linear or audio?

[daz]

I know that gain, volume, and bass pots are usually audio, but which should i get linear for? Presence treble and middle are the questionable positions. I imagine mid and presence should be linear and treble audio, no?

[pdf64]

Whichever suits you best, there's no black and white, people have their own preference.
My rule of thumb is that if a control covers a big range, then audio 10% taper, less of a range then audio 30% taper, least range then linear taper.
'Range' would generally mean the perceived difference from max to min.
For a 3 gain stage JCM800 type MV amp, I'd use 10% audio for gain and bass, linear for treble, mid, presence, and 30% audio or linear for the MV. If it was to more domestic friendly then use a 10% audio for the MV.

[daz]

Well, i just bought what i recall when i built the current amp. Any of them don't work right i'll shitcan them and buy more. I remember having trouble finding a treble pot who's travel i liked, so chances are that one will get trashed and i'll end up with some old corroded pot in the junk drawer that works better. Or just pull the old junky one out of the old amp which in fact WAS one of those old corroded junk drawer parts !

[uvacom]

We had a pretty healthy discussion about this a while back. There is no simple answer, because sometimes even when one taper would be the intuitive choice, there are some practical reasons to use a different taper - example, some people like linear taper on their guitar's pots because it allows them to back off on the volume in a way that is more suited to their playing.

[anson]

I find that reverse log pots are good for presence. Unfortunately, there's none at the local electronics shop and I haven't found any in the values that I want on the web, so I just use a regular log pot and accept its functionality being backwards to the rest of the knobs.

[anson]

Actually, what about more extreme types of log pot, like 5%, are those around? There have been places in my amp where a regular log still didn't have enough of a taper, such as pots that work as variable resistors to shunt a small cap to ground as a treble/presence control.

[daz]

Yeah, i found this when i built my amps too. I mainly found i could only get the taper right on the treble and master vol pots by trying a number till i found a few old junk drawer pots that had a less common taper that worked well. I really don't want to use old junk parts in my new build tho because i decided i want this amp to be a thing of beauty, not a mishmash of old corroded parts. So i just bought all bourns pots and whatever doesn't work i will attempt to either live with or change the taper with a resistor.

[Mark Hammer]

If you need to know where the "middle" is, then linear is what you want. So, for example baxandall-type tone controls where there is actual boost and cut, generally require linear taper because the midpoint on the pot is that point where no boost or cut is applied.

"Gain" can be set many different ways, so there is no hard and fast rule for what taper gain controls require. Volume controls generally want a log taper,. If the "gain" control on a given circuit is essentially a fixed gain stage with a volume knob determining how much of that boost is spooled out to the next stage, then you want to use a log taper because the "gain" control is essentially functioning like another volume pot earlier in the circuit. But "gain" adjustment can be implemented in other ways too, and those may require a different sort of taper.

Likewise, what gets called "Presence" can also vary in how it is implemented. In some amps, it is merely a high cut control, in which case a linear taper may be appropriate. When presence is produced via post-OT-transformer feedback, a reverse-log can be useful to dial it in.

In all instances, use of the right value but "wrong" taper will still leave the circuit functional. The question is whether the taper employed provides the desired degree of dialability. Some tapers, when misapplied, will result in all the interesting changes being scrunched in to a small arc of rotation. maximum dialability means having those changes more evenly distributed about the entire rotation of the control.

[tedmich]

too much adjustability in most amps IMO, if you are building them for one person. If you want to sell to 100+ people ok, but on my amps I find one sound I like and then use the volume knob. How many people are reefing on their presence knob during a song? Between songs? For my amps I use quiet CP/cermet pots in whatever taper I can find cheap.

now a foot actuated tone knob... that requires a precise taper!

[jrfrond]

The bottom line is that resistance is resistance. Taper just controls where it is vs. pot travel (an easy way to test pot taper is to set the wiper at the mid point and check between a hot lead and the wiper with an ohmmeter. If it is half the pot value, it is linear). The circuit will work no matter what taper you use, but the action might not be right. Application is only a rough indication of what taper needs to be used. Generally, log (audio) taper pots are used for volume controls, but sometimes a linear might need to be used, depending on circuit loading and/or design.

When purchasing off-the-shelf, limited tapers are available and sometimes you must use what is available. Try audio and linear and see what feels best. Too much trouble to switch pots around for test? Welcome to the world of R & D!

[daz]

I understand that. but the reason i asked is because that does matter to me, and a lot. particularly on the gain and master where i have had pots that make the master so touchy when i play at home it's nearly impossibly to get that perfect level thats just as loud as you can be w/o disturbing anyone but not so low theres no tone. at such low levels no taper worked till i found a particular pot that made that area of rotation much less sensitive. i think just recently i posted about my gain pot being such a mismatch with the amp taper wise that it did nothing between 12:00 and full up. Max gain was at 12. i tried several pots with the same result, then found one that worked, and they were all some form of audio too ! (or at least none were linear which i checked with a meter) then there was the treble which i had trouble finding a taper i liked for, tho that wasn't as much an issue as just preference. I was finding most 250's were giving me the max treble at 10:00 and i prefer it around 2:00 because it makes the rotation less sensitive. I found a pot that worked the way i wanted but most didn't

[jrfrond]

Well, here's a newsflash for you: cheap pots are cheap for a reason, and BTW, CTS is ALSO a cheap pot. No different than Alpha, Alps or Bourns really.

A pot's "taper" is called that because the actual shape of the resistive track is tapered from wide to narrow, and curved to accomodate a rotary control. This is for AUDIO pots. Linear pots have a constant-width track. At least, that's the way it USED to be with audio pots. Modern low-cost audio-taper pots use a series of linear tracks of varying resistance, connect-the-dots style, to simulate a tapered rolloff. While the OVERALL effect is that of an audio taper pot, the resistance change is more abrupt.

[Steve Conner]

Have you seen the Bourns Model 95 pot? It looks pretty good quality. I put one in my bass to replace the old crackly volume pot, and the taper seemed different. Not sure if it's more logarithmic or less, though. I have a spare one I could measure.

[daz]

99.999% of the reason i bought bourns is because i use a clear plexi faceplate, and when combined with the chassis face it's too thick for most pots, and the bourns has a long thread. I'm not saying nothing else does, but i already ask too many questions here so i left that one to the best i could do with my own research in order to save the more important questions i will need to ask.