Bass/Treble "roll off"

[torpedovegas]

Apologies if this was posted twice... forum is being a bit glitchy

I’m in the process of building a new custom strat (in case any of you are curious… chambered black korina body w/ sunburst finish, roasted maple neck with stainless steel frets (no front inlay) and a Wilkinson tremolo).  Basically the pickup configuration is 3 strat-shaped pickups by Harmonic Design but are basically retro-fits of a P90 (neck)- ’54 strat(Middle)-Telecaster (Bridge).  I’ve decided I’m going to wire them all to be individually on/off so I have all of the pickup config options.  Neck pickup will be reverse wound so it hum cancels with neck/middle and neck/bridge since I don’t often use middle/neck position.  I have a diagram for this that seems pretty straight forward.

http://www.premierguitar.com/articles/Stratocaster_with_Individual_On_Off_Switches

Where I’m having trouble finding some straightforward information is what I’m looking to do with the tone pots.  A friend of mine has a Reverend Double Agent that has a P90 in the neck and a “bass roll off knob” which is really cool and allows him to color the tone of the pickup between classic P90 and strat-ish.  What I’d like to do is have a tone pot that’s solely a bass roll off for the neck and a tone pot that’s a treble roll off for the bridge (tele) in case I want to take a little bit of the “bite” off of it.  Not really concerned about having tonal control over the middle pickup… in fact I usually find it to be a pain on most strats where 2nd tone pot also controls the middle pickup and usually makes it sound incredibly muddy.

 

[line6man]

The conventional wisdom is that individual on/off switches fail to be practical. They may sound like a good idea, on paper, but it winds up being a hassle to flip through them when you are in the middle of a song, and don't have precious seconds to spare.

It isn't possible to have a treble roll off for only one pickup, unless you are willing to make compromises. Tone controls work by placing a capacitance parallel to the signal path. The pickups are wired parallel to each other, however, so that makes a tone control work on both pickups at the same time. If you want isolation, then you would have to put a resistor in series with each signal path, but the resistance would reduce your output. You could put a bass roll off on each pickup, though, because those work by putting the capacitance in series with the signal path, so you could have multiple controls without having issues with interaction.

 

[Cagey]

Line6man is has it covered, I'm just piling on about the individual on/off switches for pickups. I did it twice, because sometimes I'm a slow learner. Wasn't happy either time. Too much fiddling around to be practical, at least in a real-time situation like you have when playing live. Maybe for a studio guitar, you'd have an easier time of it since time isn't so much of an issue what with the ability to do overdubs, mixdowns and all.

But, if you're bound and determined, there's some building block type information here about wiring/using a high-pass filter.

A simple schematic that would give you:

Bridge
Bridge + Middle
Bridge + Neck
Bridge + Middle + Neck
Middle
Middle + Neck
Neck
All off

With a master bass cut, treble cut and volume it would look like this...

 

[torpedovegas]

Hi Guys,

Thanks for all your help.  I meant to send that "thank you" earlier but my post wasn't posting.

Anywho, I've decided to go w/ a 7 way harness that has a 5-way blade and a push/pull pot for the bridge pickup which will give me all the options I need.  I noticed that the 500k tone pots on the harness already came with a cap on them (picture below) and I'm wondering if I should remove that cap and replace it and which poles I'll need to solder the new caps to to achieve the effect of master bass/treble roll-off.

 

[line6man]

That pot is wired as a standard passive tone control. For a bass cut, you will need a 1M pot (typically audio taper) and a 0.001uF capacitor. (Or adjust to taste.)

 

[torpedovegas]

Hi Guys,

Special thanks to cagey and line6man for their help on the previous thread.

I've drawn a diagram that you can see attached.  The desired result is 3 single coil strat shaped pickups that are retrofits of a (N)P-90 (M) '54 Strat and (B) Telecaster.  They're intended to be wired to a 5 way switch and push/pull volume pot that will allow me to engage N-B and N-M-B depending on where the 5-way switch is.  The tone pots are intended to be master bass contour/bass roll-off, mainly to sculpt the sound of the P-90 (think Reverend Double Agent) and Treble roll-off to tame the highs of the tele pickup when needed.

I'm looking for two bits of information:

A) Will this diagram as drawn provide the desired result?

B) What are your recommendations and why for the values of pots/caps.  I know that 250k is generally used for single coil to tame the highs but I'm wondering if different values would better suit this project.  I've heard a fair amount of conflicting information on this particular subject.

If it helps in your suggestions the body is chambered black korina, neck is roasted maple w/ stainless steel frets.

 

[torpedovegas]

oops, forgot the attachment

BTW, for whatever reason the interface isn't allowing me to upload jpegs only png

 

[Cagey]

For the treble pot, I'd use a .022μF cap. But, that's just me. Others have used anything between a .01μF and .047μF part successfully. More is not better. The higher the capacity, the farther back on the frequency response curve the cutoff will fall. So, the .047μF part is going to start cutting a lotta highs very early, and by the time you get all in with it your guitar will sound closer to a high-strung bass with flatwounds on it. I suspect that's the reason a lotta guys don't even use their tone pots.

For what you're calling a bass pot, you've got it wired as a low pass so it won't work. Or, more to the point, it's just another high pass in parallel with the one you already have, which will exacerbate the problem I already mentioned with excessive capacity in the tone circuit. See the drawing I posted earlier in the thread for how a bass pot has to be wired, and what values you may want to try.

Be aware that between the bass and treble pots, you may end up creating something of a notch filter that will never let the entire signal through even when they're dialed out. Once you've got them both wired, it would be a worthwhile experiment to short the bass pot and open the treble pot to see what the instrument sounds like with no tone control. Could be you end up with another push/pull switch pot  :laughing7:

 

[daniel.dimitri]

It's true a traditional treble cut (low pass filter) will work on all pickups equally if they are all at full volume, you might get a little mixing if you have multiple volumes all turned down to around 7 or 8. However if you use an inductor  like a Lawrence Q-filter in series it might prevent treble from another pickup from back feeding into the cap and being shunted.

I honestly wouldn't bother though. I would just wire it like a g&l. And forget the individual pickup controls. Unless you want to go the active route, in that case you can do more without unexpected results