Hell with electrostatic headphones and driver unit, several questions and concerns [HELP]

Equipment / Electronics / Gear / Accessories Headphone Amps
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Where do I even start. So I am not the most technically knowledgeable person, so I am coming across several difficulties with the new field of electrostatic headphones - it is not as simple as it is with dynamic drivers, where you have an amp/dac combo and it’s no more complicated than plugging the headphones in and that’s it.

Since I have multiple questions, observations, and concerns, I will number them so it is easier for anybody to help me out and answer specific questions. Warning ahead - the questions are very long and are very specific, I tried my best to get my point across, I am not the most advanced in technical terminology, so please feel free for further explanations. While the questions are long and specific, they don’t necessarily require long answers.

Here is some info: I have an electrostatic driver unit, no it is not a Stax, and neither can I reveal (yet) what brand it is. As far as I am aware, the most important specification is:

Maximum Input Voltage - 12V RMS

Maximum Output Voltage - 600V RMS

Bias Voltage - 580V

So, the questions:

  1. What I have done first was I connected the driver unit (using speaker cables and binding posts on the driver unit and the A/V receiver) to the A/V receiver, which I used as an amplifier. The A/V receiver had a CD player connected, and I had everything set up - the driver unit and the A/V receiver were connected, the electrostatic headphones were connected to the driver unit, the CD was connected to the A/V receiver.
    So, I turned the A/V receiver and the CD Player on, played a CD, and I turned up the volume on the A/V receiver.
    However. I forgot to turn on the electrostatic driver unit on. What is weird is that even though I didn’t turn it on, I could still hear the music on my electrostatic headphones. Later when I did turn the electrostatic unit on, I don’t remember noticing a difference. Needless to say, the sound quality had noise and some crackling and occasional channel imbalance, thus I will not be using it as an amplifier for the driver unit and the headphones.

Now, the question is whether there is a chance that I damaged the headphones or the driver unit due to the fact that I was playing music and had everything connected, but didn’t turn on the driver unit. And why could the headphones work and play music even though the driver unit was not turned on? The driver unit was connected to the A/V receiver but it wasn’t turned on with its own power switch.

  1. When I got the driver unit, I plugged in my other pair of electrostats that use Stax’s 5-pin PRO Bias termination. Well, when I did plug them in, only one channel was working. What happened is that the driver unit wasn’t wired correctly. The driver unit had “Bias” soldered to the wrong “pin” on the socket - it was soldered to the “isolated” pin, the pin that is supposed to be “L+” on the Stax 5-pin Pro Bias termination.
    Screen Shot 2020-11-10 at 12.57.09
    Basically the driver unit had “Bias” wired to where Stax has “L+”.

Could this have damaged the headphones? The headphones were playing music through this wrongly soldered pin layout for less than 10 minutes. Later I fixed this by soldering the “Bias” to the correct pin/socket.
Just to clarify, it wasn’t the headphone’s plug that had been wrongly wired, but rather the socket on the driver unit.

  1. While the electrostatic headphone was plugged into the amplifier (this was a dedicated amplifier that was like an all in one solution and could drive electrostatic headphones), it was unplugged on the headphone end several times while the music was still playing (the cable stayed plugged in on the amplifier end, and it was then plugged into a different headphone while it was still playing music). It was not me who was doing this, but the person whose amplifier and headphones I was testing.

Now, again, could this have damaged the headphones? It’s not as though both ends/channels were unplugged at the same time, which means that while one of the channels was unplugged, the other was working , and while one was being plugged in, it was the one which was playing music (essentially one channel was playing/not playing music for a short period of time before the other channel was plugged/unplugged). Are there any concerns regarding this?
I would never do it like that and I always make sure that the headphones are unplugged from the source and there is no music playing, that’s why this was very odd to me and it rose some concerns.

Just to clarify, the electrostatic headphone driver unit has nothing else except a power on/off switch. Inside of it there are two large transformers that connect to the two 3-pin XLR outputs and a single 5-pin PRO Bias connectors. This driver unit requires an amplifier so it can drive the headphones, and of course, you adjust the volume on the amplifier.

This is about it for now. The questions are long, but they don’t specifically require long answers (unless you are willing to spend the time to explain the technical side of things and explain why it could/could not damage the headphones). Most of these things were not at my fault and weren’t done by me, I am working with a “prototype” and not everything was perfect… some mistakes were made and I just want to make sure that they didn’t damage the driver unit or the headphones. I am not even sure if I made a single question clear enough for anybody to answer… :confused:

Just a whole lot of obstacles and difficulties regarding everything.

