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Volume pot doesn't work at 8 or below


PunkKitty

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I recently rewired my Xaviere XV-700 with Lace Alumitones. I used CTS 250k audio taper pots for volume and Alpha 250k push/pull pots for tone.

 

The tone controls work well and I love the sounds that I can get out of these pickups.

 

The volume pots are another issue. If they are set at 9 or 10, they are fine. If I drop the volume to 8 or below, they don't seem to function at all. I lose almost all volume.

 

I've verified the wiring. Everything looks as it should. I've wired many guitars before so I'm experienced at it. The only thing that I can think of is that the pots may have been linear taper instead of audio taper.

 

Any thoughts? I'm at a loss and it's really bugging me.

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Could just be a bad pot.

 

If you'd used a linear taper instead of audio taper, the sudden drop off would have been at the lower end (i.e around 3-4) instead of 8 or 9. The drastic change with a linear taper occurs in the first 10% of the rotation range (for volume that is, for tone, you want to use linear, but that's a different conversation).

 

Here's a quick description from http://www.angelfire.com/electronic/funwithtubes/Amp-Volume.html :

 

 

Linear and Audio Taper.

The taper of a pot refers to the way its resistance changes as the shaft is rotated. A linear taper pot is exactly what you would guess it to be, a graph of resistance (from one end to center) versus shaft rotation would be a straight line. If you tried to use a linear taper pot as a volume control you would be most unhappy with its performance. The sound level would go from nothing to almost full volume in about the first ten degrees of rotation and the rest would have almost no audible effect. This is because the ear responds to sound logarithmically rather than linearly. That's why sound engineers use the decibel which is a logarithmic function of power. An audio taper pot has a function which approximates a logarithmic function.


The way to identify an audio taper pot is to set it to half rotation and measure from center to each end with an ohmmeter. If the resistances are approximately equal you have a linear pot. If the resistance from the counter clockwise end to center is about 10% of the total and the resistance from the clockwise end to the center is about 90% then you are holding an audio taper pot.


These are the major kinds of tapers used in home audio equipment. There are other ones but they are of little interest to us. One to look out for is the reverse audio taper. It has 10% resistance between the clockwise end and the center. This type was used as a contrast control in older black and white TV sets. Be observant when testing pots or you might be fooled.


If you are still not satisfied, here is
than you ever knew existed.

 

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Umm, that's a strange sounding deal. Doesn't seem likely you'd get 2 bad pots. Is it possible that the 250Ks are just out of the range that those particular pups will operate in? Might try dropping in a couple of fixed series resistors just to see?

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Umm, that's a strange sounding deal. Doesn't seem likely you'd get 2 bad pots. Is it possible that the 250Ks are just out of the range that those particular pups will operate in? Might try dropping in a couple of fixed series resistors just to see?

I was thinking that adding a treble bleed cap might work. I'm not sure how to work with resistors. I also tested the pots with my Fluke meter to verify that they are not too far out of tolerance with each other. Both measured within 5% of the labeled 250k. 250Ks with .022 caps are recommended for Alumitones.

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I don't think a bleed cap will help if overall vol is dropping that much. You can just add a resistor in series with the hot line off the vol pot, to raise the overall resistance in the circuit. Since the next obvious step up from the 250K would be 500K, I'd try adding in a 200-250K resistor, (don't remember what the standard values are in that range - it's not critical), just to see what happens.

 

Since you seem to have only a very tiny range where you have vol control, it's conceivable that the 250s are too much resistance. Try adding a resistor to one control, if the prob gets worse, then you may have to try a lower value pot. Maybe 100K or so. Someone ought to know if these pups need an unusual value on the vol pots.

 

edit: another thought - you can use one resistor in series to raise total resistance; if that makes the prob worse, you can reconnect your hot line directly to the pot, and use the same resistor to bridge across the hot lug on the pot to ground. That will drop the total resistance - one or the other ought to produce some improvement. Wait - bridge between the hot lug and ground first. You don't even have to solder the resistor in, just hold it in or wrap it enough to keep it in place while you check for volume.

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I was thinking that adding a treble bleed cap might work. I'm not sure how to work with resistors.
I also tested the pots with my Fluke meter
to verify that they are not too far out of tolerance with each other. Both measured within 5% of the labeled 250k. 250Ks with .022 caps are recommended for Alumitones.

 

 

What happens when you turn the knob?

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I'm sorry, your guitar is haunted. Take it to a priest. :lol:

 

Seriously, I don't know what to say. Expected the resistance to shoot up at the same spot, meaning a bad pot.

 

I looked on Lace. This page, for deathbuckers mentions 250K pots. At the bottom is a phone number for Lace.

 

http://www.lacemusic.com/news/news_articles.php?articleID=70

 

Wish I could help more.

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I'm sorry, your guitar is haunted. Take it to a priest.
:lol:

Seriously, I don't know what to say. Expected the resistance to shoot up at the same spot, meaning a bad pot.


I looked on Lace. This page, for deathbuckers mentions 250K pots. At the bottom is a phone number for Lace.


http://www.lacemusic.com/news/news_articles.php?articleID=70


Wish I could help more.

Thanks for your input. It confirms that I'm not crazy (well, not too crazy) and that I've done my troubleshooting work. Somehow the only guitars that I own that aren't haunted are my Gibsons, Strat, and Ibanez Artcore. There's a lesson there kids.

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Check your resistance readings at the output jack. Ought to be about the same as the pot reading with the pup resistance added to it (maybe another 8-15K?). If those reading are way off from what you're getting on the pots alone you probably have some other problem. If the readings are close, I'm at a loss also - particularly if the mfgr specifies 250K, or something in that ball park for those pups.

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Sounds like you're using a Log pot in stead of a tapered pot. A log may not have a linear Decrease in volume depending on the application in which its used.

 

With Lace sensors you can use 500K and even 1 meg tapered pots. They may give you a more gradual volume drop and increase in brightness. 250K should work too. My guess is you screwed up the wiring or are using the wrong pots. Heres a guide. http://sound.westhost.com/pots.htm

 

If you do have the right pots, rewire it. You got something screwed up.

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Obviously one of those threads that keeps running in my head. Had to log back on to post.

 

WRGK is absolutely right. The prob has nothing to do with pots or pups. I'm betting you got a bad joint or broken wire coming off the jack.

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Problem solved! I added treble bleeds to the volume controls. I also rewired using standard LP 57 wiring and Mallory .022 caps instead of the generic caps that I had. The treble bleeds make just that much of a difference.

 

These Alumitones are NICE! Great sounds in SC and HB modes. They are very responsive to the volume and tone controls. Very clean sounding pickups that dirty up well. I'm still kind of getting used to how they look, but I really like how they sound and how versatile they are. The push/pull pots make a big difference.

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Sounds like you're using a Log pot in stead of a tapered pot. A log may not have a linear Decrease in volume depending on the application in which its used.


With Lace sensors you can use 500K and even 1 meg tapered pots. They may give you a more gradual volume drop and increase in brightness. 250K should work too. My guess is you screwed up the wiring or are using the wrong pots. Heres a guide.


If you do have the right pots, rewire it. You got something screwed up.

 

 

lolwut? what kind of taper?

Logarithmic pots are what he should use anyway... volume increases logarithmically...

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