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Post by gfxbss on Jan 12, 2007 22:11:55 GMT -5
hey guys, im having problems w/ some mods on a pbass. the specific problem is a design that can be seen here www.guitarelectronics.com/product/WDUH00101now, the volume output is a bit weak. then when i switch to tone(pull out the Push/Pull), my volume gets strong again. also, if i have the volume turned to half, when i switch to tone, it goes to full. some other things im doing to this bass are a 6-way varitone, a blast button, and a kill switch. the only thing that is giving me a problem is the vol/tone. Thanks, Tyler
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Post by gfxbss on Jan 13, 2007 12:50:28 GMT -5
here is a diagram for what im trying to do. <br> multimeter set to 20K with push/pull out(tone) reads 6.00. mutimeter set to 20K with push/pull in(volume) reads 19.24.
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Post by sumgai on Jan 13, 2007 13:57:12 GMT -5
Tyler, The wiring "looks" correct, but is a wee bit incomplete...... no component values. Some experiementation might be in order. Since the pickup is HB (wired in series), start with 500K and 0.033µf, and see what happens. BTW, that sixth position in the Varitone switch (the most clockwise, as we view it)..... it sure looks like the hot lead is going through the switch's common terminal to ground. Unless I've forgotten how things work around here, that's gonna hurt your volume level somethin' fierce! If I may make a suggestion, I'd ditch the push-pull scheme, and just use the Varitone setup as the only tone control (after fixing the 'leak', of course). HTH sumgai
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Post by gfxbss on Jan 13, 2007 14:30:17 GMT -5
not following you. the one w/ the wire comming off instead of the cap(furthest clockwise) is position 6. its is a bypass. the center lug is the common ground.
i would, but they guy im doing this for wants it there. im wodering if i should get a concentric pot to put in it. either that or may be i can talk him into a midrange cut/boost. that would be fun.
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Post by sumgai on Jan 14, 2007 4:03:06 GMT -5
not following you. the one w/ the wire comming off instead of the cap(furthest clockwise) is position 6. its is a bypass. the center lug is the common ground.
Follow the red brick road, bunkie, and tell me what you see.... The clue is, you are using capacitors to shunt high frequencies to ground. The corollary is, the capacitors are blocking the low frequencies from being shunted to ground, right? Then doesn't it stand to reason that if there is no capacitor in your 'bypass' mode, then won't all frequencies be shunted to ground? Try analyzing the circuit with no connection on the sixth terminal - it's open, not shorted..... what happens? sumgai
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Post by gfxbss on Jan 14, 2007 17:49:39 GMT -5
wow, i feel slightly retarded. it didnt even sink in to me how a tone knob works... at anyrate, ive doen a few axes w/ the wire, and everything works fine.
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Post by sumgai on Jan 14, 2007 23:29:50 GMT -5
Tyler,
Don't feel bad, it's a common mistake. When one sees a working circuit, and figures a simple mod like removing one part should do Some Great Thing, it's easy to forget to look for any downsides to the mod.
In such cases, do what I do..... anticipate the worst, then prove yourself right. If you come up a loser, then you win! (Dope that out correctly, and I'll Exalt ya! ;D)
In this case, at Position 6, the hot lead from the tip of the jack will go straight to ground, thus plunging your signal level to Zero dB. Fini. Signal 30. End of story. Yadda, yadda, you get the picture.
In fact, to get the fattest, sharpest tone possible, you don't want any 'tone robbing' cap in the circuit at all. Hence, just leave Position 6 open, and you'll get the full signal at the output jack, unmolested by any circuitry beyond the tone control's cap (if you leave that in).
HTH
sumgai
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Post by gfxbss on Jan 14, 2007 23:37:20 GMT -5
one more thing. when testing i was noticing a relatively low output from this bass compared to what it used to be. i decided to take a multimeter to just the wires of the pups. its reading only a 5.96 in the 20k positon. still in an accaptable output. but rather low none the less. any ideas? would repotting them help any?
