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FDP Forum / Guitar Mods, Repairs, and Projects / (Gibson content) My Firebird won't make any sound but a loud hum. Need help with wiring!

creekriversjr

USA/Maryland

Mar 24th, 2012 10:59 PM   Edit   Profile   Print Topic   Search Topic

Almost two months ago I decided I didn't like the wiring mods the previous owner of my 1999 Firebird V had done. So - having a smattering of knowledge about these things - i set forth to rewire it to my liking with independent volume and tone knobs, modern style. I was confident I could do the job.

I don't know what the hell I'm doing wrong. Everytime I plug it in to test it, I get either no signal at all or just a loud hum. I've looked at every wiring diagram I could find on the internet. I've changed out the pup selector switch and all the pots, just in case I overheated the old ones with my soldering iron. What could possibly be wrong? This isn't rocket science!

One thing I've noticed after gathering dozens of wiring diagrams, there doesn't seem to be ONE standard way to wire 4 pots, 2 pickups, an output jack and a 3-position switch, because all the diagrams differ in some way or another, most often in how the volume pot connects to the tone pot.

Anyway, here are some of the things that I've done in my latest attempt. Maybe someone will spot the glaringly obvious thing that I'm missing:

1. I've connected the cases of all the pots with wire, soldering the wire to the pot cases so it makes a continuous circle.

2. I'm using ceramic capacitors with 472K printed on them, connecting the first lug of the volume pot to the first lug of the tone pot. (I noticed on some diagrams, the connection goes to the middle lug of the tone pot. I also noticed sometimes a wire makes the connection instead and the cap lead is soldered to the tone pot case.)

3. the toggle switch has the two terminals in the middle which I bent closer and soldered together. The wire from that runs to the hot connector on the output jack. There's another terminal underneath the two terminals that i soldered together which i assumed is the ground wire and that runs to the ground connection of the output jack.

4. I wired the inner wire from the mini-humbuckers to their respective volume pots on the first lug, and the outer braid wire is soldered to the cases of the volume pots. The wires from the toggle switch are connected to the middle lugs of their respective volume pots. I grounded the last lugs of the volume pots with a short bare wire soldered to their cases.

5. The ground wire from the bridge is soldered to the case of the bridge pickup tone pot.

What do you see that i don't? I've read articles and forum posts about different ways to wire guitars and I'm still not getting it. I really wanna play my guitar! Thanks in advance for any help.

Creek
__________________
"There oughtta be a law with no bail,
Smash a guitar and you go to jail,
With no chance of early parole,
You don't get out until you get some soul." (John Hiatt - 'Perfectly Good Guitar')

FunkyKikuchiyo
Contributing Member
***

New England

Mar 25th, 2012 07:05 AM   Edit   Profile   Print Topic   Search Topic

On your ground connections, does the ground from the pickups have continuity all the way to the jack? I'm following it from the pickup to the pots, and then from the switch to the jack, but I didn't read anything about from the pots to the switch.

Double check your jack that the lead goes to the tip of the cable and the ground to the sleeve. This is a pretty common mistake and will cause lots and lots of hum.

Lead dress and good soldering can be tricky on those switches, so if you're still having problems after all of that, double check those connections.

The tone cap value sounds off. 472 is going to be .47 uf which is off by a factor of 10. 473 would be .047 uf which is in the normal range for guitar tone caps, but still is higher than what most people would go for - .022 uf is pretty widely accepted, though I can't say for sure what a Firebird had in it initially. The caps you have now will work, the guitar will just be very dark sounding.

Don't worry too much about the multiple ways to wire a tone circuit. Most of the time this is just about layout rather than alternate electronic methods. If you can follow with your finger the signal going from hot through the cap, through the pot (a side lug and the middle lug) and then to ground or from hot to the pot to the cap then to ground, then it'll work just fine.

SonicBlue

Sunbury-on-Thames

Mar 25th, 2012 09:28 AM   Edit   Profile   Print Topic   Search Topic

Have a look at the Sheraton diagram in the link. It's the same volume and tone arrangement as you described you want on your Firebird, and the clearest diagram I could find.

Sheraton wiring diagram

FunkyKikuchiyo
Contributing Member
***

New England

Mar 25th, 2012 08:31 PM   Edit   Profile   Print Topic   Search Topic

Adding that my math on the cap was wrong. 472 would have a cap value of 4700pf, which is one tenth the value of the one typically used in guitars. It may work well - I've never tried anything that small. The worst that could happen is that the tone control doesn't seem to do much.

Peegoo
Contributing Member
**********
**********

That chicken

is WRONG, baby.
Mar 25th, 2012 08:39 PM   Edit   Profile   Print Topic   Search Topic

"3. the toggle switch has the two terminals in the middle which I bent closer and soldered together. The wire from that runs to the hot connector on the output jack. There's another terminal underneath the two terminals that i soldered together which i assumed is the ground wire and that runs to the ground connection of the output jack."

The ground connection on the switch is usually on the opposite side of the switch. Perhaps your switch connections are incorrect.

See here.

Peegoo
Contributing Member
**********
**********

That chicken

is WRONG, baby.
Mar 25th, 2012 08:41 PM   Edit   Profile   Print Topic   Search Topic

Creek, where in MD are you? If you're close to Bowie, drop me an email (see my profile) and we'll get this machine back on the rock and roll highway.

