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Greetings!
I have a customers Thinline Tele with the Fender Humbuckers (new Mexican made).  He purchased a Clapton mid boost mod kit and had another luthier install it.  He brought it to me because the guitar has very low output volume.

I looked over the other fellas work and confirmed the wiring was correct for the mod.  I also resoldered any suspicious or cold solder joints.  As an experiment I isolated the pickups and selector switch to an outboard set of vol, tone controls and a jack.  The result was a normal output of volume for the guitar. 

With the Clapton mod in the circut the volume output is extremely soft until you turn the boost pot up full, and even then the output is softer than it should be under normal circutry.

Here are some resistance readings:

Bridge P/U: 8.16 kohm   Neck P/U: 7.99 kohm  (both normal)
 
With the pups wired into the Clapton mod circut, and measuring the resistance through a cable in the output jack:

Both P/Us with Vol up, Tone up, and Boost off: 70.3 kohms

Both P/Us with Vol up, Tone up, and Boost on: 43.6 kohms

I don't know enough about the Clapton mod to know if there should be this much resistance in the circut.  But it seems to me that the resistance load is causing a voltage drop and thus a drop in volume output.  Or even if it should be used with humbuckers? Although it's used on strats with the Fender Noiseless pups which are also hum canceling.  Maybe those Noiseless pups have a higher output?

Any insight into this mystery would be greatly appreciated.
 
Thanks,
littleguitargreg

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I've had the Clapton mid boost in my main Strat style parts guitar for over twenty years low output is not a problem. My lead pickup is a humbucker. The mid boost control should be fairly smooth and it should add enough gain to take you over the top into a fat dirty sound from a cleanish sound on most amps. I'd guess there's something wrong with the circuit. Are you getting 9 volts where you should be, I have feeling you can get signal on a dead battery. This is based on I haven't been gigging much in the last ten years and it's been that long since I changed the battery aaaand it still works. 

What John said,

I've done a few of these and they are all loud.  I recall we had a wiring issue with one kit (Genuine kit) with wiring colors reversed for one connection according to the instructions - it was 10 years ago and I snagged the problem by looking up the installation imagery on the web and checking the lead colors and pin-out.

Since this has been through the hands of a previous repairer and you have probably already spent the cost of a replacement kit in man-hours trying to fix this thing I suggest you ask the owner to get another kit.  Otherwize, with your present electronics capability you are going to spend the next week chasing rabbits down burrows.

Follow the links and the stuff attached - it's pretty comprehensive and may give you a clue into where this has gone wrong.

Good luck, Rusty.

Attachments:

Hi Russ,  Yep I was thinking that he needs another one, as this one is bad from the factory and yes I've got way too much time into it already. I'll take another look for defects in the pcb like Paul suggested then drop back 10 yards and punt. 

My personal thoughts though are: "You've got a humbucker equiped guitar.  What the heck do you need with a mid boost mod?  Plug the dang thing into an amp and crank it up!"  But hey, what do I know? For I am just a lonely luthier... 

Thanks!

Greg

Hi Gregory,

I just reviewed my post and apologize for the gruff manner - it wasn't meant to sound so direct.

I'm a bit negative when it comes to PCB trouble shooting having done so much money trying to fix what should have been replaced.  The low voltage/IC stuff doesn't fry and burn as much as big amps and power tools so it's much harder to find a component failure without a circuit diagram and voltage point chart.

Strats are unforgiving with humbuckers - they can sound thin and nasal with a standard output PAF style humbuckers - but the humbucker is still always loud compared to the singles - which the client may be trying to boost to get a relative sound balance when switching form HB to SC operation. Or he may be just trying to get his humbucker thickened up........

Respectfully,

Rusty. 

Hey Rusty, I like gruff and direct! Haa!  I don't think you're post was anything but helpful.

I'm old school, (or maybe just old) and I like people who are direct and don't beat around the bush.

 

Cheers Mate!

Greg

The volume pot for this circuit should be a 50k. Is that what it has?

Yes John the vol pot is the 50k, and the batt checks good.  But you may be right about a problem with the circuit board.

 

Thanks,

G.

Greg,

Probably your biggest time saver right now would be to take everything back to the "pre-installation" state and reinstall the whole thing with ALL new solder joints. Sounds like a poor contact somewhere. At least you'll have the satisfaction of knowing it was installed properly...by you. :) Also, check the PCB with a jeweler's loupe for trace fractures and questionable solder joints.

Also, check for parasitic grounding issues. They seem to be the gremlins in many of my "wth is wrong with this?" cases. A single stray ground wire strand too close to a 'hot' wire can cause this, especially in high gain circuits.

Best of luck with the diagnosis & repair.

Sounds like a plan Paul. 

 

I have already checked for possible grounding issues, but at this point a total remove and reinstall is an option, and I will check the pcb for cracks, solder. etc.

Thanks,

Greg

The dummy check (I've done this more than once) make sure the wiring is right at the output Jack, the battery should go to the ring, the ground would go to the sleeve and the output goes to the tip.

John

Thanks for all the help fellas!  And always good to share info on this forum.  It's been awhile since I've been in this cyber-capsule, and hope all are doing well.

Customer bought the mod kit on ebay and I told him it looks like the pcb is faulty, so now he wants me to rewire back to standard specs.

Hope you all have a blessed day,

littleguitargreg

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