Where are folks getting 30% taper pots

[Bob-I]

I can only find CTS and they have a dead spot from 0 to 2. I heard that it’s because they use the same resistive strip with the switched pots.

Any leads?

Thx

[martin manning]

Search for J taper. Amplified Parts and Mojo have them.

[Bob-I]

Search for J taper. Amplified Parts and Mojo have them.

Amplified parts only has CTS…I don’t see Amy on mojo’s site.

[jbrew73]

Do any of the 30% or J taper pots have a firm rotational resistance? I see them often listed as low torque or guitar pots.

[martin manning]

The ones with solid 1/4" shafts are typically used for Fender treble pots and should be fine.

[nuke]

For guitars, I've been using the DiMarzio custom taper Pro Pots.

Not available in all values and shaft types for amps, but cover most guitars.

They're CTS, but seem to have a better taper, perhaps done to custom order. I haven't specifically tested them off the "0" end as much the "10" end, where they're really great on guitars.

[Bob-I]

The ones with solid 1/4" shafts are typically used for Fender treble pots and should be fine.

Thx Martin, that’s exactly what I’ve been doing up till now. Recently I refurbished 2 amps for friends, a 61 Tremolux and a 62 Bandmaster. Both had 30% taper pots (yes I measured) and really liked the way they act.

It’s my belief, from by very unscientific tests, that the Alpha 15% are not log at all, but have 2 linear sections, 0-50% rotation, and 50-100% rotation. The 30% seemed like the 0-50% rotation was a log curve, then almost linear from 50-100%. It makes the onset of sound very controllable.

I’m beginning the think I’m beating a dead horse. The CTS are ok, but that dead spot ruins the gradual onset of sound.

[martin manning]

It’s my belief, from by very unscientific tests, that the Alpha 15% are not log at all, but have 2 linear sections, 0-50% rotation, and 50-100% rotation. The 30% seemed like the 0-50% rotation was a log curve, then almost linear from 50-100%. It makes the onset of sound very controllable.

I’m beginning the think I’m beating a dead horse. The CTS are ok, but that dead spot ruins the gradual onset of sound.

It's a fact. The curves are some approximation of a log curve. You can get the first chart below from Alpha's web site (https://www.alphapotentiometers.net/htm ... urves.html). Sellers of these products do not provide the details, only the nominal resistance/max resistance at 50% rotation, and often less than that, specifying only audio, reverse-audio, or linear taper. CTS lists a potentiometer series 450G that looks like what Mojo et al are selling, with the various taper options, including "J" (https://www.ctscorp.com/Files/DataSheet ... asheet.pdf)

[martin manning]

The CTS are ok, but that dead spot ruins the gradual onset of sound.

Note the CTS pots don't start adding resistance until ~14% of the 300 degrees stop-to-stop is exceeded, which is 42 degrees. Each number on the knob (Fender type, 1-10) is 1/9 of 300, or 43 degrees, so you shouldn't expect to hear anything until you get to ~2.

[nuke]

One possible trick is to put a small resistor on the low-leg (usually the grounded leg) of the pot so that it doesn't quite go to zero when you turn it all the way down. You'll still get the little jump, but it wont be quite the on/off jump. If you pick the value carefully, and you don't mind it going not quite to full off, it sort of solves the problem.

Other wise, one can attempt to tinker with the carbon track on the wafer.

[Richard1001]

Tube amp doctor sells CTS pots with true vintage audio taper. I used them in one of my amps and they work very well

[Bob-I]

Tube amp doctor sells CTS pots with true vintage audio taper. I used them in one of my amps and they work very well

Yes, I bought a few but they have the dead spot on the first few degrees of rotation. The vintage amps I’ve worked on don’t have that and the response is far better.

[Mr. dB]

"Dimple Back" CTS 1M and 500K audio taper pots seem to lack the dead spot.

I think the crappy taper on the regular CTS pots is due to the option for a concentric on-off switch.