Buildin' a Tonecaster: Treble bypass Q.

[bobbletrox]

Papa needs a brand new bag, so I've decided to build a really nice tonecaster.  But before I being, I've got three questions:

a) do the cap and resistor in the Kinman treble bypass filter simply go in series between the in & out lugs on the volume pot?

b) do guitar knobs fit on regular 1/4" pot shafts?  I'd be cool to be able to use tele knobs on this thing!

c) have I got the wiring correct?  :oops:



Thanks.

[lovekraft0]

a) Yes - the early Teles used just a ~150 pF cap.

b) Most guitar knobs are designed for a knurled (splined) shaft - 18 splines is normal. Use the right pots and it's no problem.

c) Looks right to me!  

[bobbletrox]

Thanks for your reply.  Perhaps I could use fender amp knobs like Muddy Waters used on his tele  

[Mark Hammer]

Where is this box going?  I ask this because the use of 250k pots is normally predicated on the perceived need to "tame" the high end on single-coil pickups.  That same pot value elsewhere in the signal path does not accomplish the same goal and indeed may compromise tone.  

The box seems to be implemented as a sort of fixed volume/tone pedal and typically such pedals have higher value pots to avoid further loss of high end.  A few months back, Craig Anderton stuck a quick-and-dirty project in GP which essentially was a variable resistance to ground, in the form of a box to stick in the signal path, to mimic the loading effects of different pot values.  What this suggests is that you could have the best of all possible worlds by using a 1meg volume pot, and sticking in, say, a 3-position toggle, to select between a 1meg pot with no loading, a 1meg pot with the loading of a 500k pot (stick an 820k resistor from pot input to ground) and a 1meg pot with the loading of a 250k pot (stick a 330k resistor to ground).  The bypass cap will function the same for all settings, so whetever you like for a 1meg pot will be fine in other loading-positions.

Another "trick" people use to achieving the "de-brittling" effect of smaller value pots for single coils while not loading down subsequent effect too much, is to stick a small value cap (680pf or less) between the volume pot input and ground.  Again, here a simple 3-position toggle will deliver up a number of sonic possibilities and make for a very flexible unit.  For instance a toggle that gives no cap, a 560pf cap to ground, and a 220pf cap to ground, in tandem with the "loading" switch, will allow you to mimic a wide array of conditions.

The bypass cap does go between in and out lugs on the volume pot, providing a low-impedance path for higher frequencies that  reduces the amount of attenuation they encounter at less-than-max volume settings.  Some people prefer to "smooth the taper" of this compensation by sticking a fixed resistor in series with the cap, but of course this is also something undertaken by factoring in both pickup properties, pot value and cap value., so there aren't any sorts of standard come-hell-or-high-water recommendations to make.

One thing I personally have found particularly useful is a bidirectional tone pot.  Here, you would use a linear pot with at least double the value of what you plan to use (since it will serve as two tone pots in parallel).  I normally use 1meg.  As you've shown it, you have a .022uf cap from one outside lug to ground.  This will introduce degree of muffling/mutedness.  If you connect a .0047 to .0068uf cap from the other outside lug to ground. you will have a tone pot that is capable of providing two different treble-rolloff "characters", one muffled and the other "rounded" and more vocal.  The centre position on the pot sticks a high resistance value (500k if its a 1meg pot) in series with each cap, yielding negligible treble-bleed on either side.  As you rotate the pot off centre, the resistance gets higher on one leg/side and lower on the other, effectively taking one cap entirely out of circuit and bringing the other one in.  A higher-value-than-expected pot (i.e., 1meg as opposed to 250k or 500k) means that in the centre position, the resistance to ground on either leg is sufficiently high that even in parallel they provide little treble loss.

An alternative to this is to simply use the wiring you've shown and some multi-position rotary control to select among different cap values.

[BDuguay]

What in Sam Hill are you talking about brother?
Being a Tele owner and player, this thread caught my eye and interest.
Only, I don't really understand  what's going on.
Please splain.
B.

[Mark Hammer]

I think the intent here is to make a switchable box that simply mimics the control cavity of a Tele.

My rather wordy posting is an attempt to pack in just about every possible version of a Tele control cavity you could want into that same box.

Note that the whole thing remains a passive design, and as such probably wants a bit of boosting somewhere earlier in the signal stream is there is to be any hope of pushing the amp in a pleasing manner.

