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Let’s build electrostatic headphones

Arno Mayrhofer Benedikt Becsi

January 2, 2018

Contents

1 Introduction 2

2 Required tools 2

3 Required materials 3

4 Building the driver 4

4.1 Design of the stators and spacers . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

4.1.1 Gcodecreation ........................................ 5

4.2 Etchingthestators.......................................... 7

4.3 Tensioning the Mylar diaphragm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7

4.4 Coatingthediaphragm........................................ 9

4.5 Cable ................................................. 9

4.6 Assembly ............................................... 10

5 Building the enclosure 10

6 Building the headband 11

7 Building the earpads 11

8 Assembly 11

9 Ampliﬁer 11

10 Measurements 13

11 What to do diﬀerent in the future 13

11.1Closedheadphones .......................................... 13

12 Collaboration & License 14

13 Appendix 15

13.1Circuitdiagramforcircuitjs..................................... 15

1 Introduction

The following document will describe the journey to construct your own electrostatic headphones starting

with zero, zilch, nada, niente and nichts. In Section 2 we will list the tools required for the building process,

which will be followed by a list of materials in Section 3. The actual construction process is split into ﬁve

parts, the building of the driver (Section 4), enclosure (Section 4), headband (Section 6) and earpads (Section

7) with a ﬁnal assembly in Section 8. Finally, the last two chapters will deal with measurements (Section

10) and things that we would do diﬀerently for the second pair (Section 11).

The whole construction is based on the Head-Fi.org thread [1], with diﬀerent and more detailed sources

([2, 4, 3]) given in the respective sections.

Figure 1: Electrical concept

The basic electrical concept of a electrostatic headphone can be seen in Fig. 1. An ampliﬁer provides

an input signal that is then transformed to yield the desired output voltage that drives the two stators.

Additionally, there is a negative DC current that keeps the diaphragm charged.

2 Required tools

To build the drivers it is highly recommended that you have access to a good CNC machine. Since we didn’t

have one of those standing around, we looked for a so called fablab, i.e. a community led workshop for

creative projects. We eventually ended up at the Viennese Metalab1which gave us access to a heavy duty

level CNC machine and an introduction on how to use it by Sebastian Bachmann2, which eased the learning

curve signiﬁcantly. The principal introduction included instructions on how to set up, start and operate the

machine and the control terminal, as well as some GGode basics (the programming language that controls

the machine’s behaviour - more on that in section 4.1.1). Most importantly, as it can be potentially quite

1https://metalab.at/

2https://www.reox.at/

dangerous to operate one of those things, it covered security basics, which is deﬁnitely the ﬁrst starting point

for anyone new to CNC. Don’t skip your tutorial lessons, kids!

Since you might be interested in the budget needed for this, it of course depends on the lab’s membership

policy - most labs we found had a monthly fee with a minimum subscription period, but we were able to

come to an arrangement with a voluntary contribution without binding membership. Most people running

those kinds of open creative space are pretty chill, so don’t be afraid to ask!

If you can’t ﬁnd a place or plan to work on more DIY-projects in the future, it might be worth it to

purchase a CNC mill for yourself or with a group of like-minded people. It’s amazing what’s going on in the

ﬁeld of aﬀordable, small-scale, DIY and hobby-use CNC in the last couple of years. Here are some links if

you’re more interested in a purchase:

https://www.millrightcnc.com/product-page/millright-cnc-m3-kit-bundle

http://www.makerdreams.it/

https://www.sorotec.de/shop/

Also, some labs require you to buy the wearout parts yourself. You can get CNC tools here:

http://cnc-plus.de/

https://www.sorotec.de/shop/

An electric drill was used for the assembly screws and headband construction. The earpads were sewn

from hand and as such only thread and needle was required for that. The step up transformer that we built

to drive the headphones required a basic electronics lab and in particular a soldering station.

3 Required materials

In this section we list all the materials we had to purchase for the headphones and our DIY step-up trans-

former. We provide you with the links where we bought the materials, but depending on where you live you

might ﬁnd better suppliers yourself.

