RockinRocket wrote: ↑Wed Aug 22, 2018 3:17 pm
Correct. The frequency range is more or less the same but the sweep is very bunched between 1-5 and then very spread out. So its not linearly even though the pot is linearly.
This isn't my experience. 5K pot with 4K7 to ground and the sweep is not bunched up at all. It actually seems to be more spread out. Presence basically does nothing from 0 up to like 12:00 or even maybe 1:30. And then you can hear the high end coming in after that.
I believe the difference is because the cap on the pot is wired differently. Joins from the wiper to a end.
No it's wired the same as without the resistor. At least in the amps I have.
My understanding is that the marshall presence control did not keep dc off the pot and does have some scratchiness due to it. Since most people set the presence for their play style and don't really touch afterwards, it's a non issue.
RockinRocket wrote: ↑Wed Aug 22, 2018 3:17 pm
Correct. The frequency range is more or less the same but the sweep is very bunched between 1-5 and then very spread out. So its not linearly even though the pot is linearly.
This isn't my experience. 5K pot with 4K7 to ground and the sweep is not bunched up at all. It actually seems to be more spread out. Presence basically does nothing from 0 up to like 12:00 or even maybe 1:30. And then you can hear the high end coming in after that.
I believe the difference is because the cap on the pot is wired differently. Joins from the wiper to a end.
No it's wired the same as without the resistor. At least in the amps I have.
The 5k pot and 4k7 reistor still has half the sweep of a 25k pot. The bunchyness is still there but not nearly as dramatic as the 25k pot and 4k7 resistor.
Check out Robertos amazing job at analyzing the circuits in this thread page 4.
FourT6and2 wrote:... The 4K7 resistor is there to block DC, right?
No, resistors do not block DC. The 4K7 provides a dc current path for the PI cathodes.
Thus keeping DC off the pot?
No. The cap keeps the DC off the pot. In the original 5K presence control the PI cathode current flows through the pot and causes a scratchy sound only when you turn the pot. The later circuit removed the dc on the pot (and the scratchiness). The 4K7 simply provides a dc current path for the tube.
I've never seen it, but I'm just a hobbyist and haven't strayed far from Fender, Marshall, Ampeg, and Vox designs. Maybe you could post the schematic of the amp you have with this configuration.
sluckey wrote: ↑Wed Aug 22, 2018 10:56 pm
I've never seen it, but I'm just a hobbyist and haven't strayed far from Fender, Marshall, Ampeg, and Vox designs. Maybe you could post the schematic of the amp you have with this configuration.
It's just a 2204 clone with a Jose master volume mod. But it has a 4K7 tied to the 5K L presence pot. And it's a new amp, not some home-brew or amp that got modded a bunch of times.
