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Old 23rd December 2008, 06:40 AM   #1
j beede is offline j beede  United States
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Default Ever been shocked by bias supply or stator?

I'll admit to being knocked cold when I accidently discharged the bank of Rubycon photoflash filter caps in the power supply of a tube phono stage I built back in 1982. I was working alone and late at night, the supply had been shut off for a while. I woke up "later"under the workbench across the aisle. No lasting harm once my vision turned back after a few minutes. Two words--bleeder resistors. Lesson learned.

Have you ever discharged a diaphram in your ESL to youself? Ever provided a human conduction path between your stators? I am building ES headphones and am considering dropping the effort since it may be "stupidly" dangerous. I have 20 MOhms in series with the bias supply, but I am more worried about the HVAC on the stators. What has your experience been?
...j
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Old 23rd December 2008, 09:36 AM   #2
Calvin is offline Calvin  Germany
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Hi,

when working with a very high resistance coating discharging even large membranes won´t knock You down. Besides others this is a major advantage of high resistance coatings. Since the membrane is encapsulated betwen the stators this helps in getting in touch with it.
But it was kind of a rebirthing experience when I accidently touched one pole of the audio trannies while playing music.....what a beat

So its the stators where You have to put Your eyes on.
A grounded safety grid could be a possible solution, but it needs an extra wire for earth connection. As far as I know no commercial design did that. Attached is a exploded view of the Sennheiser Orpheus capsules. In the middle there are the two spacer rings of which one holds the diaphragm. Then follow the two stators which were made from special hard glass with etched holes to get the right degree of transmittance. The glass was gold sputtered (I was told (rumoured) that the gold plating didn´t proof to be longtime stable.
It appears as if the gold plating is insulated with a laquer towards the membrane-side, but not towards the outer side.
A pair of rings holding kind of a membrane or extreme fine mesh seems to function as a isolation barrier to the outside.
Quad uses the trick of encapsulating the panel with a very thin film. The film would feature the best insulation values, complete encapsulation of potentially dangerous parts, easy mounting, total acoustic transparency and low cost.
Since You most often have to add some kind of mechanical resistance to control the typical high Q-value of such ´open´ ESL-designs, a thin layer of acoustic foam (be carefull with colour!) will improve safety and should improve sonics too.

jauu
Calvin
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Old 23rd December 2008, 09:44 AM   #3
Calvin is offline Calvin  Germany
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Hi,

part II:

Within the wooden frame that houses the ESL-capsule two sheets of finely stamped steel protect the capsule from anything touching it.
Each capsule is wired by a three-wire-cord to the supply, hence, there is no PE-wire leading to the HP.

The bias voltage is 500Vdc and the associated amp could put out ~400Veff (1130Vpp).

jauu
Calvin
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Old 23rd December 2008, 12:10 PM   #4
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Dear J,

Don't stop! Once you have finished building it, you won't regret. If you are really worried, I have another full set of stator and spacer for you. They are made of one sided PCB just like mine. The side that will be touching your ear is fiberglass and it should be very safe. I bias mine up to 1200V and I dare to put them against my ears. If you are interested, let me know.

By the way, I got an electrical shock when I was building my ES headphone. It didn't hurt as much as the shock from the capacitor of a tube amp.

Wachara C.
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Old 23rd December 2008, 10:26 PM   #5
j beede is offline j beede  United States
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Actually the charge stored on the diaphram can do some harm... Years ago I was following the instructions from Acoustat regarding the discharging of a panel while detaching the interface box. The gunshot-like sound and bright spark casued me to flinch and I smashed my elbow into the equipment stand behind me as I relexively pulled back!

The Orpheus solution is a good one--grounded screen to shield fingers and outer ears from HVAC. Of course, from an electrical point of view, the stators are what I worry about. Quad used front (extruded) and rear (expanded) metal grilles on the ESL. Acoustat used way thick plastic stators (fluorescent light diffusers?) and cloth. Dayton Wright used plastic bags and grille cloth. Infinity used cloth grilles, same for Sound Labs, Koss and KLH. Other than Martin Logan (and DIY ESLs) what other ESL allows the stators to be touched directly? There are some small ESLs from Holland or Denmark that look like Martin Logans, they too may permit touchingthe stator.