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Post by sumgai on Jan 15, 2007 20:17:32 GMT -5
Tyler, Nope, repotting is for quieting a pickup that is microphonic. IOW, a pup that squeals, or feeds back. The potting compound merely forces all of the air out from between the windings, thus giving them no room to vibrate on their own, in resonance with the nearby speaker. (Or one that's way too loud! ) ~ 6KΩ is acceptable, and you should have no problems on that account. However, if the pups were removed, and desoldered from everything, were they put back correctly? If they're out of phase....... And as I said before, the idea of a switchable dual-duty control is cool, but in practice, it comes up short on one end of the stick or the other. In this case, you haven't told us what values you're using for the pot/cap. As JohnH points out, each person will hear it differently, but overall, the best starting point for an HB pup is 500KΩ and 0.033µf or 0.047µf. Adjust to suit your tastes. HTH sumgai
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Post by gfxbss on Jan 15, 2007 23:00:06 GMT -5
ahh, tis a 500k push/pull w/ a .033µf.
the pups are not out of phase w/ each other as it is just a pbass pup w/ two wires. one pos one neg. i decided to see what they would register if tested alone.
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Post by sumgai on Jan 16, 2007 2:59:25 GMT -5
Tyler,
Well now that you've 'registered' them alone, why not play them alone? No circuitry at all, just pickup to cable to amp. That way, you have a base value for comparison. If the bare pickup is loud, and attaching "the works" makes it dull, then you've got a problem.
But if the bare pickup is not a real strong performer, then you've done all you can, and either it's time for a some battery powered active electronics, or perhaps a different pickup.
Further testing is in order! ;D
sumgai
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Post by gfxbss on Jan 17, 2007 21:38:43 GMT -5
alright, testing is finished! my analysis, i somehow fried the push/pull. if i put in a normal pot, eveything works fine. with one exception. my varitone doesnt seem to have any effect. im using the exact same value caps that i used in a couple of guitars ive done with great sucess. would wiring a varitone on a bass require any different value caps?
at any rate, im just going to pick up a concentric pot. then wire that up.
Tyler
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Post by sumgai on Jan 18, 2007 16:34:48 GMT -5
Tyler, Good going! We'll make first-rate troubleshooter out of you yet! Yep, sure would. Try moving everything "over" one step. Take out the smallest cap, move all the caps over one terminal, then plug in a new cap at the 'dark' end - this should be twice the value of the next cap (your old 'darkest' cap). If that isn't enough, do it all again. Don't forget, values are not precise here, just get pretty close. Or, if you can't find anything that's cheap and close to what you want, combine smaller values in parallel to make what you need. It's simple..... cap values add in parallel. For example, 0.033µf plus 0.047µf will add up to 0.08µf. If all that doesn't work as you'd like, go here, and check out unklmickey's post on older Varitone circuits with chokes. Adding one of those little beasties will definitely change what's going on with your tone! ;D sumgai
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Post by gfxbss on Jan 19, 2007 6:37:05 GMT -5
alright, thanks sg. i enjoy chokes. i used one for the midrange cut in my p-bass.
Tyler
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Post by gfxbss on Jan 27, 2007 14:31:09 GMT -5
alright, wanted to see if you guys should check the wiring on the concentric for me. for some reason, both of them are working as volumes. also, i am getting a buzz when i start to turn them down. when all of the way up, everything is great(other than tone not working). also, when i hit the blast button, i get the same buzz. Thanks, Tyler P.S. i want the tone to work as a knob for the varitone, hence there being no cap on it.
