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Old 21st March 2009, 01:00 AM   #1
dpaws is offline dpaws  United Kingdom
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Default 1K log pots

Evenin all...

Help! Where can I find top quality (5% or 1% Alps etc) 1K log pots?

OK, asking too much, but multi turn would be wonderful, as would single shaft concentric mounting for balance control with option to be motorized?

Much obliged, Steve
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Old 21st March 2009, 01:54 PM   #2
AndrewT is offline AndrewT  Scotland
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I doubt you'll find what you're after.
1.) log pots usually start from a range higher than 1k
2.) pots in general have a wide tolerance on total resistance.
3.) log pots in particular have a wide tolerance on total resistance and on tracking between the two tracks of a dual. To find 5% tolerance on the total will be difficult, to get 5% on tracking over a small part of the whole output range will be near impossible.
4.) Multi-turn pots are usually single track. Any dual track will be specialised and more likely to be linear.

Trying to combine all four of these low availability specifications into one device may mean there is only one manufacturer in the world who is able to make your specialised pot.
I wonder what they will charge for their expertise?

and motorised as well!
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Old 21st March 2009, 02:45 PM   #3
Bobken is offline Bobken  United Kingdom
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Hi,

You could try using a 'law-faking' resistor with a higher value linear pot, perhaps 10k or above which are readily available, and which as Andrew suggests are generally better spec'd., and the pot will not then be the determining factor for accuracy quite so much anyway.

I'm sure a quick 'Google' will find you stacks of information on these details, and you can end up with different log laws etc., and very high inter-channel accuracy (provided that the pot is reasonably accurate) so long as you choose close-tolerance (also HQ for good sound?) resistors for the 'law-faking'.

As a rough guide, using a pot around 10x the value ultimately required and with a fixed 'law-faking' resistor between the pot's wiper and ground a bit higher than your total resistance requirements, when these are in parallel you can end up with 1k at full resistance.

As an example, using a 10k pot with a 1k fixed resistor, you would end up with roughly 909R as the total resistance, or maybe also a quite readily-available 1k2 fixed resistor would give you approx. 1k07 total resistance, neither of which is far from your suggested goal.

Many HQ resistors should be available in the region of 1k1 in value and this would give you 991R approx, which is within 1% of what you suggest and will not affect the log-law greatly. This is likely to be better overall for inter-channel accuracy and total resistance than any dual log pot you could readily obtain in my experience, and only requires the addition of one fixed resistor for each channel on top of the pot you need to buy anyway.

Regards,
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Old 21st March 2009, 02:51 PM   #4
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State Electronics here in NJ can fulfill your needs -- they carry the Allen Bradley "Mod Pots" which are available in linear, log, reverse log, modified log tapers --

http://www.potentiometers.com/pdf/catalog70.pdf
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Old 15th May 2009, 04:24 AM   #5
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FORGIVE ME FOR HIJACKING THIS THREAD

Bobken, I need your help.... This forum will not let me email you, so I have to post somewhere you will find it... Sorry again guys.

A year ago, you wrote...
Quote:
I have plenty (possibly hundreds!) of those same Wondercaps if you want to replace them with the same types, but I wouldn't recommend it!
Please contact me. I am trying to find a decent supply of WonderCaps for a project we are working on, and would like to buy quite a few if possible. Either email me, or reply here please, and let me know if it would be possible to buy some from you. jamess@s-t-u-d-i-o.com

Thanks for everyones patience, and sorry again.

James Sauter Florida USA
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