looking for alps 20k log 45mm slider pots

[loonatron]

Does anyone know where I can get some Alps 20kohm log 45mm travel slider pots from? The device they are from is a UREI graphic eq, but are NLA as a replacement part. Unfortunately they seem to be a special OEM part from ALPS... they don't appear on the Alps database. (they look like the "superslide" series.)

thanks, from Steve

[dmfraser]

Most graphic EQs use linear pots. WHy do you need new ones? unless the slider is broken off or the resistive element is worn out, it is possible to take most slide pots apart and fully clean and relube them.

Otherwise, take a 100K linear slide pot anf put a 10K resistor between the wiper and the bottom terminal of the resistance element and you have a rough approximation of a 20K log pot.

[loonatron]

Hi dm,

thanks for that reply! The slider is for the output attenuator (yes it really does have this feature, as well as an input level slider!) so that's why I need a log fader. And yes the fader is completely ruined. (hold it up to the light and see through the resistive track!)

Tried the usual cleaning and lube tricks...

If it was my personal equipment I would be doing some kind of modification, but it belongs to my employer.

[dmfraser]

As an output attenuator, the trick I mentioned will work fine. In an attenuator application, by taking a linear pot and putting a fixed resistor value of 1/5 to 1/10 the pot's end to end resistance between the wiper and ground will give you a very good approximation of a log pot. This is how to easily get a log/anti-log pot as well when you need one.

The only thing to be aware of is that the overall end to end resistance of the pot will vary with the rotation angle. However, if the source is driven from an op-amp, this is not a problem. However, the pot's output impedance will be essentially the same as when using a real log pot.

In the USA, you can buy linear slide pots from Mouser in about 10mm increments. In Oz I would assume Dick Smith or the like could fill the need.