1. 1 mm PCB FR-4 for stators and dust protection spacers: 3

2. 0.5 mm PCB for spacers: 4

3. 3 µm Mylar (for diaphragm): 5(with that, you should have all your mylar needs covered for years to

come!)

4. 1 µm Mylar (for dust protection): 6

5. Anti-static display cleaner for diaphragm coating: 7

6. Acrylic spray for insulating the stators: 8

7. Thin and stretchy artiﬁcial leather for the earpads and headband (should be available in a textile shop)

8. Wood for the enclosure and headband, several boards with 4mm and 10mm thickness; we used lime

and spruce

3https://www.conrad.com/ce/en/product/523656/PCB-material-Photo-coating-positive-single-sided-35-m?ref=

list

4https://www.conrad.com/ce/en/product/523630/PCB-material-Photo-coating-positive-single-sided-35-m?ref=

list

5https://www.ebay.com/itm/Electrostatic-Speaker-Membrane-Dupont-Mylar-C-3um-40M/172781729300?epid=

666335680&hash=item283a97f614:g:jg0AAOSwrklVPe61

6https://www.freeflightsupplies.co.uk/index.php/products/lightweight-covering-materials

7https://www.conrad.com/ce/en/product/995207/DataFlash-DF1620-Content-250-ml?ref=searchDetail

8https://www.conrad.com/ce/en/product/1198455/Acrylic-paint-Revell-Black-matt-08-Spray-can-100?ref=

searchDetail

9. Metal rods (3mm welding rods) for the headband

10. 3 cm acoustic foam (pads and headband)

11. Cable plus connectors

12. Screws for the assembly (2,5 x 20 mm)

13. Clear varnish or glaze for wood ﬁnish

14. Two-component glue: 9

15. Contact glue for gluing the membrane to the stators and the earpads: 10

Head-ﬁ.org 11 has a more comprehensive list of material suppliers.

Materials needed for the ampliﬁer:

1. 4 Audio transformers 6V - 230V (OEP N35A002F) 12

2. 1 Power transformer 230V - 230V (Triad Magnetics FP230-25) 13

3. 2 1 Ohm wirewound resistors 14

4. 6 1kV diodes 15

5. 2 10 MOhm resistors 16

6. 6 10 nF capacitors 17

7. 1 3.9 kOhm resistor 18

8. Power cord plus plug

9. Cables

10. Test circuit board

4 Building the driver

4.1 Design of the stators and spacers

In the following the stators and spacers will be designed and the designs will be prepared for CNC milling.

As the stators and spacers are 2-D, we decided to use Inkscape 19 for our design purposes. There are plenty

of guides on how to use Inkscape around so we assume that the reader is familiar with it. But in the end we

almost exclusively used the basic objects like spheres and ellipses and boolean operators (to be found under

the Path menu).

9https://www.conrad.com/ce/en/product/478703/UHU-Plus-Schnellfest-Two-component-adhesive-45700-35-g?ref=

list

10https://www.conrad.com/ce/en/product/631802/UHU-greenit-Contact-adhesive-45401-650-g?ref=searchDetail

11http://www.head-fi.org/t/826032/electrostatic-ear-speaker-diyers-suppliers-list

12https://uk.rs-online.com/web/p/audio-transformers/2106475/

13https://eu.mouser.com/search/ProductDetail.aspx?r=553-FP230-25

14https://eu.mouser.com/search/ProductDetail.aspx?r=71-RS0101R000FE73

15https://eu.mouser.com/search/ProductDetail.aspx?r=625-RGP10M-E3

16https://eu.mouser.com/search/ProductDetail.aspx?r=594-SFR25H0001005JR5

17https://eu.mouser.com/search/ProductDetail.aspx?r=75-564R30GAS10

18www.aliexpress.com

19https://www.inkscape.org

(a) Stator (b) Front spacer (c) Back spacer

(d) Spacer for dust protec-

tor

Figure 2: All PCB driver components

In general the ellipse which contains all driver components is 130 mm high and 94 mm wide. The inner

ellipse that determines the active area is 110 mm high and 74 mm wide. The holes drilled into the stator only