I'm sure some folks would see such a unit as bland and pointless, but it bears noting that sometimes one's hands are just a tad too busy at the moment to work the controls, so the feet have to take up the slack.  This little box lets the feet do that.

If it were me, I would get myself a 1H choke, a 12-position rotary switch (w/chicken head of course) and a couple more caps.  Some time back, I made one of those passive tone controls that Anderton has in EPFM (his reworking of the Gibson Varitone midrange dip control).  Looking at it, I realized that: a) shunting the choke in an LRC circuit gave you a treble cut control, b) shunting the cap but leaving the choke in gave you a bass cut control, c) shunting both the caps and choke gave a basic attenuator function.

So....if one left in the 250k tone pot, and used the selector to pick from any of a number of caps (with the 12th position no cap), and also included a switch to shunt the choke, a bunch of tonal controls (including the original one in the diagram) could be created.  I recently made something I called a "Hippy Dippy" for a buddy who has a professional studio, which packed in a Stratoblaster with variable gain (to offset the passive loss of the tone circuit) and precisely such a midrange dip circuit, with a wider range than Anderton used.  A LOT of different sounds can be gotten from it.  Midrange dips can be VERY useful for Teles and Strats.

Now does it all make sense Brian?

(P.S.: We went to our niece's wedding in Waterloo this past weekend, and our instructions for finding the reception hall afterwards included "looking for a Tim Horton's" on King St. in downtown Kitchener.  After driving up and down the street a few times, I had to laugh.  Yeah....now THERE's a distinctive landmark that will clearly indicate a location....a Tim Horton's, on a main thoroughfare, in an Ontario city.  Right up there with "Look for a street corner". :lol:  I don't think our American brethren will quite grasp the reality that while Americans *like* doughnuts, Canadians *need* them, hence we tend to have a great many doughnut outlets.  Whatever it is that Americans do in those dank bars with the Budweiser and Pabst signs, Canadians do at a Tim Horton's with a medium double-double - because there is no rim to roll up on a small - and a cruller.)

[Mark Hammer]

Oh yes, and the Calgary Flames rule!!!

[BDuguay]

You said it Mark.
And I look forward to the "wordy" replies. Like the commercial
says, "there's a lot to said for clarity".
Oh yeah, Calgary will win the cup.
Mark my words Mark.

[bobbletrox]

Ahhh - I've been Hammerized!

Thanks for the info Mark.  I didn't think of the Tone control as actually sucking the tone.  Some things I looked into for the original tonecaster thread were implementing a 'vintage cable' simulator or even a varitone...so perhaps I could scrap the tone knob and just have the volume pot and a rotary switch with a selection of caps to ground.  I'd like to at least have a cap value in there that mimics a fully rolled off tone knob, because it can come in handy when using an Ebow or Octave pedal.

[Mark Hammer]

In fact, that's exactly what I have on one of my guitars.  Just a 3-position toggle (man, I love those things!) with no treble bleed, or a choice of two cap values.  One of them simply rounds off the edges on the single coil, and the other is more of a conventional muffling value.

The tone control doesn't really "suck tone" in the way that impedance mismatches do.  It just bleeds treble.  Remember that the load it places on things is dependent on frequency, since there is still that cap between the pot and ground.

Anderton's little "vintage-izer" box does more of the selectable tone-sucking, since it is simply a resistance linking hot and ground, so full bandwidth impact as opposed to the partial-bandwidth impact of the tone-control.

Of course, the tone-sucking impact of changing the load depends very much on what it is you're feeding that load into.  If you're feeding the mic inputs of a mixer, that are expecting to see a 150-600ohm vocal mic, I seriously doubt whether tacking a 100k resistor in parallel with the pot will make a huge difference.  I mean, if a jumbo jet is 15,000 feet or 33,000 feet in the air, you still have to tilt your head back and look up to see it, right?

Just one word of caution, and that is that cap-switching can lead to very audible popping during the switching process.  I'm not sure what context you plan to use this in, but I wouldn't want to be rotating that switch on stage.  One thing you might try if you do plan on doing that is to simply shunt the hot and ground leads with a momentary pushbutton while switching caps.  Then when you have your tone cap selected, release the momentary to restore signal flow-through.