Telecaster with Varitone

[frets]

Hey Guys, as I stated yesterday, I’m working on 5 Tele’s each with a different harness.  This first one is quite easy.  It’s a simple Volume tied to a Rotary that serves as a cap switch.  I called it a “Varitone” although it really is a Cap Switch.  The key to these is using the right rotary switch that fits the Tele Cavity.  Alpha Korea makes a 6 or 12 position brass shaft rotary pictured below.  These can be found on EBay and fit neatly.
I typically “do” these Varitones usually on a 6 position, the guy wanted a 12 position.  I selected the cap values.  Anyway, it’s an easy but powerful harness with regard to tone. To be authentic, one needs a Chicken Head Knob.🐔

[JohnH]

I like this. All that cap variation should provide a really wide range of different tones, instead of just dulling the same tone like a normal treble cut.

Plus, having the no-load setting is a good feature to expand the tone, particularly with the series setting that can sound a bit too thick sometimes.

Diagrams are looking clear too. So is this the Visio software? I think I can get a freebie install if I want it, from the uni where I teach.

[frets]

Thanks John, I still can’t get Visio to run on my computer. I have to call Microsoft - Groan!! So I’m still using DIYLC, I just drew my own components and made them bigger.

[ourclarioncall]

What’s the difference between a varitone and a normal tone control ?

[frets]

Hey Clarion, how you been?

It’s really quite simple. Im going to give you the 30,000 foot view.
As you know, a tone pot is a variable resistor with a capacitor on it. Kinda limited. Usually just 1 cap - usually a 22nF or 47nF; but, you can mod a tone pot for two caps (right to left roll; e.g., .022 on one side and .047 on the other).  Still limited. 
Enter the Varitone, a device that vastly expands your tonal choices. It is a rotary switch that usually has 6 or 12 positions (but you can buy ones with 4 or 8 positions, etc. I even have one with 21 positions!! Ha!).
Anyway, this rotary switch has lugs on it that you solder a sequence of “increasing in value” capacitors. The switch is then usually sent to the volume pot or directly to the jack. It also can be connected to a tone pot in place of the one capacitor.
As you turn the rotary switch, you engage the nF of the capacitor; thus, you can go from “bypass” (no tone) to light to medium to deeper tones. Now these rotary cap switches are all called Varitones. But to be a true Gibson-like  “Varitone” one must induct the caps with a 1.5 to 2.2H (you can go higher if you want - these are just the typical values) Audio Signal Transformer that runs from all the grounds of the caps to one ground.  They also traditionally have 1 10 moHm resistor per cap to prevent popping noises when you turn the switch. Here is a pic of a 6 position True Inducted Varitone I made.  





There are some subtle differences on how guys make them, some include a 100k resistor on the hot, I never do that as I think it monkeys with the cleanliness of the tone.
But, they are really easy to create and in 90% of my guitars, the Varitone “is” the tone pot - if you know what I mean.
You should try one in your next build.🎸🎸🎸

[b4nj0]

Impressively neat soldering. I can't even see the soldering terminals on the tiniest SMDs Frets let alone waggle a hot iron at them! I tried to make some SMA mounted calibration loads for a two port analyser using SMD resistors to minimise stray inductance in the loads, and it was an epic failure for me. I fell back on using through hole components! SWMBO bought me some magnifying spectacles for my birthday this year. Yikes!

The Varitone without the the inductance is just another way of rolling off the highs, this time in discrete steps rather than the normal variable voltage divider approach, but the result is the same? The Varitone with the inductor is a switchable selection of series tuned circuits. Series tuned circuits are low impedance at resonance so each position deploys a tuned circuit at different resonant frequency. It is like a variable band stop filter that notches out different sections of the audio and dumps them to ground. I read somewhere a long time ago that Gibson obfuscated the value of the coil in their Varitone circuit diagram to put potential plagiarisers off the scent, but compensation is possible in the selection of capacitor values to achieve the same resonant frequencies so it was a pretty pointless excercise. Only the "Q" changes when you vary the L & C at any given resonant frequency, and that I believe is kind of irrelevant at audio frequencies?

I love your work BTW. Always interesting, I wish I still had your commitment. Keep on keeping on.

e&oe ...

[newey]

Aug 22, 2020 18:36:27 GMT -5 frets said:

But to be a true Gibson-like  “Varitone” one must induct the caps with a 1.5 to 2.2H (you can go higher if you want - these are just the typical values) Audio Signal Transformer that runs from all the grounds of the caps to one ground.

OK, just to be clear here (at 30,000 feet!), the Varitone requires an inductor. But small audio signal transformers are readily available, and a transformer is actually 2 inductors wired together, a "primary" and a "secondary". For the purposes here, frets is just using one-half of the transformer as the inductor, and ignoring the second half.

