Grayhill 7 pole 20 position rotary switch
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 6th April 2004, 08:03 PM #11 Bill Fitzpatrick   diyAudio Member     Join Date: Jun 2001 Location: Eugene, OR There is now 1 of these switches available.
 7th April 2004, 12:21 AM #12 Bill Fitzpatrick   diyAudio Member     Join Date: Jun 2001 Location: Eugene, OR Switches all sold. Thanks.
 8th April 2004, 02:46 PM #13 Bas Horneman   diyAudio Moderator Emeritus     Join Date: Apr 2002 Location: The Netherlands Can anyone tell me how to aproximately (or exactly ofcourse)calculate values so that I can use this switch as a volume control. Thanks in advance. Regards, Bas
Elso Kwak
Banned

Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Stepped Volume Control

Quote:
 Originally posted by Bas Horneman Can anyone tell me how to aproximately (or exactly ofcourse)calculate values so that I can use this switch as a volume control. Thanks in advance. Regards, Bas
Hi Bas,
Do you want to use the switch as a series ladder attenuator or as a shunt attenuator?. In the first case I have been using a graphical method on logarithmic paper.

In the latter case as I am now using I have one (only ONE) resistor in series with the signal and I switch each volume setting a different resistor to ground. So contrary to the first case the signal travels only through one resistor and there is only one resistor to ground. For the shunt attenuator the dB's attenuation are easy to calculate with dB= log V^2. Assuming a 10k series resistor I calculated for f.a. 13.5dB attenuation:
10logV^2=13.5
20logV=13.5
V= 4.7315
Then 1/V= 0.21113 as we need attenuation. The voltage is 1/4.7315 I assumed an input voltage of 1V to keep calculations simple.
R= 10k x 1/Vout /(1-1/Vout )
R =10k x 0.2113/0.7887= 2k68 or nearest standard value 2k7.
And so on, and so on....

Are you still with me?
Better I post a list of values for a 10k series resistor.
I also checked all values with a small program from Old Colony called Rescalc.
With the shunt attenuator the switch must be shorting meaning that in between two steps two resistors are switched to ground lowering the volume between detents. Suppose the switch is non shorting there will be no resistor to ground between settings and the volume would be maximum between detents giving loud bangs. I made my 47 position Shallco for 1.5 dB steps except a few of the very loudest settings giving a huge range. For the ear this pot feels as linear but of course it is logarithmic.

 8th April 2004, 08:52 PM #15 Bill Fitzpatrick   diyAudio Member     Join Date: Jun 2001 Location: Eugene, OR This will be of some help. http://www.quadesl.com/attenuator.html
Bas Horneman
diyAudio Moderator Emeritus

Join Date: Apr 2002
Location: The Netherlands
Quote:
 Are you still with me?
Not yet

Before I check it out...would it work with this kind of attenuator?

Thanks Elso and Bill
Attached Images
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 8th April 2004, 09:16 PM #17 dhaen   diyAudio Moderator Emeritus     Join Date: Jun 2002 Location: U.K. Bas, I think the shunt resistor should be on the output.
Elso Kwak
Banned

Join Date: Dec 2001
Location: Zamboanga, City of Flowers, Mindanao
Shunt Attenuator Schematic

Quote:
 Originally posted by Bas Horneman Not yet Before I check it out...would it work with this kind of attenuator? Thanks Elso and Bill
Hi Bas , This is the idea, though I wouldn't draw it that silly......
http://www.goldpt.com/schm_shunt.html
This is more clear. The MINI-H in the link:
http://www.goldpt.com/compare.html

 8th April 2004, 10:08 PM #19 dhaen   diyAudio Moderator Emeritus     Join Date: Jun 2002 Location: U.K. The switch is non-shorting, so a series attenuator as Bas drew) must be the way to go.
 8th April 2004, 11:47 PM #20 Peter Daniel   diyAudio Member     Join Date: Jul 2002 Location: Toronto, Canada I would rather place the shunt resistor on the output side, otherwise as it is drawn, the ground connection to the load is being interupted and switching noise is unavoidable.

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