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Topic: Linear vs. logarithmic question. |
George Kimery
From:
Limestone, TN, USA
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Posted 13 Sep 2018 7:40 am |
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| Were the old AB pots that seem to be the gold standard for pots linear or logarithmic? Which type is preferable for a volume pedal. |
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Ken Byng
From:
Southampton, England
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Posted 13 Sep 2018 7:43 am
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Log pots are the real deal for pedal steel.
_________________
Show Pro D10 - amber (8+6), MSA D10 Legend XL Signature - redburst (9+6), Sho-Bud Pro 111 Custom (8+6), Emmons black Push-Pull D10 (8+5), Zum D10 (8x8), Hudson pedal resonator. Telonics TCA-500, Webb 614-E, |
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George Kimery
From:
Limestone, TN, USA
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Posted 13 Sep 2018 10:38 am Linear vs. logarithmic question.
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| Well, looks like I just bought something worthless. Brand new AB 500k linear pot. Made in the USA. |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 13 Sep 2018 11:02 am Re: Linear vs. logarithmic question.
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| George Kimery wrote: |
| Well, looks like I just bought something worthless. Brand new AB 500k linear pot. Made in the USA. |
Well, how worthless it is depends on your set-up and where the pot is going (I guess it's in the VP), as it is rather easy to turn a linear pot into a quasi-logarithmic one. I do it all the time so I can adjust the curve more exactly for the job. One additional resistor is all it takes. |
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George Kimery
From:
Limestone, TN, USA
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Posted 13 Sep 2018 1:16 pm Linear vs. logarithmic question.
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Geoege, yes it would go into a 120 back-up pedal. I can use a soldering iron, but that is about as far as my technical knowledge goes. If I had the size or number of a resistor and where it needs to be connected, I could handle the job, as long as it doesn't change the sound of the pot. The sound is the whole purpose of using the AB pot to begin with.
It was cheap, only $8.00. I did not know they came in different tapers. I don't think it's worth converting. Just cut my loss and look for a log version . |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 13 Sep 2018 2:17 pm Re: Linear vs. logarithmic question.
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| George Kimery wrote: |
| It was cheap, only $8.00. I did not know they came in different tapers. I don't think it's worth converting. Just cut my loss and look for a log version . |
Probably best – sound is something personal.
For those interested; turning a 500K linear pot into a quasi-logarithmic pot in a VP, is achieved by soldering a resistor with a value between 68K and 100K, between signal and GND lugs on the jack leading to the amp. Along with the amp's input impedance such an arrangement produces a pretty even logarithmic curve … beats all but the highest-quality real-logarithmic pots (not many of those around).
Such a quasi-logarithmic pot works best for those who have a buffer between PU and VP, but despite its varying load caused by the extra resistor it isn't too bad without a buffer either. |
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Paul Arntson
From:
Washington, USA
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Posted 13 Sep 2018 5:14 pm
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I think Georg's solution would sound better than most commercially available (and affordable) log pots, per this wiki article:
https://en.wikipedia.org/wiki/Potentiometer#Logarithmic_potentiometer
The curve that you get with a parallel resistor has more pronounced curvature than a true log, and probably more appropriate for music performance.
Wait a minnit ... math error. I am wrong about the second statement.
_________________
Excel D10 8&4, Supro 8, Regal resonator, Peavey Powerslide, homemade lap 12(a work in progress)
Last edited by Paul Arntson on 16 Sep 2018 8:43 am; edited 1 time in total |
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George Kimery
From:
Limestone, TN, USA
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Posted 13 Sep 2018 5:44 pm Linear vs. logarithmic question.
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| Interesting, I will probably give this a try. In the meantime, I have found a rebuilt AB log lot for $15.00. I think I will go ahead and get it. |
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Jim Sliff
From:
Lawndale California, USA
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Posted 13 Sep 2018 8:11 pm
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IMO it's not worth messing with. Passive volume pedals have used standard audio (lo) taper pots - they work just fine. The only differences in the ones used in most rocker-type pedals (volume, wah etc) is the shaft is usually longer; many replacements for specific models are also equipped with the stock gear or string attachment hardware.
