Pickups & Wiring

Comment

Comment by Ted Crocker on February 25, 2014 at 10:02pm

Can we assume that you plugged another guitar into the cable and amp?  

By looking at the underside of the pickguard, it looks like the pots are grounded via the metal guard.  Is the lug on the neck pot grounded to the back of the pot?  Use a multimeter to check continuity between the jack ground lug and all other ground points.

It looks like the one leg of the cap has a clear plastic tube over it, check that where that leg comes out of the cap isn't touching the pot, it's hard to tell on the pic. A better pic of just the pots might help (switches too). 

It also looks like the pickups only have a single wire coming out, which means the pups themselves are also grounded thru the pickguard.  Maybe touching a temp jumper wire to the metal pup and the neg lug on the jack will tell you something.  If there is a braided shield on the pup wires, try touching the jumper to them and the jack ground.

If all else fails, desolder the pickup wires from the switch and test with jumpers going straight to the jack lugs, that'll narrow it down to the pups or the rest of the circuit.

Good luck.

Comment by madurobob on February 25, 2014 at 9:58pm

Sam, how is the bridge grounded?  Hard to tell from the pics, but it looks like its not... and that may be the cause of the buzz.

Thats an easy test: lay the pickguard in place, then put one string on and plug her in.  Assuming it buzzes, does the buzz go away when you run a short jumper from the metal of the output jack to the bridge?

The rest of it looks in pretty decent shape.  Of course, those foil pickups can be a real pain in the butt.  Folks love the tone, but they are a bit delicate.  If its one of the pickups making the buzz, you should be able to identify that by throwing the on/off switch for each pickup one at a time to see if that fixes the buzz.

Comment by Wichita Sam on February 25, 2014 at 7:36pm

need help/advice.  just picked up this Japanese guitar from the 60's(?).  It has gold foil pups, metal pic guard, on/off switches what looks like separate volume pots (500k) and a single tone pot (500k).  The pups make music, but there is a horrible buzz that appears to be a ground fault.  Before I jump and in a resolder what looks like original installation, is there anything I should check first?  Thanks in advance...

Comment by jeff weins on April 29, 2013 at 2:48pm

     Just came across this video-Identifying Pickup Wires & Polarities - Humbucker  

It's very informative, the guy explains things very clearly It's long 20 mins but worth the time if you need help  understanding pickup wiring like i do.

Comment by darryl.kernaghan on April 16, 2013 at 4:57am

thanks for the advice guys,i think that the "passive preamps"that i have are essentially a vol and tone pot in a tidy casing with no preamp capability,time to hack one apart and see what,s within,might work ok with a mag pup as a siple vol,tone circuit if i put a 2mm pin on the leads and plug it in place of p/rod

Comment by Ted Crocker on April 15, 2013 at 4:04pm

OOPS, I meant decreases the impedance in parallel, thanks Michael.  A blond moment...

Comment by Michael Recchione on April 15, 2013 at 3:24pm

Another note about piezos in parallel and "quack":  I've suspected (but didn't research) the notion that one of the reasons wiring elements placed in different locations of the guitar seems to mitigate "quack" was that the quack is caused by the extremely non-linear response of the piezo element, and that a second piezo in parallel acts as a load that deforms in response to the other piezo, dissipating some of the energy in the initial spike of the first piezo's response, and so on. 

I did a little googling on "piezo elements in parallel mutual loading", and lo and behold - there's some stuff out there about the effect being used to damp vibrations in mechanical systems.  Not guitar related, but it's the same idea.  So it sort of confirms my experience that a second piezo, placed far enough away from the first one to see the acoustic waveform with a delay, will smooth out the signal and mitigate the "quack".

Just a thought...

Comment by Michael Recchione on April 15, 2013 at 3:13pm

Ted, I think you may have that wrong about putting piezos in parallel increasing the impedance of the guitar as seen by the amp. The impedance of two impedances in parallel is given by Ztot = Z1Z2 / (Z1 + Z2).  For two identical impedances, Z, this becomes Z/2.  So it cuts the impedance in half (relative to a single piezo) if you wire two identical piezos in parallel. 

I like piezos in parallel - it seems to reduce the "piezo quack".  The tone I get out of them is actually pretty nice if they're placed correctly.  I don't think that's because of impedance matching, though - I think it's more because of the smoothing/smearing you get because the audio waveform hits the two elements with a (very) slight time shift. 

Comment by Ted Crocker on April 15, 2013 at 2:15pm

I believe by definition a preamp is powered.  I'm not aware of a way to boost a piezo's output passively (without a power source).  There may be a way to use unpowered circuitry to change a low impedance piezo signal into high impedance, but I do not have a circuit diagram for that.

(Active circuit = powered, passive = non-powered)

I do know that wiring multiple piezos in parallel increases the impedance of the piezo circuit, but is far from the effect of using a traditional preamp powered by a 9V battery.

Comment by Scott aka Farmer Ted on April 15, 2013 at 1:40pm

Oh, forgot, no, I don't know how to power one like that. Maybe Ted Crocker would have an idea.

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