andru
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Post by andru on Mar 26, 2009 20:29:20 GMT -5
Hi there, I've recently installed a blend pot on my new Jazzmaster. It 'seems' to work; however, funny things are happening: 1. Only neck (full CW) and only bridge (full CCW) work perfectly 2. Middle position is super backed off output from normal 'both pickups on.' I can tell both pups are on; however, it's really lifeless and lacks the output. 3. When in the middle position (or any 'in between' position), the tone seems to act as a volume 4. The tone works fine when only neck or only bridge Please help A.
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Post by newey on Mar 26, 2009 20:41:31 GMT -5
andru-
Hello and Welcome! We're glad you signed in, because you are our 1500th member!
Unfortunately, I don't have an answer for your problem, but someone will be along. Posting some pix of your wiring might prove helpful.
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andru
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Post by andru on Mar 26, 2009 20:46:31 GMT -5
Oh wow! Did I win something?? lol Thanks for the welcome Unfortunately, I cannot take the thing apart at the moment. However, could the fact that it's 250K blend have anything to do with it? Does it send the opposite ends as 'pure signal' and then send the mixed signal through the potentiometer circuit? Here's the blend pot wiring: www.diyguitarmods.com/diyprojects/2pickupblendpotmod/BlendPotWiring-Dia..gifA.
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Post by newey on Mar 26, 2009 20:59:07 GMT -5
One of those Homer Simpson moments: "Doh!" After rereading your post, something ChrisK said awhile back about Blend and Pan Pots suddenly popped up in my neural net: Read the full real deal here: Blend And Pan Pots
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Post by ashcatlt on Mar 26, 2009 21:37:24 GMT -5
newey's linked you to my initial answer.
This doesn't really explain (to me) your tone control issue. A picture or drawing of the rest of your circuit would help in diagnosis.
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Post by ChrisK on Mar 26, 2009 21:50:27 GMT -5
As they say oot there in Minnesooooota, ya, you betcha! (I can talk this way as I'm half Sweeeeeedish meself.) ;D ;D It's a PAN pot. Now, to be fair, the supplier didn't actually lie when they sold you something as a blend pot. In order to actually lie, one has to have a hint of a clue about what something actually is in order to misrepresent it. Most parts suppliers are still struggling with differentiating their burro from a burrow.
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Post by sumgai on Mar 26, 2009 22:04:08 GMT -5
ash, At the "blend-pot's" mid-rotation, each pup is feeding almost to ground, which is in parallel with the tone circuit. The tone pot is really "trimming" the value of the pup-to-ground resistance/impedance, in series with the capacitor. Not a good idea. andru, You've wired the thing backwards, ala most Gibson Les Pauls. Try swapping the output and ground lines with the two incoming pickup lines. That won't help your overall volume issues, for what are by now obvious reasons. (You have read the thread reference by newey, haven't you? ) But at least this will make your tone control work as expected. HTH sumgai
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andru
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Post by andru on Mar 26, 2009 22:50:33 GMT -5
Wow,
Thank you all for your help!
Sumgai: Right now, it's rotating the way I like it (CW neck and CCW bridge). Thus, in the GIF above, Source A is hot neck and Source B is hot bridge. You mentioned that the Sources should be switched with the Output and Ground; (1) which go where?
(2) How can I get my hands on a 'true blend'?
(3) Will putting a push-pull phase reversal (on bridge pickup) affect any of this?
I wish I found this forum eons ago!
Cheers,
A.
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Post by ashcatlt on Mar 26, 2009 23:44:13 GMT -5
ash, At the "blend-pot's" mid-rotation, each pup is feeding almost to ground, which is in parallel with the tone circuit. The tone pot is really "trimming" the value of the pup-to-ground resistance/impedance, in series with the capacitor. Not a good idea. I had trouble understanding the situation from this perspective. My suspicion was that the series resistance of the "top half", in conjunction with the lower parallel resistance from the "bottom half" might cause the cutoff frequency of the overall filter to be so low as to attenuate most of the audible guitar spectrum, and that turning down the tone control exacerbated that situation. Looking at it now, I'm pretty sure that's the same thing Sumgai said. I 5Spiced it, and I think we're both right. Interestingly, this same thing happens on any guitar (with possible exception of those afixed with a "treble bleed" mod) if you turn the volume down a ways.
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Post by newey on Mar 27, 2009 3:31:29 GMT -5
andru-
After you posted this and I linked you to the Blend and Pan Pots thread, we had a brief flurry of added postings there. The upshot is, get your true blend pot from Fender. ChrisK listed the part nos there.
No, the phase switch is wired as a separate module from the blend pot. The phase switch would go across the bridge pickup leads "upstream" of the blender. With it pulled up, you'll blend the bridge in OOP.
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Post by ChrisK on Mar 27, 2009 18:55:55 GMT -5
What you can do if you're stuck with a Blend Pan pot is to use each half in a rheostat mode (a two-terminal variable resistor). In essence, in the center detent position, you will have a 40K resistance in series with each pickup. As you turn the knob one way, the resistance in series with one pickup will decrease and it will increase for the other. Conversely, well, uh, reverse things will happen.
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andru
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Post by andru on Mar 28, 2009 13:05:37 GMT -5
Chris,
So, I can just de-solder the ground completely and solder it to the side of the pan pot?
Does fender have an on-line order outlet for the rare 'true blend' pot?
Thanks again for all your help,
A.
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Post by newey on Mar 28, 2009 13:30:14 GMT -5
andru- We've been in an ongoing discussion on just that topic over on the "Blend And Pan Pots" thread. GuitarPartsResource has them, and as was discussed, the 500K part number matches ChrisK's number, so that should be a true blend. The 250K we're not so sure about 'cause it's a different part number than Chris had. Also, any Fender authorized service center should be able to order you one if they don't stock it. No, just desolder it, don't go to the side of the pot. You're making it into a two-conductor Rheostat.
