A Worthy Tribute

Epiphone Les Paul Tribute PlusEpiphone Les Paul Tribute PlusEpiphone Les Paul Tribute PlusEpiphone Les Paul Tribute PlusEpiphone Les Paul Tribute Plus

My new Epi Les Paul Tribute Plus arrived yesterday for my birthday, and it’s a beauty!  These things are hard to find- none of the local stores have inventory, and every online retailer is backordered.  I managed to get Guitar Center’s last one in the country(!) – from the store in Tonawanda, New York.  The store manager there was great- sent me some pics, played it for me to confirm it was all good, gave me a great July 4th discount, and shipped it over for free.   Thanks Chip!

Cosmetically, it’s really nice.  Clean, well-defined flamed maple top and cream bindings.  The cherryburst finish looks near-perfect- with rich warm coloring- not the bright overexposed yellow in the pictures at Guitar Center’s website.  The Grover locking tuners feel fantastically smooth, and the switch, knobs and jack all seem good.  And after some quick adjustments, it plays pretty well (but still needs some fine tuning).

Push/Pull for Series/ParallelThe ’57 Classic pickups sound really dynamic, rich and beautiful – they’re warm when played gently, and crank when spanked. Love em.  There’s quite a range of sounds with the push/pull series/parallel switching on the tone knobs.  When a tone knob is pulled, the humbucker’s two coils are wired in parallel giving a lighter, brighter, thinner sound, somewhat reminiscent of a single coil (though different).    It’s completely different from the ultra-thick and heavy series-humbucker sound (knob pushed in).  This is a really versatile setup: a total of 8 different sounds using the 3 switches, not to mention the variations you can get by adjusting the volume knobs in the middle switch position.

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Treble and Bass

G&L S-500 Schematic closeupIn my tone capacitor video, I demonstrated the typical use of the capacitor as a low-pass filter in a guitar tone control.   On a home stereo, this would be called a treble control, as it is used to roll off the high-end treble frequencies.

But what if you also want a bass control- a high-pass filter to roll off the low bass frequencies?

In the circuit diagram shown here, from the G&L S-500 guitar, you’ll find both a treble and bass control.  They call it their PTB system (which presumably stands for passive treble bass, but I’m just guessing here). 

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Tone Pot as a Low Pass Filter

A reader recently asked me a question about the low pass filter in a guitar tone circuit:

Will a 250k tone pot with a .02uF capacitor sound the same as a 500k pot with a .01uF capacitor (all else being equal)?

This is an interesting thought experiment, and the answer is simultaneously obvious and non-intuitive.

imageAt first glance, you might be tempted to look at this standard low-pass filter schematic (borrowed from the LPF wiki), imageand the associated formula for cutoff frequency as 1/2piRC, and conclude that the two circuits would behave identically (since 250k*.02uF is the same as 500k*.01uF).  However, the problem there is that the R in the formula is not the tone pot!   That R is really the internal resistance of the guitar, or the resistance of the pickup.

Circuit with toneIn the tone circuit, the pot actually sits above the capacitor C, but below the branch to the output Vout, as shown at left.   So, the formula for the cutoff frequency is more complex.  In this analysis by a guitarist/mathematician named Bill, he suggests a formula for the cutoff frequency as follows:

How’s that for insanely non-intuitive?!  Bill points out that the lower square root term only works with tone resistances less than about 20k (since otherwise the value would go negative producing imaginary numbers in the square root), thus explaining the often limited useful range of tone pots, and why log taper pots are more useful for tone than linear.  Nevertheless, this seems to be an over-idealized formula, since in practice, I do see more variation in the tone pot even at higher resistances.   This formula doesn’t seem to capture the full complexity of the reactive network made up of pickup inductor, and overall circuit resistance and capacitance (including cable capacitance).

Ok, so math is clearly the wrong way to think about this!!  Too complicated!   Back to the original question.  Let’s think of it more simply.  Imagine you turn both pots down to zero- you’re basically eliminating the variable resistance pot and wiring the cap directly to ground.  Of course, the larger capacitance .02uF will sound darker than the .01uF.  So they’re obviously not equivalent circuits.  

