Home » Audio » Thermionic Emissions » What about volume pot impedance?
What about volume pot impedance? [message #10081] Fri, 25 July 2008 07:50 Go to next message
Bill Epstein is currently offline  Bill Epstein
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Registered: May 2009
Location: Smoky Mts. USA
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Both my sources have output impedii (?) of less than 1000 ohms. I just received a 10k PEC pot to try in place of the 100k in my passive.

Seems like 100k is a de facto standard for pre-amps pots and attenuators. If most of these have output impedances below 1000 ohms and the favorable ratio is 1:10, why is this?

Re: What about volume pot impedance? [message #10082 is a reply to message #10081] Fri, 25 July 2008 15:06 Go to previous messageGo to next message
Wayne Parham is currently offline  Wayne Parham
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Registered: January 2001
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Used to be in the old days, you tried to match impedance for maximum power transfer. Now days, it is more common to maximize voltage transfer, which means keep the source impedance low with respect to the load. The two form a voltage divider, so if equal, then the voltage is the same across both. If the load is a lot higher impedance than the source, then most of the voltage is across the load, not the source. In either case, it is very important that the source limits not be exceeded, because that will probably do bad things like increase distortion or possibly even break something.

You could exceed voltage limits if the load impedance were too high, or you could exceed current limits if the load were too small. In many cases, you have a pretty wide working range, and in that case the load impedance can be set as needed, within reason, perhaps anything above a few hundred ohms. But in some cases, the source limits can be reached with values much narrower in range, maybe 20k on the low end hits a current limit and 250k on the high reaches a breakdown voltage. The only way you can know is to study the particulars of the output and input circuits, especially the active devices. Capacitors have a breakdown voltage, so while that isn't usually an issue at preamp levels, it could be in some tube circuits.


Re: Just listened to the 10k pot [message #10083 is a reply to message #10082] Fri, 25 July 2008 23:30 Go to previous message
Bill Epstein is currently offline  Bill Epstein
Messages: 1088
Registered: May 2009
Location: Smoky Mts. USA
Illuminati (2nd Degree)
My phono stage has an output impedance of less than 100 ohms, the CDP, 600.

There seems to be a bit more gain and the bass is better defined compared to the 100k. I'll leave it in the passive and use the 100k in the Aikido which I have resumed building and hope to finish soon.



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