Vin on Wiper Voltage Divider

[seten]

I cant formalize why you cant put Vin on the wiper and Vout on lug 3 for a volume pot at the end of a pedal (other than I think now output impedance is fixed at the total resistance of the pot rather than it being varied if its properly set up with Vout is on the wiper) .

With wiper fully CCW, Vin is grounded. No output. As you turn it up, there is more resistance between Vin and ground, and less resistance between Vin and Vout; output is increasing. Fully CW, Vin is continuous with Vout with a healthy resistance to ground and only a neglible amount of the input is shunted to ground; output is max.

Please dont give me the benefit of the doubt, seems like im either having a brain fart or I have a serious misunderstanding of how circuits (or at least voltage dividers) work.

[vigilante397]

You just independently invented the sag control of a fuzz factory The results will differ depending on the circuit, more voltage doesn't directly equal more volume.

Quick note though, grounding Vin is a very bad idea. Your power supply will not like it.

[antonis]

Not so much for power supply itself, as Nathan said, but definately big problem for last stage out..
e.g. In case of CE amp, Collector is directly grounded, where in the "conventional" pot wiring it pernanently "sees" GND via pot body resistance..

In case of wiring proposed by seten, resistance seen by Collector is valriable, hence CE amp Gain is also variable (due to parallel combination of pot resistance & Collector one), so it's primary Gain control and secondary Volume control...

Same stands, of cource, in a CC (buffer) configuration with also severe Emitter loading, resulting into Gain much less than unity..
(and some awful non-linearities..)

[PRR]

> Vin on the wiper and Vout on lug 3 for a volume pot

This can work. Look at the older Fenders. Two preamp tubes drive wipers of two pots, tied together at tops, output taken there.

https://robrobinette.com/images/Guitar/Deluxe_Models/5C3_Schematic_Signal_Path.gif
https://robrobinette.com/Fender_Deluxe_Models.htm

One objection is that at way-way-down the signal source is near *shorted*. It may distort early. It may need an extra large coupling cap (0.1u instead of 0.02u).

Another is that the output impedance to the next stage/box gets very high. INside an amp, you can plan around that, even use it for mixing. Going OUTside the box, having most of a 250k pot in series with a long cable sucks your highs off; or not, if the cable is not-long.

[seten]

Interesting. Guess I wasnt completely off.

You just independently invented the sag control of a fuzz factory The results will differ depending on the circuit, more voltage doesn't directly equal more volume.

Quick note though, grounding Vin is a very bad idea. Your power supply will not like it.

Youre talking about Vin as the power supply and Vout as power to the pedal though right?

[vigilante397]

Youre talking about Vin as the power supply and Vout as power to the pedal though right?

Correct.

[seten]

Youre talking about Vin as the power supply and Vout as power to the pedal though right?

Correct.

Whats the advantage of doing it that way instead of just a standard voltage divider? Seems like this would be the case where youd definitely want Vin lug 3 and Vout on the wiper so like you said theres no risk of grounding Vin (though I guess you would just put a resistor between lug 1 and ground so its never completely grounded?)

[vigilante397]

Whats the advantage of doing it that way instead of just a standard voltage divider?

In the case of a sag control you do it to make it adjustable. Different people like their fuzz with different levels of sag, so putting it on a potentiometer lets everyone have what they want. You use a voltage divider when you know what voltage you want to get and you don't want it to change, like when you want Vin/2 as a Vb for op-amps and such.

[seten]

In the case of a sag control you do it to make it adjustable. Different people like their fuzz with different levels of sag, so putting it on a potentiometer lets everyone have what they want. You use a voltage divider when you know what voltage you want to get and you don't want it to change, like when you want Vin/2 as a Vb for op-amps and such.

Right, I get why youd put it on a pot - but why put Vin on the wiper and Vout lug 3 instead of Vin lug 3 Vout wiper?

https://www.stewmac.com/articles-and-video/online-resources/learn-about-guitar-pickups-and-electronics-and-wiring/understanding-guitar-wiring-i-4000-4.html

This answers my question for guitar vol controls, but I'm still curious why you would use one vs the other for a sag control. (to be clear you were saying that for the fuzz factory power sag its Vin wiper Vout lug 3? The schematics ive found just have a Stab control thats just a variable resistor - 9v to lug 1/2 and Vout lug 3)

[vigilante397]

Right, I get why youd put it on a pot - but why put Vin on the wiper and Vout lug 3 instead of Vin lug 3 Vout wiper?

You're absolutely right, sag controls are generally variable resistors instead of pots. I don't see where I said Vin was on wiper and Vout is lug 3, I just meant that using a potentiometer (as a variable resistor) is a typical method of a sag control.

[seten]

You're absolutely right, sag controls are generally variable resistors instead of pots. I don't see where I said Vin was on wiper and Vout is lug 3, I just meant that using a potentiometer (as a variable resistor) is a typical method of a sag control.

Ahhh gotcha - I think our misunderstanding started at the very beginning. I see what youre saying now.