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My DIY electrostatic headphones - Page 98

post #1456 of 1608

This is a 100mm diameter stator and diaphragm pair.

 

 

 

It took me a while to figure out how to make the PCB software generate gerbers and drill files to do this job since it is not really what the software is intended to do. I can get the diaphragm supports (spacers) in 0.6mm. The stator can be 1.6mm, this is cheapest. The stator can be covered with solder resist, except where there are pads. The mounting pad holes are M2, intended to accommodate Nylon bolts, the custom pads are just slightly larger than the holes which are M3.   Total cost for 20 (5 sets) would be ~$110 delivered. $22 per set before postage. I still need to figure out some connection points on the edge.

 

These are not large capsules, but they fit into board dimensions which are available under the very best deal from China. I could go for 100*150mm rectangular or oval. This would increase the cost to $190 or $38 dollars a set.

 

 

 

This would relieve constructors of the need for a CNC mill, and access to different thicknesses of PCB, plus the stators could be resist-coated, one less process.

 

Fred


Edited by wakibaki - 7/8/14 at 8:01pm
post #1457 of 1608
Thread Starter 
Hi Fred,

Your designs look really nice.  I think the prices you got were quite reasonable too.  

Can they do 0.5 mm PCB as spacers?

For your information, the SR007's stators are 0.8 mm double sided PCBs.

Wachara C.
Edited by chinsettawong - 7/9/14 at 3:18am
post #1458 of 1608

That does indeed look great!

post #1459 of 1608
I can get 0.6, 0.8, 1.0, 1.2, 1.6, 2.0 mm thicknesses. 0.6 & 2.0 cost extra. It's unfortunate that 0.5 is not available, but I hope that the 0.6 will still prove acceptable

I thought that for the stator the stiffest one at no extra cost was the one to go for, but 0.8 is the same price. Do you think there is an advantage to the thinner one? In sound quality?

I have kept the capacitance as low as I could conveniently, I can maybe improve it slightly.

The prices are absolutely rock-bottom, but I know from experience that the quality will be acceptable.

Fred.
post #1460 of 1608
I might be interested in a kit if that proves possible smily_headphones1.gif
post #1461 of 1608
Quote:
Originally Posted by davidsh View Post

I might be interested in a kit if that proves possible smily_headphones1.gif


Now that is one heck of an idea.

post #1462 of 1608
Quote:
Originally Posted by Hutnicks View Post
 
Quote:
Originally Posted by davidsh View Post

I might be interested in a kit if that proves possible smily_headphones1.gif


Now that is one heck of an idea.

Isn't that the idea? Seems we talked about just that earlier in the thread. A kit, also with a bit of mylar in the package, that would be perfect. Only a housing, some wires, suitable coating and some stretching is needed then.

post #1463 of 1608
OK, what do you mean by a kit? A set of 4 PCBs or an assembled capsule with a pretensioned diaphragm? That is a much bigger ask.

Edit: Cross post - I see what you mean by a kit.

I can visualise building a stretcher to apply a constant tension from diaphragm to diaphragm, but that would be a time consuming task to calibrate, and would probably force me to take on MOT status, which I am reluctant to do, whereas I could supply PCBs at cost+, which I do already for other items.

There is also the question of which of the 2 designs to go with.

Our wonderful health service are spending tens of thousands of pounds on my treatment, no-one has suggested that I have less than six months left. At the same time I don't have so much to leave my wife and pets that I would want to burden them with the expense of unsold boards, so I'd need some assurance that they wouldn't be sitting on my hands.

I am happy to make the Gerbers available if anyone wants to pursue getting their own PCBs made.

Fred
Edited by wakibaki - 7/10/14 at 3:50pm
post #1464 of 1608
Thread Starter 

Hi Fred,

 

0.6 mm spacer is definitely OK.  You'll just need to turn up your volume a little more when listening.

 

I've been using 1 mm PCB as stators.  I think it's good enough.  Stax's SR007 has 0.8 mm stators, but they're double sided PCB.  I'm not sure if the extra copper on the other side adds up to its capacitance though.

 

About the two headphone designs, if I were to choose for you, I would go with the round one.  For one thing, the ear pads are a lot easier to buy - if you choose not to make them yourself.  With good diaphragm tensioning, I'm very sure they can sound as good as the Original Omega.

