slejhamer
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Post by slejhamer on Aug 8, 2006 14:07:45 GMT -5
Hi folks. Hope you can help explain a problem I've got with a blend pot in my Squier '51. Simple setup: strat-type single coil at neck, humbucker in bridge, both run to the blend pot which is being used in place of a 3-way toggle switch. Output from the blend pot goes to dual-concentric pots controlling volume and tone. Treble bleed cap attached to the volume pot. For the blend pot, I wired it as per the top Stew-Mac diagram found here: www.stewmac.com/freeinfo/i-4137.htmlHere's the situation: when the blend pot is at either extreme, I get good tone and full power from the respective pickups. Turn it all the way in one direction I get the neck; all the way the other I get the bridge. So far, so good. The problem: as I move the blend pot toward the middle (from either extreme), the tone gets very thin and nasally - the bass just drops right out. The blend is basically unusable in anything but the the extremes. The volume and tone controls don't change the effect, other than by doing what you'd expect them to do. Could my pickups somehow be "out of phase" with each other, and that's what's causing it? If so, how do I correct the problem? I checked the wiring and it seems okay; all the connections are tight and everything seems properly grounded. Thanks for any help!
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Post by ChrisK on Aug 8, 2006 14:17:20 GMT -5
First, reverse the single coil wires from the neck. See if that helps.
Also many blend pops are really pan pots meant for mixers. In the middle position (center detent), a 250K pan pot will have 40K from each pickup. For a 500K pot, it's 80K.
Weak is.
I use Fender bass replacement blend pots which are truly 0 Ohms in the center position.
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slejhamer
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Post by slejhamer on Aug 8, 2006 14:24:14 GMT -5
Thanks Chris. I'm not sure what you mean "reverse the single coil wires." Just take the current "hot" wire and send it to ground, and take the current "ground" wire and use it as the hot?
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Post by UnklMickey on Aug 8, 2006 14:49:56 GMT -5
yup, i'm sure that's what he meant.
before i even got to the end of your post, the thin, nasal part screamed Out of Phase.
i'd check for that first, if that ain't it, it would stand to reason the resistance IS too high when the blend pot is in the middle, as Chris suggested.
the ugly thing about parallel blend pots using a standard tandem pot:
if the pots are resistive enough to not affect the tone by loading, they are way too resistive to couple properly in the middle.
i think JohnH would be a good person to ask here, but i imagine you might have better results with a series blend configuration.
(unless of course you can get your hands on one of them thar fender pots)
what is the value of the pot you're using?
unk
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slejhamer
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Post by slejhamer on Aug 8, 2006 15:16:32 GMT -5
Thanks; I'll try reversing the wires on the neck pup then. Should be an easy enough fix, if that's the cause. Oh, all the pots (vol/tone and blend) are 500k. Anyway, I've used these components before with different pickups and did not have a similar problem, so I don't think the blend pot's resistance is the main culprit. But you never know ... Mmm, series blend ... that sounds interesting. Would love to see a simple wiring diagram for that if there's one available.
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Post by UnklMickey on Aug 8, 2006 16:08:39 GMT -5
Mitch, here is a very simple configuration: the blend pot should be a fairly high value (500k) to prevent loading (and loss of treble). linear taper of course. the problem with this circuit.......it's all "both" until you get close to one end or the other. but................... you could actually use something like 10k or 50k. and modify it to become a no-load pot in the middle. our resident "Blendmaster" JohnH did this to a pot he was using for series and parallel blending in his "Tonemonster 2" guitarnuts2.proboards45.com/index.cgi?board=schem&action=display&thread=1130243150there is a picture later in his post, that shows him scraping a break in the middle of the carbon track. as to what the optimum value would be for a modified pot for series only, John would be a better resource than me. but, my guess is 20k (10k on each side of the center break) won't make too ugly of a jump when the wiper hits it. best part about the no-load mod..... the pickup that isn't being shunted has NO load from the blender so you lose none of the highs from it. unk
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slejhamer
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Post by slejhamer on Aug 8, 2006 16:22:02 GMT -5
Thanks unk.
Wow, Tonemonster is the right name for John's axe!
But I saw this in his post:
"Also note that the pots sold as blender pots at Stew-Mac etc wont work with this design (they are not linear)."
Of course, mine's a Stew-Mac blender. Oh well, it was nice to think about. I'll stick with the basics for now and try reversing those wires.
