How to pair an amplifier with an electrostatic headphone energizer/transformer?

So, I tried understanding this better, but no luck. I know that there are several people here who are very knowledgeable and wise regarding electrostats, so I hope somebody can help me out.

First of all, I want to clear up that I am not the most technically educated and knowledgeable person. This means that I don’t understand the majority of the technical stuff, e.g. all the specification of an amplifier and forumals for matching, what is what, etc.
For me the majority of that stuff is complicated, but I also never have shown a great amount of interest (expect for some speaker amplifiers a few years back)… and have never been dedicated enough to learn this.

Here is my situation. I own what I believe is an electrostatic headphone energizer. This device has no knobs, on the front there is only a single power switch and outputs (two 3-pin XLR, one Stax 5-pin Pro Bias), on the back there are only binding posts. On the inside there are two large step-up transformers, thus I believe this is what people call electrostatic transformers, energizers, adapters, or drivers. This device cannot drive the headphones on its own, that’s pretty clear to me. The closest energizer that resembles what I have is the Mjölnir Audio SRD-7, it also only has a power switch in the front, an output, speaker binding posts on the back, and that’s it.

Here are some specs (that I don’t fully understand):
It has a Bias voltage of 580V, maximum output voltage of 600V RMS, impedance of 100 Ohms at 20Hz, and a maximum input voltage of 12V RMS.

Now, I do not know at what specification I should look at to know if its compatible with a particular speaker amplifier. I was told that the maximum input voltage (12V RMS) is important, but at no speaker amp is there an output power specification that is in volts, it’s usually in watts… this led me to get lost and confused how to choose the correct integrated amplifier to pair it up with (I doubt there is a headphone amp that can output enough power, thus form my understanding I should choose a speaker amp)

From what I saw, the energizer is connected to the amp via the speaker binding posts. Also, the energizer has a power cable that is plugged into an AC outlet, something I forgot to mention that is also located at the back.

My question is how do I pair this up with an amp so it can drive electrostats? What specification should I look at to know if the amp is too strong or too weak to be paired with this energizer?

Also, do I need anything else besides the amplifier? I read somewhere that somebody had a pre-amp with their energizer setup, why would this be the case? Another person mentioned a power amplifier.

Also, once this energizer is matched with the correct integrated amp, I’m assuming I probably need a DAC, correct?

I tried my best at keeping this short, but I wanted to make sure not to miss out any details so it is the easiest for anybody to help me out. I am definitely new to the electrostatic world, and it is definitely quite a bit more complicated than what I am used to (planar magentics and dynamics)…

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I’m sure some folks with experience will help you soon. Maybe a few pictures of the equipment you describe can make it easy.
Good luck!

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Hmm, no Stax transformer box I know has two 3-pin XLR outputs on the front.
A picture is worth a thousand words here…


I agree with JonL here, they usually have either Normal Bias, Normal and Pro Bias or only Pro Bias STAX outputs on the front. STAX sometimes don’t have binding posts but red, green, white, and black wires.

I’ve had the earlier SRD-4 and SRD-6 units. You can look them up on the internet. STAX used to recommend an amplifier that put out 20 watts ( 10 x 10 ) to 100 watts ( 50 x 50 ) RMS into 8 ohms as appropriate to drive the energizers. When I used an energizer I had somewhat more powerful amps, but was careful about volume. Just don’t try to reproduce concert-level volumes, which are not good for your ears, either!. If you have a good quality amp of lesser wattage, you can probably drive them to reasonable levels.

I used the SRD-6 for about 25-30 years with my STAX SR-5N headphones. They were offered with the SRD-4, but I upgraded from that within a few weeks

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There are a few differences from a STAX unit - such as that there is no provision for a pass-through to speakers. That’s what the binding posts are for on the STAX units.

I have no clue what is going on with that little board inside, nor would I trust output of the 3 PIN XLR connectors without checking them with a meter. The STAX connector is 5 pin, so it’s Pro Bias. This looks like a unit that someone built - I can’t find any equivalent in a quick online search. I would think that something in the 20 to 100 watt RMS range would be reasonable to try, just take it easy and make sure that your volume is turned off when connecting, and follow precautions if you haven’t been able to ensure that there is nothing wrong with the unit first.