GP
Contributing Member
******

SW Burbs of Chitown

ILL, where our Gov's make our plates
Mar 25th, 2012 11:13 PM   Edit   Profile   Print Topic   Search Topic

One thing to watch when soldering the braid on the back of the pots is that there is enough braid length that the heat doesn't transfer up the braid and melt the insulation of the inner wire. This will cause a dead short which will cause the hum like shorting your guitar cable plug. Ohm meter across the braid and the center wire at the pot connection will show this if less than the PU DC resistance. The wiring should be the same as a standard LP or like the Sheraton diagram above. I have 65 diagram which uses a slide switch but is the same basicly as a LP. Also check the jack when plugged in that the hot wire soldered to the jack doesn't touch the ground of the cable plug. I have seen excess wire sticking out of the solder terminal do this.

One thing I would change is the bridge ground. Move it to one of the pot cases. I would not rely on the PU case for a ground.

(This message was last edited by GP at 11:23 PM, Mar 25th, 2012)

creekriversjr

USA/Maryland

Apr 10th, 2012 01:09 PM   Edit   Profile   Print Topic   Search Topic

Thanks so much, everybody. The guitar is now making guitar-like sounds. I did solder the ground wire from the bridge onto one of the pot cases. The ground wire from the jack to the switch is now on a terminal which sits below (not opposite from)the other terminals.

The trouble now is that the tone quality is weird. Both pups have a synth-like quality, as if certain frequencies are seriously suppressed: The bridge pup sounds glassy, and the neck similar to what you'd get with a wah pedal rocked way back.

The caps that came with the guitar is a .047 lemon drop and a real old bumblebee whose impedance i'm not sure of.

Thanks again for all the suggestions. You helped me get this instrument much closer to the stage.

amphead4

Cincinnati, USA

Apr 10th, 2012 02:28 PM   Edit   Profile   Print Topic   Search Topic

I would start with just disconnecting one end of each cap to see how it sounds without them in the circuit.

Peegoo
Contributing Member
**********
**********

That chicken

is WRONG, baby.
Apr 10th, 2012 02:51 PM   Edit   Profile   Print Topic   Search Topic

Yeah, it's still not right...

FunkyKikuchiyo
Contributing Member
***

New England

Apr 10th, 2012 07:23 PM   Edit   Profile   Print Topic   Search Topic

"I would start with just disconnecting one end of each cap to see how it sounds without them in the circuit."

+1. People also mess up values quite often, so being off by a factor of ten or so can make quite a difference.

Are you also certain that the pickups are completely functional?

uncle stack-knob
Contributing Member
**********
****

united kingdom

Apr 11th, 2012 02:01 PM   Edit   Profile   Print Topic   Search Topic

Here is the official Gibson support diag. (pdf)
Note how the earth between the pots does not connect the two tones.


Stack-Knob.

click

(This message was last edited by uncle stack-knob at 02:01 PM, Apr 11th, 2012)

FunkyKikuchiyo
Contributing Member
***

New England

Apr 11th, 2012 02:30 PM   Edit   Profile   Print Topic   Search Topic

USK - I'm not sure why you're pointing that out in this instance... the would have continuity to one another, though there is no wire or BUS there, unless it is mounted on a shield.

SonicBlue

Sunbury-on-Thames

Apr 12th, 2012 07:58 AM   Edit   Profile   Print Topic   Search Topic

By not 'completing the circle' of earths on the pots they have stopped the creation of an earth loop. In an area of high RF interference, near stage lighting for example, preventing an earth loop is one more small step in the never ending quest to stop hum.

FunkyKikuchiyo
Contributing Member
***

New England

Apr 12th, 2012 08:49 AM   Edit   Profile   Print Topic   Search Topic

SB - you need two different ground potentials in order to have a ground loop, like having two wall outlets with different grounds.

If it was that easy to create a ground loop, you'd get one every time you played a barre chord. The bridge and strings are grounded, and then they get "looped" when they contact the fret.

Where you CAN have ground loops within a guitar is when you have a stereo set up, or (as was pointed out to me in another thread but I don't quite understand yet) with active pickups since you have differing voltages. I've also heard lore that heavy ground resistance in guitar cables can do this, too.

Ground Loops

amphead4

Cincinnati, USA

Apr 12th, 2012 10:37 AM   Edit   Profile   Print Topic   Search Topic

I think ground loops in a passive guitar are a myth.

You get them in amps when the chassis is used as a ground plane because not all connections to ground are really at the same potential. This is due to the chassis being a current carrying conductor.

The chassis has resistance and there are currents from all the stages flowing through the chassis to where the power supply is grounded. This puts those chassis connections at different potentials due to Ohm's law. V = IR You have current and you have resistance so different points on the chassis end up at different potentials.

But in an electric guitar with passive pickups, the current is so low that any resistance in the various ground paths back to the jack doesn't really matter. A passive pickup can create a voltage across the volume pot but face it, it doesn't put out any real power, hence the current that's next to zero. If no current, then all grounds are at the same potential and effectively, there is no ground loop effect.

Just my 2 cents...

FDP Forum / Guitar Mods, Repairs, and Projects / (Gibson content) My Firebird won't make any sound but a loud hum. Need help with wiring!




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