How are you guys protecting yourselves and others from feeling the stator "pain"? Is there a coating I can apply in my basement workshop?
...j
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Old 23rd December 2008, 10:53 PM   #6
j beede is offline j beede  United States
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Quote:
Originally posted by chinsettawong
Dear J,

Don't stop! Once you have finished building it, you won't regret. If you are really worried, I have another full set of stator and spacer for you. They are made of one sided PCB just like mine. The side that will be touching your ear is fiberglass and it should be very safe. I bias mine up to 1200V and I dare to put them against my ears. If you are interested, let me know.

By the way, I got an electrical shock when I was building my ES headphone. It didn't hurt as much as the shock from the capacitor of a tube amp.

Wachara C.

Okay, okay, I'll keep going Wachara, what size holes and hole to hole spacing in your perforated PCB material? If I can find some aethetically pleasing, high carbon steel mesh I will probably adapt my design to include inner and outer grounded shields. I hat the idea of having to run ground wires--but I hate being shocked more! As I mentioned earlier, I worry about the reliability of the ground path to the shields--easy to forget about until they fail.
...j
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Old 24th December 2008, 08:31 AM   #7
Calvin is offline Calvin  Germany
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Hi,

@jbeede: If You want correct information...reading helps!
The Orpheus doesn´t use grounded grids!
The protector film has the advantage that it is a ´passive´ protection, that doesn´t rely on any connection to PE or special circuitry. Too even the smallest things that may protrude through to the stators or even the diaphragm, e.g. hair, is prevented from doing so. Ageing effects should be reduced as well.
A grounded grid probabely won´t prevent hair from getting in contact with the stators.

jauu
Calvin

oh, btw. My stators can be touched without any harm at full play too ;-)
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Old 24th December 2008, 02:12 PM   #8
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OK, I'll probably become the poster boy here!
Disconnected some Acoustat 2+2's from interface about 10 yrs.
ago to move (8ft ceiling, so had to dissasemble and tilt down
to get them out). It's a nice quick jolt!, but is over in less
then a second. I know the Acoustats use about 5KV. to charge.
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Old 24th December 2008, 03:05 PM   #9
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Quote:
Originally posted by j beede



Okay, okay, I'll keep going Wachara, what size holes and hole to hole spacing in your perforated PCB material? If I can find some aethetically pleasing, high carbon steel mesh I will probably adapt my design to include inner and outer grounded shields. I hat the idea of having to run ground wires--but I hate being shocked more! As I mentioned earlier, I worry about the reliability of the ground path to the shields--easy to forget about until they fail.
...j

The holes are 2 mm and the hole to hole spacing is 2mm. I do not know the total open area, but they do really sound wonderful.

Wachara C.
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Old 24th December 2008, 10:29 PM   #10
j beede is offline j beede  United States
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Quote:
Originally posted by Calvin
Hi,

@jbeede: If You want correct information...reading helps!
The Orpheus doesn´t use grounded grids!
The protector film has the advantage that it is a ´passive´ protection, that doesn´t rely on any connection to PE or special circuitry. Too even the smallest things that may protrude through to the stators or even the diaphragm, e.g. hair, is prevented from doing so. Ageing effects should be reduced as well.
A grounded grid probabely won´t prevent hair from getting in contact with the stators.

jauu
Calvin

oh, btw. My stators can be touched without any harm at full play too ;-)
Hello Calvin,
Is it your habit to insult people whom you don't even know? I do read English rather well, your reply I cannot easily decipher.

You have measured the resistance to chassis ground from the formed screens on your Orpheus? Hard to imagine that Sennheiser would allow any metal to float in the presence of an electirc field. Why would I care if my hair touched a stator? I should think that woven hair would make a fine, if impractical stator insulator. You have simultaneously touched your front and rear stators harmlessly? Are they coated like Martin-Logans?
...j
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