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Protecting the audio source from a plasma speaker

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Franky

Sat Oct 29 2011, 02:41PM

Registered Member #1940 Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34

Dear all,

I have been building plasma speaker for several years now. I always used my computer as an audio source. I placed an old computer speaker with a headphone output between the computer and the plasma speaker. This seems to work well. My computer never died. However, the old computer speaker is a really bad one. It is causing strange noises in my plasma speaker. Up till now the sound quality of the plasma speaker itself was the limiting factor. Not any more. So it is time to replace the old computer speaker.

How do you guys protect youâ€™re audio source from the plasma speaker?

Many thanks in advance!

Frank

Antonio

Sat Oct 29 2011, 03:29PM

Registered Member #834 Joined: Tue Jun 12 2007, 10:57PM
Location: Brazil
Posts: 644

You are not protecting anything in this way. Almost surely when you plug the plasma speaker input plug in the socket you are connecting it directly to the computer.
A true ground connection and a pair of zener diodes (in series) across the audio line is probably enough.

Xray

Sat Oct 29 2011, 04:28PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

Franky wrote ...

Dear all,

I have been building plasma speaker for several years now. I always used my computer as an audio source. I placed an old computer speaker with a headphone output between the computer and the plasma speaker. This seems to work well. My computer never died. However, the old computer speaker is a really bad one. It is causing strange noises in my plasma speaker. Up till now the sound quality of the plasma speaker itself was the limiting factor. Not any more. So it is time to replace the old computer speaker.

How do you guys protect youâ€™re audio source from the plasma speaker?

Many thanks in advance!

Frank

What do you mean by "protect your audio source from the plasma speaker"? I also have a plasma speaker, and it does not do anything weird that would damage my audio source!

It would help if you could show us a schematic diagram of your plasma speaker. That way we could determine what (if anything) might damage your audio source.

Franky

Sun Oct 30 2011, 08:43AM

Registered Member #1940 Joined: Tue Jan 27 2009, 02:34PM
Location: Netherlands
Posts: 34

Antonio wrote ...

You are not protecting anything in this way. Almost surely when you plug the plasma speaker input plug in the socket you are connecting it directly to the computer.
A true ground connection and a pair of zenerdiodes (in series) across the audio line is probably enough.

Not directly. My first plasma speaker was plugged into my walkman. This didnâ€™t work because the walkman went crazy. Stopping and starting the tape, going in to reverse etc. Placing the computer speaker between the plasma speaker and the walkman solved this problem.

A true groundâ€¦.. I think the closest I can get to a true ground is connecting it to the radiator of the central heating in the house. I hope that is good enough.

Pair of zener diodes you say. I guess you mean something like this.
Audiojack

Xray wrote ...

What do you mean by "protect your audio source from the plasma speaker"? I also have a plasma speaker, and it does not do anything weird that would damage my audio source!

It would help if you could show us a schematic diagram of your plasma speaker. That way we could determine what (if anything) might damage your audio source.

For example this schematic. This is the first schematic I used. It definitely gave problems with the audio source (as described above). This is a bad schematic. But I'm not taking any chances with my new computer.

I'm wandering... Can a computer audio output withstand a short-circuit?

Xray

Sun Oct 30 2011, 05:01PM

Registered Member #3429 Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288

There are a couple of things that could be causing erratic behavior of your audio source. You are obviously getting high frequency pulse "noise" from the fllyback driver circuit into your audio. One thing that I noticed in the schematic you show is the lack of a power supply bypass cap between the 12v rail and ground. It's good practice to put a relatively large electrolytic cap (say, 470uF, AND a small ceramic cap, say, 0.1uf) across the power supply input connections. You also should pay attention to your component layout. That is, keep the high power, high frequency components (such as the mosfet and the flyback) away from the audio input components. The schematic diagram is laid out in much the same fashion as the phyical layout should be. The audio input is on one side of the drawing, and the mosfet/flyback is on the other side. You'll run into trouble if you have a "U" shaped circuit, where the output wires wrap around to the same side of the circuit board where the audio input is located. That's a common mistake that new electronics hobbyists often make. It may also help to reduce erratic behaviour in the audio source by placing ferrite beads on the audio source wires. Those beads look like tiny torroids, and they help to keep high frequency noise from getting into the audio. Another thing that might help is to mount all of your plasma speaker components in an aluminum enclosure (except for the flyback of course). The enclosure will help to shield all the components that generate electrical noise.

Those things that I mentioned could help reduce the noise problems that you are having. Those, in addition to the zenor diodes that were also mentioned, should protect your computer from getting damaged by your plasma speaker.

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