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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 14th November 2017, 02:13 PM   #11
EUVL is offline EUVL  Europe
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IXTH10P60 is 600V and stock at Mouser.
But do what please you.


Cheers,
Patrick
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Old 14th November 2017, 03:58 PM   #12
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by EUVL View Post
IXTH10P60 is 600V and stock at Mouser.
But do what please you.


Cheers,
Patrick
I've seen them a few days ago, but somehow I missed them in the last search -too many searches in companies and distributors, for bipolar, mosfets, bmos, etc in a short time.

Still, for 1400Vpp three of those 600V mosfets are needed x2, =6 per stator x 4 stators =24 transistors total for the output stage! Too many in comparison to 8 normally.

It's not just a matter of personal preference, it's the principle of trying first to achieve the best and more efficient, although most difficult, before accepting a compromise.

Last edited by MrMagic; 14th November 2017 at 04:02 PM.
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Old 14th November 2017, 05:05 PM   #13
kevin gilmore is offline kevin gilmore  United States
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if you want full power response at 20khz into a stax standard load you will need an output stage current of at least 18ma.

current kgsshv-carbons run at +/-450 volt power supplies and can swing at least 800 volts peak to peak stator to ground. 1600v stator to stator

the cfa electrostatic amp can be built with stacks of 4 transistors and up to +/-600v
power supplies.
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Old 14th November 2017, 06:23 PM   #14
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by kevin gilmore View Post
if you want full power response at 20khz into a stax standard load you will need an output stage current of at least 18ma.
The output stage of my current self-designed DIY amp draws in total 44ma which is 22ma per channel (11ma per output), and a bit less on the transistors for a DC-250Khz freq response. Which is why I said previously that 5ma is not enough. I'm going for a higher voltage and more powerful design though.

Quote:
Originally Posted by kevin gilmore View Post
current kgsshv-carbons run at +/-450 volt power supplies and can swing at least 800 volts peak to peak stator to ground. 1600v stator to stator
As I mentioned previously, that's not right. If each stator swings between +400V and -400V, then measuring stator-to-stator you will get the maximum voltage difference when one stator has +400V and the other -400V (as they have 180deg difference) which will be equal to 800V peak-to-peak, exactly the same with a single stator peak-to-peak measurement.

Quote:
Originally Posted by kevin gilmore View Post
the cfa electrostatic amp can be built with stacks of 4 transistors and up to +/-600v
power supplies.
Thanks, but first I have to try to avoid stacking transistors on my design.

BTW, how come NO ONE has measured THD on their electrostatic amps, or other reviewed ones along the full audio band, even in websites dedicated to measurements that have measured several amps for dynamic headphones (like innerfidelity.com)? Is it that bad?

Last edited by MrMagic; 14th November 2017 at 06:34 PM.
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Old 14th November 2017, 06:34 PM   #15
jcx is offline jcx  United States
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I'd guess its more that its not easy than done and hiding - I don't expect the hi V divider probes for the o'scope to be good enough

you need a (polystyrene?) C divider load that is better than what you want as a measurement floor

and then the ES headphone cable connectors are all custom so you have to hack - possibly sacrifice a extension cable...
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Old 14th November 2017, 06:41 PM   #16
00940 is online now 00940  Belgium
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It's a lot easier to send the output of a typical headphones amplifier into a soundcard input. You just need a cable splitting the signal and a pair of resistors.

To measure the electrostatic amp, you need quite a setup. You may need to open the amp and be comfortable with high voltages.

It seems to me quite obvious why there aren't more measurements. Reviewers usually don't have a degree in electrical engineering.
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Old 14th November 2017, 06:55 PM   #17
EUVL is offline EUVL  Europe
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> the cfa electrostatic amp can be built with stacks of 4 transistors and up to +/-600v

A BJT version of hesener's X5HV with cascaded transistor to make up the voltage.
X5HV - the F5 principle applied to a headphone amp


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Old 15th November 2017, 07:25 AM   #18
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by jcx View Post
I'd guess its more that its not easy than done and hiding - I don't expect the hi V divider probes for the o'scope to be good enough
you need a (polystyrene?) C divider load that is better than what you want as a measurement floor and then the ES headphone cable connectors are all custom so you have to hack - possibly sacrifice a extension cable...
Quote:
Originally Posted by 00940 View Post
It's a lot easier to send the output of a typical headphones amplifier into a soundcard input. You just need a cable splitting the signal and a pair of resistors.

To measure the electrostatic amp, you need quite a setup. You may need to open the amp and be comfortable with high voltages.

It seems to me quite obvious why there aren't more measurements. Reviewers usually don't have a degree in electrical engineering.
How about:
1. The manufacturers,
2. The DIY hobbyists who build and design electrostatic amps.

I see DIY schematics here and there, what's the point on designing another different amp, without aiming at better specs?
Because if you don't measure it, you don't care and you cannot optimize it.
If you have measured it and you don't show the results, then it sucks. Simple as that.


As for the rest, it's not that hard to locate each amp's output.
You only need one output and a ground connection -close to the output.

And you only need a resistor divider, a high upper resistor in the range of several hundreds of KΩ up to MΩ to avoid loading the output, split in three or more smaller ones in order to minimize the parasitic capacitance, and a low second resistor in the range of a few hundreds Ω in order to provide a low-z output that will not be affected by the load (probe + instrument) -especially by its capacitance, and will ensure an unaltered high freq. response.

Since a ground connection is not usually provided on the output jack, you have to open the case and do the connection internally,
preferably directly on one output before a capacitor (if any) and a ground connection close to that output.
Also, you should have different dividers for different output voltages in order to keep the current and the output voltage the same.

example (adjust if necessary):
for a +-500V output, 3 x 330K in series (=990K) + a 430 Ω will draw 0.5ma peak (less than 0.2 W rms) and will provide 430mVpp output.

I think that since there is no standard, the actual divider used for the measurement should be mentioned.
Each divider should be placed inside a probe, so there would be different probes for different output voltages.

Of course, the amp should be measured with the headphones connected.

Last edited by MrMagic; 15th November 2017 at 07:30 AM.
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Old 15th November 2017, 10:20 AM   #19
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by MrMagic
Quote:
Originally Posted by kevin gilmore View Post
current kgsshv-carbons run at +/-450 volt power supplies and can swing at least 800 volts peak to peak stator to ground. 1600v stator to stator
As I mentioned previously, that's not right. If each stator swings between +400V and -400V, then measuring stator-to-stator you will get the maximum voltage difference when one stator has +400V and the other -400V (as they have 180deg difference) which will be equal to 800V peak-to-peak, exactly the same with a single stator peak-to-peak measurement.
OK, that's the worst thing I've said -and insisted too, the last few days -embarrassing and my apologies. Probably because I just started with hardware again after many years break. I confused the peak measurement between the two stators (800V) with the peak-to-peak measurement (800V) of a single stator. Unbelievable.
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Old 16th November 2017, 12:45 AM   #20
PRR is offline PRR  United States
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Kevin, what is the capacitance of these (any?) headphones? 50pFd? 5,000pFd? I have no clue.
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