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Post by ChrisK on Mar 28, 2009 19:10:26 GMT -5
Sure, if you're into grounding the pot shells. Remember, you are only using two terminals on each element (as shown) Blend and Pan Pots
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andru
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Post by andru on Apr 8, 2009 21:15:04 GMT -5
Hello all,
The suggestion about removing the ground pot did not fix the problem with the tone. It's very strange: as soon as the pan pot is turned (minutely) away from bridge / neck, the tone control acts to cut almost ALL signal. I wired one of these pan pots in a tele, and did not have the problem at all. I used to the diagram above (with ground) before.
Something specific about a jazzmaster's wiring that makes this case different?
As sumgai mentioned, do I have something backwards here?
On a positive note, the push-pull phase works fine.
This pan pot issue is very annoying; I am thinking about moving to a 4-way rotary to get series and parallel.
Any last minute advice on fixing the tone issue?
Thanks again,
A.
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Post by sumgai on Apr 8, 2009 23:00:54 GMT -5
andru, Sorry I missed your previous post requesting enlightenment. Since you're contemplating moving to, or adding on, another circuit modification, it would help if we could see a diagram of what you have so far. The "extract" that you linked to previously doesn't give us the whole picture, so we're really just guessing at what's happening "under your hood". And no, the fact that it's a Jazzmaster (my alltime favorite, BTW) has no bearing..... it's likely a mistake in either the wiring job, or in the planning stage - that diagram I mentioned a moment ago. BTW, you can post an image directly into your message here via the tags. See those square icons above the textarea where you enter your text? (To the right of "Add Tags:".) The lower of those two rows, the fourth icon from the left.... that icon inserts the image tags. When you're through, the whole line should look like this: [img src="www.your_photo_host_site.com/your_folder/your_image.ext"] When you preview the message, the photo will show up just like in the real forums. If not, you've got a chance to track down the problem. If you're using Photobucket, there's a box of cut-and-paste code at the bottom of the Upload Confirmation screen. Within that box, you'll find a line that starts with [url.... That's for you to copy directly from there to a posting on some forum or Bulletin Board, like this one. Makes life easy, no? HTH sumgai
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andru
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Post by andru on Apr 14, 2009 22:41:03 GMT -5
Sumgai: I recently opened the thing up, and starting sketching a diagram. I really don't quite get the J-master wiring; I understand that a dpdt 'throws' the hot neck and 'hot tip' from the top circuit to the bottom circuit. Fender just seems to have way more grounding (and complicated) than needed. I figure it's easier to just build the damn thing up from scratch, since I am not fond of the cheap wiring used anyways. Can you sketch over this SD diagram www.seymourduncan.com/support/wiring-diagrams/schematics.php?schematic=jazzmaster and show me where exactly a pan pot should be placed, and phase reversal? Also, can you sketch the wiring of the pan pot? Right now, the phase is on a push-pull and I believe it to be working (bridge pickup). I used this for the push-pull dpdt: alexplorer.net/guitar/mods/phaseswtch.jpgI used the red as hot lead (bridge) and pink as ground lead (bridge). Hope you don't mind helping out! Thanks, A.
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andru
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Post by andru on Apr 15, 2009 0:05:44 GMT -5
Sumgai:
I am thinking now about wiring this thing a-la Gibson (i.e., two independent volumes and tones). Thus the roller system up top would be for the neck, and the southern pots for the bridge. I'd thus omit the push-pull for phase, as I could use the slider dpdt for phase reversal.
Next question: Can you send the hot outs from each independent volume to a 'master volume'? I am sure you can; however, are there any downsides to this? Signal loss, etc.?
I am thinking this would be cooler than a pan pot, since it wouldn't cut half of each pickup when both are on.
Also, would this be combining the two in series or parallel??? Basically, the hot outs from each independent volume control would be sent directly to the 'in' terminal on the 'master volume'.
Thanks,
Andrew
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Post by sumgai on Apr 15, 2009 1:29:15 GMT -5
andru, I'll try to cover all your questions, but if I miss something..... First, the Jazzmaster isn't so complicated as all that. And that "overgrounding" is part of what makes the guitar so quiet, even though it uses single coil pups. In essence, the rhythm pup's hot lead goes to a switch. The switch takes that wire to the rhythm circuit, or the the lead circuit. The other side of the switch controls which of those two circuits goes to the output jack. Easy, yes? I'll have to beg off of drawing anything just now, it's late and I need to get up early (for a rare change!). But that's obviated by your latest post anyways...... You can certainly "split" the two pickups to each have their own controls, it'd be wired like any Gibson Les Paul or SG. The circuit selection switch is perfect for becoming a phase switch, and the three-way selector is even the same as one would expect on an LP or an SG. The two "independent" pickup-and-control sections would be wired in parallel, in this scenario. If you want to do it in series (too, or instead of parallel), that can be done, but you can't use the same pickup selector switch. See any of the many dozens of schematics on this board for an idea of how to wire two coils in series. As for adding a master volume control to all of this, I can only recommend that you give that some more thought. Besides adding complexity, there's the issue of providing yet another path for the signal to get to ground. Not a real bad thing, but it will noticibly affect your overall tone. It's up to you whether the effect will be tolerable, or not. And it goes without saying that adding another pot entails drilling holes, etc. Even if your rig is not a collector's wet dream, experiment on an El Cheapo pickguard - you'll thank me for that one tidbit, trust me. HTH sumgai
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