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Post by sumgai on Jan 27, 2007 15:59:08 GMT -5
Tyler, Your blast button is on the ground side. When you hit it, it lifts the ground from the volume pot. Lifting the ground from that point does not cause the signal to bypass the pot. Indeed, whatever value is currently set by the wiper, that value will still be in the circuit between the pickup Hot and the output. Only now, there's no ground (no third connection), so there's no voltage division going on. That's a good source of hum, when you hit the switch. Plus, it not very likely to be doing your tone any good, either. Reconnect it so that when you want that instant full volume (blast), the Hot and Wiper terminals are shorted together - I'm sure you'll like that much better. The tone control is also wired incorrectly - you have the right-most terminal on ground. The wiper, having the pickup Hot signal, will simple decrease the resistance value between max and zero, thus acting as a volume control - it is shunting the pickup Hot to ground in the manner of a rheostat. Those six capacitors are in parallel with the wiper to ground connection, so they aren't doing much good for your tone, either. Remove the ground wire from the right-most terminal, move the Varitone switch wire from the wiper to that now-vacant terminal, and all will be well in gfx-land. HTH sumgai
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Post by UnklMickey on Jan 29, 2007 10:19:42 GMT -5
hi Tyler, i've made a couple of changes to your drawing: 1 -- the tone pot now feeds your capacitor switch. 2 -- i have drawn in a treble bleed cap at the volume control. try about 1 ~ 2 nF. also you might like it better with a 220k resistor in parallel with the cap. experiment, season to taste. 3 -- if that wasn't enough, i've also moved the common for your capacitors to the low lug of the volume control. it will get lifted from ground when you "blast". that should make things a bit brighter. let me know how it all works out. have a blast, unk
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Post by gfxbss on Jan 29, 2007 15:26:35 GMT -5
thanks unk, i already had the treb blead. i just didnt feel like tossing it in the dawing. i may try the resistor in w/ it though.
Tyler
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Post by sumgai on Jan 30, 2007 1:44:50 GMT -5
Tyler, You recently asked me (via PM) why I cast doubt on your version of the blast switch (lifting ground). I thought an answer here would be of use to other readers/members of this forum. I'm surprised unk also replicated your switch design. You see, when you lift the ground like that, what's left is a resistor in series with your pickups, heading straight to the output jack. That resistance, whether it's large or small (pot turned way down or way up), is adding some reactance to the pickup's signal - that'll affect the tone somewhat. It's also adding a pure resistance to the voltage level, which will tend to knock down the overall volume level from the pickup's maximum. Yes, hitting the switch will increase the current level to a greater value, but it's still not full bore. My suggestion is valid, both tone-wise and from a good engineering standpoint - move the switch such that it shorts the Hot and wiper terminals when depressed. This will automatically send all possible pickup signal to the output, while retaining that important ground connection on the other side of the pot. The only drawback may be, if the pot is turned down to 10% of its value (or less), the resistance to ground might be low enough to still bleed off some of the signal. For a 250KΩ pot and a 8KΩ impedance pup, I'd calculate that value to be somewhere in the range of 25 to 30 KΩ - about 3 to 4 times the impedance of the pup. (But that's all a calculated guess, you understand. ) It only takes a moment to see if my way results in better tone, and quite probably, a higher volume level. But if you really want the best chance of meeting your desired goal, then use a DPDT switch, and hook up both methods - yours and mine! ;D sumgai
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Post by UnklMickey on Jan 30, 2007 2:09:16 GMT -5
......But if you really want the best chance of meeting your desired goal, then use a DPDT switch, and hook up both methods - yours and mine! ;D
sumgai a DPDT is the best choice, but since they are much less common than SPDT in momentary push-button, i suggested the ground lift method. when you get to the lowest setting of the volume control, the pass thru method will not work because the pickup will be completely shunted. having 250k in series will produce some serious tonal issues, but the treble bleed cap should do a reasonable job of mitigating that. remember, the bottom lug of the volume control is no longer a path to ground.
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Post by sumgai on Jan 30, 2007 4:01:36 GMT -5
unk, Momentary, as in spring-loaded? Err, if my right hand is holding down the switch, what am I doing to make sound, hammering and pulling like crazy with my left hand? I just buttumed the switch was latching. A blast would insinuate that a musical passage was about to come down the pike, not just a short "loudening" of the current note before we move on to the next note. But what do I know....... Lifting the ground does indeed kill the potentiomter functionality of the 3-pole variable resistor, but recall that before there potentiometers, there were rheostats - which is what we have here. Inserting an additional resistance in series with a voltage source converts our voltage generator (the coil with its excited magnetic field) into a current source - Ohm's Law decrees that. And thanks to Kirchhoff's Laws, and some judicious use of Thevenin's Theorem, we are forced to find that some appreciable voltage drop will occur across that resistor, thus we have the condition of 'less-than-full' signal at the output jack. And while I can't speak for Tyler, I don't think that I'd be cranking the volume level from say 10% or even 20% up to full-bore, and then back down again, all on a very sudden transition. More likely, the control would be no less than 50%, where the sudden increase wouldn't be so harsh. But I repeat, that's just me, Tyler may have other ideas of what's acceptable use. ;D sumgai
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Post by gfxbss on Jan 30, 2007 6:27:04 GMT -5
hey guys,
well, i cant make that call either. you see, its not my bass. it is my girlfriends brothers(mmray). so i would have to talk to him about what he wants done w/ it. i want to say he is looking for a tom morello style sound on bass.
