My DIY electrostatic headphones
Oct 14, 2014 at 10:47 PM Post #1,576 of 4,064
I have taken your advice. Thank you.
I have found a used SRM-1 pro Mk2 PP version C.
This was the last of this model maybe... Perhaps you can correct me here.
Now for a question. Would it be fairly straightforward to make the bias voltage adjustable?
What would be a good way to achieve this? A separate box perhaps, a separate supply I mean.
I say this because it seems to be something that accomplished DIYers in this thread are doing when testing their creations.

Yes that's the last version of that amp.
Another option for variable bias supply is to get one of the proportional high voltage DC-to-DC supplies from a place like EMCO.  They can output a voltage high enough for speaker ESLs.  Read the spec sheet to check the input voltage, but I think it's something like 0-15V.
Oct 16, 2014 at 10:53 PM Post #1,577 of 4,064
Hi everyone, I've been trying to re-coat a pair of old Gamma Pro drivers using antistatic cleaning liquid, and I've run into a strange problem. The volume of one of the drivers always drops when music isn't playing (despite being charged by the bias), then starts to rise and it eventually becomes louder than the other driver. Is this to do with the coating, or perhaps I've overstressed the wire that connects the bias to the stator?
Oct 17, 2014 at 1:24 AM Post #1,578 of 4,064
Did you recoat both drivers?  If so, one side or both sides of the diaphragm?  This isn't being driven from one of the self bias transformer boxes right?
Oct 17, 2014 at 2:24 AM Post #1,579 of 4,064
Yes, I recoated both drivers, but the answer is that I've broken the foil that connects the bias to the stator. The reason it still works at all is because I added a second wire to "buff up" that connection previously.
Anyway, how do you guys make sure that you've applied the same amount of coating on both drivers?
I coated both sides of the diaphragm, because I noticed that the diaphragm was always getting stuck on the uncoated side, and it would stop sticking after I coated it (to an extent). I'm using an SRM-T1S.
Oct 17, 2014 at 3:33 AM Post #1,580 of 4,064
Hi Tachikoma
I am quite new to this scene but a couple of things occurred to me from your description. 
First,  I believe there shouldn't be an electrical connection between the bias signal and the stators. You said you broke the foil that makes this connection. That puzzled me. The bias connects to the plastic film diaphragm only and the modulated (audio) signal connects to the stators. The foil could be the bias connection to the diaphragm?
As far as I know,
the inner stator connection,    (next to your ear)  
the bias connection,        
and the outer stator connection,  
must be kept separate.
Second, your antistatic coating must not contaminate the spacers between the diaphragm and the two stators. I imagine that weird behaviour might result if this happened (But I don't know as I haven't experienced this myself this yet). Since you are re-coating your diaphragm it remains connected to the spacers yes? The diaphragm must be kept connected to a spacer in order to maintain its tension. I can picture myself in your situation, covering the spacers with thin strips of masking tape first, before spraying.  
Just my thoughts. (I have probably stated the blindingly obvious! If so I am sorry) Perhaps someone else more experienced than I can add something to this?
Oct 17, 2014 at 5:13 AM Post #1,581 of 4,064
If you look closely at and, you'll see a tiny strip of foil connected to the bias terminal on the driver. The strip of foil terminates at the stator on the opposite side. I'm not really sure how biasing works in electrostatics tbh, maybe the bias conducts to the diaphragm via the stator? I always thought the bias was applied across the stators to create a potential across the driver.
The spacers in these Stax drivers are separate from the diaphragm, so there's no contamination issue to worry about.
Oct 17, 2014 at 5:45 AM Post #1,582 of 4,064
Hi again Tachikoma.
I am studying the pictures now...
I can see there are just the three connections. These would seem to be the inner and outer stator connections and the diaphragm connection. 
As to how this all works, there isn't a potential 'across' the diaphragm as such. This is a static charge placed on the diaphragm. This means it only needs one connection and this connection 'leaks' charge out onto the diaphragm surface where it stays for a while, so long as it can't find a way to leak away.
The usual way that I have seen this done from pics and explanations on this thread is by attaching a flat foil or a thin metal (such as copper) conductor that surrounds and contacts the entire circumference of the diaphragm on its coated side. Within this circumference the static charge is maintained by the bias voltage. Interestingly the DIYers here are usually coating only one side of their diaphragms (someone correct me here if I am wrong).
This thin conductor ring or  "charge ring" must not make any electrical contact with any stator.
Conversely, unlike the diaphragm, to operate properly, the stators must not hold any charge. They are receiving the audio signal at a high voltage and they must change their voltage as the audio signal changes. 
The stators receive their respective voltages 180 degrees out of phase so that when one stator is 'pulling' on the diaphragm, the other is 'pushing'.
I hope this makes sense. 
On the SRX mk3 picture it looks to me as though the centre black lead is the bias for the diaphragm and the yellow lead is the connection for the inner (ear side) stator while the greenish lead at the top of the picture is for the outer stator. 
btw there is an article that explains very well how all this works: "Notes on DIY Electrostatic Headphones" by Chu Moi
Oct 17, 2014 at 12:17 PM Post #1,583 of 4,064
Hello arnoud.
I wonder, do you have those measurements for the Stax diaphragm tension? 
I am running through the options of what diaphragm size and shape to make, spacing and how to seal against my head (circumaural) with shaped
ear cushions, and then there is the idea of angling the drivers and what the distance should be from driver to ear... the list goes on!
Trying to find out what the reasoning was for making the Lambda drivers an elongated circle shape as opposed to circular, or oval shapes. 
I got myself an SRM-1 mk2 PP amp, hoping that it will be able to drive whatever I end up creating. This is the first electrostatic amp I have ever acquired.
 I hope it will be a good amp.
Oct 17, 2014 at 11:18 PM Post #1,584 of 4,064
Hello again all,
I am glad as always that this thread continues to be as active and inspirational as it does.  My own headphone making studio has been somewhat dormant as other interests and jobs took over my time.  Fortunately, I've got some time now to reboot the machinery and see if I can't crank out a few sets of drivers.  Before I start ordering bits, I thought I would poll you about a couple of issues:
1. Do you suppose the size of the stator holes affects sound?  In which way?  I was thinking that generally having more, smaller holes would ensure that the signal reached the diaphragm in a more uniform fashion, but I don't know that that is supported by fact...
2.  I understand that some of you etch out the extra copper on the stator.  How does this affect the thickness of the stator?  I would be worried about creating a stator with a thicker center than rim -- being unable to keep the air gap between the diaphragm and stator constant.  How have you dealt with this?
3.  Regarding cables and connectors, do you have recommendations for cable types and connector housings?  For those of you located in the US, do you have a reliable source for these parts?  I was thinking of using an XLR connector with the guts ripped out and a custom delrin insert holding 6 of the larger pin sizes (which seem to fit the Stax jack nicely), but didn't know if there was another connector housing which normally has the pin-base (the part that the pins sit in, not sure the proper term) sitting flush with the front, rather than inset.
I hope to someday be a part of the question-answering community here on head-fi DIY, but for the moment, I will do my best not to repeat questions!

