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Electrostatic Headphone Amplifier Review & Comparison

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could not find the probe i wanted, so a different way. absolutely identical to using an attenuator on the ap
note: victoreen or similar glass resistor absolutely required at these voltages. when amir can duplicate this picture with his
ap, then the rest of the tests will be meaningful.

also note that this is 10% higher voltages than the max of the keithely.

ok, pictures
first is just the 10x tektronix probe about 400 vpp
next is box under test
next is the 100 megohm victoreen resistor in series with the 10x probe making a 110x probe
next is 1100 volts peak to peak stator to ground.

so the koss box does in fact meet its peak to peak voltage specifications of 2200vpp differential

now back to our regularly scheduled channel of reverse engineering a GROSSLY overpriced serbian headphone amp with .6% thd :D
 

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Cortes

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@Amir,

thanks for this review. It was really necesary, since there's nothing like this in internet.

The results are what I expected.... now, pls, try to test new Stax units and the uber-expensie electrostatics amps promoted in other forum from garage companies. I expect even worst results.
 

solderdude

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anyone want any more pictures?
We want accurate H & IM distortion plots !
You can't see distortion on scopes unless it is really bad. ;)
Thanks for measuring though.
 

Cortes

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I've been going with the T8000 in Yodabashi for hours, comparing it with my SRM-727II. The only conclusion I reached is that I was almost unable to distinguish them, and that I liked a bit more the valve distorsions of the SRM-007TII.
 

bobbooo

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and here is a square wave at 1100vpp showing the attenuator does no damage to the signal

anyone want any more pictures?
Frequency response (at different levels), THD FFT plot, IMD, THD+N vs power?

yes i have listened to the koss vs kgsshv-carbon on the same headphones. many times. No i can't even think of a way of actually measuring the differences because the koss clearly tests better. If someone offered me $100k in any test gear i wanted, it would still be doubtful that i could corelate sound quality to any publishable numbers.
If that wasn't blind and level-matched listening, and you cannot even conceive of objective measurements that would explain your subjective claim that the Koss amp sounds 'awful', the most likely explanation is nothing more than just cognitive bias.
 
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JohnYang1997

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Frequency response, THD FFT plot, IMD, THD+N vs power?



If that wasn't blind and level-matched listening, and you cannot even conceive of objective measurements that would explain your subjective claim that the Koss amp sounds 'awful', the most likely explanation is nothing more than just cognitive bias.
I think the idea is to show output swing is much better than with 100kohm ?
 

JohnYang1997

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the point was not to measure the thd of the koss box. I have to order special parts to do that.
the best for my setup would be 2x probes with a 1 meg input impedance. and 2kv trimmer caps.
Can we get an accurate measurement of distortion at around 100Vrms to 200Vrms? Maybe a bit higher voltage even.
 

bobbooo

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I think the idea is to show output swing is much better than with 100kohm ?
Yes that is very useful information. This, along with the THD measurement solderdude linked to of the Stax SR-007 driven by the SRM-007t showing just 0.1% distortion at 1kHz, almost 20 times lower than the 1.8% from that amp alone shown here, are enough to confirm that the measurements in this review are null and void really. More proper measurements of the Koss amp in addition to just output swing would be great though to see if the THD figures and odd frequency response changes with level shown here are also inaccurate due to the 100kohm load.
 
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koss measured single stator to ground. stator to stator gives lower numbers, but i need to build attenuator to get to 700rms differential.
noise higher than expected. 350vrms is about 20 volts below clipping. Into 120pf.
 

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JohnnyHonda

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Though the measurement may be challenging and time consuming, I’m very happy to see the continued effort in measuring the electrostatic amplifiers. I’m enjoying seeing all of the measurements of the various equipment from Amir and I recently became a low level donor to support. I’ve always wondered about the electrostatic amplifiers (I currently have and have had Stax headphones and electrostatic amplifiers). In particular, I’m hopeful to see a good analysis of the current amplifiers such as the 353x and other amplifiers like the KGSS and KGSSHV and the Carbon. Kevin, I hope you’ll continue with your support, please keep it up!
 
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amirm

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Thread Starter #197
Amir already did:


At 1kHz I see at least 60dB distance and some of the noise there may well be surround noises picked up by the mic.
I assume Amir used the SRM-007t for this so better than 0.1%.
You are misreading the above measurement. Only second and third harmonics are counted in the total above, not total as THD in electronic measurements show. It is also an entirely different measurement system (chirp versus steps).

Finally, no I don't remember if I used the tube amp. Most likely not as I had to go and fetch them whereas the solid state was right next to my workstation.
 
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amirm

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Yes that is very useful information. This, along with the THD measurement solderdude linked to of the Stax SR-007 driven by the SRM-007t showing just 0.1% distortion at 1kHz, almost 20 times lower than the 1.8% from that amp alone shown here, are enough to confirm that the measurements in this review are null and void really.
The only thing null and void are your faulty conclusion and assumptions. As I just noted -- and you should have waited for me to comment -- you don't know which amp was used for testing. And that the measurements are not comparable since they were not meant for this use. Acoustic measurements of distortion are quite tricky anyway so you best not use one to validate/invalidate the other unless we have proper proof of correlation.

Really, this kind of non-objective, fanboism is what has soured me on this thread. Owners send me tons of products and none ever act the way some of you act when your favorite product is tested. They take the good with the bad. Hell, in this case I own the poorly measuring products and you are the one crying on my shirt over the measurements?
 
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amirm

amirm

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ReaderZ

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"....Dropped by the garden (what's left of it) to see if the persimmons are ripe enough to pick and my heart fell to the ground. ..."

Fruit & Veg. are supposed to be good for you. Pretty well accepted truth universally, but I so clearly remember the first time I took my first bite out of a not-yet ripe persimmon. I thought someone had filled my mouth with slivers of glass. Youch! Talk about 'astringent'.
Amirm, what variety of persimmon are you growing? [yes, I realise I haven't uttered a single technical term on this forum. hehehe]
Many years ago when I was a student in California, the tree right outside of my rental unit, that no one ever bother to take care of, has the best persimmon I have ever eaten. Yet, no one else in the same building is even interested in trying them.
 
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