cover this active area and are laid out such that approximately 40% of the active area is open, i.e. covered by

holes. The distance between the holes is 0.8421 mm in vertical and 0.88 mm in horizontal direction and each

hole has a diameter of 2 mm. To generate such a tiled array of holes in Inkscape draw one hole and then use

the Create tiled clones option that can be found under Edit - Clone. The holes outside the active are where

removed manually. The resulting stator can be seen in Fig. 2a. A total of four stators need to be milled

from 1mm FR4 PCB. The eight cut-outs that are present in each driver component were designed to allow

easier screw insertion in the enclosing. It turned out though that we only needed four screws in the end and

it would have been possible to work without those cut-outs at all. At the bottom of the components there

is a varying number of half-circle cut-outs. These ensure that cables can be connected at other components

and provide insulation to the present one. The front and back stator seen in Fig. 2b and Fig. 2c are made

from 0.5 mm FR4 PCB. The dust spacer in Fig. 2d is made from 1 mm PCB. Each spacer needs to be

produced twice, one for each side.

A few general design guidelines that we found on the head-ﬁ thread indicated the following. The diameter

of the holes (2 mm in our case) should not be larger than the distance from stator to spacer. The reason for

not having the holes cover the whole stator is that this increases the stability of the stator. A large diaphragm

size is quite important as this improves low frequency response. Obviously, if the open area becomes too

large then the diaphragm will be too ﬂexible and touch the stators which will cause it to discharge. Because

of this the ratio of spacer thickness to diaphragm width should not be larger than 1:120. If this ratio is very

large a lower bias voltage can be used to avoid the membrane touching the stators.

All *.svg ﬁles that are used for the CNC milling can be found in the resources.zip which can be found

on github.com20.

4.1.1 Gcode creation

After creating the *.svgs with the outline of all shapes the next step is to produce Gcode, i.e. the instructions

for the CNC machine that can be understood by it. Note that we were using a CNC machine that was using

LinuxCNC and it pretty much understood the Gcode produced by the tool presented in the following. The

ﬁrst important step is to create a milling strategy. For all FR4 parts (stators and spacers) we decided to

use double sided tape to glue the FR4 boards to a ﬂat piece of scrap wood. This means that all paths will

20https://github.com/Azrael3000/headphone-guide/raw/master/resoures.zip

be cut 0.2mm deeper than the FR4 thickness. This ensures that the milling is deep enough and only leaves

some scratches on the scrap wood.

Before we start with the Gcode creation we need to decide on which drills and end mills to use. Our

choice for the FR4 milling consisted of a 2mm drill and a 2mm diamond coated end mill. The drill is only

used for the creation of the stator holes and the end mill is used for everything else. The end mill used in

our case would allow us for a vertical feed rate of 300 mm/min and a horizontal feed rate of 1000 mm/min.

The spindle speed was set to 24000 rpm.

To create the Gcode from the Inkscape ﬁle we use www.makercam.org which allows a platform independent

operation. It’s a ﬂash tool which allows for 2.5D designs and does everything we need for the headphone

construction.

After creating the *.ngc ﬁle a few manual modiﬁcations needed to be made in our case. What is required

here exactly depends on your CNC machine so either use your own personal experience or talk to someone

who knows the machine you are using to avoid damaging it. In our case we needed to warm up the spindle

ﬁrst starting with 6000 rpm and then increasing it slowly to 24000 rpm. An exemplary Gcode ﬁle is listed

below where we only took the ﬁrst few lines of the ﬁle as only those need modiﬁcation.

(Generated by PartKam Version 0.05)

G21 G90 G40

(drill 1)

G0 Z15

T0 M6

G17

G0 X11.05 Y65

G1 Z-1.1 F300

G3 X11.761421319796954 Y53.845177664974614 I87.68274111675127 J0 F1000

Let us go through this line by line now. The ﬁrst line is a comment as indicated by the brackets around

it. The second line G21 G90 G40 sets the units to mm relative to the zero position of the part and turns

oﬀ cutter radius compensation. It is again followed by a comment. Line four then has the ﬁrst movement

command G0 Z15. The G0 indicates that it is a fast move, i.e. a move in the air and not inside the material.

