10kohm series/shunt 23 position resistor attenuator. - diyAudio
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Old 29th April 2016, 12:51 AM   #1
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Default 10kohm series/shunt 23 position resistor attenuator.

Can anyone verify that this is close to being correct for a log curve 10kohm 23 position switched resistor pot??

Thanks George
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Last edited by georgehifi; 29th April 2016 at 12:57 AM.
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Old 30th April 2016, 08:24 AM   #2
AndrewT is offline AndrewT  Scotland
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I am calculating, but I have to assume two bits you have omitted.
Rs = ? I'll set that to zero ohms
Rload = ? I'll set that to infinity.
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Old 30th April 2016, 08:29 AM   #3
AndrewT is offline AndrewT  Scotland
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6k8 >-3.17dB
5k6 > -5.29dB
4k3 > -7.50dB
3k3 > -9.72dB
2k4 > -12.31dB
1k8 > -14.89dB
1k5 > -16.7dB
1k1 > -19.1dB
820 > -21.6dB
620 > -24.1dB
500 > -26.0dB
360 > -28.8db
300 > -30.5dB
220 > -33.1dB
160 > -35.8dB
133 > -37.4dB
100 > -40.1dB
56 > -45.1dB
34 > -49.4dB
18> -54.9dB
10> -60dB

BTW, some years ago I posted an ms excel spreadsheet that does that for you and it included an Rload option in the calculation.
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Old 30th April 2016, 08:34 AM   #4
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Top one is min vol, 10kohms series and 0ohms to ground
Bottom one is max vol, 0ohms series and 10kohms to ground
That's all there is.
Here is a link
Kikitronic -- DIY Audio Kits: Attenuator for volume control

Cheers George
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Old 30th April 2016, 08:53 AM   #5
AndrewT is offline AndrewT  Scotland
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Quote:
Originally Posted by georgehifi View Post
Top one is min vol, 10kohms series and 0ohms to ground
Bottom one is max vol, 0ohms series and 10kohms to ground
That's all there is.
Here is a link
Kikitronic -- DIY Audio Kits: Attenuator for volume control

Cheers George
He/she forgot about the effect of Rs and Rload.
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Old 30th April 2016, 08:55 AM   #6
cabirio is offline cabirio  Spain
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Below is what I get when I plot it in Excel (minus the first position, which would be -infinity). It doesn't look bad but you have ~26dB attenuation at 50% rotation, vs. ~20dB for a typical 10A taper pot. I assume that's what you want?

Cheers,

Cabirio
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Old 30th April 2016, 08:56 AM   #7
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Quote:
Originally Posted by AndrewT View Post
He/she forgot about the effect of Rs and Rload.
My RS will be 250ohm and RL will be 100kohms

Cheers George
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Old 30th April 2016, 09:01 AM   #8
cabirio is offline cabirio  Spain
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Quote:
Originally Posted by georgehifi View Post
My RS will be 250ohm and RL will be 100kohms

Cheers George
The difference vs. Rs=0 and Rl=infinity is in the hundredths of a dB.
Cheers,
Cabirio

Edit: sorry, strike that: max. difference ~0.2dB at 100% rotation.

Last edited by cabirio; 30th April 2016 at 09:04 AM.
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Old 30th April 2016, 09:30 AM   #9
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That's what I thought, virtually no effect.

So as it stands do you think that the resistors used from min to max are somewhere in the region of a log curve?
Sorry just saw your attachment it look more lin than log to me

Cheers George
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Old 30th April 2016, 09:34 AM   #10
cabirio is offline cabirio  Spain
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Quote:
Originally Posted by georgehifi View Post
That's what I thought, virtually no effect.

So as it stands do you think that the resistors used from min to max are somewhere in the region of a log curve?

Cheers George
Sure, the plot I posted is in dBs so a perfect log curve would be a perfectly straight line, which isn't far from what you get, in fact it's probably much closer than the standard log pot made with two linear segments.

Cheers,

Cabirio
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