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Tbx And No Load Questions


asristir
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Hello, folks. I've got a question concerning concentric pot potential. Hope someone can enlighten me!

Basically, I want to wire a concentric pot so that the bottom portion is a TBX tone that, when dialed up to the 10 position, cuts the circuit out creating "no load" tone. Is it possible to do this?

Thanks for your time.

Edited by asristir
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I can't say with any authority but I would imagine that simply by sending the signal through any type of component, especially a tone pot, you're going to create some resistence....therefore a "no load" pot isn't possible. The only way to have no load is by not loading the signal with anything.

I also doubt that you could have a concentric pot & a TBX because the TBX is two stacked pots & so is a concentric one. You'd need to somehow replace the bottom pot of the concentric pot with the TBX...which, even if you managed to do it, would create three stacked pots...which would be too deep for some cavities. I might be completely wrong, hopefully someone with more experience can offer more advice. Personally I can't see how it would be possible.

The TBX on it's own should offer enough treble or an easier alternative would be to have a tone control bypass switch.

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If you take a pot apart and scrape the conductive material off of the end of the pot's sweep furthest from the ground connection, then you've created an essentially no-load pot and don't need a bypass switch. I mean, sure, with it all the way open you'll add an ohm or two between your pickup hot line and the jack (as would a bypass switch), but you won't have the 250K or 500K to ground anymore, which is what really loads the guitar's output.

But yeah, a TBX control is already a dual pot, as is a concentric pot. So you can't really have a concentric pot with, for example, volume and TBX. I mean, you could, but I've never seen a concentric single/dual pot. I guess you could make one from a concentric and stacked pot, but you'd have to fabricate parts and like biliousfrog said it would be pretty thick.

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Thanks for the info!

Guess I'll just scrap the tbx+no load on top of a blender. A regular tone that tops out with 'no load' seems like it would be the simplest solution.

Is it possible to wire a tone knob to increase treble INSTEAD of bass response?

Another query: What do you think of varitones? A friend advised that they "thin" the sound somewhat. Yet I thought different capacitors would occasion different results... thin, thick, etc.

I'm going for broke and giving this guy's 12-position varitone a try:

http://alexplorer.net/guitar/mods/varitone.html

I think it's quite over-the-top, but it would at least be useful to try out bunches of different capacitors and weed out the "bad" ones. (bad being subjective, of course)

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In a guitar, if you don't have batteries, there are no active tone controls, period. What that means is that any tone control can only decrease amplitude of certain frequencies, never increase them.

A normal tone control actually works by shunting some of the high frequencies to ground (treble cut). This is a low-pass filter and works by having the input signal go through a resistor (the tone pot) then has signal out with a capacitor to ground. You can make a tone control which shunts low frequencies to ground (bass cut), a high-pass filter, by reversing the position of the cap and resistor - you would have the input signal go through a resistor, then have your output signal and a resistor to ground. I've never tried this in the context of guitar wiring, although it's common in other areas of electronics. The same values you use for a normal tone control may or may not work.

Edited by jnewman
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jnewman already covered some of this, but I somehow managed to leave my computer without hitting "submit"... so I'm a-post it anyhow. <chuckle>

---

Sounds to me like you need some active electronics. If you want flexible tone-shaping on the guitar itself, that's the way to go. Any tone-control variations (including the Varitone) will only de-emphasize regions of frequencies, never boost them. For example, and active circuit like EMG's SPC can BOOST the mids, whereas the TBX cuts treble and bass, reducing overall output. The resulting EQ curve is similar, but the decibels of output are different.

Many active tone circuits can work with passive pickups, which will also give them the other benefits of active electronics such as less signal loss over long cable runs, as well as obviating the need for a DI.

Greg

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GregP: tell me more about active pickups. I'd read a blip that mentioned something about the pickup having a preamp of some kind... is that configurable? Or is it set up at the factory or something? Couldn't find any documentation detailing what they can DO... just a bunch of installation crapola. Enlighten me, please!

Jnewman: Thanks a bunch! I want to see about using this concept for my neck pickup.

I'm ordering a body and neck from Warmoth tomorrow, so I've got at least another month to figure out the finer details. Thanks for the words.

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There are two general categories of pickups, labeled "active" and "passive." "Active" pickups have a very low output level and REQUIRE a preamplifier to give them the juice to make it to the amp at any volume. "Passive" pickups have a lot more of the bit that actually picks up the signal, so they have a higher output, which can go directly to the amp without a preamplifier. However, you can also use a preamplifier with "passive" pickups, you just don't have to. To recap: You can use a preamplifier with ANY pickups, but active pickups actually require one.