It moves the the tip of our tool to a position which is 15mm above 0 at it’s current x and y position. Note

that in our case the x axis indicated left and right, y front and back and z up and down. You should ensure

that you know the movement axes of your machine. The next command T0 M6 is a tool selector. As our

CNC machine did not have the capability to change its tools this irrelevant and will be deleted. The G17

command sets the working plane to the XY axes. The M3 command turns on the spindle. Not that it

does not indicate a spindle speed so we need to change this. G0 is a fast movement command, as X and Y

positions are speciﬁed, no movement in Z direction will happen. Such a movement can be seen in the next

line, i.e. the G1 command. This is a linear movement to the speciﬁed, in this case Z position. In contrast

to the G0 command, this movement does not happen at maximum speed but at the speciﬁed one, here

F300 speciﬁes 300 mm/min which corresponds to the plunge rate. The G3 command speciﬁes a circular

interpolation and for us indicates the begin of the horizontal movement with a feed rate of 1000 mm/min.

We make some modiﬁcations to this ﬁle as can be seen below. The ﬁrst change is that we move the tool

to Z5 before starting the spindle. The spindle is then switched on and set to 6000 rpm with the M3 S6000

command. The following G4 command indicates a pause which is speciﬁed to last 60 seconds in our case.

After that the spindle speed is increased to 12000 rpm up to 24000 rpm with 60 second dwelling periods.

This allows the spindle to warm up for milling. Note that the duration of this warm up period depends on

your machine. After this warm up a ﬁrst movement in the X-Y plane is performed as above which is followed

by a 5 second pause to check whether everything is correct. Next, the mill is lowered and the main part of

the program starts.

(Generated by PartKam Version 0.05)

G21 G90 G40

(profile 1)

G0 Z5

G17

M3 S6000

G4 P60

S12000

G4 P60

S18000

G4 P60

S24000

G4 P60

G0 X11.05 Y65

G4 P5

G1 Z-1.1 F300

G3 X11.761421319796954 Y53.845177664974614 I87.68274111675127 J0 F1000

After milling it is particularly important to deburr the stator holes, but it also makes sense to sand down

the edges of all workpieces.

4.2 Etching the stators

TODO-BB: Write particularly about what areas are left with copper (maybe a diagram) Etching the PCB

board ensures that electrical contacts are only where they absolutely need to be. Furthermore, having less

copper surface will result in a reduced capacitance and they will be easier to drive because of that. Toner

transfer can be used to deﬁne the areas that should not be etched.

http://www.instructables.com/id/Stop-using-Ferric-Chloride-etchant!--A-better-etc/

Etching is achieved by using 2 parts Hydrogen Peroxide (3%) with 1 part Hydrochloric acid (30%). Most

PCBs have a photosensitive coating that needs to be removed for this to work. The etching can be achieved

by using a paintbrush to apply the solution to the desired location. The copper will be taken away rather

quickly and the solution will turn greenish.

4.3 Tensioning the Mylar diaphragm

Mylar with 3 µm thickness is used to create the diaphragm. Thinner Mylar will cause a lack of bass, while

thicker one will cause problem in treble and mids. The tensioning should be high enough as otherwise the

diaphragm will collapse onto a stator, loosing its charge, but also low enough in order to not reduced the

bass. Two diﬀerent ways of tensioning the Mylar were established in the head-ﬁ thread. The ﬁrst method

can be seen in Fig. 3 and consists of using several weights equally distributed around a circular surface. This

is also the method that we will use in the following. The other option, shown in Fig. 4, uses a bicycle tire

that is ﬁxed to the outside of a cylinder. The Mylar is stretched over the cylinder and ﬁxed on the bottom

using adhesive tape. The tire is then inﬂated until the desired stretching has been achieved. A discussion

on this method can be found on the head-ﬁ thread21 . As mentioned above we will use the method with the

weights in the following. In our case we used 8 weights with 1 kg each and attach it to the Mylar. A picture

of our improvised jig can be seen in Fig. 5. We used a pan and placed a thick sheet of paper on it in order

to provide a ﬂat base for the Mylar to lie on. Gaﬀer tape was used to attach the weights equally around the

