Log, Lin or W? - UK Vintage Radio Repair and Restoration Discussion Forum

ITAM805 · 27th Apr 2018, 2:19 pm

Does anyone know what "W" indicates on this dual pot, and can I sub it with a log or lin type? It's an input gain or volume control on a multi-FX unit

many thanks

Station X · 27th Apr 2018, 2:41 pm

I don't know what 'W' means, but you could try plotting a graph of resistance against angular position. This generally reveals two straight lines with different slopes.

Craig Sawyers · 27th Apr 2018, 2:46 pm

The W probably refers to the resistance taper. If the pot is ALPS, W is similar to 3B (which is the usual volume control)

Alps tapers are here https://www.alps.com/prod/info/E/PDF...eter/TAPER.pdf

Craig

ITAM805 · 27th Apr 2018, 3:10 pm

Thanks guys. Craig I dont think the pot is ALPS, well it doesn't say as such but I did read somewhere that it's the taper you suggest in your link. I reckon I could sneak a Log in there and nobody would notice.

David G4EBT · 27th Apr 2018, 4:01 pm

Ordinarily, potentiometers made in Asia and the USA are usually marked with an "A" for logarithmic taper or a "B" for linear taper; "C" for the uncommon reverse/inverse logarithmic taper. Others, particularly those made in Europe, may be marked with an "A" for linear taper, a "C" or "B" for logarithmic taper, or an "F" for reverse logarithmic taper.

So in the UK, you can't rely on a pot marked 'A' being log taper as it depends entirely on the country of manufacture. I got caught out by that some time ago with a pot from Maplin. They'd had Omeg (British made pots, then changed to an imported type. Both marked 'A' but one was log - the other linear.

Haven't got a clue what 'W' signifies, but presumably at least one of the tracks is intact so a check with a meter will soon solve the mystery. As a rule of thumb, a log taper will measure 10% at the mid point. Hence a 10K pot - depending on which end one prod is placed - will read 1k/9k, whereas a 10K linear would (obviously) read 5k/5k.

ITAM805 · 27th Apr 2018, 4:28 pm

Thanks David, I did measure as per Graham's post and it seems like a log (audio) taper or near as damn it, as it's intermittent mid way through its travel

Terry_VK5TM · 28th Apr 2018, 1:44 am

W taper is log/antilog.

Here is a graph of function (part of a question on stackexchange), top graph:-

https://electronics.stackexchange.co...-or-linear-pot

ITAM805 · 28th Apr 2018, 9:19 pm

Thanks for the info Terry, alas they appear to made from unicorn horn such is their availability, at least to fit this particular job

Terry_VK5TM · 29th Apr 2018, 3:45 am

Alpha Products do a BW taper that may be similar enough.

http://www.alpha-products.com/cd_cat...ots/tapers.htm

They used to do W taper but it seems to have been discontinued.

No idea on costs of their products.

RF Burn · 29th Apr 2018, 1:21 pm

Try this:
https://www.ebay.com/itm/2-x-16mm-Al...-/262198041006
Looks like the job.

Adrian

ITAM805 · 30th Apr 2018, 1:52 pm

Hi Adrian and many thanks, that does indeed looks like the right job, well done for finding it. I had searched ebay and found nowt, maybe I should search '.com' rather than '.co.uk' in future when trying to source parts?

Anyhow, I have a log pot ordered which should be here tomorrow and will try that, but it's good to know that the right parts are still available

27th Apr 2018, 2:19 pm	#1
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Log, Lin or W? Does anyone know what "W" indicates on this dual pot, and can I sub it with a log or lin type? It's an input gain or volume control on a multi-FX unit many thanks Attached Thumbnails

27th Apr 2018, 2:41 pm	#2
Station X Moderator Join Date: Jan 2003 Location: Ipswich, Suffolk, IP4, UK. Posts: 21,288	Re: Log, Lin or W? I don't know what 'W' means, but you could try plotting a graph of resistance against angular position. This generally reveals two straight lines with different slopes. __________________ Graham. Forum Moderator Reach for your meter before you reach for your soldering iron.

