Pulldown resistor after volume control?

[moro]

Hello,

Sometimes, I'll see what I assume to be a pop-prevention pulldown resistor after a volume control at the output. Like this (warning--link to PDF):

http://www.generalguitargadgets.com/pdf/ggg_ff5_sc_b69.pdf

Does that resistor serve a purpose? Isn't the output cap always connected to ground anyway?

Thanks.

[m_charles]

your pulldown should be the very last thing before the switch....

[yeeshkul]

however if i understand well, the volume works like a pull-down then ... i was thinking about the same thing when i saw the same cirguit some time ago

[mac]

the volume pot is the pulldown resistor in the above link, so the 1M is not necessary.
but in a rangemaster the volume pot is followed by a capacitor so maybe a pulldown resistor of about 1M is needed. as a matter of fact I had to add one to mine.

mac

[JHS]

This R is not for pulldown.
Sometimes a resistor is connected to the wiper and ground to get a more even sweep of the pot
Sometimes you see a resistor connected parallel to the pot for altering the value of the pot.

JHS

[yeeshkul]

If 1M resistor is ment to adjust the volume pot value, then it makes it 330k. That seems to be a bit subtle solution for just a volume pot .

[moro]

Thanks for the responses, everyone. I guess I can just ignore that resistor.

I don't understand why it would be used to change the sweep of the pot though. Surely, Mike Fuller can have custom pots made?

[John Lyons]

Keep in mind that some of the original FF level pots were not 500K but closer to 330K.
Tapering that level pot with the 1M resistor is a hell of a lot easier and cheaper than ordering a batch or 330K pots!
Assuming this is the case and not a typo.

John

[yeeshkul]

then it is clear John 

[moro]

Keep in mind that some of the original FF level pots were not 500K but closer to 330K.
Tapering that level pot with the 1M resistor is a hell of a lot easier and cheaper than ordering a batch or 330K pots!

Ah, that's interesting.

Assuming this is the case and not a typo.

It's possible it's a mistake. This is supposed to be the Fulltone 69, I believe, but the schematics that are floating around don't seem to match the gutshots.

[m_charles]

wait, now I'm confused.

I've always routinely put a pulldown on the out, whatever the out pot value. Is this wrong? unnecessary?

[John Lyons]

The reason circuits pop is that the output/input cap is (possibly) charging with DC voltage. When that voltage does not have a path to ground (1Mish pull-down resistor or volume pot) the voltage will build up and pop once you switch the pedal in or out. The pop you hear is the DC discharging into the signal path.

With a volume pot right after the output cap you have a path to ground so the possible DC voltage is consistantly drained to ground...no pop.
If you put a pull-down resistor from the wiper/lug 2 to ground off the pot you are changing the taper of the pot and the impedance of the circuit. What this is doing is putting a parallel resistor across lug 2 and ground which is redundant for pop protection and is tapering the pot to be a very wide ramp up audio taper. It's also cutting a little volume.

This can be a good thing if that's what is needed, but for pop protection only it isn't helping and most likely hurting the circuits level and volume pot "feel" which will be quiet most of the way and them ramp up fast.

John



John

[m_charles]

hi john,

so what are the situations you would definitely want an out pulldown?

thanks for your help...

[John Lyons]

Any time that you have a capacitor that has no resistance to ground you should have a pull-down resistor. For instance if you had a volume control followed by a buffer you would need a pull-down resistor. Any circuit with a volume pot at the last component does not need a pull-down resistor.
The input should always have a pull-down resistor as well unless you have a pot there as well. Some fuzz face circuits use a volume control at the input to control the gain amount.
Switching between caps is a good place for them as well. (although caps in parallel will not pop with a single pull-down before them in the input)

John

[yeeshkul]

Also avoid the mistake of putting the pulldown resistor right on jack, that wouldn't work it must be between circuit in/out cap and the main switch. Volume at the end of the circuit works as a pull down, so there is no need to put an extra resistor(for sake of pulling the cap leakage down the ground). Also i had a bad experience with some ways of SPDT wiring - it was popping (just in one case but still ...) too. Use the simplest one first.