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 Post subject: Re: potentiometer differences
 Post Posted: Thu Dec 11, 2008 1:19 am 
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BlueAngel and all, thank you. That is a bit, but I understand the principals better now. Thank's Mark


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 Post subject: Re: potentiometer differences
 Post Posted: Sun Dec 14, 2008 5:24 am 
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What Blue Angel said. And to counter some of the "spikeyness" from using higher value volume pots, especially on humbuckers, I like to use .033 tone caps. You can get that value either by wiring in parallel two common values: .022 and .01, or you can surf and find the .033 tone caps. I did actually find a place that has the orange drops in all the values so you can experiment.


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 Post subject: Re: potentiometer differences
 Post Posted: Sun Dec 14, 2008 5:28 am 
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I wanted to post this separately having to do with the volume pots. The reason for the greater or lesser load to ground is that the third unused lug of a volume pot is usually grounded for safety. SO, one way to have the treble stay up is, of course, the small value cap in parallel with a resistor across the pot to bleed treble through to the hot lead as you turn down the control; but another way is to insert a resistor between the unused lug and ground so there is more resistance to ground and therefore less ground "loading" of the pickup.

Again, it is different than just using a different value pot because of the resulting hybrid ramp as seen from the ground side, but it is another way to fine tune and tailor your overall tone.


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 Post subject: Re: potentiometer differences
 Post Posted: Sun Dec 14, 2008 8:26 pm 
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Quote:
I wanted to post this separately having to do with the volume pots. The reason for the greater or lesser load to ground is that the third unused lug of a volume pot is usually grounded for safety. SO, one way to have the treble stay up is, of course, the small value cap in parallel with a resistor across the pot to bleed treble through to the hot lead as you turn down the control; but another way is to insert a resistor between the unused lug and ground so there is more resistance to ground and therefore less ground "loading" of the pickup.
The third lug on a volume pot is not unused or grounded for safety - it's the zero end of the potential divider. Without this connection, it won't work as a proper volume control, and won't go to silent - in fact it will work exactly the same as the 5th knob and just reduce the volume slightly. If you put a resistor in this connection it will do the same sort of thing - it will act as a fixed lower limit on the volume range and stop it going to zero, although lower than with no connection.

By the way, I recently noticed a mistake in the wiring schematics for the 5-knob models (apart from the Dual Mono one) on the website - the 5th knob is shown as having its third lug grounded, which it doesn't.


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 Post subject: Re: potentiometer differences
 Post Posted: Sun Dec 14, 2008 8:48 pm 
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While we're talking pots, is the DPDT switch on 4003s now a 500K or 330K? Reason I ask is, the boutique only sells 500Ks. I ordered a few and they look very much the same as the stock push-pull pot.

Quote:
OK, and now for something completely different: I like a hybrid curve on my controls between straight linear and pure log audio. So, I usually purchase the highest quality 500kohm audio taper pots I can find, leave them be for overwound humbuckers, and add bridge resistors to bring the overall value down as the application requires. Remember your ohm's law about the reciprocal of the sum of the reciprocals in parallel to get the effectve value. Bridging with:
a 2 meg resistor gets you a 400kohm value;
a 1.5 meg resistor gets you a 375kohm kohm value;
a 1 meg resistor gets you a 333 kohm value;
and, of course, a 500kohm bridge resistor gets you a 250 kohm value, which is good for a tone control, but starts getting too linear to use for a volume control.

And if the pot is not exactly "spec," as most pots have a 20% tolerance, then I can fine tune the resistor accordingly to get what I need.


Nice innovation! Let me just ask, is a "bridge resistor" just a resistor applied the same way as most caps are, i.e., connected to one lug and grounded to the pot? Or is it wired into the next connection, i.e. to the output jack or elsewhere?

Using the same method I suppose you could use a 10M resistor to get a 476K pot. Not that you would--I doubt there is much difference between that and a 500K.