Next up, experiment!  Grab a couple pots, caps and some alligator leads and try it out!  You’ll find that they do indeed sound quite different.  The larger capacitance with the smaller pot resistance sounds darker, no matter how you slice it, when compared to the 500k pot and .01uF cap.  Even with both pots up full, the larger capacitance with the smaller pot sounds a bit darker. 

This all begs the question, why do guitar manufacturers often pair a 250k tone pot with a .047uF cap,  versus the .022uF cap with 500k pots?   The former will produce a darker sound both because of the larger capacitance but also because of the increased load on the pickup from the smaller resistance.   “Double whammy” as Bill points out at the end of his paper.

Ideas for Treble Bleed Problems

Treble Bleed ProblemA while back, I described some problems with trying to use treble bleed on a guitar with multiple volume pots.  When turning down one volume pot, that pickup retains brightness, but the other pickups get duller.   In the diagram at right, with middle and neck pickups in a blended switch position, the middle volume is up full and the neck volume is turned down.  The middle pickup high frequencies have a path to ground through the neck treble bleed cap.

This problem even exists on your typical two pickup, three way switch guitar (Les Pauls, ES-335’s, Sheratons, etc).  But, with only two pickups, the switch has two non-blending positions which completely isolate a pickup.  When one pick up is isolated, there is no issue with having a path to ground through the other volume control’s treble bleed cap.   However, in the middle switch position, the two volume pots are tied together and you’ll hear the dullness problem if you turn down one of the volume knobs.  In this case, it’s not so bad (and most people won’t notice) since you’re blending the sounds anyway.

But with three volume pots and a three way switch like my Epiphone Riviera P93, there is no way to isolate one pickup.  The middle pickup is always on in all three switch positions, so there will always be bad interactions with the treble bleed.  The stock Epiphone G-400 Custom  exhibits this problem, with treble bleed caps on all three pickups.

I punted on a solution for my Epiphone Riviera P93, and just left it without treble bleed.  However, I’m finding that the way I use this guitar would really benefit from some treble bleed.

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Difficult Decisions

Difficult QuestionsNearly every day, I receive a question like “I have a Custom Slender Flatoblaster with Fleemore Dunkin pickups.  What brand and values of pots and capacitors should I buy to get a killer sound for Jazz Country Electro Fusion Metal Ambient Rockabilly?”

I’ve tried to be clear in my posts and videos evaluating guitar electronics, that these things are really subjective and a matter of personal preference.  I could tell you that I like CTS brand EP0086 500k audio taper pots for both volume and tone, and Orange Drop 715P .01uF tone capacitors, and these work really well for me.  But, you may buy these same components and hate them. 

Field of PotentiometersWith potentiometers, there are many very subjective factors: torque (how hard/easy they are to turn); the taper (audio or log versus linear), since human perception of loudness is extremely dependent on the particular ear and brain of the listener;  and the resistance value (typically 250k, 500k or 1Meg for passive pickups)- you’ll get different brightness and a different feeling taper out of each.


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The Cap’s New Clothes

Kernel Of Wisdom Bumblebee Uncloaked

Today, let’s take a look at some really fancy boutique tone capacitors.  You can hear these in the yesterday’s tone cap shootout.

Luxe Grey Tiger The Luxe Grey Tiger is billed as “a faithful recreation of the famous Cornell-Dubilier Grey Tiger from 1956” and typically sells for about $40.

Gibson Reissue Bumblebee The Gibson Bumblebee is marketed as being “specially designed to replicate the original parts used by Gibson in the late 1950s”, and typically sells for over $100 for a 2-pack.

Have you ever wondered what special manufacturing and fabrication techniques they use to make these ultra-boutique capacitors?

Well, Steve over at Kernel of Wisdom has taken a knife to the little guys.   And what have we here?  Inside a Gibson Repro Bumblebee is really a Wesco polypropylene film cap, all wrapped up in black and stripes   And inside a Luxe Grey Tiger, we find a General Instruments PIO cap.  