27th Apr 2018, 2:46 pm	#3
Craig Sawyers Dekatron Join Date: Nov 2010 Location: Oxford, UK. Posts: 4,982	Re: Log, Lin or W? The W probably refers to the resistance taper. If the pot is ALPS, W is similar to 3B (which is the usual volume control) Alps tapers are here https://www.alps.com/prod/info/E/PDF...eter/TAPER.pdf Craig

27th Apr 2018, 3:10 pm	#4
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Log, Lin or W? Thanks guys. Craig I dont think the pot is ALPS, well it doesn't say as such but I did read somewhere that it's the taper you suggest in your link. I reckon I could sneak a Log in there and nobody would notice.

27th Apr 2018, 4:01 pm	#5
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,761	Re: Log, Lin or W? Ordinarily, potentiometers made in Asia and the USA are usually marked with an "A" for logarithmic taper or a "B" for linear taper; "C" for the uncommon reverse/inverse logarithmic taper. Others, particularly those made in Europe, may be marked with an "A" for linear taper, a "C" or "B" for logarithmic taper, or an "F" for reverse logarithmic taper. So in the UK, you can't rely on a pot marked 'A' being log taper as it depends entirely on the country of manufacture. I got caught out by that some time ago with a pot from Maplin. They'd had Omeg (British made pots, then changed to an imported type. Both marked 'A' but one was log - the other linear. Haven't got a clue what 'W' signifies, but presumably at least one of the tracks is intact so a check with a meter will soon solve the mystery. As a rule of thumb, a log taper will measure 10% at the mid point. Hence a 10K pot - depending on which end one prod is placed - will read 1k/9k, whereas a 10K linear would (obviously) read 5k/5k. __________________ David. BVWS Member. G-QRP Club member 1339.

27th Apr 2018, 4:28 pm	#6
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Log, Lin or W? Thanks David, I did measure as per Graham's post and it seems like a log (audio) taper or near as damn it, as it's intermittent mid way through its travel

28th Apr 2018, 1:44 am	#7
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,339	Re: Log, Lin or W? W taper is log/antilog. Here is a graph of function (part of a question on stackexchange), top graph:- https://electronics.stackexchange.co...-or-linear-pot __________________ Terry VK5TM https://www.vk5tm.com/

28th Apr 2018, 9:19 pm	#8
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Log, Lin or W? Thanks for the info Terry, alas they appear to made from unicorn horn such is their availability, at least to fit this particular job

29th Apr 2018, 3:45 am	#9
Terry_VK5TM Nonode Join Date: Oct 2010 Location: Tintinara, South Australia, Australia Posts: 2,339	Re: Log, Lin or W? Alpha Products do a BW taper that may be similar enough. http://www.alpha-products.com/cd_cat...ots/tapers.htm They used to do W taper but it seems to have been discontinued. No idea on costs of their products. __________________ Terry VK5TM https://www.vk5tm.com/

29th Apr 2018, 1:21 pm	#10
RF Burn Hexode Join Date: Apr 2008 Location: Ramsgate, Kent, UK. Posts: 252	Re: Log, Lin or W? Try this: https://www.ebay.com/itm/2-x-16mm-Al...-/262198041006 Looks like the job. Adrian

30th Apr 2018, 1:52 pm	#11
ITAM805 Nonode Join Date: Jul 2010 Location: Folkestone, Kent, UK. Posts: 2,172	Re: Log, Lin or W? Hi Adrian and many thanks, that does indeed looks like the right job, well done for finding it. I had searched ebay and found nowt, maybe I should search '.com' rather than '.co.uk' in future when trying to source parts? Anyhow, I have a log pot ordered which should be here tomorrow and will try that, but it's good to know that the right parts are still available