Volume Pot problem

[jazzy]

Hi,

Excuse me i am not an engineer.

Bought an American Std. Natural (see-through) Swamp Ash Fender Stratocaster back in 1999. My 1st electric guitar. Had been playing with my brothers guitar in the 80's and 90's now and then.
As i can remember there was a scratchy/crackling noise when turning the volume knob from the day or week i bought it.
I usually let the knob at 10.
I noticed that when turning the volume down that at about 8 the tone changes quite drastically (less fat and less output).
The same point that, when not playing, a hum intensifies or changes character (lower).

Today i performed the tests described at guitarnuts2.proboards.com/page/gn1-pages.
Had a spare new jack, opened it and introduced it in the guitar.
Measured resisances at the + and - of the jack.

Resistance values for the bridge pickup a little higher (7.3k) than the neck and middle (about 6k) when volume at 10.

With neck pickup selected i measured tehse values:

Volume at 10: 6k
Increasing when lowering until about 7-8: then max=nearly 70k
and thereafter a decrease.

The site (guitarnuts) mentions that usually 125 will be reached at volume of about 5.

Could anybody teach me something here.
Is this volume pot bad, or is this a correction for the brightness of the ash....
And what can i do about the crackling sound? spray?

Jazzy

[D2o]

Hi Jazzy,

The bridge is normally a higher resistance than the neck, and the wood is irrelevant to the electronics ... so all of that sounds fine.

The "125" measurement is intended to be taken with the meter set at 2000k ohms, not 20k ohms, while turning the volume from 0 to 10.

Contact cleaner should alleviate the scratching (actually, I've heard of people being very happy with a little bit of brake cleaner)

I hope that helps.

D2o

[newey]

From your description, this problem has become progressively worse over time, and now has gone beyond the usual "scratchiness" due to a dirty pot. My suspicion would be that the pot is bad. But a good cleaning would be a start, if it solves the problem, great, if not, pot replacement is easy enough to do.

I would not, however, use anything as aggressive as brake cleaner. A can of computer "Dust Off" is a good start, if that doesn't help, some electrical contact cleaner, judiciously applied, is in order.

[jazzy]

Thanks you both.
But how will i exactly apply this?

[ChrisK]

The pickup resistance values appear to be fine.

The site (guitarnuts) mentions that usually 125K will be reached at volume of about 5.

This would be for a 250K pot with a linear taper. This would read half value at "5". This value is from the wiper to either end terminal.

For an audio taper pot (the ones used in Strats) the midpoint of the resistance occurs at about 7-8.

A 250K pot will have a nominal resistance of 250K Ohms. With a +/- 30% tolerance (a normal tolerance for consumer components) the actual overall resistance will be between 175K and 325K worst case.

Volume at 10: 6k. Increasing when lowering until about 7-8: then max=nearly 70k and thereafter a decrease.

This indicates an audio taper pot.

A. Bear in mind that the pickup's resistance from ground is in series with the resistance from the wiper of the pot to the"10" terminal on the pot.

B. The resistance from the wiper to the "0" terminal on the pot also goes to ground.

The wiper and ground are the measured points.

The resistance noted in "A" is in parallel with the resistance noted in "B".

Could anybody teach me something here?

Sure.

The theoretical basis for this as well as what can be derived from this information can be found in my post on Discerning Paralleled Resistances.

Per your measurements;
Rparallel = 6K
Rmax = 70K

--minor algebra + the quadratic formulae applied per aforementioned theoretical basis--

Rpickup = 6K134
Rpot = 273K87, well within the stated tolerances.


Synopsis: Your volume control value is fine.
Diagnosis: Your volume control is noisy, clean it.

Pot cleaning

Solvent

or RadioShack.

A new volume pot is aboot $3 U.S. You choose the path.


That will be $1 U.S. please, to the charity of your choice.

[Please pardon me, I am an engineer.]

[ashcatlt]

Holy frijoles! $15 for what?

You could just pull the pot out of the guitar before you spray it for free.

A good cleaner could come in handy if you have any other electrical audio type devices, and can probably be found a bit cheaper (or in smaller quantities) than that can of De-Oxit.

The best way to clean the things is with nice clean distilled water inside an ultrasonic vibrator type cleaning jobber, but that's getting a bit overboard...

What's the deal with the brake cleaner?

[jazzy]

GREAT INFO,
Thanks ChrisK and others.

I was already wondering how the circuit would be. Tried to find it at the Fender site to do some resistance-algebra i once (long ago) did at school.
The fact that 125k was mentioned at guitarnuts.com started me thinking that something was wrong.
Just when i logged in (and was also posting about it at the fenderforum) the doorbell rang and a brand new pot was delivered by Fender....How about that?