_________________
No chops, but great tone
1930's/40's Rickenbacher/Rickenbacker 6&8 string lap steels
1921 Weissenborn Style 2; Hilo&Schireson hollownecks
Appalachian, Regal & Dobro squarenecks
1959 Fender 400 9+2 B6;1960's Fender 800 3+3+2; 1948 Fender Dual-8 Professional |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 14 Sep 2018 1:09 am
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Let me add a few details to (potentially) clarify things:
1: a pot doesn't "have a sound". What those who prefer a totally passive set-up – PU to VP via cable to AMP – hear, is the effect the varying series resistance and load has on the PU's frequency characteristics.
Nothing wrong with that, as that's what we're used to and like, but the pot itself still doesn't "have a sound".
2: all such entirely passive chains vary with the AMP's input impedance. The "old" rule is that for a pot's inherent curve/taper to be close to specified, the AMP's (or whatever follows the VP) input impedance has to be more than ten times higher than the pot's given value, and for a 500Kohm pot that is >5Mohm. As most AMP's input impedance is in the 200Kohm to 500Kohm range, the pot's curve is anything but as specified – even a perfectly linear pot becomes "quasi-logarithmic".
Nothing wrong with that either, but changing AMP (or whatever comes first after the VP) most often will change the 500Kohm pot's curve/taper. Don't blame the AMP (or whatever), as that's how all pots (and other dividers) work  |
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Tim Whitlock
From:
Colorado, USA
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George Kimery
From:
Limestone, TN, USA
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Posted 14 Sep 2018 8:58 am Linear vs. logarithmic question.
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| Tim, thanks, but been there, done thst. I had two 120 pedals for the last few years. One had the Bradshaw pot and the other the AB. I always used the Bradshaw one because if I wore it out if was replaceable. I wasn't so sure about the AB pot pedal, so I only carried it as backup. I bought an Omni pedal that claimed to have a pot close to the AB, which it was. Just not close enough for my ears. So I have sold both pedals and just have the one AB pedal now. I will be trying a Lehle pedal in October on a 30 day return. If that doesn't work out, then I am getting another 120 and installing a reconditioned AB log pot. |
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George Kimery
From:
Limestone, TN, USA
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Posted 14 Sep 2018 10:12 am Linear vs. logarithmic question.
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I am learning things here. So a pot does not change the tone directly. It causes the amp to change the tone, technically speaking. Using a pot changes the tone, but indirectly. I just plugged my guitar directly into the amp, bypassing the volume pedal. The sound is completely different.
If I understand correctly, a linear pot will reach most of its gain about half way on. After that, it doesn't increase volume to a great degree. If that's true, I may have a linear pot in my pedal. The volume does zoom up more the first 50% than the last 50%. This is not a problem because I only depress the pedal until it is parallel to the floor. I don't play on the front of the pedal. If I need that much volume, I just crank up my amps volume. I have a Stereo Steel and a Stuart 1.2 power amp with my Evans pre-amp. Both systems have more horsepower than I will ever need. |
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Georg Sørtun
From:
Mandal, Agder, Norway
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Posted 14 Sep 2018 10:54 am Re: Linear vs. logarithmic question.
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| George Kimery wrote: |
| I am learning things here. So a pot does not change the tone directly. It causes the amp to change the tone, technically speaking. Using a pot changes the tone, but indirectly. |
The pot causes the PickUp to change tone, because the PU is sensitive to load variations.
| George Kimery wrote: |
| If I understand correctly, a linear pot will reach most of its gain about half way on. After that, it doesn't increase volume to a great degree. |
That's what a linear pot's curve/taper will sound like, yes. |
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George Kimery
From:
Limestone, TN, USA
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Posted 14 Sep 2018 11:07 am Linear vs. logarithmic question.
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I understand everything now, I think. I can see why a linear taper, although it would work, would not be the best choice.
Thanks for everyone's help. I have learned a lot about something I knew nothing about. |
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Donny Hinson
From:
Glen Burnie, Md. U.S.A.
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Posted 14 Sep 2018 1:42 pm
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I used a linear (UA) taper pot for a few years. It's certainly different, but it's not unusable. Once you become accustomed to the different feel of the taper (it "comes on" faster), it works pretty much like any other pot.  |
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