A final thought - you could just paint it purple and ship it to @DarthPool and ask him to evaluate it.


What does this exactly mean?

Regarding the board, I am also not 100% sure what it does.

Do note that I listened to this unit properly paired up, it works perfectly good. No flaws.

I have plans regarding the color job. Let’s just say purple is in my mind, I’m like @DarthPool, purple is the way to go. We need more purple in this hobby.


Well, in the old days, a lot of STAX headphones were sold without dedicated amps. I only got a Mjölnir - modified SRM-T1S tube amp a couple of years ago. We used those energizers. Typically, we would put these things into an existing stereo system.

As your main amp (integrated amp, or receiver) was driving your speakers, and not all amps were set up with a switch for Speakers A or B, or maybe you ALREADY had two sets of speakers, well then, what do you do to drive the headphones? That headphone jack on the front of the Fischer receiver will never drive STAX.

So you put the energizer IN LINE with a set of speakers. The red, white, black and green leads went to your power amplifier. You put the speaker wires (we didn’t have interconnects in those days, so we made do with “wires” - you can still get them at Lowe’s or Home Depot) into those binding posts on the back of the energizer. It was set up with a switch so you could go from regular speakers to the “earspeaker” or STAX.


Well that sounds pretty complex.

The way this energizer was set up was that positive (red) and negative (from the energizer) were connected the (positive and negative) binding posts for speakers on an integrated amplifier (it was an old Technics), and that’s it, you adjust the volume on that amp. But receivers already have issues since they aren’t the best value-wise in terms of their amps (imagine buying an integrated amp at the same price as a 5.1 receiver, obviously there is a drawback).

I did listen to a tube amp too, gorgeous. What else can you say for tubes, pure nostalgia, beauty, and performance!

Which headphones are you using? When I was a kid, there was “Hi-Fi” that was only ONE channel. When I was old enough to read, most Hi-Fi had become glorious Stereophonic TWO channel sound. In college, some people got Quadrophenia - not just the Who album, but 4 channel. A room mate and I got a DynaQuad image adapter, and used it with 4 Rectilinear III speakers - my Highboys and his Lowboys. Everybody thought it was great, but there were almost no quad-encoded records (By then they were black round vinyl, usually, and not Grandma’s cylinders) so it sort of simulated 4 channels. That .1 stuff like 5.1 is from when I was already grown and married. And I never got over stereo.

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And people wonder why I won’t get into e-stats… Look at this thread. Sheesh.



I resemble that remark.

But this is about a legacy probably DIY box. Try explaining SCSI storage devices to someone who thinks USB 3 is old.


I am using two, one of them is Kaldas Research RR1 Conquest… but since I haven’t set up everything, I didn’t have any chance to listen to them (outside of the time when I visited the manufacturer who had everything put together as it should be)

I don’t blame you. This definitely seems like a whole different world than planars and dynamics. However, if you just buy an all-in-one package like an electrostatic amplifier, you have less things to worry about (the transformers are inside, the amplifier is inside)

Oh, btw, @pennstac how would I go about a DAC? I mostly play my music on my laptop (Spotify), so I was wondering how I could connect this whole setup (energizer and integrated speaker amp) to my MacBook Pro (Early 2015)?

MacBookPro --> (USB or optical cable) --> DAC --> integrated speaker amp --> (speaker connections)–> energizer.

Most energizers, like the Stax SRD-7 that pennstac posted a photo of, also have connections on the back to be connected to a pair of regular speakers, and a front panel switch so the user can elect to listen to the e-stat headphones or the stereo speakers. Your DIY unit does not have that.

Instead, per the labels, it has panel connections for a set of non-e-stat headphones, using dual-3-pin-XLR connectors. You probably don’t have any headphones with dual-3-pin-XLR connectors. But if you wanted to try these outputs (very carefully), you could buy a Y-adapter with male 3-pin XLRs on one end and a conventional female phono (headphone) socket on the other.

Carefully because without more doco or research, you don’t know how the the full power output from the amp is being attenuated for headphones inside this device.