Oct 18, 2014 at 2:04 AM Post #1,585 of 4,064
Hi OnyxOcelot,

Most of us here are DIYers. We make the headphones base on trials and errors. I encourage you to do the same as I don't believe that you'll only make one pair. :)

1. I am not sure that smaller holes are better. I have been drilling 2 mm holes on all my stators, and I like all of them.

2. I use chemical etching method for etching out the unneeded copper. I think it etches out copper very evenly.

3. As for cable, try to get an extension cable of Koss ESP950. It's good and cheap.

Have fun!
Oct 24, 2014 at 1:02 PM Post #1,587 of 4,064
You are right Onyxocelot,
Time to build and mess up a few times in order to find the right path. Me too here!
Now then, the Sennheiser HD800 is a great set of headphones, its large sound stage being particularly good (so I hear - pun intended) and this set me thinking. It uses a 56 mm driver with a hole in the centre. I am considering using the same (as far as I can make it) ear cup shape with angled driver to fit a slightly bigger electrostatic driver located in approximately the same place. I am thinking around 60 mm  to 65 mm diameter might be possible while preserving the carefully designed enclosure shape. Of course this new driver won't have a hole in its centre. I want to duplicate the shape and volume of the HD 800 ear cup and experiment with the micro-mesh walls of the ear cup enclosure. I assume the mesh restricts the movement of air in and out of the enclosed space.
Is that right?
Since Sennheiser have also been extolling the virtues of a planar wavefronts with their ring driver it occurred to me that an electrostatic driver can do a better job making planar wavefronts than any ring driver anyway.
I am wondering if anyone has any views on whether this idea might be workable and what problems I might encounter when attempting this. For instance, can a slightly larger electrostatic diaphragm produce a bottom end coming anywhere close to the smaller area ring driver in the HD800? I mean, can its extra area make up for its presumably lower excursion?
cheers all
Oct 24, 2014 at 3:00 PM Post #1,588 of 4,064
The volume of the cup is pretty large on the HD800.  You may need to use thicker spacers and run at a higher bias to get the bass you're looking for.  Lining the interior walls with the right material will be important to get rid of unwanted reflections.  Sounds like a very interesting project though :)
Oct 24, 2014 at 3:07 PM Post #1,589 of 4,064
I like the idea of the project from an aesthetic point of view, but I imagine a fair amount of difficulty achieving the desired fidelity. Are you hoping to get the benefits of the SR-Sigma in an HD800 package?
Oct 25, 2014 at 10:14 AM Post #1,590 of 4,064
  The volume of the cup is pretty large on the HD800.  You may need to use thicker spacers and run at a higher bias to get the bass you're looking for.  Lining the interior walls with the right material will be important to get rid of unwanted reflections.  Sounds like a very interesting project though :)

I have never experienced any evidence that higher bias affects the sound in any way. It simply increases the volume with a lower signal voltage on the stators.

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