CTS pot taper observation

[Mick Bailey]

I've just had some new CTS 1MA pots and noticed there's almost no change in resistance for the first 1/6th rotation, then the resistance jumps. Pretty much no low-volume graduation. By comparison Alpha pots are well graduated and much better at low volume. I've got some older CTS pots and they have a smooth taper too. Anyone else notice this?

Just got a Two Rock Classic Reverb in for repair and was surprised to see Alpha pots in such an expensive amp, where maybe you would have expected CTS.

[soundmasterg]

I've noticed this too....I am not impressed with CTS or any of the cheaper pots these days....the Alphas have decent taper but they are not as high quality as some others. RS Guitarworks has CTS make pots to their specs and they are much better but come with a much higher price too. The PEC 2W sealed pots are nice but spendy.

Greg

[pdf64]

That's bad news.
Are these CTS still 10% of total track resistance at a 50% rotation setting?
Do you mind revealing where you got them?
Thanks - Pete

[R.G.]

There are almost no modern pots that have anything like an accurate taper other than linear. "A" and "C" tapers are approximated by making different sections of linear. This is much easier to manufacture than actually changing the resistivity along the track or tapering the track on the pot wafer. It can be pretty good if care is taken in the straight-line approximations, and this used to be pretty good.

Unfortunately, industry's race to the bottom for costs means that most pots these days use only two sections. The low part of the pot is linear up to some point, then it's linear at a higher rate for the rest of the way.

You can use linear and add tapering resistors to get a much better approximation of a log or anti-log pot. See The Secret Life of Pots at Geofex.

[Mick Bailey]

These were bought from Hotrox by a customer and dropped off with an amp. I've also checked some I bought last year and they're the same. Coincidentally I have another (recent) amp in for service with CTS pots and there's nothing until 2 on the volume, so it isn't tied to one supplier.

[loudthud]

I found some Alpha Audio taper pots that were intended to optionally have the back removed and a switch installed. The signal is off until you rotate the shaft to almost 9:00 o'clock. They were from Radio Shack and stamped Alpha Taiwan on the back.

[R.G.]

It's worth a note here. In my day job, we use enough pots that we will occasionally ask for and get custom pots. Pot makers are willing to make custom pots for enough quantity. The funny thing is that the quantity may be as low as 1000 or 5000, unlike some other things. That's a trivial number of pots for a manufacturer to need, but a disastrous number for an individual to need. So there exists a profusion of semi-custom pots in equipment and on the surplus market that may do odd things indeed. Special tapers, taps, odd rotational qualities, continuous rotation, etc. can all be found.

Distributors will only buy a few of these profusion of types that are as generic as they think they can sell, so the ones-and-twos market we get personal stock from is very limited.

[Mick Bailey]

I found some Alpha Audio taper pots that were intended to optionally have the back removed and a switch installed. The signal is off until you rotate the shaft to almost 9:00 o'clock. They were from Radio Shack and stamped Alpha Taiwan on the back.

I never thought of that. I just tried a switched pot and the switch clicks at about 1/6th to 1/5th rotation - coincidentally where my CTS pots begin their 'proper' resistance change.