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Electrostatic headphones require a special type of amplifier made ONLY to be used with them or again a very specialized amplifier that has VERY specific plugs to use them with.
The amplifier they Require is generally called an energizer. You CANNOT use them on a regular AV receiver or any Normal amplifier without a special adaptor box that properly converts the energy.

From what you posted you seem to own electrostatic headphones but no energizer to use them with.
Your signal chain will require a source and possibly a DAC also. Sorry if I am missing something but that was what I got out of your post.
Pictures would help

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As far as I have informed myself, this would be incorrect. An energizer consists of only the transformers, whereas an electrostatic headphone amplifier is what I believe you are referring to - this device consists of both the transformers and the amplifier. The energizer converts the energy, or that is, the step up transformer increases the voltage from the amp.

Not only can you not use them with an amplifier or receiver because they require a special adaptor (energizers/transformers are also called adaptors), but you also usually don’t have a Stax 5-pin Pro Bias output on amps or receivers…

However, if you own an energizer, you will absolutely need an amplifier that has enough power to power the headphones - speaker amps usually do the job, whereas headphone amps are too weak. You will be only able to control the volume from the amp, as though energizers don’t have volume knobs.

If this was the case, I wouldn’t have been able to connect the headphones to the receiver. I did explain in the beginning of my question that I do own an energizer, I connected this energizer thanks to the speaker binding posts (this is also how you would connect most electrostatic energizers, Mjölnir Audio and iFi Pro iESL are just two examples)… however, as stated, I ran into some issues.

As you can see in the pictures above, there is a Stax 5-pin Pro Bias output, on the inside (I am referring to the inside of the energizer, see picture 3) it was incorrectly wired, it didn’t match the way a Stax connectors are wired, and this caused only one channel to work. Hence my question was could this have caused any damage to the energizer or the headphones themselves. Later it was re-soldered to match Stax’s configuration.

The link you attached is pretty good for the most part, but I don’t think it did a good job at explaining everything. They do not require special amplifiers, but rather require the electrostatic transformers, without them they can’t function. As you can see, I own an electrostatic energizer/transformer/adaptor, call it whatever you want, but you don’t need any special amp to pair it up with, you can use most speaker amps (although you have to make sure it supplies enough power - this is something that I didn’t get a clear answer to yet, how do you determine how if an amp is a good match).
Another thing they got incorrect is that iFi Pro iESL is an electrostatic amplifier - completely wrong. I mean even from the pictures you can see that there is no volume knob… that is an electrostatic energizer, iFi markets it like that. You need to hook up an amp to it in order to drive your electrostatic headphones. For example, iFi recommends their Pro iCan (marketing purposes), their flagship amp.

I still didn’t get answers to my questions… but due to the complex technical nature of electrostats, you really would need to know just about everything about them to help me out. I got some help from another forum where there are some older folks, and I learned that many people stay away from electrostats purely due to their complex nature… they are not quite plug and play.

A source would be a CD Player, Vinyl, something of that kind? You say I “possibly” need a DAC too. Why is that? I would need the DAC if I wanted to play from my laptop, or from a USB, right? Those two are digital, unlike CD’s and Vinyl’s.

Seems like my reply is longer than the original question…

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Basically you connect that to the speaker out of a standard audio chain, DAC-> Pre -> Power Amp or DAC to Integrated.
The issue with that “converter” is there is no safety circuit I can see, nothing to limit voltage or current, it should be OK if you start at 0 volume and turn it up slowly.
Volume is just Volts.
I assume it’s designed for an 8 Ohm speaker load, this matters for some power amps, and you can damage them by connecting them to a very different load, though most SS amps won’t have an issue.
I would talk to whoever you got the box off and see what they have to say.
An energizer is generally an amp that is designed to output the very thigh voltages and low currents electrostatics need, what you have is a converter, BUT, that box is making assumptions about the driving amplifier and you should talk to whoever made it.

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Dac > Pre > Power Amp seems like the expensive option… quite expensive. I think I will try to stick to a Dac > Integrated Amp set up.

Hm, but my unit looks almost identical to Mjölnir SRD-7, which I believe does the same job as this one.

There is that little circuit board that I am not sure what it does entirely… nor do any other members (you can see it in the top right corner of the device in picture 3).

I will try to speak with the builder

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What I have is basically what allows a normal speaker amp to work with the headphones, and this is all thanks to the step-up transformers inside, whereas, from what you are saying, an energizer is an amp that is capable of delivering this high voltage without the transformers? Or perhaps the transformers are built-in?

