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Allison One image control


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I know I saw somewhere that there was a way to modify the Allison One crossovers so that some image control of the two panels could be used ala the IC-20. I believe that Roy himself came up with the modifications. Is this on this forum somewhere? Can someone point me to it or supply some info? I believe it was done with resistors and manual toggle switches.

Thanks,

John Bergman

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I know I saw somewhere that there was a way to modify the Allison One crossovers so that some image control of the two panels could be used ala the IC-20. I believe that Roy himself came up with the modifications. Is this on this forum somewhere? Can someone point me to it or supply some info? I believe it was done with resistors and manual toggle switches.

Thanks,

John Bergman

Hello John, I drew up this schematic based upon Roy Allison's description of the alteration of the Allison 1 midrange and tweeter arrays for changing the imaging of the systems. I posted this image to the (Yahoo) Allison forum (photo's) where you can also find Roy Allison's description of the wiring changes. Please note that this schematic represents my own set of model ones and the schematic does not show the frequency contouring switches and resistors since I removed them. -Tom Hpost-102905-0-25195300-1300543797_thumb.

Yahoo Allison Group

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Hello John, I drew up this schematic based upon Roy Allison's description of the alteration of the Allison 1 midrange and tweeter arrays for changing the imaging of the systems. I posted this image to the (Yahoo) Allison forum (photo's) where you can also find Roy Allison's description of the wiring changes. Please note that this schematic represents my own set of model ones and the schematic does not show the frequency contouring switches and resistors since I removed them. -Tom Hpost-102905-0-25195300-1300543797_thumb.

Yahoo Allison Group

Thanks for schematic. A couple of questions: is the resistor to the right of the "blue" tweeter actually 1/2 ohm? why did you remove the frequency contouring switches?

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Thanks for schematic. A couple of questions: is the resistor to the right of the "blue" tweeter actually 1/2 ohm? why did you remove the frequency contouring switches?

Yes, the .5ohm resistor is what Roy Allison specified in his description of the modification. I removed the frequency contour for 2 reasons. First off I always ran the systems in the flat position (prefering to use the parametric EQ built into my HT preamp if needed). The second reason is because the selector switch contacts had become intermittent (my speakers were made in 1976 and I suspect they were stored in a barn or garage). If you systems are close to the age of mine I suggest you check the electrolytic capacitors in the crossover for value drift. Mine had drifted (midrange and woofer circuits). -Tom

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Yes, the .5ohm resistor is what Roy Allison specified in his description of the modification. I removed the frequency contour for 2 reasons. First off I always ran the systems in the flat position (prefering to use the parametric EQ built into my HT preamp if needed). The second reason is because the selector switch contacts had become intermittent (my speakers were made in 1976 and I suspect they were stored in a barn or garage). If you systems are close to the age of mine I suggest you check the electrolytic capacitors in the crossover for value drift. Mine had drifted (midrange and woofer circuits). -Tom

Thanks, Tom. Have you modified your Ones with the image control parts then? If yes, do you ever use the option? The only place I can position my Ones is on the narrow wall which is just over 11' wide. So if I keep the Ones 2' from each side wall and the Ones are 1' wide, this allows 5' between the Ones. If I move them farther from the sidewalls, then the spacing between gets even smaller of course. So I was thinking maybe I could use the image control and reduce the output toward the side walls - I really don't know what the recommended spacing for the Ones is. What spacings do you use? Maybe, I will have to consider Threes for this room.

John A. Bergman

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  • 4 weeks later...

Sorry for the late reply. Yes, my set of Allisons are modified with this circuit. For the most part I had been using them in the "focused" setting because of the systems having to be about 20 or so inches for the corners. It had the effect of creating a more precise stereo image. I also had to use a small amount of bass EQ to reduce the bass output a bit which was due to the positioning near the walls. Do the mod and see how you like it. You could rig up a relay with a wired remote (basically a switch and battery) to do a comparison at the listening position of both settings. I think Allison offered a wired or IR option with the Allison IC10 (basically a Allison 1 and 2 hybrid) to change imaging effects for different music / recording types.

-T

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