potentiometers

[imsellingmyfoot]

I have a question that probably has an obvious answer. I have been building a simple amp based on a National Semiconductor chip. The spec calls for a "10K log pot" for each channel of the audio input. Firstly, what is a good potentiometer for me to use? Searching on Digikey gives me way too many options to know what to do with. I like the cosmetics of the slide potentiometers, but I am more concerned with sound quality and function. Secondly, how do I mount these? I was planning on having the pots mounted next to each other through a hole in the aluminum faceplate of my enclosure.


Thanks

[bob91343]

The brand and mechanical details are unimportant; buy something that pleases you. Log pots (also known as audio taper) are less popular than linear but still there are plenty.

You might want to get a dual pot, one knob for both channels, and add a balance control sort of like most stereos have. Slide controls are cute but not pleasant to use for an audio system; they are hard to adjust a little bit without a finger on the panel.

[imsellingmyfoot]

So if I were to decide on a dual pot, how do I mount it on a piece of sheet aluminum? Is it as simple as punching a hole for the threads at the base of the shaft and putting an appropriately sized bolt on it to sandwich the aluminum?

[Mooly]

Rotary pots come with a nut and washers to secure... single hole is all that's needed.

[Bonsai]

If you are looking for a decent pot, try the Alps RK27 - also known as the 'Bluevelvet'. for the best control of volume (i.e. ausio level), you must use a log pot, also known as an 'audio taper' pot or just a 'taper' pot. If you use a liner pot, the volume increases too rapidly and you loose the fine control needed to set the volume accurately and this is related to how your ear works and the science of phsycoacoustics.

Its not cheap, but its a great pot. Farnel also carry them I believe.

For a stereo system, its conventional (and probably wise) to use a dual log potentiometer for the volume control. If you look at my web page below, there is an article on a pre-amp and some comments about the RK27 and on mounting and grounding - quite important stuff if you want a noise free design.

Good luck with your project!

[wakibaki]

Originally Posted by imsellingmyfoot

So if I were to decide on a dual pot, how do I mount it on a piece of sheet aluminum? Is it as simple as punching a hole for the threads at the base of the shaft and putting an appropriately sized bolt on it to sandwich the aluminum?

Yes, but be aware that many pots also have a short pin or lug sticking out of the same face as the shaft. This is intended to stop the pot rotating when the shaft is turned to its end stop, and requires a second, smaller hole in the aluminium sheet, otherwise the pot may not sit properly flush. It is often possible to cut this lug off with a pair of heavy wire cutters, but then the pot is free to rotate and the retaining nut may slacken off.

w

[Redshift187]

Rather than make a second small hole for the lug, I just use two nuts, one on either side of the panel, and tighten them well.

[nigelwright7557]

The lug is easy to make a hole for.
Just put the pot in and turn it slightly and the lug will mark exactly where it goes.

[linuxworks]

that 2nd hole is a PITA. I never use them. they are entirely optional if the rotation force is not very hard (and on pots, its not). I've found a simple lock washer to be all you need.

less drilling = better

[wakibaki]

Originally Posted by linuxworks

that 2nd hole is a PITA.

Until the day your pot doesn't rotate.

The trouble is: kids. Or other unexpected sources of high torque. In many instances it's true that 2 nuts applied in a locking configuration are fine, and a drop of locktite doesn't hurt, but those little lugs do just what they're intended to.

In many instances you can't fit the pot properly unless you bend the lugs or cut them off or provide the hole. The pots that don't have the lugs are PCB mounting, the PCB keeps them from rotating. The pots that do are chassis mounting, and if they free off they can carry the wires and additional components they often have soldered to them round and round.

I like to use PCB mount. It's better all round, except perhaps for valve designs done point-to-point.

w