Taming Fender Blues Deluxe Abrupt Volume Control

[hasserl]

This seems to be a common complaint with these amps, the Clean channel Volume control (as well as the dirty channel master volume) seem to have a very abrupt action between about 1 - 2, with very low volume at 1 and pretty much full volume at 2, making it difficult to dial in the right volume for a given situation. I've spent a couple of hours searching the net for a mod to correct this, and haven't found anything of any value yet, I was wondering if anyone around here has come up with anything?

Most things I've found on the net center around a claim that Fender used linear taper pots on the volume control, and that a change to an audio taper will correct the problem, but the schematic I have shows a 250k audio taper pot for the clean channel Volume, so I'm not sure why everyone seems to think it's a linear pot. Maybe someone posted it was once on a forum and everyone has been repeating that ever since, I don't know. In any case, looking at the schematic there doesn't seem to be any logical reason for the abrupt action of the pot, 250k audio pot should give a nice gradual and controllable increase in volume.

In any case, anyone have any experience with this they'd share, it would be appreciated.

Thanks,
Hasse

[Leo_Gnardo]

This seems to be a common complaint with these amps, the Clean channel Volume control (as well as the dirty channel master volume) seem to have a very abrupt action between about 1 - 2, with very low volume at 1 and pretty much full volume at 2, making it difficult to dial in the right volume for a given situation. I've spent a couple of hours searching the net for a mod to correct this, and haven't found anything of any value yet, I was wondering if anyone around here has come up with anything?

Those controls do have - some sort of - "audio curve" but there's a lot of signal riding atop that pot, too. What I do is put a resistor across the pot, 56K or 68K. There's already a voltage dividing resistor in series with the pot, and the addition of a resistor reduces the maximum volume that can be set (still excruciating don't worry) and "opens up" the volume control's scale of effect on volume, iow, it's not all crammed down there at 1-2 anymore. Same can be done for the od channel's master volume - 100K works well there.

[Dave H]

This seems to be a common complaint with these amps, the Clean channel Volume control (as well as the dirty channel master volume) seem to have a very abrupt action between about 1 - 2, with very low volume at 1 and pretty much full volume at 2, making it difficult to dial in the right volume for a given situation.Hasse

That is because they have used the controls as variable resistors (rheostats) in conjunction with a series resistor (which destroys the log taper of the controls) rather than as potentiometers. It's done that way for the channel switching. A 10% log pot set to half rotation would normally attenuate the signal by a factor of 10 but look at the Master, if it's set to half rotation and it's 1M 10% log that would be 100k but it's working with a 330k resistor so the attenuation is only a (330+100)/100=4.3

[hasserl]

Ahhh, I see that series resistor and that makes sense now. Thank you guys for pointing that out. Leo, do you put that resistor across the left & right legs of the pot? Doesn't that make it quite lossy?

[guitardad]

1-2 is for at home

2 and up is to keep up with a drummer and gives plenty of headroom for pedals.

[J M Fahey]

What dave h said. [+1]

[Leo_Gnardo]

Ahhh, I see that series resistor and that makes sense now. Thank you guys for pointing that out. Leo, do you put that resistor across the left & right legs of the pot? Doesn't that make it quite lossy?

Yes, right across hot to ground. I s'pose you could put a resistor in, wiper to ground, that wound "bend" the curve a little as well as reduce overall volume with the pot at 10. We could do with some signal loss here, that's the point. Or you can unsolder the series resistor and increase its value. I chose the lazy route.

[Dave H]

I could understand connecting it as it is if they were using an LDR or JFET for channel switching but they have a relay with an unused change over contact. Why didn't they wire the controls as potentiometers and use the relay to switch the output between the pot's wiper and cw terminals?