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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 8th December 2017, 03:55 PM   #81
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by MarcelvdG View Post
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.
Hopefully, because I find it hard to significantly increase the bandwidth given the capacitive load and current consumption restrictions -and I haven't yet gone to double that for two headphones...

BTW, I just found the following excellent article about recommended headphone amplifier specs that for phase it says: "The error should be under 1 degree from 10hz to 10Khz where spatial information is most critical" which coincides with my current achieved specs but I'd prefer some margin.

For THD+noise it says that due to masking, 0.01% is enough, but 0.005% is definitely inaudible (already achieved), which is why I'm after the lowest numbers: to ensure that any distortions will be way bellow the audible threshold and above any religious/subjective opinions -as the numbers don't lie

NwAvGuy's Heaphone Amp Measurement Recommendations Page 2 | InnerFidelity

Still, I'd like to hear from truly high-end reviewers what specific models worth $$$...$$$ of dolars provide.

Last edited by MrMagic; 8th December 2017 at 04:15 PM.
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Old 8th December 2017, 06:10 PM   #82
MarcelvdG is offline MarcelvdG  Netherlands
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I think we are stuck; it's clear you don't understand what I mean, and I have no idea how to explain it more clearly. Hopefully someone else does.
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Old 8th December 2017, 08:04 PM   #83
MrMagic is offline MrMagic  Greece
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OK, I got it, the graph implies the same delay for the whole signal independent of frequency, so it's useless and meaningless, whether it is 250ns or 100 million ns (=100ms) -it doesn't matter at all for a headphone amp or for loudspeakers unless someone uses different amps to drive multiple speakers simultaneously and wants them aligned to milimeter!

I was confused by the logarithmic plot. I made the frequency axis linear and the graph was a straight diagonal line from 180 degrees and 10hz down to 178.2 degrees and 20Khz (=-1.8deg). That implied a constant delay independent of frequency. Then I set it to show the "group delay" instead, across the same audio range and it showed an arc that only changed the 4th or 5th decimal digits and beyond of 253.8ns =linear.

BTW, before that, I did some changes to the input active stage and now the group delay went down to 60.8ns (180 to 179.56) less than a half degree -but it doesn't matter anyway.

Now the questions is: what does the article above means then by "1 degree at 10khz"?
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Old 8th December 2017, 09:28 PM   #84
MarcelvdG is offline MarcelvdG  Netherlands
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OK, I'm glad you got it now!

Either the writer of the article means deviation from linear phase, or he or she hasn't given it enough thought. 1 degree deviation from linear phase means that you, for example, have a phase shift of -1 degrees/kilohertz at low audio frequencies, but -11 degrees instead of -10 degrees at 10 kHz.

By the way, when you want an almost linear phase response over the audio band, be very careful with high-pass filters, such as DC blocking capacitors and DC servos.
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Old 8th December 2017, 10:12 PM   #85
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by MarcelvdG View Post
OK, I'm glad you got it now!

Either the writer of the article means deviation from linear phase, or he or she hasn't given it enough thought. 1 degree deviation from linear phase means that you, for example, have a phase shift of -1 degrees/kilohertz at low audio frequencies, but -11 degrees instead of -10 degrees at 10 kHz.
I thought so. I would prefer a more intelligent plot with the deviation alone instead...

Quote:
Originally Posted by MarcelvdG View Post
By the way, when you want an almost linear phase response over the audio band, be very careful with high-pass filters, such as DC blocking capacitors and DC servos.
I haven't taken care of this yet. I prefer a complete capacitor-less drive and DC offset stabilizer (either with a microcontroller or other circuity). Tiny caps just for feedback compensation are excluded of course. We'll see...

Last edited by MrMagic; 8th December 2017 at 10:35 PM.
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Old 8th December 2017, 11:16 PM   #86
MarcelvdG is offline MarcelvdG  Netherlands
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If that DC offset stabilizer is a feedback loop, you probably get the same kind of phase response as with a normal DC servo or DC blocking cap. You won't get any phase errors at all if you only calibrate out the offset at start-up, but then you don't compensate for temperature drift and things like that. As a compromise, you could first calibrate out the offset and then make the loop very slow to track drift.

