Alpha pot help: A versus B

[Rockdog]

Hello all,

I searched the forum and could not come to a firm conclusion, so I apologize upfront that I'm posting on a redundant topic.

I purchased two Alpha pots from GFS: an audio and a linear. The GFS site suggests audio for volume controls and linear for tone controls.

I got them in and the tops of the pots read:
A250k
B250k

Here's where I need help:
1) From my research I gather that A = audio and B = linear...correct?

2) I've read several threads that seem to go against the advice of GFS and suggest instead using audio for tone and linear for volume. I guess there's no right or wrong, so is this simply a matter of preference?

Thanks!

 

[fyl]

From my research I gather that A = audio and B = linear...correct?

For recent pots, yes. Vintage models used A for LIN and C for LOG.

I've read several threads that seem to go against the advice of GFS and suggest instead using audio for tone and linear for volume. I guess there's no right or wrong, so is this simply a matter of preference?

IMO, the volume pot should always be a Log type, tone can be either Log or Lin. But you may perfectly prefer other combinations.

 

[Erwin]

Fyl is correct,

Volume pots need to be logarithmic as human hearing is logarithmic. If you where to use a linear pot it would only have an effect on the last part of its travel.
In general log pot are also used for tone controls.

 

[Rockdog]

OK thanks guys. So...

A = logarithmic = volume pot
B = linear = tone pot

Yeah?

 

[limbe]

To have the letters A and B to tell you if the pot was linear or logarithmic would be fine IF the markings were the same all over the world.A means linear or audio taper (logarithmic)which means that B can be log. or lin. A simple method to determine what kind of pot you´ve got is to set the pot in the midway position of its track,same distance from the wiper to both end lugs.Then measure the resistance from the wiper to both endlugs (one at the time.If both resistances are equal you´ve got a linear pot.

 

[Rockdog]

Thanks limbe, I'll try that.

 

[fyl]

To have the letters A and B to tell you if the pot was linear or logarithmic would be fine IF the markings were the same all over the world.

Agreed. European codes are reversed (B for LOG, A for LIN). But we're dealing with Alpha (Taiwan) pots, which use the A for LOG, B for LIN convention.

Anyway, getting the pots data sheet is quite easy.

 

[Wayne Alexander]

I'm going to suggest that you use audiotaper pots for tone and volume. I personally don't like the behavior of linear pots in guitars in any position, tone or volume.

 

[TNO]

I second that.. the Alpha B linear pot acts almost like a switch it's so abrupt.

 

[David Collins]

Either audio ("A" mark on your Alphas) or linear ("B") will work fine for volume, but traditionally tone pots are almost exclusively audio.

In traditional volume controls, audio pots will put a more rapid roll off at the top, somewhat of a plateau of slower change in the middle, and a smooth fade out at the bottom. This works great for quick clean up from overdrive at the top, a decent range of volume control in the middle, and smooth swells at the bottom. Playing clean (especially with solid state gear) however, some feel that audio has too much effect toward the top, dropping to half volume or less by the time you reach around 7. For these cases, or for double master volumes like a Les Paul, many prefer linear volume pots. When playing clean, they will have a much smoother, more consistent fade in between 10 to around 2. Their biggest downsides are that they have a more abrupt shut off at the bottom end, and if you want to use volume to clean up from distortion you have to roll it way down before hearing much effect at all. You can go either way with volumes though, depending on personal preference and other factors in your gear.

Tone controls however, are rarely considered compatible with linear pots. This is where they end up working more like an on/off switch at around 1 or 2. Manufacturers are split about 50/50 on using audio or linear for volume controls, but I can't think of any that use linear for tone in a traditional passive circuit. So if you're stuck with just one linear and one audio pot that you're going to wire in, the audio should go in the tone position, and the linear in volume.

There are exceptions to this rule. Danny Gatton for example, actually did use linear pots for his tone control. The reason was because he actually wanted to pack all the effective range down to perhaps the bottom 40-60 degrees of the pot's rotation. This made it easy to do quick tone swells keeping within the bottom third of it's range, and by the time you got to around 3 it was almost the same as being full up on 10. Good for quick swells if you know how to use it, but not so good for setting a spot on the tone that you're going to stick with and play in. It makes fine tuning a set position very touchy, and most people don't like it.