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The caps and resistors at the top are just a filter/impedance matching thing I would guess.
The transformer like all transformers convert current into Voltage and Vice Versa.
So it transforms the 12V or so in to 600V out with greatly reduced current.
The issue is that speaker amps are designed for specific loads, usually 8 or 4 Ohms and most function well enough down to say 1 Ohm because the impedance of modern speakers tends to drop at bass frequencies.
The load that box reflects on the amp is the reflected impedance of the Electrostatics through the transformer. I haven’t done the math and can’t without a greater knowledge of the transformer being used, but if the result is much more than 8 Ohms, you’re running the amp outside it’s intended design, most SS amps will just deliver less power, though who knows how it will impact the sound. Some valve and FET amps will if your lucky blow a fuse, or trip a protection circuit.

If you have a lower cost speaker SS amp, it’s probably fine, just plug it in and turn it on with the volume at 0, then slowly turn it up, you probably want the headphones plugged in the entire time the amp is on.

But I didn’t design the box, so YMMV.

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Yes, in some cases they will use transformers, though it’s quite possible to build an energizer without them.
Examples

I’ve never looked at what’s in a Star energizer or the KOSS one

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It would make sense it’s designed for 8 Ohm speaker load… but again, doesn’t say that anywhere.

If it is indeed designed for 8 Ohm speaker load, is there anything I should worry about?

Hm, if you can direct me as to what I should ask the builder, what would that be? What useful information can I supply here (or anywhere else) to make it easier for people to help me?

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Honestly if your amp wasn’t several thousand $$ I’d just plug it in, wouldn’t expect it to be indicative of the best possible sound from whatever headphones your using.

Transformers have bandwidth limitations, and they change the sound of what you push through them, good audio transformers are silly expensive. Audio note will sell you a single transformer for upwards of $3500, though they obviously have cheaper options and there are good options even at $100.

If you just want to make noise through the headphones with that and most cheaper SS amps, your probably fine, if your looking for the best amplification for the headphones, a high end version of something like that might be something you would look at coupled with a higher end power amp, or just buy something designed for the job.

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In protection circuits we trust!

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Most SS amps are insensitive to load, they just “work”, might drop the power and again might affect how they sound.
More expensive discrete designs can get a bit finicky, my power amps blow the fuse at about 20 Ohms, or more commonly if I forget to connect the speakers.

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Hm, I do care about quality. I connected the device to an AV receiver and the sound was absolute shit. Noise, crackling, sounded like occasional channel inbalance, I unplugged them pretty quickly.

Would a Auris Audio Fortino 6550 work?
I am trying to figure out what would be a good match from speaker amps… but I am getting confused. For example, why does Fortino 6550 have a pair of 3 binding posts… I am used to a pair of two: L+, L-, R+, R-. And then, an amp like the NAT Single HPS, has only two binding posts for each impedance (0 ohm, 4 ohm, 8 ohm)… how does this work? How do you plug the + and - into a single binding posts… or am I too stupid for this?

Btw the energizer (my device) does have a fuse, forgot to mention that… if it makes any difference.

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AV receivers are generally terrible amplifiers, they are usually class D designs and that’s probably not a good match for that box.

If you care how it sounds, pick up an energizer.
The Koss one isn’t terrible, or you can get an older used Stax unit, though the cheap ones aren’t great.
There is the bottle head stat.
I mean first port of call on these things is talk to the headphone manufacturers and see what they suggest.

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I don’t know specifically.
50W into 8 Ohms will give you a maximum of about 6V, so you might have a volume problem.
It’s also a transformer coupled valve amp, so it could also blow a fuse/protection circuit if it has one and worst case damage the amp. Again no way to know without knowing more about the amp and more about the box.

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Yup, that’s what I thought.

Hm. Another forum member told me that Stax used to recommend 20W - 100W RMS amplifiers to be matched with their SRD-6 and SRD-7, so I understood that that can apply to my unit as well… but from what you are saying, that isn’t the case?

I am not knowledgeable enough to understand why Fortino 6550 could get damaged… so overall it’s a whole mess…

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Running into limiters and OCP is working in the most technical sense.

Depending on how the transformers behave (in general, their impedance decreases with rising frequency). So that box may require a 2 ohm stable amplifier to work correctly.

Depending on the design, the lack of bias current may cause issues.

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So, how do I determine what amp is suitable?

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Yes the issue is the load is a part of the circuit between B+ and ground, without it you just have the primary of the transformer which causes excessive current flow though the valve/cathode resistor and pop.

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Trial and error, asking other owners, etc.

From those, sadly no way to tell.

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