Question about highway 1 p bass tone pot

[primedynasty]

I am starting to do some work on my hw1 p bass and when I opened it up
I found two disc capicitors. The wiring diagram confirmed it. I know that one is resposible for bleeding off the highs to ground (or I think that is right) but what does the other do? I have an orange drop on the way but I want to make sure I am wiring this right.

[primedynasty]

here is a picture of what I am talking about



what does what? I am guessing that the .100mdf is the tone capacitor, or is it? I bought both a .100 and a .047 orange drop just to see what the difference in sound is. Which one would it replace? Any help or education would be greatly appreciated.

[Nighttrain1127]

I believe that is called the grease bucket circuit and it is different from the classic p-bass circuit. If you want the classic p-bass tone then just put in the single orange drop and remove the resistor and caps.The grease bucket has a lot more upper mids and highs than the classic p-tone.

[primedynasty]

interesting, might have to try both setups out and see what I like better.

[primedynasty]

Is it possible to run both a traditional Precision circuit and a Grease Bucket circuit and use a DPDT switch to go between the two? Has anyone done it?

[Cernael]

I'm pretty sure it can be done.

However, it could be that the way I've scribbled it out means that the pot goes in reverse when you switch; that full tone is the same position as zero grease, and vice versa.

I'm not gonna share my scribble, as I don't know how my parent's scanner works, and can't be bothered to redraw the diagram on computer. Someone else'll probably give you a better solution, anyway.

[primedynasty]

i have been starring at this wiring diagram all day and I am just not understanding how this thing works. On the standard circuit the tone capicitor is attached to middle pole of the tone pot, which is the sweeper, so the resistance is changing on that pole when you move the pot, right?

On the Grease Bucket, the sweeper is attached to the capacitor and that is it. So what effect is the larger cap having on the circuit, versus the smaller cap, which is going to the resistor and then to ground? What is the purpose of the metal film resistor?

Any Grease Bucket experts out there?

[Cernael]

The large cap is attached between the right and centre lugs of the tone pot. I'll map out the current flow with the tone at 10 and 1, respectively;

10: Vol pot -> large cap (in parallel with) 100% of tone pot -> 0% of tone pot -> small cap -> resistor -> output.
Simplified: Vol pot -> large cap -> 0% of tone pot -> small cap -> resistor -> output.


1: Vol pot -> large cap (in parallel with) 0% of tone pot -> 100% of tone pot -> small cap -> resistor -> output.
Simplified: Vol pot -> 0% of tone pot -> 100% of tone pot -> small cap -> resistor -> output.

That helpful?

[primedynasty]

that does help a little, but what function are the large cap and the small cap serving. What effect is the cap having on the tone of the bass? Is the large cap still doing the heavy lifting, therefore having an impact on tone, and the small is allowing for the restrained bass increase?

[Cernael]

I'm not sure here, but...

With the pot in the position I've labelled "1", the bulk of the pot is in the signal chain, meaning it blocks the higher frequencies from bleeding off.

With the pot in the "10" position, you're got both caps and the resistor in series. The resistor just means the pot doesn't go all the way down to 0. The caps...I *think* that, with them in series, they both wotk like they would have on their own, with the effects added together. Tha large one is about double the size of a standard, meaning its cutoff frequency is a bit lower; the small one is slightly below half the size of the usual one, so that cutoff is a bit higher. Taken together, the cutoff curve'll be more drawn out, less defined, than with a single cap.

With the tone at half, things probably get a little more complicated, as the large cap is in parallel with half the pot, and in series with the rest of it. I THINK that both the amount of cut, AND the apparent cutoff frequency will change as you turn the pot, but in what direction it'll do so, I couldn't say.

[Cernael]

Hey, I did it! Here's a push/pull tone/greasebucket diagram for y'all.

[primedynasty]

wow you rock

[Cernael]

Thank you, I know.

Also note that this is my second design; the first had that reversal problem I alluded to earlier, this doesn't.

[Cernael]

Oops.

I looked over my diagram again, and realized it's not perfect.

I now think you'll need a third pole to the switch, that disconnects the wire from C1 to the centre lug of the pot, when the switch is in "regular tone"-mode.

Sorry.

[primedynasty]

so a 3PDT? I might lose the push/pull pot and go to a mini switch, so should I pick up a 3pdt switch?

[Cernael]

Yeah, a 3PDT. I've drawn it up in pencil - I'll redo it in Paint later, when I have the time.

[Cernael]

So, here it is.

A wire goes from the centre lug of the centre pole on the 3PDT switch to were it's supposed to go on the volume pot, if that's unclear.

[primedynasty]

well crap, i already have a dpdt on the way and i can't find any flat 3pdt mini switches. guess i will think about whether it is worth it to do it or not.

[Cernael]

'kay, try the first one I posted, then. I honestly don't know how much different from a regular tone setup it'll sound in "tone" mode - the difference might be imperceptible anyway. It's just not entirely neat, and that bugged me.

The "greasebucket" setting is unaffected by the mishap, anyway.

[primedynasty]

i ended up using two switches which while not at all practical, was visually pleasing to me. I didn't expect to hear all that much difference between the two circuits but it really is quite distinct. I need to play with the bass some more, but I am pretty happy about the mod overall.