Trib Kiloton Tone Control Has Minimal Effect

[Dirkster]

It’s a difficult question to answer in text but how much effect should I expect out of the tone pot on my Trib Kiloton? Until today turning it thru max/min had me wondering if it was doing anything at all.

I wondered if it might be a bad pot and replaced it; no change; I also downloaded the G&L wiring diagram and from a point/point perspective mine is not wired precisely the same way; from an electron flow perspective it may be (the three position switch and volume pot work fine). In addition my PU (presumably that’s where it’s coming from) has an extra black wire, not shown on the diagram, that lands on the ground bus (the back of the pot cover on the back).

The two instrument jack conductors were (until today) via a shielded, single conductor cable configured such that the shield was used as one of the conductors. Today I disconnected the shield from the jack end, kept the other end connected to the volume pot and replaced the signal link with a single conductor from back of the volume pot (part of the ground bus) to the jack. My thinking was that if shielding was needed for the white conductor within then it wasn’t getting any. I recognize that the circuit doesn’t have a separate shield drain to Earth and still grounds via a signal pathway but that was a close as I could get to proper shield termination. After doing that I no longer wondered if the tone pot was doing anything; it was but it didn’t seem like very much and any audible contribution varies by string being plucked and PU configuration (series, single, parallel) which probably makes sense; additionally any change that I can detect occurs during the last 5 to 10% of CCW rotation of the tone control. I question whether or not an audience would notice any difference and so wonder if mine is working properly.

All that said:
What should I expect from the tone control?
Does my description of tone control sound normal? There’s definitely a change but it is far from Earth shattering.
Is the Fullerton KT wired the same way, with the same sorts of wire?
In all the wiring there’s the one, single conductor shielded jumper; what’s with that? If shielded wiring is needed why aren’t the others, or at least the other final signal wire, shielded? Or are they just using whatever wire is on-hand at the factory?

Or, as in the following post, this behaviour is normal and I should just mess around with different caps (or ignore the whole thing) and replace my 20' cable with a shorter one? viewtopic.php?f=4&t=2939&p=18181&hilit=kiloton+tone+control+knob+#p18181

Any help greatly appreciated,
John Clay

[Ricky Rioli]

There's a comprehensive set of demos from 3'20" here

https://youtu.be/qHAgFD4TyyY

[Ken Baker]

All that said:
What should I expect from the tone control?

It might not get "dubby" dark, but full-on should be CLEARLY noticeable.

Is the Fullerton KT wired the same way, with the same sorts of wire?

I doubt that they are wired exactly the same. The two may be electrically equivalent, but sometimes that isn't enough.

Or are they just using whatever wire is on-hand at the factory?

While this is actually doubtful, stuff like this makes you wonder. If they're going to use shielded cable in the cavity, fine; just do it right.

Or, as in the following post, this behaviour is normal and I should just mess around with different caps (or ignore the whole thing) and replace my 20' cable with a shorter one?

Consider that, in isolation, there should be essentially no difference between what this tone pot should be doing and a tone pot in a Precision. Should even be wired the same. Hot lead to one of the outside lugs, cap between middle lug and ground. That's it! In your case, if the cap is being grounded to the pot's case, be certain that the case is grounded. Some L Series basses have used a .1µF cap instead of the 0.47µF; then again the L-2x00 uses .047µF. Some even have .047µF at the treble/tone pot and an additional .1µF cap hard-connected from signal to ground - a swamping cap. Go figure.

Oh! And lose that 20 foot cable! Unless you have a pedal that presents a low impedance to your amp. Then 20 feet is okay.

Ken...

[Dirkster]

Thank you guys for the information.

Response to the tone pot in the KT video Ricky linked sounds a fair bit more authoritative than mine; that was very helpful.

I really ought to reconnect the shielded signal pair to the jack as found and then back to the way I terminated them a couple of times to check myself but I feel reasonably confident that the magnitude of the tone change was enhanced by clipping the shield at the jack, and that my perception wasn’t just my getting tuned in to the sounds.

“Clearly noticeable”….In a quiet practice room with me dimeing the tone, plucking a string (not so much the E though) and then spinning the knob to the other extreme….yeah it’s clearly different but not as pronounced as in the video. But it’s definitely there on the A, D & G strings, and a wee bit on the E.

I think I’ll get a bit of single conductor with shield to replace the jumper I substituted for the other half of the signal to the jack and do some re-work. And with caps differing by an order of magnitude I think I’ll fool around with those too.

Meantime: Does anybody have a photo of a Fullerton KT (or any other passive) wiring harness?

What's with the extra ground coming from the PU?

I’ll get a shorter instrument cable.

Thanks again, all.

[Ken Baker]

Meantime: Does anybody have a photo of a Fullerton KT (or any other passive) wiring harness?

How about a hand drawing by Paul Gagon?

What's with the extra ground coming from the PU?

The green lead is the one we've all come to know and love. The blue lead is used with single-coil-capable pickups to provide cleaner tone with zero impedance mis-match. It's late, past my bedtime, and I'm not going to explain it.

I’ll get a shorter instrument cable.

Yea!

G'Night!

Ken...