21http://www.head-fi.org/t/498292/my-diy-electrostatic-headphones/1095#post_9907534

Figure 3: A Mylar tensioning rig using weights

Figure 4: A Mylar tensioning rig using an inﬂatable tire

outside. Next, we put our two back spacers on the Mylar and drew the outline onto the Mylar. Gluing both

spacers at the same time ensures that the tension is the same on both sides. The spacers were then removed

and both the spacer and their outline on the Mylar were covered with a thin layer of UHU Greenit. This

is a contact cement or synthetic rubber glue, alternatives include UHU Por, 3M 4693. The glue is allowed

to dry for 15 minutes, after which the spacers are placed onto the Mylar and pressed ﬁrmly onto them. We

actually used a rolling pin to increase the pressure and thus the glueing strength22. After this, the weights

can be removed and the excess Mylar can be cut away from the spacers. Note that it is very important to

not have any Mylar overlap the edge of the spacer. We used a small scissor and then went around the edges

with an old soldering iron to ensure this. After completing this step the spacers can be knocked on the side

of a table to check whether the sound of both diaphragms is similar. If not, a hot air gun can be used to

loosen the tension of a diaphragm.

An idea on how to identify the correct tension of the diaphragm by checking the free-air resonance

frequency (should be between 100 and 200 Hz) using a white noise generator on one side and a microphone

on the other was also mentioned in the thread23, but we did not try this.

22http://www.head-fi.org/t/498292/my-diy-electrostatic-headphones/1215#post_10400583

23http://www.head-fi.org/t/498292/my-diy-electrostatic-headphones/1770#post_11440100

Figure 5: Our Mylar tensioning rig using weights

Note, while this step sounds easy, it is actually the most diﬃcult one to get right and has probably the

most signiﬁcant impact on the sound of your headphones. Because of this is makes sense to actually produce

a few extra back spacers to try diﬀerent conﬁgurations. Alternatively, UHU Greenit can be removed from

the spacers using Acetone, so a new attempt can be made.

4.4 Coating the diaphragm

As Mylar is not conductive an additional coating is required so that it can be charged. It basically should

act as if it was a capacitor, so a coating that is conductive and has a high resistivity is ideal. Coating agents

mentioned in the thread are:

1. Staticide 6300 (anti-static cleaner for monitors)

2. Licron antistatic spray

3. Swash Floor cleaner

In our case we simply bought a anti-static spray for computer monitors, which worked without any issues.

Coating is achieved by applying a small drop of the coating agent onto the diaphragm and then spreading it

with a sponge or microﬁbre cloth (lint free). The coating only happens on one side of the diaphragm namely

the side pointing away from the spacer. It should be ensured that the coating also happens on the part of the

diaphragm that is above the spacer, i.e. all the way to the edge. After the coating has dried the surface can

be cleaned again with a dry lint free cloth. It is advisable to check the surface before the assembly to ensure

that there is no dust on it. Otherwise pressurized air or masking tape can be used to clean the diaphragm.

Diyaudio.com also has a thread about coating24.

4.5 Cable

The cable that connects the headphone with the step up transformer consists of three about 3m long litz

wires (0.14mm2)that were braided together. One side was soldered directly onto the stators and one spacer

whereas the other side was ﬁtted with banana plugs to connect the headphones to the transformer.

While this might not be the perfect solution in terms of elegance and signal transmission it was a

inexpensive and functional way to make the headphones sing.