This is a good thread. I recently applied the 4002 tone circuit to my Jazz Bass out of curiosity and that was a good experiment--although I don't think I'll keep the mod necessarily. Anyways, I really value all of the smart people we have on this forum to help enlighten us about guitar electronics because I find it really fascinating.


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 Post subject: Re: potentiometer differences
 Post Posted: Sun Dec 14, 2008 9:31 pm 
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Could different pots,and or added resistors for the pups, help control what I call "barky" output from the upper end performance of the pups? I love the tone of the bass,but I hoped to find a way electronically to "pad" the pups out put to at or just below that thresh hold. Thank's Mark


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 Post subject: Re: potentiometer differences
 Post Posted: Sun Dec 14, 2008 11:41 pm 
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Could different pots,and or added resistors for the pups, help control what I call "barky" output from the upper end performance of the pups? I love the tone of the bass,but I hoped to find a way electronically to "pad" the pups out put to at or just below that thresh hold. Thank's Mark


Absolutely. That's mostly how they get used in guitars/basses--to control the signal that gets sent to the amp. The vintage cap that we all talk about is just a way of siphoning off lows and isolating highs for clarity. A resistor can do the opposite.

You may want to look at some of the circuits available under Service>Schematics and see what is possible.

Now, as to how to achieve what you're doing, I'd think you'd want some sort of a limited low-pass filter, because if you cut off much of the high-end you're going to get a really muddy instrument. Mess with the EQ settings on an amp that has a parametric and isolate the exact settings that get you the sound you want, then record which frequencies you want to get rid of. I suspect they are pretty high into the kHz range, probably 1e2 kHz or more, because that's where a lot of "artifacts" live and those are what a lot of people get annoyed at.

That said, you COULD just use a para-EQ to set your sound up, rather than messing with the guts of your bass.


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 Post subject: Re: potentiometer differences
 Post Posted: Mon Dec 15, 2008 4:28 am 
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Cassius, thank's Bro, That is great stuff. I know what I want, I just don't know how to go about accomplishing it. I have a bro, a real tube head, who has an oscliscope. I was thinking I might see what the signal looks like in the "barky" range, and then lower the levels until clean, and see what freq I needed to limit it to. What do you think of that approach? Am I on the right track? Thank's Mark


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 Post subject: Re: potentiometer differences
 Post Posted: Mon Dec 15, 2008 5:06 am 
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As far as I know, all the push-pulls are 500kohm, give or take the manufacturing tolerances. I have them all the way from 400kohms to 517kohms, but they are all "nominally" 500kohms. Just the nature of manufacturing. The bridging resistor to bring down the effective value of the pot bridges across the center wiper and the hot lug in, NOT the ground.

Yes, you could pad the pickups with inline resistors, as I do with the neck pickup on some of my other guitars to better balance the bridge pickup, in order to cut the peaks, but then you'd effectively be limiting yourself to a "9 1/2" volume control. You're better off either reducing the input gain slightly and/or adding a touch of compression.

One of the easiest ways to alter the tone curve is to change out the tone capacitor to change the hinge frequency. For example, on a lot of guitars, the "standard" tone capacitor is .022. But that doesn't get mellow enough for me in the neck when I want to only roll off slightly, say to 6 or 7 on the knob, so I use the intermediate value (which, admittedly, is sometimes hard to get) of .033. The "standard" bass value of .047 cuts too much treble for my taste for use on guitar.


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 Post subject: Re: potentiometer differences
 Post Posted: Mon Dec 15, 2008 7:04 am 
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Quote:
I have a bro, a real tube head, who has an oscliscope. I was thinking I might see what the signal looks like in the "barky" range, and then lower the levels until clean, and see what freq I needed to limit it to. What do you think of that approach? Am I on the right track? Thank's Mark


It'll be a bit difficult to really tell what's going on frequency-wise with an oscilloscope. What you really need is a spectrum analyzer, preferably one made for audio frequencies. These will show you the various frequency components and their relative amplitudes.

Now, finding someone who has one is a lot harder, but you might ask your friend with the 'scope to see if he knows where one might be found.


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