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Help please with notch filter

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Serratus

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Hi everyone,
I am a newbie here, and a bit of a novice with electronics, so any replies in straight forward english if possible please!

I am attempting to put lights into an electric guitar and want to use EL string, which runs from a 4KHz invertor and 1.5V batteries. Unfortunately the 4KHz tone produced by the invertor can be heard through the electronic pickups of the guitar. So I think I need to put a notch filter into the guitars wiring to cut out the 4KHz tone (I realise that this will also affect the tone of the guitar, but I think if the filter only cuts out a narrow bandwidth then this will not make too much difference).
After a bit of research I think I may be able to do this with a MF10CCWM capacitor filter, but I don't know anything about them or how to use them. So can anyone tell me if this will do what I want, and if so how do I use it? (I think I have to put certain resistors across certain contacts on the MF10 to get the desired frequency and Q, and I guess that using certain contacts uses the MF10 in different ways - ie as a notch filter, or high-pass, etc, etc ???).

I would really appreciate any help you could give me.
regards,
Rich
 

E-design

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Why don't you get a inverter that runs above the audible freq range (>20kHz)?
 

Serratus

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E-design said:
Why don't you get a inverter that runs above the audible freq range (>20kHz)?

Good idea, but as far as I know the only invertors I can get to run EL string are all within the audible range (from around 900Hz to 6500Hz), I'm not even sure that the EL string will run off that high a frequency.
 

Sceadwian

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Have you tried shielding the inverter? Using a metal case connected to the circuit's ground might help reduce the interference. Sorry I can't help you with the filter itself.
 

Serratus

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Sceadwian said:
Have you tried shielding the inverter? Using a metal case connected to the circuit's ground might help reduce the interference. Sorry I can't help you with the filter itself.

Yes, I tried that but it makes no difference. In fact I have tried having the invertor along way away from the guitar, but the 4KHZ AC that's in the EL string itself produces just as loud a tone through the guitar. So no amount of shielding on the invertor will work, as the string can't be shielded aswell. Thanks for the idea anyway.
The only thing I can think of is to have a filter, but I need a design for one :(
 

batdin

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Narrow-band notch filters have very bad and prolonged transients.No kidding.
Wide-band notch filters have effect also on the useful signal.
What do you choose?I can provide you with a circuit,but I need to know what the central frequiency and the bandwidth of the notch must be.
 

E-design

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The problem is that you will have the noise at say 4kHz, but also some at 8kHz and 12kHz etc. Filtering is not an elegant or effective solution. I once made a small switcher to replace a small faulty module that drives a EL strip (used as blue backlight for LCD readouts) in a Philips scope. As I recall this frequency was quite high >>20kHz. Have you tried running the EL strip on a high freq?
 

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E-design said:
The problem is that you will have the noise at say 4kHz, but also some at 8kHz and 12kHz etc. Filtering is not an elegant or effective solution. I once made a small switcher to replace a small faulty module that drives a EL strip (used as blue backlight for LCD readouts) in a Philips scope. As I recall this frequency was quite high >>20kHz. Have you tried running the EL strip on a high freq?

Some one else has just told me the same problem regarding 8kHz and 12kHz so I think you're right, an audio filter is not the way to go. I haven't tried running the string at a higher freq, I assumed that I couldn't, but maybe that is the answer. I'll email the manufacturers of the string and ask them, I think. If it will run at 20kHz, will I easily be able to get an invertor at this frequency that will run from batteries?

Many thanks,
regards,
Rich
 

Sceadwian

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E-design, EL's use high voltage (over 100 volts or so) you can't run that on DC from a couple 1.5 volts batteries, that's what the inverter is for in the first place. It's not practical to use a high voltage battery pack cause you'd risk killing the user if there was a short. Inverters are only capable of producing VERY low currents so they're intrisincly safe. You can get inverter circuits that will run at pretty much any frequency you want if you can build it. The higher the frequency the more finicky the circuit can be which is why they typically use audio frequency ones, they're cheap. You could do it with a micro controller (I use 8 pin devices that can easily produce 100khz) and a carefully selected transistor and transformer with some basic back EMF protection circuitry.
 

E-design

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E-design, EL's use high voltage (over 100 volts or so) you can't run that on DC from a couple 1.5 volts batteries,
I never suggested that he run it of a high voltage battery pack or on 1.5VDC. I was just making a point that the frequency seem unimportant and maybe it will even run of a DC supply that is high enough.

that's what the inverter is for in the first place.
I think we all know that!

Inverters are only capable of producing VERY low currents so they're intrisincly safe. You can get inverter circuits that will run at pretty much any frequency you want if you can build it. The higher the frequency the more finicky the circuit can be which is why they typically use audio frequency ones, they're cheap. You could do it with a micro controller (I use 8 pin devices that can easily produce 100khz) and a carefully selected transistor and transformer with some basic back EMF protection circuitry.

What's your point, are you asking me, or telling me? Inverters can produce any voltage or current that you want them to produce, depending on the design. Higher frequency designs only gets tricky over a couple of 100kHz. There's no real reason why a low frequency switcher will be cheaper than a 20-50kHz one. I think it is more a question of meeting EMI requirements.
 

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Okay, so it seems I can run the wire at 20kHz which would then not be audible.
BUT, I can't find anywhere that sells a suitable inverter. I've opened up the inverter I have (which is 4kHz) and the board looks pretty simple so I figure I could probably make one. So has anyone got a circuit design for a simple inverter that could power EL string at 20kHz and run from batteries (either 1.5V or preferably 9V)?
Thanks in advance.
 

E-design

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The simplest design will be a flyback topology. What sort of current does your EL strip require from the minimum voltage to energize it?
 

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