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I have some 3-prong attinuators and I need help installing them so I can adjust the volume on a pair of compression drivers.
Is the middle prong unnecessary? Is this device connected in a parallel circuit to a single connection wire between the crossover and the compression driver; right? Do you use only the left and right prongs?
Thank you.
http://www.hostboard.com/forums/hbmc.../2012/11/1.gifQuote:
Originally Posted by robertbartsch
A picture is worth 1000 words, isn't it? :)
thank you!
Being naive, I would have guessed that using connections 2-3 would simply act as a variable R?
What is the purpose of connection #1? Is it some sort of negative feedback?
You can use just 2 legs as a variable R, it's an old trick. But that's not the point of the L-Pad. The point is that it presents a more or less constant impedance to the amp and/or crossover. So the crossover always sees 8 ohms, or 16 ohms, depending on the model. A simple pot would vary that impedance and change crossover points and other things. The L-Pad allows you to attenuate and not change impedance. Np matter where you turn the knob, it's approximately 8 ohms.
If you dope out the circuit, there is a series resistance and a parallel to "ground'. As the series resistance goes up, the parallel resistance drops.Quote:
Originally Posted by gortnipper
Think it thru. An 8 ohm speaker with a 4 ohm series resistor is 12 ohms. Referring to Ohm's law...24 Ohms in parallel is needed to bring it back to 8.
So you attenuate more, and have 8 ohms in series (16 total)....16 in parallel gets you back to 8.
Get the idea? As series goes up, the parallel has to go down.
You can calculate and put in fixed resistors...many do.
For the math impaired, a parallel resistance calculator...for the series value just add.
PARALLEL RESISTOR CALCULATOR
As was aptly put "approximately 8 ohms". there are no perfect components. Fixed resistors are closer to ideal than variable, since to be 'perfect' a variable would have to "track' exactly, and none do. Also, if you go fixed, you can hand select components.
On original Model 19 XO's. Altec only used 2 taps on the L-pads on the Mid-freq and High-freq. attenuator. Why ?
Here are my original unmolested 19 XO's.
http://www.hostboard.com/forums/hbmc...2012/11/62.jpg
http://www.hostboard.com/forums/hbmc...2012/11/63.jpg
http://www.hostboard.com/forums/hbmc...2012/11/64.jpg
http://www.hostboard.com/forums/hbmc...2012/11/65.jpg
I suspect the signal was not passing thru that L-pad to the driver. That one likely was wired to "short" (shunt is a more proper term) a bandpass filter to 'ground" rather than reflect a constant impedance. You can't "boost" a frequency in passive, just attenuate one. Or actually a "band" So to get extra highs the driver has to be turned up, then the mids attenuated. Wiring it as an L-pad would have attenuated the whole driver.Quote:
Originally Posted by Altec Best
Ta-da! Here is the HF portion thx to Messrs. Marquardt and Easley. Note wired to ground.
http://www.hostboard.com/forums/hbmc...2012/11/66.jpg
Thanks OG ! :Big smile: From that schematic it looks like tap #3 is unused or goes to the ground. Am I reading it right ?