[chinsettawong]

Hi BillG,
 
You're very welcome here.  As I see it, you are no beginner and your experience can surely help us here.
 
I'm very interested to learn about how you make the electret diaphragm.  Can you please teach me?
 
If you have any questions, please do not hesitate to ask. 
 
Wachara C.

 

[Pirx]

analogsurviver < Thanks for explanations. It seems worth trying then

 

[analogsurviver]

  analogsurviver < Thanks for explanations. It seems worth trying then

The original article from Wireless World 1979 : http://www.amateuraudio.fr/images/ww5.pdf

 

[Ali-Pacha]

   
That's the kind of design I don't like.  By the way, are those spacer rings metal?  Or are they made of PCB?
 
The problem could come from the coating deteriorates over time especially around the corner where it's suppose to contact with the charge ring.  If the rings are made from metal you might want to put more coating around the inner circle edge to help getting the bias voltage from the ring to the diaphragm.
 
By the way, I think your coating spray works just fine.  Otherwise, the sound should be softer as you have already cleaned out the old coating.
 
Wachara C.

Hi Wachara,
 
I've made further investigations :
- spacer rings on my SR-5/NB look like PCB, where those from my SR-X are stainless steel / aluminum
- I've tried more agressive coating with my SR-X right channel (still crackling) : lots of coating with a very light brush, especially around the inner circle edge, then slightly wiping coating marks / residues with microfiber tissue. Mint looking when finished (no holes, no black points)
The result : almost no more sound on this unit ! 
 
My coating is crap indeed, I've to test anything else. Anyone did test rinse aid ?
 
Ali

 

[BillG]

Thanks for the link to the Wireless World 1979 article.  I've just finished reading it and noticed the fairly close correspondence between what he had done and what we have been doing here in this thread.  One thing that hit me right off was that the author was applying polarizing charge to both sides of the diaphragm (I'm not sure that it matters).  The other point he made was that coated diaphragms were not generally needed unless the charge had bled off and the relative humidity was extremely dry. I think our anti static cleaner/gel takes care of that nicely. I think that today's 3 to 6 micron thick mylar will be a far better performer. 
 
What was most important to me at this time was the description and schematics for the solid state amplifier and power supplies.  Working on a retired persons very limited income, this has some very obvious benefits for me.  Has any one of the members used this amplifier or something close to it, and how do the more modern headphones sound when they are powered by it.  Sure I would like to use Wachara's lovely tube amp but I don't want to go whole hog just yet. I'm amazed by the cost of transformers today compared to what we used to buy them for in the "old days".
 Regards,
BillG

 

[BillG]

Ali,
Can you swap over the leads from left to right and see if the crackling changes sides?  Just a thought.
BillG

 

[analogsurviver]

  Thanks for the link to the Wireless World 1979 article.  I've just finished reading it and noticed the fairly close correspondence between what he had done and what we have been doing here in this thread.  One thing that hit me right off was that the author was applying polarizing charge to both sides of the diaphragm (I'm not sure that it matters).  The other point he made was that coated diaphragms were not generally needed unless the charge had bled off and the relative humidity was extremely dry. I think our anti static cleaner/gel takes care of that nicely. I think that today's 3 to 6 micron thick mylar will be a far better performer. 
 
What was most important to me at this time was the description and schematics for the solid state amplifier and power supplies.  Working on a retired persons very limited income, this has some very obvious benefits for me.  Has any one of the members used this amplifier or something close to it, and how do the more modern headphones sound when they are powered by it.  Sure I would like to use Wachara's lovely tube amp but I don't want to go whole hog just yet. I'm amazed by the cost of transformers today compared to what we used to buy them for in the "old days".
 Regards,
BillG

Regarding amp - good, but nothing to write home about. It is the same "rear end" as say Stax SRA-12S - I actually had to canibalize my Pollock amp to replace one blown output transistor in SRA-12S - which then later went belly up because of the transformer ( that thing is simply too small/too little cooled to be reliable in the long run ).
 
LM3900 chip is nothing special, today there are many better options. What does still hold true is the absolute necessity to use the best passive components you can possibly find - and afford. That goes particularly for the feedback capacitor - difficult  to procure in required voltage/value to begin with, adding high quality request compounds the problem further. 
 
Finding output transistors nowadays is getting ever harder. 
 
Power supply I guess would be pretty similar to that for Wachara's design ( I did not look into it - yet ) ; output transistors or tubes are also more or less the "same" - built with quality parts ( which IS a must if you want your amp to sound better than conventional amp + transformer box/energizer ), one does not save much $ by going with so simple/cheap front end in the overall sense. 
 
It took me one hell of a better amp to remove even the faintest possibility of an idea that transformer might be better than direct high voltage amp.  But - at $$$$$$$$$. 
 
I did not want to discourage you, just to make it clear it is not an equivalent of a factory built amp at a fraction of the cost. But it IS listenable.

 

[Ali-Pacha]

  Ali,
Can you swap over the leads from left to right and see if the crackling changes sides?  Just a thought.
BillG

Some other tests later... 

