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Joshua Tree kit to upgrade and replace volume control in vintage preamp
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MarkvsMaximvs  
#1 Posted : Thursday, September 15, 2011 12:58:58 PM(UTC)
MarkvsMaximvs

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Hi,

I'm entertaining the idea of upgrading the existing potentiometer-based volume control in a preamp with a discrete attenuator such as the Joshua Tree. The existing volume control is a motor driven potentiometer and I was wondering if that could somehow be leveraged to control the Josua Tree. It's not a 5K linear like the pot that's included in the kit, but could the control board be modified to accommodate the resistive range of the preamp's potentiometer?

Thanks,

-Mark
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Brian Donegan  
#2 Posted : Thursday, September 15, 2011 1:07:03 PM(UTC)
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the Joshua Tree simply uses the pot as a variable voltage divider, and monitors the voltage coming out of the pot, so it would definitely work as is. The main issue would be that the existing pot (most likely) has a log curve, so you will get very little volume until close to the end of the rotation, where it will ramp up quite quickly.

I suppose this could be accounted for in special firmware, but would take some testing to get it working well.
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pinnocchio  
#3 Posted : Thursday, September 15, 2011 1:38:11 PM(UTC)
pinnocchio

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Brian,

What if he buys a ALPS dual 10K linear motorized pot and parallel both resistors together? That would drop the resistor to ~5K?

Item RK27112MC 10KBx2

Ciao!
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Brian Donegan  
#4 Posted : Thursday, September 15, 2011 1:43:39 PM(UTC)
Brian Donegan

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pinnocchio wrote:
Brian,

What if he buys a ALPS dual 10K linear motorized pot and parallel both resistors together? That would drop the resistor to ~5K?

Item RK27112MC 10KBx2

Ciao!


That won't help much unless it fits in the existing spot. It will certainly work, but the question was how to reuse the existing pot.
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Brian Donegan  
#5 Posted : Thursday, September 15, 2011 1:44:51 PM(UTC)
Brian Donegan

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Incidentally, a 10K pot will work without modification. The pot value will just affect the resolution... the divided voltages will be the same regardless of pot value.
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MarkvsMaximvs  
#6 Posted : Thursday, September 15, 2011 3:18:40 PM(UTC)
MarkvsMaximvs

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Hi Guys,

Thank you very much for your quick replies. Changing the existing volume pot to a motorized linear did cross my mind. I'd have to measure the available space with accuracy, but I think there should be enough clearance.

Thanks again
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