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east electronics 9th August 2008 08:27 AM

linear pot
 
i was reading somewhere that the use of linear pot for volume controls is better than the log .... but there is some resistor that you connect to it to give logarithmic behaviour ......

the think is that i have a bunch of log pots cheap meterial from radioohm or piher and like most of them have audible diference between left and right ....

any ideas ????

AndrewT 9th August 2008 08:58 AM

stereo log pots (dual gang) have a reputation for poor matching between channels. Dual gang lin pots sometimes/often have better matching particularly at high attenuation rates.

That is the only advantage that lin has over log, but for balance of a stereo signal it is quite important.

A log faking resistor is usually added to the wiper and ground to simulate the log law over part of the travel. Unfortunately you end up with an S shape law rather than the Log law but it works.

A lin pot is usually chosen that is 5 to 10 times higher resistance than the ideal log pot and then a resistor is added that is between 8% and 15% of the lin pot value. It's worth experimenting with resistor value to hear how different values affect the turning of the volume pot.

10k log to 20k log ~= 100k lin + 8k1 to 15k resistor.

The output impedance of the lin + faking resistor is higher than the log pot. Take care.

east electronics 9th August 2008 09:09 AM

thanks andrew
 
i will give it a try and let you know ....

yet what you said its true ......i took out something like 5 pots out of my stock ....ok they are cheap ...its not the good staff but really and especially in low levels there is audible diference and in all 5 of them

thanks andrew

Mooly 9th August 2008 01:23 PM

There is nothing worse than the stereo image shifting as you alter the volume.
How about connecting a dual gang pot to a low voltage DC supply and putting a DVM across the two wipers.

east electronics 9th August 2008 01:34 PM

not needed
 
there is no point to search in all my shop for a cheap but good stetreo log pot.....there must be almost 200 of those in my shop .....

BUT !!!! the first linear alps stero ( cheapest available) lin pot of 100k i found in the shop with a couple of metalfilm 18k sounds a lot better ....there is just a tinny diference in very very low volumes .....

Andrew T is right once more .....

though the log curve is kind of strange not what i am used to from log pots but still is very nice i think

also idont know why i thing this pot sounds better than the log any way ( may be its just my idea )

thanks


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