Edit: the specs of a bias voltage of 580V are consistent with the 5-pin front panel Stax connector … it’s designed for Pro Bias Stax headphones. (“earspeakers.”)


Hm… can’t speak too much, but let’s just say that the headphones that I am using are electrostats and do use dual 3-pin XLR connectors. I’ll say one more thing, they sound amazing. And to explain, the headphones have a removable cable (I believe they were the first electrostats in the world to feature a removable cable), and the connectors on the headphone end are mini 3-pin XLR, leaving you the flexibility of choosing the cable (that end in either a single 5-pin Pro Bias connector, or two 3-pin XLR connectors).

These 3-pin XLR connectors are not for non electrostatic headphones… because this is an energizer, I believe it would fry them. I mean… 580 volts into a non-estat… yikes.

Would you mind elaborating what exactly you mean by this?

Just to clear things up, this is not quite a DIY energizer… but I still can’t share too much. It’s a company that somehow nobody noticed… nor do I believe anybody is aware of. I will be writing a review, but it will take some months to complete (it will not be done any earlier than January next year). And no, I am not paid for doing this =)
And yes, I am hinting that there is an electrostatic headphone that nobody in the audiophile community has discovered. Not a DIY electrostat, a flagship electrostat.

Edit: Forgot to thank you for clearing up how I would connect the DAC!!

Well, this company also makes a full sized amp that can do exactly that. It can drive electrostats, dynamic drivers, and speakers too. But the energizer does not have that option

AHA! Now it all becomes clear. Whoever, whosomever, whodidthat made a dedicated box for the e-stats that you bought, and figured that whoever had those might have STAX also. The Kaldas Research headphones have removable cables, and their literature suggests that at least at one time they had or have a cable that terminates in 2 XLR ends in addition to the STAX termination, OR a cable that can go from 2 XLR to STAX. They likely made the box.

What @Doug_Dame said. I suggest a USB DAC, as many laptops have limited resolution with optical. Although it shouldn’t make much difference with Spotify.

And @ProfFalkin is just being @ProfFalkin, he thinks that e-stats are complicated, but probably has a 12 step process for wood care on his ZMF headphones.


I can’t confirm this. Kaldas Research did think that they were the first in the world to feature removable cables on estats… but this company did it in 2015, which is quite a bit earlier than them. My RR1 Conquest came with a 5-pin Pro Bias cable, perhaps they made one for one of their bespoke customers.

Not to bring Kaldas Research any trouble, I want to confirm that they have nothing to do with the box (energizer). However, the manufacturer did indeed have in mind that whoever owns their headphones might also own Stax headphones, and thus made it convenient for Stax owners to use it.

Thanks for the heads up, I’ll keep this in mind!

Ah … I was not aware of any e-stat headphones with XLR connectors. Ignore what I said then. This will drive 580v biased e-stats with either a conventional Stax 5-pin Pro connector, or via XLRs.

DO NOT connect regular headphones (dynamic, planars, etc) to this box. It’s purely for e-stats.

The “it’s not DIY” explains the better-than-normal labeling (for DIY) on the device. That surprised me, but now it makes sense. It’s a prototype, or a beta-test unit, essentially.


Something like that. It’s very exciting, and I can’t wait to share the headphones… but I want to take my time to create what will be my best piece of work yet.

I mean Kaldas Research RR1 on its own is exciting af, amazing product. It’s crazy that it’s only 500 bucks. Taking into consideration that Kaldas Research has their own factory they can sell it at such a cheap price, otherwise it would be impossible to make the RR1 at this price if you were making it DIY. From my short listen to them, the bass is amazing, weird that some called it bass light… Can’t wait to give them more listening time once I have everything set up. What can I say, exciting stuff on the way =)

I’m very pleased with my Nectar Hive e-stats, so I’m tuned in to some of the boutique manufacturers. I’ll write a more detailed review on them eventually, but with my procrastination it will probably be January.

Like the Kaldas, the manufacturer says they will work with lower bias voltages, but recommends the pro-bias. I’d like to see a comparison graph of FR at different bias voltages, just to know what, if any the effect is, other than volume. Maybe I’ll ask Nectar to show.

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