Alternatives include replacement cables for KOSS headphones. Apparently an extension cable for the

ESP-950 headphone should do the trick. 25

24http://www.diyaudio.com/forums/planars-exotics/109789-esl-diaphragm-coating.html

25https://www.head-fi.org/threads/my-diy-electrostatic-headphones.498292/page-51#post-9325470

4.6 Assembly

Before assembling the driver a dust protector needs to be built using the 1 mm spacer made from FR4 and

a 1 µm Mylar ﬁlm. The Mylar is crumpled by hand and then slightly stretched using masking tape on a

ﬂat surface. We then follow the same procedure as for the diaphragm, i.e. putting glue on both the spacer

and the Mylar, letting it dry and then pressing the two ﬁrmly together. The crumpling of the Mylar should

ensure that this ﬁlm is acoustically transparent but keeps dust out of the driver. The slight stretching is

needed so that it doesn’t touch the spacer. The dust protection is only between the ear and the driver as

the coated side of the diaphragm is also towards the ear. Because of this, no dust protection is required on

the outside.

As we chose to have no connector directly at the headphone, we soldered the cables directly onto the two

stators and the 0.5 mm front spacer without the diaphragm. Then the conducting side of the two stators

was sprayed with (in our case black) acrylic spray to insulate them. This avoids arching once the stators

and diaphragm are charged.

Afterwards the driver can be assembled. See Fig. 6 for a visual representation of the arrangement of the

diﬀerent parts. The part furthest away from the ear is the stator with negative wire with the acrylic covered

copper side pointing towards the ear. This is followed by the spacer with the diaphragm where the side with

the diaphragm and the coating points towards the ear. Next, the front spacer is added with its copper side

pointed away from the ear so that an electric connection between the diaphragm and the front spacer with

the cable is made. The remaining stator is then placed onto the spacer with the acrylic covered copper side

pointing away from the ear. Finally, the dust spacer is placed on the assembly with the crumpled Mylar

pointing towards the ear to complete the driver.

Figure 6: Arrangement and orientation of stators and spacers (missing the dust protection spacer and ﬁlm)

To perform some tests we used some clothespins to keep the driver together. Be careful when running

tests with the driver outside the enclosure as nearly all parts will be charged. The driver can be tested by

hooking it up to the amp and leave it as is for 3 to 4 hours without playing any music. The diaphragm

should not be sucked to one side during this. It is also easy to hear any arching that occurs due to dust or

other mistakes in the production. Sometimes it is easy to see where the arching occurs and it is usually easy

to correct the cause (by using pressurized air or sanding the corners). After testing and before the driver is

disassembled, e.g. for correcting something, it is advisable to connect all three wires to ground in order to

allow the parts to discharge.

5 Building the enclosure

TODO-AM

Since we were already using a CNC machine to manufacture the drivers we opted for the same toolchain

to create the enclosure. As wood is a common material in enclosure construction we decided to use it as

well. We again designed the enclosure as a 2.5-D shape using Inkscape. The Gcode was created using

www.makercam.com similarly to the driver. To machine the enclosure we used a 6mm and a 2mm 2-ﬂute end

Figure 7: Earpad cut-through; materials: wood (yellow), foam (grey), screw nut (black), artiﬁcial leather

(blue), contact cement (green)

mill.

6 Building the headband

TODO-BB

http://www.head-fi.org/t/498292/my-diy-electrostatic-headphones/675#post_8943826

Headband can be made out of a metal ruler and then covered with leather http://www.head-fi.org/

t/498292/my-diy-electrostatic-headphones/2385#post_13037825.

7 Building the earpads

The earpads should be thick enough so that the bass is powerful and deep enough. The earpad is based

on a wooden ellipse with 4mm thickness that was also manufactured using the CNC. After we had the full

enclosing together we put the front and the back of the enclosing together with this ellipse to drill four holes

for the assembly. The screw nuts were glued to the inside of the ellipse using copious amounts of epoxy.

A schematic of the earpad can be seen in Fig. 7. After the glue has hardened (see your glue for the time,

for ours it was about 24h) we loosened the screws and disassembled everything. The next step consisted of

cutting the same ellipse from acoustic foam with 3cm thickness.

The leather cover is made from a thin and stretchy synthetic leather. It’s made of two parts, a rectangular

one with dimension 4 x 32 cm and an elliptic one which is of the same size as the wooden ellipse of the pad

plus 1 cm inside and 3 cm on the outside. The rectangular patch is sewn on the inside of the ellipse and

then it’s wrapped over the foam and the wooden pad connector. The leather is glued to the wood using the

contact cement that was also used to glue the diaphragm to the spacers. Finally, we also glued a mesh to

the wood so that the ears cannot get in touch with the dust protector.

