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Topping EHA-5


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so here are some more pictures, obviously faked.  This is the kgsshv-carbon built by birgir and given to tyll as one of his 2 reference amps. Into a standard 120pf load. right at the limit of my scope probe, have to find the higher voltage probes. first picture 20 volts per division, next 2 are 50 volts per division. all are 10khz square wave. reference cap beginning to bubble due to heat.





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On 8/27/2023 at 3:42 PM, kevin gilmore said:


edit: shenzen audio is now selling these things brand new in the box on ebay for $50 off. soon it will be $100 off.

a few years ago I was on some Zoom calls with another company that wanted to make a cheap electrostatic amp. 5 guys on a Zoom call. they expected to sell thousands. To who and for what headphones?? the whole thing won't cover the salary of 1 person. sometimes I'm not sure people grasp the size of this market

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Someone asked me for my equivalent measurements of the Mjolnir KGSS Carbon HV. OK, I have a bunch of measurments. To keep them separate as it seems that image files don't automatically get labels in this forum, I'm going to post them one at at a time. Forgive me if I'm mistaken, the easiest thing for me to do is make one post at a time. Where you see the rising high frequency response at the high end, that's the noise shaping of my Prism ADC/DAC which I use for analysis in conjunction with Spectraplus. Note that at the time I made these measurements I was not aware that it would be advantageous to add a 100 pf capacitor on the load. So these are open loads, and perhaps some of the tiny ringing you see would go away. The first is a digital scope photo of a 1 kHz Square wave at 200 volts p-p from my Fluke Scope. Attached here. 


34 minutes ago, bobkatz said:

More Mjolnir Carbon measurements. See the first post in this series for description. Here is a 10 kHz square wave at 200 V p-p


In this series Mjolnir KGSS Carbon 100 Hz Square wave 250 V p-p


Edited by bobkatz
Oops, missstated the p-p voltage.
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In this series. I like to mark levels in equivalent SPL. Based on the 100 volt RMS rating of the CRBN headphones. So this is close to 100 Volts RMS. Mjolnir spectrum at 97 dB equivalent SPL at 1 kHz. As you can see, it's pure second harmonic with no other trace of harmonic distortion. Second harmonic is at the equivalent of about 10 dB SPL!image.thumb.png.4c2eada5a578d6916198867c39fce281.png

In this series, KGSS Carbon HV left channel frequency response. I'm using a transfer function with white noise, so for whatever reason at above 60 kHz, the transfer function goes funky and is unreliable. The amp is flat from 10 Hz and only -0.6 dB at 60 kHz!


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In this series, the right channel freq response is nearly identical so not worth displaying here. Just below clipping, equivalent SPL of 113.4 dB SPL at 1 kHz, produces 0.025% THD. I have an attenuator and by accident, apologize for the inconsistency, the scale is dBu, but my notes say 113.4 dB SPL equivalent. That is a remarkable 467 V RMS. THD is 0.024/0.026% THD at that point. image.thumb.png.13bc9b83c8b9bd1e02aef21df79eab48.png

In this series, Mjolnir 19-20 khz IMD. The amplitude of the 18 and 21 kHz products is not exceptional, but to my ears this is still one of the the nicest, most natural and warmest Stat amp I have ever heard. IMD measures 0.018/0.021%. Amplitude is not specified, but I suspect given my scales, it's near 100 V for either one of the partials. 


Mjolnir IMD 19-20 kHz.png

Edited by bobkatz
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In this series, Mjolnir KGSS HV Carbon noise floor in equivalent SPL is around or below -15 dB SPL. That's MINUS 15 dB SPL, folks. 


Mjolnir KGSS Carbon HV noise floor.png

Aha! In this series, I took the IMD with an SPL scale. So at the equivalent of 90 dB SPL for the Stax 007 Mk 2, here's the IMD. It's much lower than the previous IMD measurement, which must have been taken near clipping. Of course there is no meaning to equivalent SPL for a 19-20 kHz signal! But the scale is calibrated for SPL at 1 kHz so you get the idea of the amplitude of the test signal. Here, not so overloaded you can see VERY little 1 kHz difference product at the equivalent SPL of about -2 dB SPL! And no trace of 18 kHz or 21 kHz IMD. So at these already extreme levels, at extreme high frequency levels that would not be found in normal music, the Carbon HV performs exemplararily (if that's a word). 


Mjolnir KGSS Carbon IMD 90 dB SPL.png

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IN this series, THD+N versus frequency, 20 Hz - 20 kHz. At the equivalent of 100 dB SPL (100 V RMS). THD Is Very very even all the way from 20-20k. at about 0.2% THD. 


Stax 100 dB SPL THD + N.png

In this series, the THD+N at 110 dB SPL is actually LESS than at 100 equivalent dB SPL, telling us that the measurement mostly consists of noise, not THD. 

That's all the Carbon measurements I have on hand. 

Stax 110 dB SPL THD + N.png

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  • 2 weeks later...

here is a link to simmcon's takedown of the eha5. its mandatory reading for everyone.


in other news, birgir sent me a srd7 to test.

in other other news, i have finally found a company that will sell me cores and bobbins in small quantities. so making electrostatic transformers becomes a possibility.

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 i posted this elsewhere. here is a copy

Its all about size (as in core cross sectional area) and maximum flux before saturation.
its obvious from the graphs above (posted elsewhere) that the core saturation of the eha5 transformer is about 1.4 tesla indicating the cheapest of core materials.
better and much bigger transformers are available from lundahl and edcor. which will both give 20hz to 20khz +0 -1 db and will actually do 1800vpp
with a 50 watt amplifier over the full frequency band. without series resistors. without filters.

as far as i can tell lundahl does not specify maximum field strength. edcor does and its 2.01 tesla.
there are custom c cores with magic materials that can do up to 2.5 tesla. these are a bit expensive.

the ll1630 mentioned above (posted elsewhere) will NOT do this. core size is too small.
you need a transformer with a minimum of a 30 watt core. The 60 watt edcor are MUCH better.

the ifi iesl which is extremely sensitive to power amplifiers is yet another example of a poor design with a tiny transformer.
does not matter how carefully you wind the core if you drive the transformer into saturation.

the result will be a box about 3 times the size of the eha5. and a weight of about 20 lbs.
cost about $600.

nope, no cheap way of doing this.

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