Consider that a typical polypropylene film cap sells for maybe fifty cents.  Gibson is selling this for about $50, so let’s see— that’s only a about a 10,000% markup 🙂

Inside BumbleBee Reissue Here’s an interesting letter from 2004 about the reissue bumblebees from Edwin Wilson, Historic Program Manager at Gibson, as well as another tear-down of the reissue bumblebee.


This is not to say that these caps don’t sound good. However, what is clear to me (as if it wasn’t clear already) is that there is very little reason to spend this kind of money on a capacitor, unless you’ve got money to burn and it gives you warm fuzzies inside 🙂

Yet Another Tone Cap Shootout

KernelOfWisdom Tone Cap Shootout 3 Back in July, I mentioned a tone cap shootout by Steve over at KernelOfWisdom, which included some more boutique caps that I hadn’t included in my tone cap comparison project.

Well, Steve is back with another meticulously prepared and more comprehensive comparison.

In the ring this time are a Russian T-1 Teflon, Russian K4Y-9 PIO, Cornell-Dubilier PIO, Goodall PIO, Luxe Repro Grey Tiger, Gibson Repro Bumblebee, Sprague Vitamin Q, Jensen PIO, Sprague Orange Drop as well as a generic brown polyester film and ceramic disc caps.

He also has a blind comparison page (don’t peek at the answer key til after you listen).

Great work Steve!

Mystery Caps Identified

In my tone cap material types comparison, there were a couple vintage caps which I couldn’t identify.  I referred to them anonymously as the Yellow Cylinder and the Fat Gray Cylinder.

Today, a kind gentleman by the name of Bill Zumwalt was able to give me the clues I needed to track these old caps down and unmask their true identities.  The search keywords I needed were CDE and Mustard!

CDE Type WMF 1S22 Polyester Film capacitor


The Yellow Cylinder is a Type WMF 1S22 Polyester Film capacitor with a 100v rating, from CDE Cornell Dubilier.   I  guess I didn’t think to search for “CDE” – I thought it was an acronym related to the tolerance!



/Phillips Mustard polyester foil/film capacitor

And the Fat Gray is a Mullard/Phillips Mustard polyester foil/film capacitor with a 630v rating.  Apparently these were used in some vintage Vox and Marshall amps, and are quite sought after.  Who knew!?

So there you go!

Tone Cap Polarity Revisited

2010-01-31 Welcome Home Tone Thing 12 I’ve been asked a number of times whether the polarity makes any difference when connecting the common guitar tone cap, and I always answer No.

Electrolytic caps are polarized, and can fail or explode if you connect them up backwards.  But we don’t use electrolytics for guitar tone – the caps we typically use (polyester film, paper-in-oil, etc) have no significant polarity.

Now, film and foil caps (like Orange Drops and Mallorys) do have an outside foil-wrapping which is used for shielding and is connected on one of the leads of the cap.   Ceramic and silver mica caps aren’t built with an outside foil wrap.

Apparently, according to this article by Dirk Wacker in the new issue of Premier Guitar, it may actually make some difference to the sound which way you connect the outside foil of a cap.

I haven’t noticed it myself, but it obviously depends on the guitar, pickups, amp, wire, capacitors, and the ears 🙂

Caps aren’t typically marked for which is the outside foil end- and I don’t know of any way to tell which is which.  So, in short, try your tone cap both ways and if you hear that one way sounds better than other, then go for it.  If you don’t hear a difference, don’t worry about it!

Another Tone Cap Shootout

Luxe Grey Tiger There are a variety of expensive “boutique”  guitar tone capacitors out there, which I haven’t tried and didn’t include in my tone cap comparison project.

I just came across this audio comparison by “Kernel of Wisdom” which examines a bunch of the more expensive tone caps including a vintage bumblebee, modern bumblebee, Jensen Paper-In-Oil, Vitamin Q, and Luxe Grey Tiger.

Have a look and a listen!

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