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Ah, then yeah hopefully there end up being more options. Estats are really not difficult or expensive to make relative to other driver types, when we are talking higher performance tiers. Those Chinesettawong clones of Orpheus and Omega from way long ago come to mind.

I just wish Topping had designed the EHA5 around a more powerful amplifier, rather than going the route they did. Or even just selling a pair of good transformers in a box, and letting people pick whatever amp they like.
It is an odd choice to design a whole new product around this when they could have taken an existing LA90 chassis, thrown in some transformers, cut out the input switching setup to save some pennies, add bias and send it.

Price point would have been higher obviously but still undercut pretty much everything by quite some margin. Maybe there's more in the works though at higher price points eventually...
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Outside of used, there is not much in the way of entry level e-stat amps. I use the SRD7 Pro which a couple of different speaker amps to drive it. I really think there is a need for a nice entry level amp that shows the advantages of electrostatic headphones. The now discontinued Stax SRM- 252 was a decent entry level amp. The Koss E/90 amp is another decent entry amp, again the key is entry level.
Passing this on from FB… Nice that someone actually approached them about it

Let me put the complete response from the email:

"Dear Sir/Madam

Thank you for contacting TOPPING support. We are happy to assist.

There are multiple levels of protections applied in the EHA5 to protect the headphones.

A bit more insights. The caps are rated at least 1000V. The suggested output protection is not necessary. For two reasons, the transformer has certain output impedance to limit current. When for some reason the diaphragm is hitting the plate, the other side of it is the resistance in the bias circuit, 3.3M ohm will definitely limit current. And various tests with headphones are performed, including full sine wave with max volume at high gain into different headphones this shows no issues to the amp and the headphones. And when diaphragm hits the plate continuously, there's still not damage seen.
There are bias voltage detection and protection, amplifier DC protection, power supply voltage detection, over current protection in EHA5 to ensure the safety of the headphones.

Best Regards"
So I think I will wait a bit before buying one. I would like to hear more reviews and member’s experience.
TOPPING EHA5 should be a game-changer for electrostatics. Can anyone review this?
Duplicate thread merged here with existing thread. In the future @storm please do a search before starting a new thread and look for a thread that already exists and post there.

Thank you for your cooperation and understanding. ;)

I've looked into buying the EHA-5 myself to replace the SRM-Xh in my current setup with something more up-to-date and with a nicer build and feel.
Therefore, I've looked over the head-case thread quite a bit to determine if this is a good product to buy. Sadly, compared to the science of solid-state amplifiers, the science of electrostatic amplifiers seems a little underexplored to me, which makes it hard to make a good decision.

I'm not an electronics engineer, not experienced with amplifier building, not experienced with electrostatics and would put a few more disclaimers if it weren't for brevity, but something sprung to my mind while viewing the relevant thread.
The safety features criticism has been adressed by Topping and I'm not qualified to judge that myself.
I also can't speak about the power requirements or if they are sufficient to drive all kinds of electrostatic headphones properly.

However, one point of criticism in that thread is the resulting wave form after a square wave at 10kHz was amplified using the EHA-5.
Looking at the pictures attached, one might get the impression that the EHA-5 does not accurately amplify the wave.
To me, the end results looks more like the square wave was passed through a lowpass filter that cut off some of the higher harmonics. This would not be problematic at all, since the harmonics of a 10kHz wave are outside the range of human hearing anyways. In any case, a lowpass filter within the range of human hearing would produce a different waveform and show up in the frequency response measurement, so I'm not seeing the valid criticism here-- someone please correct me, did I misunderstand something about this?
I expected more comments than this. It might be because estat headphones may be a niche area. But I get the impression that because this is an estat energizer built by Topping, that this may be a hot potato issue on this forum.
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It should not be a touchy situation! It is a product from a well known manufacturer. Now if it was from let’s say from John and Abdul salvage and towing, I would be concerned! Us in the estat crowd are an odd bunch, but I am more in the let me listen to it or read people’s honest opinions. Estat amps are strange a Bunch in themselves as they measure in a different manner.
another review:
another review:
Never expected TechPowerUp to review something like this!
The published measured performance of EHA5 is pretty impressive. Is it really that good? Let’s see what those published measurements didn’t tell us.

First is the ‘appalling’ SNR of 146dB. Topping calculated the SNR using the maximum output voltage divided by the zero-signal A-weighted noise. I was able to verify that the zero-signal A-weighted noise is within spec (measured at 79uV Gain=High). However, the raw measurement without A-weighting and AES-17 filter is not that great:

Vol Pot position90k BW, no filterAES17-20k+A-wt
Mid (2:30 position)5.45mV140uV

The SNR degradation is most likely caused by large amount of ultra-sonic noise at the output. Once the unit is powered off, those noise spikes are gone. Apparently the noise comes from the unit itself, perhaps the switching power supplies (both the wall wart and the internal switching regulators for the negative rail and the bias).


