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Electrostatic Amp THD Specs/Measurments for the Full Audio Band ?
Electrostatic Amp THD Specs/Measurments for the Full Audio Band ?
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Old 29th November 2017, 07:12 PM   #71
xrk971 is offline xrk971  United States
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Electrostatic Amp THD Specs/Measurments for the Full Audio Band ?
Elvee came up with some interesting design:

Click the image to open in full size.
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Old 30th November 2017, 12:40 AM   #72
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by xrk971 View Post
Elvee came up with some interesting design [picture]
Same approach, but very different.
Although I'm trying to move to quasi complementary for better performance.
..but I keep turning back for improvements.

-What is the distortion at 1Khz and 20Khz?
-What current does it draw?
-What is the frequency response?

(measured with a capacitive load of course)

-Are the mosfets "real"?
-Do they include the input capacitance?
(I have manually added the input capacitance to be sure as I suspect it is not included, although the models are official)
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Old 30th November 2017, 01:13 AM   #73
EUVL is offline EUVL  Europe
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Build me a ss direct drive ESL amp, please

Ask the original designer.
See also post #25, 28 & 34.


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Last edited by EUVL; 30th November 2017 at 01:17 AM.
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Old 30th November 2017, 07:36 PM   #74
hpeter is online now hpeter  Slovakia
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Quote:
Originally Posted by xrk971 View Post
Elvee came up with some interesting design:

Click the image to open in full size.
I see a 22mA ccs on top, bottom Schaded fetriode =453 (6M8/15k)
PNP to FET is nice, but i dislike the dividers wiring - confusing
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Old 8th December 2017, 11:14 AM   #75
MrMagic is offline MrMagic  Greece
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I haven't tried the above design, but I can tell that it obviously suffers from many "diseases", like excessive distortion, inadequate power bandwidth, etc.
I have personally put a lot of work to reach and further lower the previously mentioned 0.025% -by using different techniques.

But I recently came up with a quasi-complementary design with the following current specs: 0.004% THD with reduced high-order harmonics at up to 20KHZ, full power bandwidth of 1.4KV (from 1500V power supply) , 250pf load, mosfets with 1400pf input capacitance (instead of 200pf of the previously mentioned Cree one) and clean square-wave response. In LTspice of course, not real-life yet.
Still I have a lot to do, from making it a dual-supply one, to lowering it further to <0.001%, to ensuring perfect stability in all conditions etc.
Another spec I'd like to add is a double headphone drive capability (>500pf) for dual-listening with a friend.

(BTW, Stax amplifiers are in the order of 0.01% and like any other ES amp, are only rated at 1Khz -which tells nothing about how the amp behaves at the end of the audio band -it might well be in the order of 0.1-0.2% @20Khz, or more -I've encountered that in some of my experiments). Or not.


The funny thing is, that as the difficulty rises exponentially in all sectors, it almost feels like fighting in a jungle of wild devices and parameters
One such parameter is phase shift. Despite the fact that my current design has a power bandwidth of 790Khz(-3db) with the load, it has a phase shift about 1.8 degrees at 20Khz -but I'm not sure how bad this is.

So the question is: what is the required maximum phase-shift at 20Khz for a high-end amp nowadays? I have looked online and in books and I can't find any standards or references about it.

Last edited by MrMagic; 8th December 2017 at 11:29 AM.
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Old 8th December 2017, 11:46 AM   #76
MarcelvdG is offline MarcelvdG  Netherlands
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I can't give you a direct answer to that either, but I can tell you that deviation from linear phase is rather more important than phase shift by itself; who cares when the music is played a microsecond later? You'll probably find that the deviation from linear phase is extremely small in your design; low-pass filters usually have almost linear phase far below their cut-off frequency.
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Old 8th December 2017, 12:00 PM   #77
MrMagic is offline MrMagic  Greece
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What I meant is the max phase shift of higher frequencies (1.8deg) vs the lower ones (zero). I'm not talking about an even signal delay. I'm not sure that is what you mean though.

Last edited by MrMagic; 8th December 2017 at 12:06 PM.
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Old 8th December 2017, 12:15 PM   #78
MarcelvdG is offline MarcelvdG  Netherlands
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When you have a constant delay, the phase shift at 20 kHz is exactly 1000 times as large as the phase shift at 20 Hz. Is that 1.8 degrees the phase shift at 20 kHz or the error compared to 1000 times the phase shift at 20 Hz?
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Old 8th December 2017, 12:33 PM   #79
MrMagic is offline MrMagic  Greece
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It's 1.8 degrees for a 20Khz period, vs almost zero degrees for a 20hz period =obviously 1/1000 of 1.8 degrees at 20hz as you said, which is constant yes, and relative to the bandwidth. The question is what is considered too much and what is considered "normal" for a high-end amplifier.
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Old 8th December 2017, 02:18 PM   #80
MarcelvdG is offline MarcelvdG  Netherlands
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If it's 1.8 degrees at 20 kHz, 0.9 degrees at 10 kHz, 0.45 degrees at 5 kHz and so on, you simply have a constant delay of 250 ns. I don't think anyone in their right mind would object to that.
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