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Taper of Potentiometers

re the two sections of a dual linear pot in series. The wiper of the first half goes to the top of the second and its wiper becomes the output. Bottom ends are both grounded.

At the centre (50%) position, this reliably gives -15dB attenuation when lo ading effects are taken into account.

At the 75% setting, attenuation is -6.5dB, at 25% it is -25dB while down at 10%, attenuation is -40dB.

..... Phil"

That is what high end audio equipment does. Have seen it a few times. It do es make for a nice smooth taper. Also in preamps it enhances the S/N ratio at lower volume settings. Usually the first pot is somewhere near the tone control circuit, if any. The second pot is right at the preamp outputs.

Actually if a volume control is "too fast" a resistor between the wiper and ground side makes a pretty decent taper.

One time a guy broings in a receiver, an upgrade from the one he had but ot h the same brand. He asked why he had to turn it higher to get the same vol ume level even though it was more power. I had to explain it so I used the accelerator in a car. I told him they could make the linkage so it is just about floored when you give it half a pedal, but does that make the car go faster ? Nope, it has the same horsepower (kilowatts for youse across the p ond) no matter how the accelerator linkage is designed. I think he understo od. I told him it gives him more accurate control.

Reply to
jurb6006
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** Is that what it's called ?

** It's so repeatable, unlike with some batch of low cost log pots, you could have the -dBs figures printed on a front panel and they would always align with the pot.
** Horrible idea - it shorts the signal at low settings and sends the output impedance high just when you want it low for noise/hum reasons.

..... Phil

Reply to
Phil Allison

Isn't that how some guitar pickups are wired ? And don't ask me why.

Reply to
jurb6006

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** Only very rarely. That method has just *one* advantage where there are multiple PUs, each with its own volume pot. It forms a resistive mixer that allows signal to pass from any pickup to the output regardless of the other pot settings.

The usual method requires no control be zeroed when PUs are switched in parallel or the instrument becomes silent.

The wiring schemes used in most electric guitars are primitive, full of dodges and compromises - good examples of how NOT to do it.

See wiring for early Gibson models.

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.... Phil

Reply to
Phil Allison

No idea what it's called, but if a log pot can be called that (even though the intended operation is exponential, i.e. opposite of log, to compensate for the log response of the ear) then this should be square-root, because the actual curve is the square function.

Clifford Heath.

Reply to
Clifford Heath

Now I wonder what kind of taper is used in the pots in a graphic equalizer. Double reverse anti-log or some bizarre shit like that ?

Reply to
jurb6006

For f*ck's sake. Am I the only one here that got the joke?

--
"I am a river to my people." 
Jeff-1.0 
WA6FWi 
http:foxsmercantile.com
Reply to
Fox's Mercantile

I don't know, but would expect linear.

someone hasn't been paying attention

NT

Reply to
tabbypurr

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** At least one source calls it a "square law attenuator" or SLA.

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A SLA closely follows the formula:

Gain = 40log(position ratio) where closed =0 and open =1

.... Phil

Reply to
Phil Allison

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** The vast majority use standard, linear slider pots - which tend to crowd most of the dB adjustment range in the last 25-30% of their travel.

A few special types have a small dead band in the middle of the track accompanied by a centre detent.

I recall seeing just one, up market graphic that had sliders with symmetrical non-linear tracks to compensate for the end crowding effect and give a linear result.

.... Phil

Reply to
Phil Allison

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