Unfamiliar rheostat pot symbol

[frets]

Happy Sunday Guys😸

I ran across the following diagram with a rheostat pot symbol (I think) that I’ve seen in several different diagrams; but, the actual connection of the lugs given the directionality of the arrow confuses me.  As an example in this simple diagram, the arrow on the pots point upward.  So does that mean lugs 2 and 3 are connected?  And if so, why would one do that on the Volume pot?
Thanks!

[newey]

Feb 5, 2023 15:33:41 GMT -5 frets said:

a rheostat pot symbol (I think)

Connect the wiper and one lug of a potentiometer and you have a rheostat. Connect all three lugs, it's a potentiometer. But it's the same piece of hardware either way.

The symbol is just a different schematic symbol for a potentiometer. Each one in the diagram has all 3 lugs connected. The rectangle is the resistive element, the arrow bent upwards is meant to represent the wiper, telling you it's a pot, not just a resistor. The arrow pointing upwards next to the symbol indicates the direction of the clockwise lug.

[sumgai]

frets,


You'll notice that every component on there is of European descent. They used the almost-standard symbol for a capacitor, but in the world of resistors, they can't be bothered to draw squiggly lines - a simple box does the job. Hence, an angled line with an arrow through the box means 'variable'. How it's hooked up (what kind of job is it doing) is left to the designer, for as newey said, the same component can fulfill multiple requirements.

I'm surprised you haven't seem more of these kinds of symbols, a lot of stuff comes out of Europe.

HTH




sumgai

[b4nj0]

I suspect that it derives from an individual's first learning experiences because for me "a resistor" is my first reaction to seeing a rectangle like that. I sketch ideas out that way too. I've always suspected that it derives from the potential for a zig-zag resistor symbol to be mistaken for an inductor symbol if it's a sloppy sketch or a low resolution internet image or poor photocopy. That said, just like American English, I'm never cussed enough to affect a need for any translation. A moment's consideration and I'm back in the saddle.

I do like to see ground/earth/return down at the bottom though! Some (typically) automotive circuit diagrams really can challenge me.

でつ e&oe ...

[frets]

Thanks guys, that is very helpful.

[thetragichero]

i'm almost always confused about outside lug placement, but in a case like this where there is a volume pot i can 'cheat' off of (knowing that lug 1 goes to ground) i can usually manage

[Yogi B]

Feb 7, 2023 11:38:55 GMT -5 thetragichero said:

i'm almost always confused about outside lug placement, but in a case like this where there is a volume pot i can 'cheat' off of (knowing that lug 1 goes to ground) i can usually manage

If you mean that you can use their orientation of the symbol used as the volume control to infer the convention used by the author — in cases very specifically like this one, you cannot, because the above diagram lacks that consistency.

For the volume control (R8), positioning the wiper closest the end of the resistance that the arrow head(s) point toward results in the most volume. However, whilst following the same positioning for the gain/pre-volume control (R7) nets you the largest (average) voltage at the wiper, that's because that voltage is (a constant) 9V and you have none of the actual signal.

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frets, if you're breadboarding this, something that might be worth exploring is fixing the gain control at its maximum (or replacing it with a trim-pot), then vary the op-amp's feedback resistor (R6) as an alternative gain control instead.

This won't have the ability to zero out the signal as with the previous example, which you may or may not see as an advantage, at minimum (R6 = 0) the op-amp will be acting as a buffer. That description also reveals another property of this alternative gain control — a buffer (ideally) gives a flat frequency response, whereas the original would always be moderately mid focused thanks to C3 reducing the gain of bass frequencies and the relatively limited gain-bandwidth product of an LM741 cutting the treble — this alternative control will shift between those extremes: the original mid-focused response at max gain, and flat at minimum gain.

Finally, this configuration has negligible DC voltage across the pot (unlike the original) so won't suffer from crackling as the pot is turned.

[frets]

Thanks Yogi, I will try it out.