One big "problem" with "passive" pickups is that while they supply plenty of voltage for the signal, they have a high output impedance (meaning they aren't very good at driving a load). As a result, every path to ground (which includes volume and treble controls) and long cable run (like a guitar cable more than 10' long) actually loads down the output and decreases the voltage that gets to the amp. Another "problem" is that as we discussed, with passive electronics you can only get rid of some signal, you can't add to it.

A preamplifier in its simplest form is just a voltage follower. This is a device which takes a voltage input, and outputs that same voltage (and so is sometimes called a unity-gain preamplifer or buffer - its gain, the ratio of output voltage to input voltage, is one) - but it does so with a much lower output impedance, which means that it can drive a load better so little of the signal is lost to controls and long cables.

The next step is to make your preamplifier variable gain. This lets you set the output level of your preamplifier at some constant multiple of the input level (it may be more or less than the input, in the context of guitar electronics it's almost always more than). This is kind of useful for some things, but if you refine it a little more, you can make your preamplifier have gain that varies with frequency - i.e. you can make a control or controls which make your preamplifier amplify or cut some part(s) of the frequency spectrum more than others. This is what is really useful.

You can also build effects into your guitar's electronics, but I personally think those are a little silly :D.

It is certainly possible to build your own preamplifier, but it is not a trivial task and for the amount of time it would take to learn the stuff if you don't already know it you might as well go ahead and buy one if it's what you want.

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In your opinion, is an external preamp more to be desired than an internal one?

The reason I ask is that I am worried that the number of things I'm sending the signal through is going to kill it.

Does a concentric pot that is wired for 2 different purposes have the same resistance (negative affect on tone), or worse or better, than a normal pot or a push/pull? I've read that using 1M pots helps; do you find this to be true?

Here is what I'm planning:

3 pickups (two humbuckers and a single coil.... all passive)

3-way selector, varitone, master volume, and each pickup to its own seperate blend/tone concentric pot

2 humbuckers also through one rotary switch each (for parallel, phase, and coil split)

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There are plenty of external preamps available... in a sense, pretty much any active volume/distortion/fuzz/drive/boost pedal is a preamp (with some other stuff added). If you're worried about an internal preamp messing with your tone, you can always wire it with a bypass switch. I wouldn't worry too much about it though - this is almost the ideal application for a small signal preamplifier. A well-designed preamp shouldn't color your tone at all - they're accurate enough that you can use them in high-quality audio apps, so I can't see it doing too much damage to a guitar signal.

How much a potentiometer loads down your output signal is purely based on its resistance, so it doesn't matter if the pot is a single, part of a push-pull, or half of a concentric pot. There is no electrical connection between the pot in a push-pull and the switch or between one pot and the other on a concentric pot. Using a push-pull or concentric pot is exactly the same as using a normal one, assuming the pots are the same value (plus you get to use the other part, be it switch or pot, for something else). Using a higher-value pot as your volume pot than normal will cause less load on the pickups output, but it'll still be less than if you use a no-load pot as detailed above.

What do you mean by blend/tone pot? Normally, a blend pot would be a special dual pot that takes two inputs and mixes them at different levels. You can not get a blend pot plus something else in a concentric pot format. Also, you're talking about a lot of switches and options, but you haven't provided for any pickup combinations - you would only be able to use one pickup at a time but each pickup would have a ton of controls.

My experience is that a lot of people who are new at modifying their guitar's electronics decide that they want a million different switching options and controls, and then end up using only a couple of them. There are people around who use all fifteen switched and ten knobs on their guitars on a regular basis, but there aren't very many :D.

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Aw crap. I was hoping to use blend pots to mix in any amount of the unselected pickups, thereby creating the pickup combinations that seem absent. Guess that won't work since a blender can only mix two signals.. Back to the drawing board on that one. The plan was: select bridge, then blend in a spot of neck and a bunch of middle... or whatever combination seemed most interesting. I'll find a way.

Yes, all of the mods that I can squeeze in will be present for 70% just to try it and 30% just to do it. I've never actually heard these things in action, so I don't know which ones will be really useful for my sound and which ones will be wastes of effort. I'll find out eventually, I suppose, and delete the excess.

Hmmmm. Maybe get rid of the pickup selector and use a volume knob for each pickup... would make for shitty pickup switching... but maybe I could mix the seperate pickups that way?

The idea is to get away from the standard strat pickup selecting. With the middle/neck or middle/bridge positions, I've always wanted to be able to mess with the volumes of the two pickups. Keep the cut of the bridge, but dial in a splash of the neck, etc.

The idea is also to have as many interesting sounds available as possible, without killing the guitar, while at the same time keeping it as simple as possible to navigate. You know, the usual quandary.

I'll find a way.

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I like Myka's setup. Ditch the master volume and it's exactly what I'd like to do.

Is it difficult to wire the volumes to decouple like that?

Thanks, fellas. It is excellent to find a forum where people actually respond to the question instead of arguing about syntax etc.

Edited by asristir
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