8 Assembly

TODO-AM write about screws.

9 Ampliﬁer

Due to the requirement of a continuously charged diaphragm and the high voltage requirements of the stators

a dedicated ampliﬁer is required for electrostatic headphones. A discussion on this ampliﬁer design can be

Figure 8: Final earpads

Figure 9: Ampliﬁer design by Wachara C.

found on Head-ﬁ.org 26. However, to not make out lives too diﬃcult we decided against building a full

ampliﬁer. Instead we opted to construct a step up transformer based on the designs of Charlie Mimbs 27.

A note of warning before we continue with the details. We will be dealing with electronic equipment in

the following which can cause serious injury or death so make sure you have a good understanding of what

you are doing and follow proper safety procedures.

Since we are not building a speaker we opted for a toned down version of Charlie’s step up that would

only lead to 580 volts at the diaphragm. A circuit diagram can be seen in Fig. 10 that was copied from

circuitjs 28.

The ﬁnal step-up transformer can be seen in Fig. 11. As can be seen, we did not put it in a nice enclosing

and this will also be part of next years project. The step-up transformer is divided in three parts, the blue

and yellow part are the transformers for the left and right stators, respectively. Each of these section consists

of one 1 Ohm resistor and 2 audio transformers from 6 V to 230 V. The OEP transformers that we used

(see Section 3) were connected on the B-D and 1-4 pins. This yields a 4000k to 95k winding ratio. The two

transformers are connected in series and the output side is connected to the step-up part of the transformer

as can be seen in Fig. 10. Note that in the circuit diagram only one of these stator sections is depicted.

The green part in Fig. 11 corresponds to the lower part in the circuit diagram (Fig. 10) and is responsible

for converting the 230 V, 50 Hz AC input to a 580 V DC current. The AC input was connected to the Triad

power transformer including a 250mA fast blow fuse. On the output side a 3.9 kOhm resister is put before

26http://www.head-fi.org/t/498292/my-diy-electrostatic-headphones/720#post_9182523

27https://jazzman-esl-page.blogspot.co.at/2010/01/update-new-toroidal-step-up.html

28http://lushprojects.com/circuitjs/circuitjs.html

Figure 10: Step up transformer: circuit diagram

the actual step-up ladder that can be seen in the circuit diagram. This ladder consists of 6 10 nF capacitors

and 6 diodes to rectify the AC current. At the end of this ladder a 18 MOhm resistor is put before the

connection to the diaphragm is made. Note that we made only one step-up ladder that is connected to both

left and right diaphragms.

Note that when operating the headphone its component will be charged and this charge will persist even if

power to the transformer has been shut down. It is necessary to discharge all components before disassembly

which can be achieved by leaving the power cord connected after shutdown and using the ground connection

of the power cord. We hooked up a cable to the ground connection and discharge all outgoing ports by

touching them brieﬂy with this cable.

10 Measurements

As part of the current build we did not perform any measurements and this will become a topic for the

future. The head-ﬁ thread suggests to perform measurements with and without seal. The latter should give

a peak at around 200 Hz which is the free-air resonance frequency. This frequency should be lower than 150

Hz for a good bass response.

11 What to do diﬀerent in the future

Allow for a little space between enclosing and driver.

Shrink wrapped cable with proper xlr connector and connector at the headphone. Space for the cables

milled out when creating the enclosure.

Earpad made out of three pieces (2 rectangular ones and one ellipse).

Proper enclosing for the step-up transformer or even a real ampliﬁer for electrostatic headphones. Addi-

tional cables to connect the step-up transformer to headphone ampliﬁers.

11.1 Closed headphones

Materials used for damping included felt, wool or other acoustically semi-transparent materials. Some also

coat the inside of the enclosure with Bitumen.

