p-bass wiring suggestions

[thetragichero]

my bassist's garage sale-special p-bass has non-functioning tone/volume controls (ie the shaft just keeps spinning and spinning with no change in sound)
i volunteered to rewire it for him, but i'd like to give him a little more versatility than just working volume and tone controls

i noticed on fender's site that most of the standard p-basses come with .05uF tone caps while the 57/62 RI and some artists models use .1uF caps
would there be enough of a difference to have a push-pull tone pot to select the different caps? suggestions on values?

also looking for good but relatively inexpensive pickups that would be better than the stock MIM one

[ashcatlt]

That'll be a whole octave difference when the tone is at (or very close to) 0.

I had a crazy idea for series/parallel w/broadbucker/half-parallel options on a P-bass, but I've yet to convince anybody to actually try it. Maybe you?

[thetragichero]

if i can find a cheap squier p-bass on craigslist, you've got a deal

[ashcatlt]

Well here's my thread on it when you're ready.

I know I figured out how to do what I was looking for, but the it's not really spelled out in the thread, and I don't remember how it worked, so...

The point is that there would be an S/P switch and a Tone switch. The action of the Tone switch is dependent on the other.

In Series mode, it moves the "bottom" of the Tone control from ground (Normal Master High Cut Tone) to the series connection (Half-Parallel).

In Parallel mode, it switches from Normal Master High Cut Tone to Master Bass Cut Tone.

I believe that I once beliegved that it could be done. If that is true, then we can figure out how to do it again.

[newey]

Well, so that I can follow this, I translated ChrisK's schematic of the Hi/Lo Cut Tone Control (The link is in Ash's thread he linked to above) to a diagram:

Which I hope is right. The diagram is shown holding the pot upright, but I didn't check an actual blend pot to see if the CW and CCW are correctly oriented- it might be mirror-imaged from what I have.

Now this is what Chris suggested as a starting point for what Ash wanted- and Ash indicated he knew how to translate it to what he wanted. I, for one, can't seem to visualize it. . .

I think we also recently discussed that, if one implemented the above wiring using a regular dual-gang pot rather than a blend pot (CW and CCW are aligned vertically on those pots, rather than having one-half reversed as on a blend pot), a variable "Mid Gate" filter could be realized. That might be interesting on a bass as well.

[thetragichero]

this is how i want to wire the push-pull pot (switch part) to switch between caps?:



should i have .05uF or .1uF as the default (switch in down position) cap?

EDIT: by .05uF i mean .047uF because those were in stock

[newey]

TTH-

That'll work fine, assuming the tone pot case is grounded.

[thetragichero]

i should've mentioned that, since i remember being chastised before not to leave assumptions up to the reader
my beautiful little package from mouser should be here in a few days so hopefully i can get this thing wired up!

[ashcatlt]

We've discussed before how disconnecting one (or both) ends of a capacitor can leave it with a charge stored. When that cap is then reconnected, it will want to discharge rapidly, causing a noticeable pop or click.

To avoid this in your case, use two of the 0.1's. One goes between the tone pot and one of the middle lugs on the switch. The other goes between the two middle lugs. The "other" middle lug still goes to ground. Put a straight-wire jumper between one set of remaing lugs - top or bottom depending on which value you want for the "default".

When switched away from the jumper, the 2 caps are in series and total 0.05 (that .003 ain't gonna be noticeable, being within tolerance for most parts.). When the switch goes the other way, the one cap is shorted and the total value goes to 0.1.

Please tell me you didn't order exactly one of each cap value!

[thetragichero]

i ordered like 7 each of a bunch of different values so i could play around with values on other guitars (also don't know what i'll need when i rewire the guild)

[Yew]

Wouldnt it be better to use a spdt switch, have both caps going to the case, then the switch selecting both caps, as that should sort out the pops, right?

Ive just realised that most p/p pots are dpdt, but you could just use one set of blades..

[ashcatlt]

If I'm reading yew right, the SPDT will still be leaving one side of the cap which is not selected hanging in the breeze holding that stored charge.

[Yew]

Would that fix the stored charge problem, using a single dpdt switch?

[thetragichero]

if that one would work, it would probably be easier to solder since i'm using big (630V) caps

[sumgai]

yew,

Sept 12, 2010 5:17:32 GMT -5 Yew said:

Would that fix the stored charge problem, using a single dpdt switch?

In a manner of speaking, yes, the stored charge issue won't rear it's head.

Of course, that's because there's no difference between the two switch positions, i.e. both caps are always in the circuit at all times. Better take another stab at it, my friend.

HTH



sumgai

[ashcatlt]

Now, if there were a dot there where the line between the caps crosses the line to ground...

[Yew]

Are you sure both caps would be in the circuit.. as what i get is that the signal goes through one (well the highs anyway) and the other has both sides grounded, hence removing the charge

sorry, i just cant work out what my mistake is so im not acusing you of lying or anything, just everything ive worked out screams that it should work :/

ashcatlt,

what doc you mean about that dot.?