[Dirkster]

I have the diagram but thank you just the same! It was hoping for a photo so I could see if Fullerton made different wiring choices, like shielded this or that; but this morning I stumbled into this thread over at Talkbass; I see a project in the fairly near future: https://www.talkbass.com/threads/jazz-s ... ng.159191/

Industrial instrumentation is (or was in the day of low voltage 4-20mA instrument circuits) wired up with twisted, shielded pairs (signal & return + grounded shield for each two wire instrument). When I get around to doing this I think I'll do that with the MFD PU's signal & ground lead, ending up with three, twisted, shielded pairs, and then apply the other shielding modifications covered in the linked thread.

In the meantime, while I leisurely gather the materials, I need to practice the instrument! By years end I ought to have an improved, electrically quiet and tone responsive KT.

[Ken Baker]

I have the diagram but thank you just the same! It was hoping for a photo so I could see if Fullerton made different wiring choices, like shielded this or that...

The drawing is a cleaned up interpretation (meaning reasonable lead length) of a real Kiloton cavity. If Paul had done the wiring . On the guitar side, I don't know. On the bass side, I have neither seen nor heard of shielded leads in cavities. They're known for leaving lots or wire in there, which is a good target for cleanup.

To return to the pickup thing above:

In consideration of G&L's large MFD soapbars found in various basses:

Standard wiring: L-100x, L-2x00, L150x, ASAT. 4 leads; black, white, yellow, and green. Black, white, and yellow are connected directly to the coils. Green has a short lead to connect between the coil and the base plate, and a long green lead going from the base plate to the cavity. This is done to provide ground to the base plate. However, doing so upsets the electrical balance between the coils a weensie bit (it's a real value, but don't ask), and this imbalance may result in a barely detectable amount of noise in the signal. Not enough to worry about and not enough to break the humbucking.

Single coil (K) wiring: L-100x, L-2x00, L150x, ASAT, Kiloton. 5 leads; black, white, yellow, green, and blue. Black, white, yellow, and green are connected directly to the coils. The blue lead is connected to the base plate and must be grounded. Coils are in electrical balance and quiet. This wiring is G&L's version of providing single coil (inners) as well as series and parallel.

M Series: M2x00. 2 leads, hot & ground. Coils are de-tuned from their L Series brothers, then series-connected internal to the pickup.

Tributes used to closely follow Fullerton's wiring diagrams. Now it seems that the folks in Indonesia may be feeling frisky.

Cavity shielding. It's good for basses with single coil pickups that might be adjusted to different levels; like a Jazz Bass. Humbuckers are naturally quiet, but their leads can pick up environment noise. G&L and Tribute basses (should have) black shielding paint in the cavities. Shield to your heart's content. There's only one possible caveat: shielding tends to darken the tone of the instrument. Being a bass, this is probably not a big deal. But some folks do like that bite.

Howzat?

Ken...

[Dirkster]

Howzat??
Tremendous!
You're a star!

House is quiet, I'll pad out to the shop and do some practice. Technology can wait.

Many thanks,
John O'Rama

[bigtone23]

I no longer wondered if the tone pot was doing anything; it was but it didn’t seem like very much and any audible contribution varies by string being plucked and PU configuration (series, single, parallel) which probably makes sense; additionally any change that I can detect occurs during the last 5 to 10% of CCW rotation of the tone control. I question whether or not an audience would notice any difference and so wonder if mine is working properly.

To boil it down, in my experiences, there are two things that have a big effect on the tone control's action and effect:
1. Cap value. On a bass, a .015uF cap will lightly roll off some highs, a .1uF cap will have a big roll off, cutting well into the mids, too. A .047uF cap is a good place to start, but I find .068Uf and larger to be more effective with the bass. However, cap value really doesn't come into play until the tone pot is rolled back a bit. You are only hearing the resistance of the pot until you get around 5 or so, then the cap kicks in. A bare wire will sound the same as a cap on the top end of the tone pot rotation. You really hear the cap around 1-2, where it's resonant peak is at the maximum. This peak often drops when the pot is fully CCW, which can be rather odd to perceive, the bass had more bass with the tone on 1 vs 0.
2. Pot Taper. Tone pots have to be audio taper. The KT wiring above shows a 250KA (audio) tone pot. Sometimes, a B/linear taper pot finds it's way into instruments. As great as linear pots can be for smoother volume control (linear volumes roll off a little slower than audio from full CW to CCW), the same can't be said for linear tone pots. They tend to act like you are describing: not much action until the last 10% or so and then it quickly rolls off. It almost acts as a switch, not a pot. Audio taper tones have a slower, more controlled sweep.

That said, I wonder if your tone pot is linear, or your cap is maybe out of spec?

Something I have adopted is not only exclusively using an audio taper tone pot, but also using a higher value pot and a bigger cap. This combo makes for a wider sweep of range and tone. A 500K audio tone pot will have a couple benefits over a 250K. First, it will reduce the loading of the electronics, which can add some life back to the signal. Secondly, it allows a little more range from the pot sweep. A 500K tone will have a little more air on 10 vs a 250K pot. However, because of the way a tone pot works, you can roll it back to around 7 or so and it will sound just like a 250K pot on 10. Same with a 1M tone. Roll it back to around 6 and it sounds like a 250K on 10, but you get more air up top, almost as much as a no-load tone control.
For example, my go-to on a stock bass with a 250KA tone pot with .047uF cap would be a 500KA tone pot and .068-.1uF tone cap. This might be a good thing to try on the KT, this way you get the bright, present bite it's designed to have, but can also roll it back and get a dubby, deeper tone from it.