Cheers, Mitch
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Post by UnklMickey on Aug 8, 2006 16:37:09 GMT -5
...I'll stick with the basics for now and try reversing those wires. ... very prudent. if that get you where you need to go, K.I.S.S. BTW, Tone Monster is actually a John Atchley circuit on the original GuitarNuts site: Tone Monster the John Hewitt (with lots of prodding by Runewalker) version is sorta that on steroids. unk
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Post by ChrisK on Aug 8, 2006 16:58:55 GMT -5
If you place the blend pot in the center detent position, turn the volume all the way up, turn the tone all the way off (up), and measure the resistance at the output jack (I'm sorry, but the signal doesn't go INTO the guitar) you should read the parallel resistance combination of both pickups. If the bridge humbucker is 10K and the neck is 5K, you should read: 10K x 5K/(10K + 5K) = 3K33 Ohms or slightly less due to the volume pot. If you read substantially higher, it's the blend pot center resistance. I've heard that the StewMac blend pot doesn't have the center resistance problem, but I've never been able to verify it. They did say that the pot was "full on" in the center, but so is a mixer that provides a -3dB attenuation (full power across the pan range). I wanted a statement of resistance in the center position, but never got it. I'm not willing to spend $20 plus just to verify data that any responsible vendor would supply as a matter of course. I guess that I'm just too used to the OEM electronics industry where customer appreciation reigns. All in all, I do suspect a phasing issue. For my take on a series/parallel blend circuit, look here: guitarnuts2.proboards45.com/index.cgi?board=schem&action=display&thread=1145315219The faint wires are in, I just emphasized each mode to clearly show the signal path. A true blend pot and a PP pot on the volume will give you parallel and series, both blended. If you wanted to be clever, you could change the DPDT mode switch to 4PDT and have a blend pot for each mode.
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Post by UnklMickey on Aug 8, 2006 17:16:15 GMT -5
... I'm not willing to spend $20 plus just to verify data that any responsible vendor would supply as a matter of course.... seems like you won't have to.........Mitch, are you willing to take a resistance measurment for us?
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slejhamer
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Post by slejhamer on Aug 8, 2006 20:16:00 GMT -5
Rewiring the single coil solved the problem! Life is good. ;D Sweet! I'll keep that in mind for future projects. Mitch, are you willing to take a resistance measurment for us? Sadly, I do not own an ohm meter. The extent of my electronics toolbag is my soldering iron, some spare wire ripped from a computer, and a thing I stick in my wall outlets to tell me if they are functioning. Otherwise, I'd gladly test it. If there's still a slight but clearly audible bump in treble at the center detent, would that indicate something? If so, there is. I don't know what it means, but it's not nearly like the out-of-phase tone and I kinda like it, though it's unexpected. Thanks again to you both for your help!
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Post by JohnH on Aug 9, 2006 7:11:55 GMT -5
Mitch, here is a very simple configuration: the blend pot should be a fairly high value (500k) to prevent loading (and loss of treble). linear taper of course. the problem with this circuit.......it's all "both" until you get close to one end or the other. but................... you could actually use something like 10k or 50k. unk Just for the record, with this arrangement, with the no-load surgery on the track, the best values are 100k or 250k. I use 100k, and there is a slight step in vol when you move off centre, but it works very well, with a centre detent to locate the middle. Without a detent, a 250k provides a wider central neutral zone, but still with the track surgery John
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Post by UnklMickey on Aug 9, 2006 9:13:14 GMT -5
John,
thanks for following up on this.
speculation and estimation are good, your real world results are better.
Mitch,
fifty lashes with a wet noodle for you!
digital volt-ohm meters are CHEAP!
go to Harbor Freight or whatever junk-tool dealer is in your locale.
buy one for $4.
okay, so maybe the tool store in your 'hood doesn't have them quite that cheap.
but, i'll be surprised if you can't find one under $10.
ONE possibility for the bump in treble in the center position:
the blend pot really is zero ohms at the center.
when you move away from the center, the resistance in series with one pickup causes a slight drop in it's treble contribution.
unk
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slejhamer
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Post by slejhamer on Aug 9, 2006 12:39:21 GMT -5
Thanks John. Mitch, fifty lashes with a wet noodle for you! digital volt-ohm meters are CHEAP! I know, I know, I should get one. If I remember I'll grab one next time I'm at the hardware store. ONE possibility for the bump in treble in the center position: the blend pot really is zero ohms at the center. when you move away from the center, the resistance in series with one pickup causes a slight drop in it's treble contribution. Interesting ... guess I'll need to buy a volt meter to know for sure. ;D
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Post by ChrisK on Aug 9, 2006 14:23:23 GMT -5
Yeah,
Working on electronic without a DVM is like trying to solve a crossword puzzle without the clues OR the word list (my favorite)!
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