EMG Pickup Installation in a Gibson Explorer (part 4)

Posted by Andy on November 20, 2007
Guitar

At this point, I’d done enough reading and looking at things to feel decently confident to go forward. I must admit that I took these crappy pictures partly to have something to refer to if I screwed something up and had to go back, but luckily I got through it okay.

I’ll start this post with a little info about the output jack. The standard output jack of a guitar is a mono 1/4 inch Tip-Sleeve (TS) female jack. The guitar cable has a TS male plug, where the signal travels on the Tip conductor, and the ground sits on the Sleeve conductor. The amplifier provides the ultimate ground reference for the guitar via the sleeve conductor of the cable. All the electronics in the guitar are grounded to the same reference provided by the amp. That said, the EMG pickups actually require a 9V battery, which they apparently don’t want to “ground” to the guitar’s signal ground. For this reason, the EMG pickups require a stereo Tip-Ring-Sleeve jack so that you can separate the signal and power grounds. Here’s the diagram from the instructions:

EMG wiring diagram

As you can see, the battery’s (-) post goes to the ring connector of the jack. This was kind of strange to me, I couldn’t completely understand why you couldn’t just ground the battery with the other signal ground, which brought me to the next question: how exactly does the battery get grounded? If you use a stereo TRS cable with the TRS jack, the ring serves as the battery ground and the sleeve is the signal ground, but when you plug the cable into the amp, does the amp’s jack have separate contacts for the ring and sleeve? I didn’t think so – my amp only has one speaker, so I couldn’t see why it would have a stereo input jack. If the amp had a mono jack (no contact for the ring of the plug), how does the battery get grounded, or does the battery voltage just float with no real ground? After I got the guitar all put together with EMGs, I discovered the answer. I tried using a stereo TRS cable to plug the guitar into the amp, because I thought there might be some reason to separate the grounds, but I found that this did not produce anything but noise from the guitar. I then tried plugging a mono TS cable into the stereo guitar jack/mono amp jack and the guitar worked perfectly… With this setup, the ring and sleeve connectors on the guitar jack are effectively grounded together on the sleeve of the cable, so I’m not sure why they separate the battery and signal grounds on the output jack. Maybe the idea is to push the ground connection as far away from the electronics as possible, I’m not sure. Anyway, this debacle actually gave me a good idea of something to try – an external power source for the pickups, which would mean you’d never have to replace the battery. I haven’t tried my idea yet, but I’ll write a post later.

Here’s a picture of the old mono jack, pulled out from the guitar:

Old mono jack

After trying to figure all that out, I finally started to de-solder all the controls. Here’s a picture about halfway through the process of removing things:

Halfway taken apart

One thing worth mentioning is the removal of the knobs from the controls. The knobs on this guitar were stuck on the pots pretty well, I couldn’t seem to pull them off without making my fingers bleed. I read a tip on the internet that said you can easily remove the knobs if you wrap an old t-shirt around the knob, and then pull up to get the knob off. I tried that, and it worked pretty well.

I finally got all the old crap taken out, here’s a pic:

Old pickups removed

Here’s a pic of the empty control cavity, the only things left are the toggle switch cable and the string ground wire.

Old controls removed

That’s enough for this post, more to come.

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4 Comments to EMG Pickup Installation in a Gibson Explorer (part 4)

  • The reason they separate the Battery ground from the signal ground is so that when no cable is plugged in, the circuit is broken. That way no cable in the guitar == electronics switched off. If you attached the battery negative terminal to the signal ground the circuit would always be turned on and your batt would drain pretty fast. They just wanted to avoid making you install a switch.

    As for an external power source, its a good idea and one I was considering myself, but due to the electronics they are using in the pickups any noise that comes from the cable will be amplified and become a real problem (or not, depending on your cable and ambient electrical noise). It really is best to use a battery even though its kinda a pain I agree.

  • Thanks for your comments!

    That makes perfect sense about the battery ground, I’m kind of embarrassed I didn’t think of that. It is definitely a good thing to have a way to break the circuit, but I really would have rather them put a switch on the output jack or something like that. I really don’t like having to unplug the guitar everytime I’m done with it.

    As for the external power supply, I was concerned that it will add noise to the signal. I might try to rig it up and see how bad it is. I just wish there was something better than putting that damn battery in the control cavity.

  • I found your site on technorati and read a few of your other posts. Keep up the good work. I just added your RSS feed to my Google News Reader. Looking forward to reading more from you down the road!

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