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29th April 2016, 12:51 AM  #1 
diyAudio Member

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 Last edited by georgehifi; 29th April 2016 at 12:57 AM. 
30th April 2016, 08:24 AM  #2 
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

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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30th April 2016, 08:29 AM  #3 
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

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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regards Andrew T. Sent from my desktop computer using a keyboard Last edited by AndrewT; 30th April 2016 at 08:52 AM. 
30th April 2016, 08:34 AM  #4 
diyAudio Member

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 
30th April 2016, 08:53 AM  #5  
diyAudio Member
Join Date: Jul 2004
Location: Scottish Borders

Quote:
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30th April 2016, 08:55 AM  #6 
diyAudio Member
Join Date: Sep 2015
Location: Spain

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 
30th April 2016, 08:56 AM  #7 
diyAudio Member

My RS will be 250ohm and RL will be 100kohms
Cheers George 
30th April 2016, 09:01 AM  #8 
diyAudio Member
Join Date: Sep 2015
Location: Spain

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. 
30th April 2016, 09:30 AM  #9 
diyAudio Member

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 
30th April 2016, 09:34 AM  #10  
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Join Date: Sep 2015
Location: Spain

Quote:
Cheers, Cabirio 

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