[100VoltTube]

@Muamp Nice headphones yet again. I'm envious of your Pink Floyd experience. 

 
I'm becoming proficient with librecad, so I should be able to make a pair of headphones soon. My time recently has been consumed with an OTL amp build; basically a crack with a different input tube and a different operating point for the output one. It sounds good, but is buzzing.
 
I have yet to make a diaphragm tensioner or an amp. I'll make an energizer (trafo box) for now, then a direct drive amp. I have been working on a design and consulting Kevin Gilmore. That design should be finished soon.
 
For tensioners, where did you get your tire from?

 

[Muamp]

Hi 100VoltTube,

The Pink Floyd was good, but if you haven't listened to Gorecki's "Symphony of sorrowful songs"' then I really recommend you do a spotify on it.

I currently use a tyre stretcher, a 12" diameter bicycle tyre. I bought it from Halfords (car & bicycle shop in UK). It fits perfectly on the rim of a 'Celebrations' plastic sweet box. I cut a hole for the tyre valve. Insulating tape or duct tape to tape one edge of the Mylar round the back and onto the other side. Then pump up the tyre.

To test the tension, after the spacer is glued, I use a wooden stick to tap the rim whilst holding the rim tightly. I measure the resonant frequency with a microphone and Audacity software.
Some one early on in this thread said Stax resonance on the membrane is between 120Hz and 150Hz.

I am still experimenting with different tensions. I do tension it VERY tight. I am testing tensions from 3% to 5% stretch. 5% is very tight and has a resonant frequency of about 175Hz. (2um Mylar).
I am still testing, but when finished, I will publish a chart of tension to resonant frequency.

David.

 

[100VoltTube]

Ok Thanks. I thought that you needed a special type of tyre (or tire).

I actually have a Celebrations tin as well, but I also have a Cadbury's Roses tin handy. Decisions, decisions... (For anyone interested in using a chocolate (or sweets) tin, but doesn't have any, I would recommend a Roses. You would need to dispose of all the chocolate before you can use it as a stretcher.

) Edit: roses tins are smaller, but not by a ton.

I have 3 micron mylar, so I might need to stretch a different amount. @chinsettawong might have experience with that detail.

I will check out Gorecki's "Symphony of sorrowful songs" Thanks for the recommendation.

With regards to the chocolate tins, in case you were wondering, I am in the US, and it is not normal to have Roses and Celebrations tins lying around. I have Irish family who send them over sometimes.

Also, for those of you who who have amps with variable bias, how do you do it? The only ways I am currently aware of that provides variable bias efficiently is using a 555 or similar chip to create AC at a voltage controlled by a potentiometer, then to feed the AC through a voltage multiplier, or to use a FET (or tube) as an amplifier, amplifing a control voltage, with a very high voltage power supply created by a voltage multiplier fed by the mains. That last one might sound confusing, and if anyone is confused or interested, I can post schematic.

Edit: Also, a simple voltage divider with a trim pot will work fine

 

[chinsettawong]

I don't stretch the diaphragm that much anymore. For the last few pairs that I made, I stretched the diaphragm only until it's just enough to give good stability. I had to do and redo again about 4-5 times before I got them just right. It's not an easy job. In the future, I will try to make a small table and use the weights to tension the diaphragm. If I can get it right, then making the next pair would be very easy.

Wachara C.

 

[Muamp]

A month ago, I made a stretcher with eight 2 litre (milk) bottles, all full of water. 1 litre of water = 1kg.
This gives a total of 16kg evenly distributed around a round frame.
I measured the stretch at 1%. This was NOT enough.
I thought of doubling the weights up to 32kg..... a lot of milk bottles.
That is why I went back to the tyre (well,.. inner tube) stretcher. The tyre stretcher will go upto 5% at full stretch.
Then I measure the resonant frequency with a microphone.
Wachara C., If you use weights to stretch, how much weight do you use?

David.

 

[100VoltTube]

Wachara, would you mind posting your CAD files for a pair of floats? Not the images, but the DXF's or whatever format they're in. 
 
To all: How do you hold your drivers together? Do you use glue or screws?
 
With regards to stretching diaphragms, I think that the thickness of the membrane makes a difference. what works for 2 micron membranes won't work for 3 micron.

 

[Muamp]

Hi 100VoltTube,

The way I hold my drivers together is by clamping them within the surrounds. I firstly use insulating tape, tightly holding in 6 places evenly distributed around the circumference. This acts as a way to keep them in place before clamping in the surround. Then the surounds hold everything together when enclosed.
A lot of people drill bolt holes and use nylon bolts.
The guys who make big floor standing ESLs use glue.

2u or 3u - The choice is yours..... Same principles for both. Both good.
I use 2u. If I had 3u I would try it, but happy to stick with 2u.

David.

 

[chinsettawong]

Hi 100VoltTube,
 
Here is my stator dxf file for JF clone:  https://www.dropbox.com/sh/ox8vc6x8wqyr1pw/AACTBT-cLVb4rvbXRtZKwsTLa?dl=0
 
I don't mind sharing my designs as long as people don't use them for commercial purposes.

 

[100VoltTube]

Thanks! Could you post the spacers too? I'm interested in having a reference pair of the exact same design as you so that we can compare to a reference. I notice that for the most part, people have been comparing their headphones to the SR-009 and SR-007, but as far as I'm aware, no one in my area has a pair. There are multiple Focal Utopias, an Orpheus, and a few R10's, but no Staxes other than lambdas that I'm aware of.

 

[chinsettawong]

Hi 100VoltTube,
 
I've just updated the link to my CAD files.  Please check.
 
If you have any idea, please share it too.
 
Wachara C.

 

[ts8051]

Hello,
I  downloaded the files and please let me know if these are pieces of pcb boards fully covered by copper layer. If yes, there is a mistake in design because the capasitance between stators and spacers is high and there is a problem with high frequencies. 

 

[chinsettawong]

 
Hello,
I  downloaded the files and please let me know if these are pieces of pcb boards fully covered by copper layer. If yes, there is a mistake in design because the capasitance between stators and spacers is high and there is a problem with high frequencies. 

 
Hi ts8051.
 
Etching out the unneeded copper around the stator or not is totally up to you.  There is actually no problem with high frequencies if your amp is capable of driving it.  I like to etch it out, but some of us here leave it there.  It actually sounds warmer if you leave it there.  Try it.
 
Wachara 

 

[analogsurviver]

 
Hello,
I  downloaded the files and please let me know if these are pieces of pcb boards fully covered by copper layer. If yes, there is a mistake in design because the capasitance between stators and spacers is high and there is a problem with high frequencies. 

Aside mentioned problem, there is another aspect - that of possible arcing across the sharp demarcation edge of the stator and diaphragm if striving for the highest efficiency when you remove the copper layer under the spacers. Depending on the actual implementation of the driver and amplification, both variants can be viable. 

 

[ts8051]

Hello,
I will try. Now I have a CNC machine and I can try with minimum cost. 

 

[ts8051]

Hello again,
I show that on the stator you have many holes per inch and a center big hole rectangle in shape. Why you have this central hole ? I think that  the high density in stator holes minimizest the strength of electrical field between stators and also zero in the center of stator.