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Old 12th November 2008, 03:46 PM   #1
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Default Reducing volume of planar tweeter

I own speakers that allow the tweeter output to be manually adjusted by connecting a resistor across terminals mounted at the rear of the speaker. Anything from a straight wire for no attenuation, to several ohms is acceptable depending on one's taste and all are 5W rated. What I'd like to try to rig up is a rotary switch with 6 or more different resistor values so that I don't have to power down everything, change resistors, power up and listen again. It's too difficult/slow to fine tune.

My problem now is that I have no idea what current rating the switch must be and I'm hoping someone here can help me with this. I think a DPDT, 6 pos. rotary is what I need, but at what current rating for it's contacts? I use 10W/ch to 20W/ch rated amplifiers.

thanks for any help!
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Old 12th November 2008, 09:20 PM   #2
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At only 20W potential max amplifier power, I think you'd be safe with any switch with a 1A or higher rating. There is less power in the treble signal usually, so I'd be surprised if you ever needed 8W of treble - an assumption based on an 8 ohm tweeter impedance drawing 1 amp through the switch.

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Old 12th November 2008, 09:29 PM   #3
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Wouldn't a rotary L-pad do the trick?
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Old 17th November 2008, 06:52 PM   #4
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If you connect a resistor or network of resistors that changes the impedance seen by the passive xover the xover point will shift in frequency. So it is important to preserve the impedance when doing this, unless it is just for experimentation to determine a relative level between the tweeter and whatever else is playing...

That means an "L" network at least.

I wouldn't use a variable "L Pad" myself, if this is for a "serious listening" type system, as the point contact in the L Pad is not to my personal liking...

For just testing, almost any switch will do fine. I use clip leads for testing such things myself.

For permanent use a FAT contact rotary switch is bound to be preferable to a standard toggle switch, especially if you hot switch. That will cause arcing, and the wiping switch is self cleaning, the toggle is not. A relay might be a sweeter way to go, multiple contacts, and this permits remote switching back at the listening position too.

There are several discussions of relay types and sources for speaker level uses that you can search here on DiyAudio...

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