The info on this forum is inspiring..

I am considering modding myself (will start with a cheap squier to get ome experience)

THANKS.

Jazzy

EDITED by Newey to delete double-posting

[newey]

Jazzy-

So, you snookered us by having already ordered a new pot before you posted!

That's fine, we hope you'll stick around. Modding a Squier, or other inexpensive guitar, is a good idea.

And Ash-

D2o brought up the brake cleaner. There was a rather spirited discussion on the TDPRI forums a while back about using such solvents for cleaning pots, which quickly devolved into 2 camps, pro and con. I recall people saying they used carburetor cleaner, I don't recall anyone advocating for brake cleaner. Carb cleaner is basically just pure ether, same stuff they sell as "starting fluid". It evaporates rapidly and is also highly flammable.

Brake cleaner has some other "stuff" in there. It would probably attack any plastic parts.

I don't know what's in the cans of electrical contact cleaner they sell, but it's probably about the same stuff as carb cleaner- only more expensive.

[jazzy]

Hi Newey

Snooker (here in the Netherlands thats a poolgame) Will check my dictionary this afternoon

No honestly only mailed a question to a guy at Fender that had helped me before for some info/tips and big surprise this morning a pot arrived, no accompanying letter or note, no mail back, but deducted from the address it must have been from Fender.
Think i will first try what is said above before soldering (which i am not very experienced at), and when i change strings one of the next weeks i will open the guitar again and if it looks like something even i can do i will give it a try.

Nice first step for modding

Jazzy

[ashcatlt]

Oh, now it's carb cleaner? When you say ether you mean like petroleum ether? Sold in the painting section of hardware stores as NAPTHA for even cheaper than cab cleaner, though it's not in a spray bottle...

[D2o]

Sept 26, 2008 8:59:46 GMT -5 ashcatlt said:

Oh, now it's carb cleaner? When you say ether you mean like petroleum ether? Sold in the painting section of hardware stores as NAPTHA for even cheaper than cab cleaner, though it's not in a spray bottle...

Whoa! Not from me it isn't.

I hadn't seen the debate on the Fender forum. I actually stole the brake cleaner idea from the T-60 forum. Specifically from Chip Todd, the creator of the Peavey T-60 (which I presume bestows more credibility upon the idea than when I suggested it).

www.peaveyt60.com/forum/forum_posts.asp?TID=5114&KW=berryman%27%27s

Use spray can brake cleaner, preferrably Berryman's or 3M. Most cleaners leave an oily film which attracts dust.
Chip

www.peaveyt60.com/forum/forum_posts.asp?TID=5677&KW=berryman%27%27s

Don't use a control pot cleaner as they have a lubricant in them that attracts dust and grit. Any good brake cleaner will probably do, but I use Berryman's because it doesn't make the skin between your fingers burn as some do.
Chip

D2o

[newey]

Yeah, Ash, same stuff.* And, as D2o indicated, the objections thereto centered on whether it left a residue or not. The brake cleaner idea was new to me.

*Not the medicinal anesthetic so beloved by Dr. Gonzo, that wouldn't work. Although, if you used that, you wouldn't notice that your pots were scratchy!

EDITJazzy, sorry for the slang, I forget how many overseas members we have who may not comprehend. "Snookered" means "fooled", the term probably comes from the game of the same name, not sure on that, though, as I've never played it.

[gumbo]

As an old auto restorer (yeah, ok!), I can say that brake cleaner does a lot of interesting things (at least the stuff they sell in this island) a lot of which I'm very glad not to have to still encounter...carb cleaner does seem to evaporate with less residue..I agree with everyone else's reservations about using ANY of the stuff near anything with plastic and paint that you value...

...and the other thing...don't forget to NOT inhale ...and keep away from kids and pets..

I suppose with brake cleaner though, at least you'd be able to stop within 25 feet of the end of a number... (engineering calculation)...

[ChrisK]

which quickly devolved into 2 camps, pro and con.

There are two kinds of people in this world;

those that believe that there are two kinds of people in this world,

and those that do not.

[pete12345]

Sept 29, 2008 22:40:47 GMT -5 ChrisK said:

which quickly devolved into 2 camps, pro and con.

There are two kinds of people in this world;

those that believe that there are two kinds of people in this world,

and those that do not.

There are 10 types of people in the world: those who understand binary, and those who don't...

[ChrisK]

Binary is fine with me, it's them Binars (Star Trek reference) that get me.