[Yew]

Wait, I think i get what you where on about ash,

the the vertical line on the right ( going between the caps) is supposed to join the caps to the ground, i though since i didnt put an arc over them that would be shown

EDIT: Like this



Also, if you used an ON/ON/On switch, and you used the pot as a master tone. you could use it as a master volume with the switch in the middle position.

[ashcatlt]

Yeah, the dot shows positively that it actually connects there, and that works.

A variable resistance to ground- even without the cap - will act more like a tone control than a volume until it gets way down toward 0, then it will get very quiet very fast.

[sumgai]

yew,

Your "fix" works better, thanks.


As it happens, a capacitor pops because of an instantaneous change of state. IOW, it goes from being connected with a charge on it, to being disconnected. That doesn't usually sound out, as we disengage it, but when we re-engage it, and it still has some charge on it, that's when we hear the pop.

With your diagram, it's likely that the switch will not connect the two caps for a brief period, before it disengages the undesired cap. IOW, there's a short period of time when both of them are out of the circuit, and that's when we get a popping sound, when one of them is then engaged.

The usual fix is to discharge the cap while it is disengaged from the signal path. Hook up a high-value resistor across the cap (i.e. in parallel with it), and that's usually enough to make the pops go away. 2MΩ to 10MΩ is the usual value of choice here. High enough to ensure it won't load the pickups and thus affect the tone, yet still able to quickly discharge the cap. A 1MΩ resistor will also work, but when the volume is turned down, that value starts to audibly affect the tone, for most pickups anyway.

HTH




sumgai

[Yew]

Okay, so ive made a solution that already had a much easier solution (in terms of wiring at least)

There wont be a pop will there? as when the switch is in the up position, both sides of C2 are grounded, and hence wont give any residual charge

also, im rather happy to how neat that drawing looks, should be easy to modify it to a phase switch drawing too

[sumgai]

yew,

It took me a moment to think it through, but yeah, your solution should work as planned. If it doesn't, then the resistors might still be in order. Read on for more data......

One thing I haven't been clear about......

The popping usually comes from a very sudden increase in some DC voltage applied to the amp's input but it can also come about as a result of a similarly sudden decrease in that voltage. These two actions are exactly what I'm talking about, above, when I say that a cap with a charge is suddenly engaged (or as happens on occasion, when it's suddenly disengaged). The pop is a result of that large voltage swing, from 0 to whatever high voltage, in a very square-wave like manner..... like "whoosh!", and it's there. The amp can handle this, and we hear a "pop" out of the speakers. Sadly, speakers don't handle such things very well at all, and of course our ears are hghly upset by this kind of activity.

Normally we use a blocking capacitor directly in front of the amp's input in order to prevent this. But that has an adverse effect on tone, so we try to not use this trick, if we can help it. This means, in turn, that we must look at all of the signal path (the input circuit) to make sure that no sudden excursions of square-wave like voltages occur. And of course, you've guessed it by now, that means that we watch ourselves when using capacitors in tone circuitry.

As noted, a discharged cap should not present a problem when it's engaged. But disengaging a partially/fully charged cap might cause a popping sound, and in such a case, there's no avoiding the shunting resistor I previously mentioned. For that reason, and because it's both cheap and easy, and because it doesn't harm the tone, I almost always just drop in that shunting resistor, and be done with it. One less possible reason to have to open the axe back up, yet again. ;D

HTH



sumgai

[Yew]

Okay, so my circuit would pop bnecause the capacitor is suddenly grounded, but using a resistor it wouldnt pop as its a more gradual discharge.

Thanks for being understanding and helping me learn. Its the way to exhaltation

[thetragichero]

is there any benefit (or detriment) in using a 2 or 10 MOhm shunting resistor?
not sacrificing tone is of course my only concern.... so whichever one has the least effect on tone is my cup of tea

[ashcatlt]

I'm not completely convinced that you need the pulldown resistors in this particular situation, but yes the bigger the better. This resistor will be basically in parallel with the other resistances in the circuit, and will help to determine how much of the highest frequencies you'll hear when everything is at 10.

If we assume a 500K volume and 1M amp input -
500K||1M = ~333K
500K||1M||1M = 250K
500K||1M||10M = ~ 323K

Even if you don't understand what those numbers mean, I think you can see that the bigger resistor gives a total closer to that of the circuit without it.

[thetragichero]

FINALLY got this to work
i guess because i first wired this up using an 8$ chinese ebay soldering iron, i fried the tone pot
picked up one of those weller gun irons and i don't know how i ever lived without it!
i used ashcalt's idea, but instead of the second .1uF cap i used two .047uF caps in series (just to have a few more pF difference between the two)

anyway, thank you all for your help!