 

If I can do anything to help, please let me know.  :wink_face:

 

Wachara C.

post #1465 of 1608
Thread Starter 

After getting the headphones back from Tyll, I sanded and repainted my wood cups with Danish oil, and they look so much better than with polyurethane.  :L3000:

 

 

 

The phones sound very nice even with a cheap Stax SRM-252A.  :bigsmile_face:

 

post #1466 of 1608
Heineken! You deserve a better beer for such a good repainting job!
post #1467 of 1608

Hello to all...

 

...and congratulations to your remarkable results. Even though I have known about ESLs I have only started documenting seriously for a few days and the amount of enthusiasm from all the DIYers who got to finish making headphones or speakers got to me, too. Unfortunately, for now all I have are ideas and plans, for the lack of means behind them, but that may change in the future as I plan to actually build (at least) a pair of headphones, even if it's just to satisfy my curiosity.

 

Still, I have a few questions that, after reading all(!) the 98 pages, seem to be unanswered and I couldn't find information in other links, even though I can make some guesses. In the end, what I value most is a practical answer to a theoretical one, so here it goes:

 

1) For a direct drive amplifier -- considering an average one -- what would be the peak voltage at maximum swing? For example, I have seen examples of tube amplifiers supplied at +/-350V, so the peak voltage must be at ~20V~30V, but I have also seen a solid-state amplifier supplied at 300V, which would imply at least half peak voltage (150V), so I am confused.

 

2) Since the capacitance of a headphone speaker is very small, by my calculations less than 100pF (for example a 100x100mm square with +/-1mm spacing would have, in theory, 44.25pF, not counting dielectrics&co), will a series resistance with high values (kOhms up) influence the response or can it be left there to prevent accidents (wire breaks, touches your face). I know the biasing supply is no danger due to the ~tens~hundreds of MOhms series resistance, but the signal wires are a different matter. For example, for a 50pF headphone and a 100kOhm series resistance, the -3dB frequency would be ~32kHz, no worries for the spectrum, but also harmless for a high-voltage swing in case any accident happens.

 

There may be more questions about minor details like these but, for now, it's these two, only.

 

 

Anticipated thanks,

Vlad

post #1468 of 1608
Thread Starter 
Quote:
Originally Posted by arnaud View Post

Heineken! You deserve a better beer for such a good repainting job!

 

:bigsmile_face:  Unfortunately, we don't have that many selections around here.  

post #1469 of 1608
Thread Starter 

Hi Vlad,

 

Welcome to the DIY world.  :L3000:

 

1.  For typical tube amps, the amps are coupled with output transformers, and therefore the output voltage swing isn't all that high.  However, the amps for electrostatic headphones are connected directly to the headphones.  The voltage swing is as much as the power supply.

 

2.  Voltage swing from an amp can indeed be lethal.  So, we have to make sure that the headphones are safe enough to wear.  We normally use single sided PCB as stators.  The insulated side is safe enough for headphones.  The dust cover also acts as an extra protection.

 

Wachara C.

post #1470 of 1608

Hello Wachara

 

And thank you for the welcome. If the voltage swing, for a direct drive amplifier, is as high as the supply, then it goes into saturation (clipping). Normally the output stage has to stay within the linear region so as to have as little distortion as possible. While they can go rail-to-rail in theory, in practice it would be lower.

 

Still, by pure luck, I found with Google an article from TI, snaa046, which gives an example of solid-state amplifier and some numbers: for a 400V supply (class A), output has ~200Vpp and its supposed to be able to drive Stax type 1 headphones (whichever those may be, I have never had any in my hands). At any rate, that was the info I needed.

 

On the other hand, I see no series resistor to the output, so, even if the plates and stator are isolated inside the earcup, the wires might still present a problem if they somehow break (I have seen, many times, people feeling a sudden urge to get up, forgetting the headphones they were wearing, and this is just one example... :-) ). The resistor cannot carry high current since the impedance for a 50pF at 20kHz is ~63.7kOhms, so with the 200Vpp (from TI's appnote) there would be ~1.11mA RMS (thus ~78mW dissipated power). In theory, a 10kOhm resistor could be placed in series and the gains would be: no sacrificed bandwidth and protection against high-voltage signal (not to mention it would be the cheapest protection of output stage at shortcircuit).

 

Well, thank you for the answers and, if I'll have more questions, you'll know... :-)

 

 

Vlad

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