063afa0.JPG

     

    then cut off the excess copper mesh with a nicking tool.

    IMG_2768.thumb.JPG.dbbff15c61b09e5816f4dcbdccbea89c.JPG

    IMG_2769.thumb.JPG.05019300930000feb484a6195d831257.JPG

    IMG_2770.thumb.JPG.f4d828bcca306cb29491f679cb1f458f.JPG

     

    Stators mesh size in the picture below ranges from #180 to #400,It is better to use a higher number mesh for making DIY mesh stators, the mesh with lower number size is difficult to glue...This may be the reason why stax no longer produce the original omega . Both omega and x9000 use about #80 mesh for their stator,  and it is not easy to fix #80 mesh by hand, x9000 solves the problem by using thermo compression bonding...::)

    IMG_2774.thumb.JPG.73e93c48385e666c840995424aeda603.JPG

     

     

    • Like 7
    • Thanks 1
  11. 1 hour ago, Pirx said:

    Really nice job. I would love to have such skills :)

    How do you measure headphones?

    I bought a 711 clone rig on Taobao, here is the link: https://item.taobao.com/item.htm?spm=a230r.1.14.18.b2407a72U22HcB&id=41416109881&ns=1&abbucket=3#detail  
    Contains a clone coupler based on IEC-711 standard, a preamp, a silicone pinna and a calibration file based on B&K4128C.
    the clone coupler has been confirmed by the headphone factory to perform almost the same as the G.R.A.S RA0045.
    Unfortunately , the silicone pinna is not a standard pinna clone from G.R.A.S or B&K, resulting in an additional 5k~6khz attenuation in the frequency response diagram.

    • Thanks 1
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