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Old 3rd May 2010, 01:49 PM   #21
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Hi,

Quote:
Originally Posted by zhoufang View Post
1200V RMS figure is encouraging, as I have hear tens of kVs from other places, which is impossible for direct drive.
Disregarding all else tens of KV drive would imply tens of KV Bias. At such voltages making things work with reasonably small gaps and solid insulations will be great fun... Even at Kilovolt levels it gives me the heebee jeebees...

Ciao T
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Old 3rd May 2010, 03:33 PM   #22
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The max bias voltage is related to the insulation used and the breakdown of air.
6kv seems to be a practical maximum... the current in the bias voltage is nil... not in the drive though...

Since ESLs are a capacitive reactance, the "transformer" or direct drive amp can only match properly at one reactive impedance, aka at one frequency.

Peter Walker covered this fully in his articles in the British magazine Electronics World (iirc) back in the 1950s.

This is one reason that his Quad 57s are a three way system.

He showed that you could match for high sensitivity, and get narrow bandwidth, or match for wide bandwidth (eg. Martin Logan CLS?) and not get high sensitivity.

The trade offs come in terms of voltages, voltage ratios and input impedance, as well as the frequency response...

Strickland taught a neat solution to the problem - use two transformers on the same cell!

So, most "direct drive" amps afaik need equalization to get a flat response...
(as do most single transformer drive methods...)

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Old 5th May 2010, 10:10 AM   #23
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It is a pain to drive electrostatic transducers properly and even the headphones require amps that are beasts. Stax realized this and marketed the SRM-T2 which is 18kg, draws 200W+ from the wall and runs hot enough to cook eggs on it (60C+). Our DIY version of that circuit is even more insane...

Quote:
Originally Posted by chinsettawong View Post
Hi,

If any of you are interested in making electrostatic headphones, have a look at my thread: http://www.diyaudio.com/forums/headp...headphone.html

Wachara C.
I somehow missed that project. Since the driver specs are similar to what Stax are doing (0.5mm D/S spacing) has anybody tried them off a Stax Pro bias amp? Also, if you are looking for a cheap 6-core ribbon cable, get somebody in the US to buy for you Koss ESP950 extension cables. They were about 10$ last I heard which is a lot cheaper then the Stax cables. When I was experimenting with DIY 'stat panels that's the cable I used for them.
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Old 5th May 2010, 12:42 PM   #24
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Quote:
Originally Posted by ThorstenL View Post
Disregarding all else tens of KV drive would imply tens of KV Bias.
Why is that? (I'm not second guessing, just enquiring.) In my understanding, the bias voltage only determines the charge on the diaphragm, and therefore the efficiency. In my understanding, it can be made much lower than the drive voltage -- there will be a penalty in efficiency, not in sound quality.

Kenneth
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Old 5th May 2010, 02:43 PM   #25
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Quote:
Originally Posted by spritzer View Post
I somehow missed that project. Since the driver specs are similar to what Stax are doing (0.5mm D/S spacing) has anybody tried them off a Stax Pro bias amp? Also, if you are looking for a cheap 6-core ribbon cable, get somebody in the US to buy for you Koss ESP950 extension cables. They were about 10$ last I heard which is a lot cheaper then the Stax cables. When I was experimenting with DIY 'stat panels that's the cable I used for them.
Hi Spritzer,

Can you please let me know where in the USA I can buy the Koss ESP950 extension cable?

Wachara C.
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Old 5th May 2010, 03:07 PM   #26
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Quote:
Originally Posted by chinsettawong View Post
Hi Spritzer,

Can you please let me know where in the USA I can buy the Koss ESP950 extension cable?

Wachara C.
Directly from Koss is the only way I know of. I had a buddy in the US order them for me a few years ago but any of their distributors should be able to order the cable as well.
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Old 21st May 2010, 08:33 AM   #27
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This might already be covered... don't forget the headphone-to-ear interface is completely sealed (e.g. Omega 2). The leather pads form an almost air tight seal. You can push the drivers and hear the diaphram hitting the stators from the air pressure. You can get away with quite a bit because of this. A driver that sounds thin and lacking bass can be excellent with a sealed interface to your ear.
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