Using capacitors, there are tricks to improve the phase response at the expense of getting a bump of a few decibels in the magnitude response in the subsonic region, such as making a DC servo loop with a higher than first-order filter in the feedback path, or using a bootstrap circuit instead of a plain old DC blocking capacitor with bias resistor.
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Old 8th December 2017, 11:57 PM   #87
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by MarcelvdG View Post
As a compromise, you could first calibrate out the offset and then make the loop very slow to track drift.
Why is that a compromise? Of course the less you need a filter in an offset stabilizing circuity, the better, ie it should do the least work possible or be eliminated completely, but even if the amp itself is not drifting, the source might have a dc component, so a clever rather than a dumb circuit would help in this case for faster and more efficient response. It can be done without an mcu, but if I use one for other purposes (safety, health check, etc) why not use it for that important task too?

On my first priorities is also an absolutely flat DC to supersonic response, so I really cannot picture any bumps on that straight line!

Last edited by MrMagic; 9th December 2017 at 12:08 AM.
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Old 11th December 2017, 05:51 PM   #88
hpeter is offline hpeter  Slovakia
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i think you are in mood to invent a non existing miracle. i hope you energy will not dissipate soon..

why bother with THD and measurements, if you are listening with ears; not with calibration microphones.
THD to dB - convert percent % to decibels dB percentage voltage % vs per cent converter THD+N total harmonic distortions calculation signal distortion factor attenuation in dB to distortion factor k in percent decibel damping - sengpielaudio Sengpiel according to this, it is about -72dB.
i took a listening test, where nasty sound was mixed into music, i could not hear it at -70 or -75dB.
so, a 2nd (even hds) will be absolutely negligible.
even a 2% 2nd is not a big deal.
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Last edited by hpeter; 11th December 2017 at 05:56 PM.
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Old 11th December 2017, 09:04 PM   #89
MrMagic is offline MrMagic  Greece
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Quote:
Originally Posted by hpeter View Post
i think you are in mood to invent a non existing miracle. i hope you energy will not dissipate soon..
Why dissipate? It is fun pushing numbers down.

Since you mentioned it, here is today's numbers: 0.0008% THD = -102db.
Third harmonic is -103.8db down (second and others are lower), but I haven't "treated" those higher-order harmonics yet, as I changed topology -they will be lower.

So I have already surpassed my second goal of 0.001%, (first one was 0.01%) but I'll keep pushing them down a bit more, because that makes me improving the circuit and actually pushing down the real numbers that will be measured when I build it.

And most importantly, those numbers were made with the previous topology after improving it further.
That means cost reduction -less mosfets. So I have left quazi-complementary for now -I don't think I'll come back, although the very low distortion (about the same) proved the rumors false.

Quote:
Originally Posted by hpeter View Post
why bother with THD and measurements, if you are listening with ears; not with calibration microphones.
Actually, our ears are far better than dumb microphones, not only because they adjust the dynamic range from quiet to bombing, but are also able to decode multiple sound reflections and locate sources in 360 3D space. Try that with a set of "calibrated" microphones. Of course, there are more to learn -we don't know everything yet.


Quote:
Originally Posted by hpeter View Post
according to this, it is about -72dB.
How did you arrive to -72dB?

Quote:
Originally Posted by hpeter View Post
i took a listening test, where nasty sound was mixed into music, i could not hear it at -70 or -75dB.
so, a 2nd (even hds) will be absolutely negligible.
even a 2% 2nd is not a big deal.
There can be a huge quality difference between two tests, that doesn't prove anything. Someone else may come with a different test and prove you the opposite.

I'll wait until an extensive, independent and serious scientific research is done.
Note that I'm NOT religious with sound either - if I was, I wouldn't demand a scientific research.

So, until then, having a practically "perfect" amp (at a reasonable cost), guarantees that it will be totally transparent to the music you listen with it.

Cheers.

Last edited by MrMagic; 11th December 2017 at 09:09 PM.
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