The basic flaw in the p-bass

[sethlow3]

I am REALLY diggin' the grease bucket tone circuit in Precision American Specials. They claim to resolve exactly what the OP has suggested. I do notice a difference between the two as I also play an MIA P5 a lot as well.

Like others have posted though, turn the knobs on your amp.

 

[petrus61]

Interesting post! Thanks for fleshing out my idea.

I understand that the original Gibson varitones contained an inductor to preserve high frequences, thus turning a standard set of capacitors in parallel into a crude notch-filter of sorts.

They also contained resistors.

 

[David Jayne]

But couldn't you just EQ that low mid bump via the amps settings? Considering I like to run wide open I would think the difference was negligible?

If you had exactly the right EQ point with exactly the right Q, sure. But if it is available on your bass, at your fingertips for free why not use it? It's the sort of thing best used with a treble roll off anyway. IMO.

 

[kohntarkosz]

They also contained resistors.

I thought they were purely there to take the 'pop' out of the switch by removing any stored charge in the caps?

 

[petrus61]

I thought they were purely there to take the 'pop' out of the switch by removing any stored charge in the caps?

Not entirely sure if that's their sole purpose in the circuit or not. I built an outboard varitone (technically a decade box) and just used caps with no resistors or inductor. I use it for trying out different cap values and messing around. I used a 'make before break' rotary and that eliminated the popping I was getting with the standard rotary switch. I built it into a can.

 

[David Jayne]

I thought they were purely there to take the 'pop' out of the switch by removing any stored charge in the caps?

Pretty sure that's right. Interestingly someone here built one recently and found that once the bass was plugged it, each switch position would pop once, but once the switch was fully cycled would not pop again until the bass was unplugged, then plugged in again.

 

[thiocyclist]

The resistors actually make the varitone do weird things to the mids so it can really scoop your signal, not as tone-friendly as a simple rotary of various caps IMO.

 

[kohntarkosz]

The resistors actually make the varitone do weird things to the mids so it can really scoop your signal, not as tone-friendly as a simple rotary of various caps IMO.

I thought it was the inductor that caused the scooped mids, because it adds high frequencies back into the mix whilst the capacitors are cutting mid frequencies (and would also cut treble if left unchecked).

 

[petrus61]

I thought it was the inductor that caused the scooped mids, because it adds high frequencies back into the mix whilst the capacitors are cutting mid frequencies (and would also cut treble if left unchecked).

The caps only cut the highest frequencies, if I recall correctly and the resistors are there to perhaps cut the mids with the inductor functioning as stated above. I think the stored charge is in the switch itself. A make before break switch has a "dummy" leg following the initial contact to discharge what is stored up on the plate, but I may have that wrong.

 

[jcanderson]

I thought they were purely there to take the 'pop' out of the switch by removing any stored charge in the caps?

I think this might be on the right track...

I just took a look at a Varitone schematic, and the resistors to each cap are 10M ohms, which is HUGE. Such a large value, in series, should effectively isolate any unselected cap from having a significant effect on the frequency response.

However, when a cap is selected, the 10M for that cap is bypassed by the switch, thus connecting the cap into the circuit.

Why the 10M ohm resistors? Why not delete them, if they're isolating the caps? I don't know, but they do provide a charge/discharge path to equalize the DC voltage across all of the caps (albeit with a very long time constant). I suspect that's the answer.

 

[petrus61]

I think this might be on the right track...

I just took a look at a Varitone schematic, and the resistors to each cap are 10M ohms, which is HUGE. Such a large value, in series, should effectively isolate any unselected cap from having a significant effect on the frequency response.

However, when a cap is selected, the 10M for that cap is bypassed by the switch, thus connecting the cap into the circuit.

Why the 10M ohm resistors? Why not delete them, if they're isolating the caps? I don't know, but they do provide a charge/discharge path to equalize the DC voltage across all of the caps (albeit with a very long time constant). I suspect that's the answer.

Has anyone figured out the correct inductor value? I saw some at my local Radio Shack and was thinking of building a proper varitone box, but in all my searching, nobody seems to recall the inductor they used! It would be merely for tinkering's sake, because as was mentioned, a classic varitone does some odd things to a bass guitars frequency...particularly the mids. The values I ultimately chose for my box (using a 2 pole/6 pos rotary) were bypass, .01, .022, .033, .047 and .1. It seemed to me the most gradual tone change from high to low and back. It would be cool to make a wah out of it...the effect is that perfect back and forth. Until then, Id have to manually induce wah (kind of counter intuitive with a detended rotary!)...but yes, it sounds like a wah when I cycle the caps. It was a fun project.

 

[jcanderson]

Has anyone figured out the correct inductor value? I saw some at my local Radio Shack and was thinking of building a proper varitone box, but in all my searching, nobody seems to recall the inductor they used! It would be merely for tinkering's sake, because as was mentioned, a classic varitone does some odd things to a bass guitars frequency...particularly the mids. The values I ultimately chose for my box (using a 2 pole/6 pos rotary) were bypass, .01, .022, .033, .047 and .1. It seemed to me the most gradual tone change from high to low and back. It would be cool to make a wah out of it...the effect is that perfect back and forth. Until then, Id have to manually induce wah (kind of counter intuitive with a detended rotary!)...but yes, it sounds like a wah when I cycle the caps. It was a fun project.

I googled around a bit. Looks like the value could be from 1.5H to 7H. You might just want to get a handful and experiment.

Check out this TB thread: http://www.talkbass.com/forum/f38/simple-varitone-circuit-your-bass-596256/

Deep in it you'll find some several posts on using transformers (from Mouser) as the inductors. Also some interesting circuits, such as the one from Anderton, and the Gibson "Ripper".

 

[scotch]

Not entirely sure if that's their sole purpose in the circuit or not. I built an outboard varitone (technically a decade box) and just used caps with no resistors or inductor. I use it for trying out different cap values and messing around. I used a 'make before break' rotary and that eliminated the popping I was getting with the standard rotary switch. I built it into a can.View attachment 372619
View attachment 372620

Awesome! Love the Grinch can!

 

[ToneMonkey]

I generally prefer an active J bass, but sometimes an old school passive P bass is the right tool for the job, which is why I own one, quirks and all.

 

[4andnomore]

It's a characteristic. Not a flaw.

 

[Jbass4me]

There's knobs on the amp...use them. It's not rocket science

 

[eukatheude]

P-basses only have one flaw, and that's the pickguard-mounted output jack, right at the thinnest, most fragile part of that pickguard.

(note how that was corrected in the subsequent design, the jazz bass.)

Also the fact that you have to take the strings off to work on electronics. And the straight headstock.

 

[kohntarkosz]

Also the fact that you have to take the strings off to work on electronics. And the straight headstock.

I'm always leary of working on P-basses for this reason. Having the electronics mounted on the pickguard, but the pickups screwed into the wood, freaks me out. I'm always worried I'm going to move the pickguard too far from the body and yank a pickup wire and cause some damage...

 

[Flabass]

The "two tones of a P bass" attitude is kind of understandable. I don't think it's true, but that's beside the point.

I'm interested in the comment about Roger Waters. I thought that the vast majority of his Pink Floyd playing was done on a Precision. Am I wrong?

Right, why else would Fender issue the "Roger Waters P Bass?"

 

[oysteivi]

Also the fact that you have to take the strings off to work on electronics.

You do?

Unless I'm planning to touch the pickup, I'll just lift the pots clear of the body cavity and slide the pickguard out from under the strings, rotating it so that the pots don't move too far from their original positions. Feels a bit clumsy, but I haven't had any problems from it.