GERMAN Version
Last update 16. August 2001
Index
Introduction
How it works
Instructions for building
Parts
Resonanz coil
Working Instructions
The End
Update 8/2001
The new Modulation Part is finished. It is now a
complete Tube design. The modulator is now more efficient. The old
transistor modulator, you find the schematic in the builders links, was
not the best. With the new modulator the tweeter can play louder ! You
can connect the modulator direct to the Loudspeaker output of your amp.
The modulator need no power from your amp because it is voltage driven.
Only 2Vss is needed for full output.
Schematics
Pictures
Introduction
The first time I heard a Plasma-Tweeter was at a Hi-Fi show in the
80´s. I was really impressed by the sound. I had also the chance to
talk to the development engineer Dr. Siegfried Klein but he told me
nothing about the functional details. Few years later a defect IONOFANE
601 Plasma-Tweeter was brought to me for repairing. With this sample I
was able to study the details and built my own prototype.
back to Top
How it works
It is really simple. It is a modulated RF power amp with a controlled ionic discharge.
By modulating the oscillator with the audio signal the flame size
changed and so the air pressure changed also . You hear the sound
directly through the air without modulating a diaphragm.
So there are no moving parts, no distortion and none of the problems
other tweeters have. The signal is quite low in level ( I measured 82
dB with my prototypes ) but it is the cleanest sound I ever heard. I
use no horns to increase the sound pressure so you dont have to sit in
axis of the tweeter, the sound is everywere in the air.
You need a lot of RF power to get a ionic flame so I use a tube
(valve). I choose a EL519 you can also use a PL519, the PL has only a
different heater voltage ( 40 Volt / 300 mA ). The RF power is easily
modulatet on G2 of the valve. I use a transistor, it was the simplest
method for the prototype. ( Aug. 2001 )The tube modulator is now finished.
|
|
The loudspeaker input go´s through a passive 6dB crossover to the first
tube. With the 47K resistor and the 1n cap the crossover frequency is
at 3,4Khz. I messure the frequency response at a distance of 1 meter with passive crossover at 5Khz.
The ripple you see in the curve is from the room because I measure in 1m distance.
|
|
|
For the picture the gain control was put to maximum to get a large flame. In normal operation the flame is appr. 5mm high. |
Click on the thumbs for large pictures.
back to Top
Instructions for building
Please note that a careful building in a steel or aluminium chassis is
strongly recommended. The part with the power tube and teslacoil is
covered with perforated steel. The holes are 3 to 6mm. There is a lot
of heat coming out.
I have divided the tweeter in two sections. One section for the tube
and teslacoil and one section for the rest. If I had a second chance I
prefer 3 sections to separate power and amplification because it was
not so easy to get the noise from the powersupply away from the
amplifier. The sections are separated with a aluminium plate. I use
this plate also as heatsink for the transistors. In the perforated
cover I cut a 50mm hole over the place were the teslacoil is
positioned. The electrode of the teslacoil comes out of this hole. Over
this hole I put a ball made of 2 teasieves, which I soldered together.
In that ball you have to drill a hole ( 6mm dia.) in the height of the
electrode. See the ball picture how this looks like.
That's the mechanical part. The potis and connectors are placed on the rear.
See rearpicture. The wireing is like in old tubeamps "free air". Be careful with the grounding otherwise the speaker gets hum !
back to top
Parts
I tried to use standard parts. The transformer is a 120VA type,
secondary voltage 230V. The heater voltage depends on the tube you use.
For the EL519 you need 6.3V, for the PL519 you need 40V. All resistors
are 1Watt metall types. The 18 Ohm Anode resistor is a 5Watt wire type.
The RF coil ( DR in the schematic )is a Siemens 100uH / 1Ampere type. I
tried other RF coils but they did not work properly. ( If someone has
realy problems to get this type of coil, I have some spares but this is
not my business)
back to top
Resonanz coil
|
|
This is the main part of the speaker. You have to build it by
yourself. Don't worry it is easy. You can even do it with a glass of
beer or wine on the building desk.
What you need is a ceramic body with 35mm diameter, aprox. 70 mm long (
length is not critical). I get my ones on a ham radio flea market. ( I
spent 5$ ).
The wire I use is 0.9mm paint isolated copper wire. It is often used by
radio amateurs. You have to make 15 turns on the upper end of the
ceramic body. +/- 1 winding is not critical. My ceramic body has little
holes so I could easy lock the wire with screws. At the top end I fixed
a 30mm long electrode made of 3mm copper wire with little screws to the
end of the coil. You can't solder it because it get very hot. At the
bottom end of the electrode we need a "free air" 3/4 turn for the
feedback to the grid of the tube. I use 0.5mm teflon isulated wire.
Details you can see on the photo. |
I got many questions about building the resonanz coil so here are
some detail pictures . Click on the thumbs for larger pictures, use
your browsers "backbutton" to come back.
back to top
Working instructions
Some comment for working. Flame size depend on how good is the tube.
The flame does not start itself ! It needs a little help. Put the poti
for flame size in middle position. Turn the power on. Wait two minutes
until the tube is ready. If you wonder about the little hole in the
elektrode cover here is the answer.
You have to put a little isolated ! screwdriver trough the hole to the
electrode and pull it slowly back. A ionic discharge between electrode
and screwdriver will happen. If you pull back the screwdriver
completely the discharge will be established between electrode and the
air. If not turn the flamesize poti to more gridvoltage and try again.
The circuit is designed to work in paralell with your speakers. With
the volume control you can match it to any speaker. But note the
speaker has only about 82db efficiency. If your main speakers are
louder you have to match it. The flame size in operation is appr. 5 -
10mm thats enough for music. If you want more level or "show" flame
size can be adjust higher. ( 20 - 40 mm depending on good tubes)
back to top
Builder's
Here are the links to people who build this tweeter :
http://www.geocities.com/ResearchTriangle/Thinktank/1866/plasma.htm Allessandro Galavotti has build a working prototype
http://www.ece.villanova.edu/~cdanjo/plasma.html This is Colin, Joye's page with very usefull tips for building
http://www.hardcoreaudio.de Sebastian Mainka a German has buid it. His site is only in german.
http://members.aol.com/andreragee This is the Tweeter from Mr. Andrerage from France. His Site is in french.
http://homepages.ihug.co.nz/~andrewp/plasma_speaker.html Andrew Parsons from Hamilton , New Zealand
The End
One thing on the end. The speaker produce OZON. Normaly this is a
radical and dangerous to your health but with the little amount the
tweeter can produce there is no danger at all. After hours of operation
you smell it in the air in closed rooms. Open your doors and it is
away. So good luck if you want to build it and let the ionic force be
with you.
Ulrich in August 1998.
back to top
This page is
optimised for 1024*768 viewing area. I take no responsibility for the accuracy of
information in these pages, or consequences of doing something
stupid after reading these pages. (c) Ulrich Haumann, 1999, 2000, 2001
This page is part from WWW.PLASMATWEETER.DE