Years ago, in a thread discussing the Torres "Q-filter", ChrisK noted:

Interesting concept, this "Q" filter.

Hmmm, Gibson "Varitone" anyone?


Now, these run aboot $20. One can misuse a secret electronic device that only costs about $2 - $4.

They're called audio signal transformers. Mouser, DigiKey, and many other's carry them. If you only connect the high impedance primary leads, and don't use the secondary, they become (gasp!) inductors.

(Transformers - more than meets the eye.....) ;D ;D

These are specified at 1Khz. The one with a primary impedance (Z) of 10K Ohms will have an inductance value of;

Z/(2*Pi*1,000) = 1.6 Henry.

A 1 Henry unit will have a primary impedance of 6.28K Ohms. Gee, they have a 7K one for under $4.

This is the Mouser link.

[frets]

Guys,
Newey brought up the topic of Audio Signal Transformers.  I use these often and took a picture of four I use all the time.  The first two are Chinese.  #1 is red in color, #2 is a dark green.  They are inexpensive but you must buy them in lots of five or ten.  They require soldering the two coils together to reach significant inductance.  

Unfortunately, the “go to” AST, the Mouser (Xicon) 42TL021 Blue 1.5H AST has been discontinued. I asked Mouser to give me an alternative, they yet have responded back.  But the 42TL018 Mouser (Xicon) 2.6H can still be purchased. But they usually average about 2.2H. They are a lighter medium green color.  On the Xicons, you use only the primary coil, cutting the center tap and secondary leads.  You can see that on the third AST. The last AST is my favorite.  It’s an SMD that averages around 1.7H.  On these, you solder the hot to the ground going in to the top left and the ground coming out to the top right.  These can be found on Chinese electronic sites.  I have posted a pic of a 3 way Varitone that uses one.

[b4nj0]

I'm curious; why is there a copper foil screen on a metal plate?

e&oe ...

[frets]

Simply for aesthetics. The guitars I put these plates into all have shielded grounded cavities throughout. The “all copper look” is just a “Wow” factor when they look at the photos. Makes everything look integrated.

[JohnH]

Your wiring is immaculate, Id want to wear it on the outside of the guitar! Or, maybe not, keep it clean and safe on the inside and open it up every few years just to have a look.

[b4nj0]

Thinking it through- it certainly saves on the potential for galvanic corrosion Frets. (No irony ontended). I opened up my 1973 Strat last year and the 3-way switch and pot covers all sported a healthy "fur"!

Edit: Sorry- meant to write "no pun intended". D'oh ...

e&oe ...

[reTrEaD]

Aug 22, 2020 16:37:42 GMT -5 ourclarioncall said:

What’s the difference between a varitone and a normal tone control ?

A 'normal' guitar tone control is a shunt-type high-cut filter.

A Varitone is a specialized notch filter that Gibson used on several of its guitars including BB King's Lucille (a variant of the ES-355). When switched into the circuit, it adds a 100k resistor in series with the output and a capacitor and coil (in series with each other) in parallel with the output. The value of the capacitor is selected by the same rotary switch which enables the Varitone.


Many hobbyists have used variations on this concept and retained the name Varitone.

[frets]

John,
Thank you so much for the high praise!!🤗. It took a long time and a lot of harnesses. Ha!

[rabo]

I found a tele/strat style selector 2p5t switch, tiny caps, tiny resistors, and a printed circuit 6.3 h inductor.
The inductor fits flat against the backplate in a standard tele route, as do all the components .
With a fidelitron neck and hot rails bridge, it nicely notches frequency reponses with all pickup selections.
And it looks exactly like any other "blade" selector.
Both volumes and both tone pots are 500K. I also found a tele top plate with three pot holes and the "blade" hole.
For now I have the tome pot switches either go to standard tone rolloff with a single cap or switch to go through the varitone
Sorry< i didn't keep track where I found all these parts, but they were all online.

[frets]

Hi Rabo😀,

Thanks fo sharing this. I’d be very interested in learning more about that printed inductor. 6H is a big value. Do you have a photo of it? Or could you share where you got it. I’m always looking for inductors.

[syddd]

My understanding is that you only get the popping with caps if there is an inductor between the caps and the ground?

I have a bass with a similar set-up without any resistors and havent noticed the popping sound, I will have to plug it in to give it a go.

[b4nj0]

Maybe you have a MBB switch instead of BBM?

e&oe ...

[davidofchatham]

There's been a lot of talk about inductors in this thread — due to the Varitone connection — but am I understanding correctly that the design in the OP is for a tone control that works sort of backwards from a normal treble attenuator, in that the amount of cut does not vary, but the frequency of the cut does vary? So it's like having a tone control permanently turned all the way down (except in the bypass position), but being able to switch the caps instead?