 
- rinse aid does work !!!!! Finish is ugly, but who cares when no one sees the mylar ?
- early SR-X/mk3 diaphragms have metal spacers since latest SR-5/NB have PCB spacers
- metal spacers are probably thinner than PCB ones : when I use a diaphragm from my SR-X in my SR-5/NB, no crackling (see below), but there is a clicking noise as soon as charge bias comes in (barely noticeable on SB boxes, indeed)
- crackling noise from my SR-X has nothing to do with diaphragms nor cable, but there is probably something with the stators on both sides
 
All these facts except the first one should rather be on a Stax thread, but I'll sleep a bit less dumber tonight.
 
Ali

 

[davidsh]

So you tried the rinse aid for repairing your bugged out sr-5? Glad to hear it works!
I've got a question about the general principles of electrostats. Basically, we are talking a charged film suspended in a varying electric field. Anyway, the charge on the film is one variable that is correlated to the efficiency of the 'stat. The charge depends on the capacitance of the film and the voltage, no?
What determines the capacitance of the film, though? Can you somehow alter it?

 

[chinsettawong]

Hi davidsh,
 
When you want to change the efficiency of the electrostats, you either change the bias voltage or the spacer thickness.  The capacitance on the film has nothing to do with the efficiency. 
 
What you want to achieve when coating the diaphragm is that you want it to be conductive and hold the charge for as long as possible.  The coating materials that I recommended in my earlier posts will give the resistance of around 10-100 M ohm per square.  Think of the diaphragm as a capacitor and the coating as a bleeding resistor connecting on it.  The bleeding resistor slowly bleeds away the charge.
 
Wachara C.

 

[BillG]

  Hi BillG,
 
You're very welcome here.  As I see it, you are no beginner and your experience can surely help us here.
 
I'm very interested to learn about how you make the electret diaphragm.  Can you please teach me?
 
If you have any questions, please do not hesitate to ask. 
 
Wachara C.

Hi Wachara,
That really goes a long way back.  There wasn't a lot to it.  I machined an aluminum cup about an inch in diameter outside, and 3/4" inside.  A short distance down from the rim of the cup there was a small flange. Next I made a ring which fit over the cup and was screwed down with nylon screws  to the flange.  The  aluminized mylar film was held over the top of the cup and the ring was bolted down to the flange tensioning it somewhat. with everything properly insulated I connected a 300VDC power supply between the cup and the conducting side of the mylar. The capsule cup and mylar then went into a household baking oven, power was applied, the oven raised to some 350 degrees F.for about an hour.  Then the power supply was turned off and the oven left to cool slowly.  The mylar was charged and the assembly converted for use as a microphone.  It worked as a microphone into a high impedance vacuum tube amplifier (hi gain stage). and was still working more than a year later.  Sorry, but that is all I can tell you about it. 
 
You might want to try that procedure with one of your Jacklin Float capsules.  I have no idea how much if any volume you could get with it.  Let me know if you have any success at all. Regards,
BillG.

 

[davidsh]

  Hi davidsh,
 
When you want to change the efficiency of the electrostats, you either change the bias voltage or the spacer thickness.  The capacitance on the film has nothing to do with the efficiency. 
 
What you want to achieve when coating the diaphragm is that you want it to be conductive and hold the charge for as long as possible.  The coating materials that I recommended in my earlier posts will give the resistance of around 10-100 M ohm per square.  Think of the diaphragm as a capacitor and the coating as a bleeding resistor connecting on it.  The bleeding resistor slowly bleeds away the charge.
 
Wachara C.

What puts me off is that coloumbs law states that the force exerted on a static object in an electric field depends on the charge of the object and the magnitude of the electric field (the electric field depends on spacer thickness and the voltage potential between the stators).
The charge that the diaphragm will hold is dependent on the capacitance of the diaphragm as well as bias voltage as I see it. In other words the number of electrons that you can stuff onto the diaphragm.
 
More charge = more electrons = more capacitance and voltage = greater force

 

[dude_500]

  What puts me off is that coloumbs law states that the force exerted on a static object in an electric field depends on the charge of the object and the magnitude of the electric field (the electric field depends on spacer thickness and the voltage potential between the stators).
The charge that the diaphragm will hold is dependent on the capacitance of the diaphragm as well as bias voltage as I see it. In other words the number of electrons that you can stuff onto the diaphragm.
 
More charge = more electrons = more capacitance and voltage = greater force

 
This is all true, however the only thing affecting capacitance here is surface area of the film/stators, and the distance between the film and the stators. Coating material or thickness does not affect capacitance (of course you have to reach a certain amount of coating in order to actually charge the capacitor, but that is all).
 
So, to increase the capacitance, you either increase the surface area, or decrease the area between the two stators. C = epsilon A / gap

 

[chinsettawong]

You don't really want to have high capacitance.  That will put more load on the amp and the high frequencies will be tamed down.

 

[davidsh]

Thank you, I am acquinted with what both of you said. I am merely stating that to my logic the force on the diaphragm also depends on the charge of the diaphragm, eg. how many electrons there are on the diaphragm. Any thoughts?