Tyler
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Post by UnklMickey on Jan 30, 2007 9:19:23 GMT -5
...And while I can't speak for Tyler, I don't think that I'd be cranking the volume level from say 10% or even 20% up to full-bore, and then back down again, all on a very sudden transition. ... believe it or not Sumgai, that's often just the way these things are used. ...Inserting an additional resistance in series with a voltage source converts our voltage generator (the coil with its excited magnetic field) into a current source .... Sumgai, this is true....only in the fact that the series resistance limits the maximum current possible. if the series resistance is much, much larger than the external load placed on the circuit, a current source is a reasonable model. this should not be the case here.
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Post by sumgai on Jan 30, 2007 21:27:15 GMT -5
Call Ripley, I don't believe it.... j/k ;D Who'd a thunk it. Guess I live in the fuddy-duddy age of expression. Or well..... unk, you can't limit current if you don't have it to limit, right? While the resistor can, and does, act as a current limiter, it does so by reacting to the voltage presented to it, in this case, the coil's output. We needn't concern ourselves with how the signal is transferred to the amp (current, power, or voltage), we're only concerned at this point in time with the raw resistance factor. The question is, does the resistor actually reduce the level of the signal in any way whatsoever? And I contend, yes, it does. Ohm's Law, Norton and Thevenin, Kirchhoff, all of these principles state pretty clearly (to me) that a resistance cannot be ignored when present in a circuit, it must be accounted for. The percentage of it's effect may be quite small, but it will be present, nonetheless. We are now concerned only with the degree of that effect. I say, it's signficantly noticible, and you say.......? sumgai
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Post by UnklMickey on Jan 30, 2007 23:28:18 GMT -5
i say it looks pretty good: the right hand side is just the resistances, ignoring the tone pot. i'm sure you can guess why i chose 100 volts for the source. 86% of the voltage is still seen at the amp. (this is with a Fender Deluxe. with an Ampeg, you get even more.) i think it will still look good if our pspice friends do a sim on it. interesting note, if the tone control is rotated toward zero, with the blast button pressed, the tone gets brighter. that part could be useful, or it could get ugly.
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Post by sumgai on Jan 31, 2007 2:11:42 GMT -5
unk,
The right side shows a 13.8 percent drop in signal level (about 1.3 dB), but as you said, that is a simplistic sim. Not a huge loss - at the stated resistance value..... inquiring minds would like to see a range of response curves, please. Assume a 500K pot, the P-bass pup is a humbucker.
Where're the values for the left-side sim? Show us the money, eh? ;D
sumgai
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Post by gfxbss on Feb 2, 2007 22:23:03 GMT -5
alright guys, i just wired it up the way unk changed my diagram. im still having the same problem. still buzzing. if i turn the tone knob all of the way down, then it goes away. so, obviously it has somthing to do w/ that, but how can i fix it?
Tyler
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Post by sumgai on Feb 3, 2007 6:27:06 GMT -5
Tyler, Sounds like it's time for some simple continuity checks. Seems to me that you have a bad connection to ground somewhere, or possibly a bad solder joint. Unholster that multimeter, and poke around a bit. sumgai
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Post by gfxbss on Feb 3, 2007 14:07:22 GMT -5
alright got it all finished. i made what could be the most elementary mistake ever. i wired the jack backwards.
ill post some pictures w/ the final results when i get time.
Thanks guys! you bailed me out yet again.
Tyler
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