Figure 11: Step up transformer from the top

12 Collaboration & License

This work is licensed under a Creative Commons Attribution-ShareAlike 4.0 International License 29 . The

oﬃcial repository for this guide can be found on github.com 30. There is an issue tracker available if you do

not know how to work with L

Xand git. We very much jumped into this venture without prior knowledge

of a lot of things that we had to tackle. Because of this there might very well be mistakes in this guide or

in our approach that we are happy to learn about. So do get in touch with us if you have any remarks and

want to help us improve this document. We plan to build version 2 of the headphones in 2018 and with this

we will also update and improve this guide.

29http://creativecommons.org/licenses/by-sa/4.0/

30https://github.com/Azrael3000/headphone-guide

13 Appendix

13.1 Circuit diagram for circuitjs

This ﬁle can also be found in the resources.zip ﬁle which can be found on github.com 31.

$ 13 0.000005 146.80153516788286 47 120 28

v 448 512 448 352 0 1 50 230 0 1.5707963267948966 0.5

c 720 352 800 352 0 1e-8 -121.77903323034391

w 608 512 608 608 0

w 608 512 768 512 0

d 768 512 800 352 1 0.805904783

d 800 352 832 512 1 0.805904783

d 832 512 880 352 1 0.805904783

d 880 352 912 512 1 0.805904783

d 912 512 960 352 1 0.805904783

d 960 352 1008 512 1 0.805904783

c 800 352 880 352 0 1e-8 -188.52952984256655

c 880 352 960 352 0 1e-8 -148.45206709826482

c 768 512 832 512 0 1e-8 -188.38552969850758

c 832 512 912 512 0 1e-8 -148.28294550190276

c 912 512 1008 512 0 1e-8 -133.83898987162684

r 1008 512 1216 512 0 18000000

w 1216 512 1264 512 0

w 608 608 1328 608 0

v 416 96 416 288 0 1 200 6 0 0 0.5

T 560 96 656 112 0 4 20 -0.0002165438913044398 0.000008783616360946498 0.999

T 560 176 656 144 0 4 20 0.00021654389130444608 -0.000008783616360946477 0.999

T 560 240 656 208 0 4 20 0.00021654389130505795 -0.00000878361636097594 0.999

T 560 288 656 256 0 4 20 0.00021654389130505323 -0.000008783616360975917 0.999

w 656 128 656 144 0

w 656 240 656 256 0

r 544 96 464 96 0 1

w 544 96 560 96 0

w 544 208 560 208 0

w 544 144 560 144 0

w 544 208 544 256 0

w 544 256 560 256 0

w 544 208 544 144 0

w 544 144 544 96 0

w 560 128 528 128 0

w 528 128 528 176 0

w 528 176 560 176 0

w 528 176 528 240 0

w 528 240 560 240 0

w 560 288 528 288 0

w 528 288 528 240 0

w 416 288 528 288 0

w 464 96 416 96 0

w 1328 608 1328 192 0

w 1328 192 656 192 0

31https://github.com/Azrael3000/headphone-guide/raw/master/resoures.zip

w 656 208 656 192 0

w 656 192 656 176 0

w 656 288 768 288 0

w 768 288 768 160 0

w 656 96 768 96 0

c 768 96 768 160 0 2e-11 -328.31758099807905

T 608 352 528 192 0 2 1 -4.752600223090209e-16 -0.18138620921599558 0.999

r 608 352 720 352 0 3900

w 448 512 528 512 0

174 448 352 512 352 0 1000 0.5 Resistance

w 512 352 528 352 0

o 16 64 0 2083 1280 0.00009765625 0 -1 0

o 49 64 0 2083 1280 0.0001953125 1 -1 0

o 51 64 0 2083 5 0.0015625 2 -1 0

o 1 64 0 2083 320 0.0015625 3 -1 0

o 3 64 0 2083 640 0.0015625 4 -1 0

o 54 64 0 2083 640 0.4 5 -1 0

References

[1] Wachara Chinsettawong. My diy electrostatic headphones, 2016.

[2] Jarosz N. Electrostatic headphone design and construction, 2013.

[3] Pollock N. Electrostatic headphones. Wirless World, 11, 1979.

[4] N.N. Electrostatic headphones, 2012.

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