The frequency response looks pretty flat, except for the slight uptick near 20KHz. Did anyone wonder what it looks like beyond 20KHz? Here it is:


The Gain switch is set at High. A 10:1 attenuator is added at the input of Audio Precision unit to extend the measurable voltage range to cover the maximum output voltage of EHA-5. Adding the attenuation ratio of 10x (20dB) on top of the curve, the actual gain of EHA5 is about 45dB at 1kHz.

We can clearly spot the 6dB gain peaking at about 32.7kHz. Beyond the peak, the response drops quickly. The time-domain impulse response below proved the existence of a resonance peak, which corroborates with the poor square-wave response posted here.

Impulse Response.png

Most people noticed the increased THD in the low end (see here). The spec shows output level of 700Vrms, which seems to surpass most direct-drive eStat amps. How do those two parameters play together? Below is THD+N vs output level at different frequencies. We can see that at 20Hz, EHA5 can only output up to 229V before the amp goes to protection, and the distortion is close to 3% already. The high end output level is also limited. In order to show the real-world distortion figures, the measurement used 90kHz bandwidth and no weighting.

THD+N Ratio vs Measured Level_Annotated.png

Topping told us the EHA5 can output 700V, what was left out is that it can’t output 700V across the entire audio frequency range.

From the simplified block diagram, we can see this somewhat unusual low pass filter between the op amp buffer and the volume pot. Dr. KG describes the low pass filter as a slew-rate filter. I consider it having two purposes; one is to limit the high frequency component from entering the main amp (we’ll see the reason later), the second is to compensate the gain peaking of the output transformer resonance so that the frequency response is near flat up to 20kHz.
block diagram.png

The frequency response from the amp section with the transformer disconnected looks like this:


Both curves are about -1.8dB down at 20kHz and -3dB at about 27.65kHz. In other words, the amp section is pre-eq’ed to make the overall FR look flat (up to 20kHz).

Going back to the question why EHA5 uses an opamp buffer in the front like the O2 headphone amp, and a volume pot value as low as 1k Ohm. The noise measurement at the beginning of this post answered part of the question. The main amp probably has a poor current noise density spec, which means it can only work with low source impedance in order to reach the desired SNR. The THD FFT also shows a not-so-great moment (see below). This is the amp section driving a 10 ohm load with the volume knob at roughly 1 o’clock position. The second harmonic is roughly at -90dB of fundamental. This is still decent, but not as superb as you would typically see in a Topping headphone amp measurement review. That seems to indicate that the main amp’s input stage is not that linear, even slightly larger source impedance would add quite a bit of harmonics. The silver lining here is that the gain selection is done in its feedback path, making the linearity in the low gain position better than in the high gain position. That would be a relief if you don’t need the high gain position.

FFT Spectrum_Harmonics_vol_pot_2clk.png

Speaking of the transformer, they are slightly larger than the ones in my SRD-7SB. The difference is quite small, though. The impedance measurement of the EHA-5 transformer is shown below with its output open, at 100V and 200V driving a Stax SR-404. At the low end, the impedance drops due to the limited primary inductance. The situation gets worse due to core saturation under high output level (green curve). At the top end, the impedance seen by the amp dips to only 2 to 3 ohms at around 40kHz. That’s probably why the LPF is added to prevent large ultrasonic signals from entering the main amp.

Impedance Magnitude and Phase.png

Compared to the impedance curve of the SRD-7SB below, we can see both transformers follow the same trend. The EHA5 transformer has less impedance kinks in the low end. We can see its improvements compared to the SRD-7SB, but the inherent limitation of a transformer-based solution is still there. It explains why the top end and low end output levels are reduced compared to 1kHz. Driving large amplitude into a very low impedance load is too much to ask for a headphone amp module like the ones in the EHA5.

Impedance Magnitude and Phase.png

The takeaways of this measurement session is the following: If we only test the same parameters the manufactures test their units, under the same conditions the manufactures test them with, we can expect to get the same results that the manufactures want us to see. Occasional we catch a test escape or a unit that is out of maintenance, which doesn’t necessarily reflect the majority of the units in the market. To understand the true performance of the unit, we would need to get a bit more creative.
What load was used for these tests ?
Thanks for that indepth data, did you do any testing of the FR at higher voltages (Say 150vRMS?) I found that quite interesting when comparing the SRDs and Lundahl transformers to see if the transformers easily saturate at lower frequencies and how flat they hold at louder volumes.
So not a real contender for the expensive Ifi Audio iESL. Probably the best in the market if you get your speaker amp right.
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