Non-Master Volume - Audio vs Linear Taper

[jgab]

Hi,
Is it ok to use a Linear taper for the volume controls in a Marshall Super Lead? Has anyone tried this and what negative effects would be noticed?

I hear people flipping back and forth when it comes to guitar pots but I don't hear much about Marshall amps.

Thanks,
J

 

[Jon Snell]

Using a Linear pot will mean the output increase/decrease will be a linear action; half way = 50% 3/4 = 75%.
Using a Log pot will mean at 25% = 50% and 60% = 90% due to the way the resistor is laid out. Matching what our our Logrithmic ears expect to hear, rather than a Linear pot.
Log means a faster increase of power with respect to the dial position.

Hope that explains it.

 

[21fret]

Linear taper

IIRC in a 1959 the TMP are linear.

 

[JohnH]

I haven't tried this myself.

But, if you swap between a linear pot and a log pot of the same Ohms value, you'd expect to cover the same range of tones, and the rest of the circuit would not feel any difference. The only difference should be where on the pot turn a given level is. Starting from zero volume, a linear pot would build up faster in the first half turn and then less in the second half, as compared to a log pot.

How that relates to where you set the knob, how loud it really is and whether it's clean or crunchy etc, will depend on how its used and on the amp design, but all the same tones and levels would exist somewhere on the dial.

 

[Frodebro]

A linear pot will ramp up much faster, and as a result will be harder to make incremental adjustments to in the lower range.

 

[jgab]

Awesome answers!

If a Linear pot ramps up fast, I think using a Linear pot with a Master Volume amp like an 800 would be a bad idea. These Master Volume amps (2203/2204) already ramp up fast. However, with a Non-Master Vol amp, the Volume I and II would probably work just fine seeing that I run the amp with an attenuator and search for the sweet spot from about 11 o'clock and onward.....If I am understanding this correctly, Linear would work better with a Non-Master amp compared to a Master Volume amp?

Glad to hear it doesn't affect tone.

 

[JohnH]

Awesome answers!

If a Linear pot ramps up fast, I think using a Linear pot with a Master Volume amp like an 800 would be a bad idea. These Master Volume amps (2203/2204) already ramp up fast. However, with a Non-Master Vol amp, the Volume I and II would probably work just fine seeing that I run the amp with an attenuator and search for the sweet spot from about 11 o'clock and onward.....If I am understanding this correctly, Linear would work better with a Non-Master amp compared to a Master Volume amp?

Glad to hear it doesn't affect tone.

Lets try to map that from log to linear! This is just numbers and YMMV, but anyway:

Lets say currently you have a log pot on your NMV amp, and you set it at 11 o'clock which is about 4 on the knob, or maybe sometimes at 6, or sometimes at 8, or 10 = max.

Log pots are usually made with two linear parts on the track , changing at half turn. Lets say your log pot gets to 15% of the total at half turn (12 oclock = 5 on the dial). At 4 on the dial it would be at about 12 %. On a linear pot this setting would be at just above 1 on the knob (actually 1.2 with these values but pots aren't as consistent as that).

6 on this theoretical log pot would be 32%, so just over 3 on the knob of a linear pot

8 log will be 66% so about 6.5 on the linear pots knob

10 goes to 10

All theory but maybe that gives some insight?

 

[jgab]

Thanks for the detailed insight. The way I run the Super Lead, a linear pot would probably work for me.

Basically, my situation is I have a period correct Linear 1M pot, but not a period correct 1Meg Log. The amp came with a modern 1Meg Log in Volume I, and I want to get rid of it. That's why I asked the question about using the Linear pot because I want to know if it would work well enough.

Where should I put this Linear 1M pot?

I could replace the Volume II pot with this 1M Linear, and place the 1Meg Log from Volume II in Volume I since I use Volume I the most. Or, I could move the Bass 1Meg Log pot to Volume I and put this 1Meg Linear pot in the bass spot? Would need to keep the bass pot super low though. I don't like using much bass btw.

Any suggestions? I just want to get rid of the modern pot in Volume I.

 

[Pete Farrington]

Using a Linear pot will mean the output increase/decrease will be a linear action; half way = 50% 3/4 = 75%.
Using a Log pot will mean at 25% = 50% and 60% = 90% due to the way the resistor is laid out. Matching what our our Logrithmic ears expect to hear, rather than a Linear pot.
Log means a faster increase of power with respect to the dial position.

I think you may have it muddled up there
With a log taper, 50% mechanical rotation produces 10% electrical output.
See p5 https://www.omeg.co.uk/wp-content/uploads/2019/07/OW20BU.pdf

 

[duffhuff]

A linear pot will be almost unusable as a volume pot unless you typically have it turned up very high. At low volume settings you'll find the slightest change to the pot will have a huge affect on volume compared to the log taper version.

 

[jgab]

Ok. Screw it then. I will just look for a log 1meg pot. Does anyone have one for sale? A vintage one?

Just PM if you can help me out...Please.

Thanks for all the comments. I learned a lot.