GFS really recommends linear pots for tone? That amazes me.

 

[Rockdog]

Well, I took another look at the GFS site and it's not exactly a recommendation:

"We stock both Audio and Linear Taper- Many prefer a Linear Taper for tone controls- We always use Audio for Volume Controls."

Before we go any further, maybe I should lay out exactly what my project is...I am building an Esquire and wiring it to Rob DiStefano's specs with the dummy coil and cocked wah in the front position. I also planned on applying the Ted Greene/Fezz Parka mod (connecting the tone pot to the middle lug of the volume pot). The pickup will be a SD Broadcaster.

As far as my style goes, I don't use the tone pot much in general, but it seems to be an integral part of this particular wiring scheme.

 

[jefrs]

IMO vol can be Log or Lin but tone is always Log. I never use Log for volume controls.

A linear pot on the tone control will place all the adjustment between 0 and 2. Nothing much happens on the tone knob until its resistance gets down below 100k.

On modern pots A is for audio/log an B for linear but you may well find old pots where A is Lin and B is Log. C is usually reverse-log. You can get 10% or 30% Log pots, the tone knob in the guitar is a 10% one.

 

[bluesky636]

I use audio (log) taper for both tone and volume. I also use only CTS pots.

 

[jefrs]

Full-size CTS and Alpha are about equal quality.
And although different size screws, both are actually metric fittings.

 

[bluesky636]

Full-size CTS and Alpha are about equal quality.

I'll stick with CTS, thank you.

 

[limbe]

Agreed. European codes are reversed (B for LOG, A for LIN). But we're dealing with Alpha (Taiwan) pots, which use the A for LOG, B for LIN convention.

Anyway, getting the pots data sheet is quite easy.

It´s fine that you knew what the markings meant in this case !
Me,I´ve got boxes of pots of unknown standard.I stick with the opinion that the fastest (and only way) to figure out what kind of pot I´m dealing with is to measure it.Which kind of taper you prefer is of course a matter of personal opinion though.Personally I use log for volume and lin for tone.

 

[Rockdog]

Thanks all for weighing in! I'm in no rush, so I have plenty of time to test different combinations.

 

[Vizcaster]

I find that the behavior of a linear taper or audio taper pot will make itself more apparent when using a good amount of distortion on the amp (or pedals). On a clean amp channel it's a lot harder to discern much of an effect on the volume knob. No surprise that Les Paul players like to drive an amp hard with those humbuckers, and in those musical genres there are good reasons for each type of pot. Gibson's main production facility (distinct from the custom shop Historics) has for the most part used linear taper pots for volume controls (still audio taper on tone though). In fact, RS Guitarworks sells a custom-tapered pot they call an "RS Superpot," manufactured by CTS for them, which has a taper that's somewhere between log and audio that works well on a Les Paul.

Since I like to keep my tele's just on the edge of breakup in a nice reverby Fender amp, an audio taper volume pot works just fine for me. With a humbucker equipped guitar where I might want a lot more crunch from the amp, I dislike audio taper since it's too abrupt between 10 and 8 where I usually like to tweak the distortion at the amp using the guitar's volume knob. This is important with tube amps or germanium transistor fuzzboxes, and has really no importance if you're using an analog (not digital modeling) solid state amp.

On second thought, nevermind. Just a big old +1 on what Collins said.

 

[jefrs]

I'll stick with CTS, thank you.

No really, Alpha may actually be better than CTS.
I've had no problems with full size Alpha, many years, but I've had several CTS inexplicably pack up, open circuit the track. I do use both. Alpha are available in more values and tapers. They are both made in the far east.

 

[jefrs]

The RS/CTS "special taper" is probably nothing more than a bog-standard 30% log pot i.e. it is 30% of its value at halfway whereas the normal 10% log pot is 10% of its full value. The 30% log is sometimes used in amp tone controls = somewhere between linear and logarithmic.

A log pot is not truly a log taper pot but three or four linear strips laid end to end, cunningly our ears don't notice.