[sdiy] Music Easel sliders determined to be linear

[mark verbos]

Although that makes perfect rational sense, in practice they are all  
50k linears, don't ask me why. Although, the 120k tapering resistors   
tone down the audio-ness of them.

Mark




On Jun 28, 2009, at 1:05 AM, Aaron Lanterman wrote:

> On Jun 5, 2009, at 1:39 AM, Aaron Lanterman wrote:
>
>> Anyone have any particular knowledge of which pots and sliders on  
>> the Music Easel are linear taper and which are audio (log) taper?
>
> I was able to figure this out using the resistor chart for the plug- 
> in board near the back of the Easel manual.
>
> They are LINEAR. So if you need to replace a slider on your Easel.  
> now you know which one to get.
>
> The Easel uses a 13.5 V source to drive the various CV controls, and  
> just connects or disconnects this voltage from the card or the front  
> panel controls to turn things on and off.
>
> Using the resistors values in the chart for settings 10, 8, 6, and  
> 4, supposing things go to a virtual ground summing node, for the  
> given resistor values of 120K, 150K, 200K, 300K, and 620K  
> respectively, I get currents of 0.1125 mA, 0.09 mA, 0.0675 mA, 0.045  
> mA, and 0,021 mA.
>
> The 50K sliders in the Easel are hooked to a couple of 120K  
> resistors; the current flowing through one of the 120K resistors  
> essentially (with a lot of handwaving) controls the various  
> controlling bits. Again, let's assume these go to a virtual ground  
> summing node. (This is rarely actually the case but it's a place to  
> work from.) Calling one leg of the pot R, and the other 50K - R, we  
> wind up with Ra = (50K - R) || 120 K and Rb = 50K || 120K, and then  
> the current through the 120K resistor going into the Easel boards is
>
> (13.5 V / 120 K) Rb / (Rb + Ra).
>
> When I do this calculation, assuming a linear pot, I get currents of  
> 0.1125, 0.086, 0.066, 0.046, and 0.026 mA.
>
> Ladies and gentlemen, we have a match!
>
> Whew, I dreaded trying to work out the case of assuming an  
> logarithmic pot...
>
> - Aaron
>
> P.S. I will post this finding a couple of other relevant lists.  
> Apologies if you get multiple hits.
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