Monthly Archives: November 2007

EMG Pickup Installation in a Gibson Explorer (part 5)

Posted by Andy on November 20, 2007
Guitar / 4 Comments

I finally got everything totally dismantled, which meant that it was time to undertake the job of putting it back together with all new parts. I must have gotten a little lazy during this, I forgot to take pictures along the way. I think the first thing I did was connect the new pots using the provided washers and nuts. I then connected all the controls together with ground wires. The metal casing of all the pots gets soldered to ground, which was a little bit of a pain. Because the solder only bonds if you heat up the metal quite a bit, it takes some time for the whole pot casing to heat up enough to bond with the solder. It was kind of scary holding the soldering iron on the parts for so long, but it seems to have worked okay. Next, I routed the new pickup wires in from the pickup cavity and soldered them to the volume controls. After that, I made all the toggle switch connections, and then finally the output jack connections, along with the battery connector. It all seemed a little bit too easy, and I was sure I had done something wrong, but I wouldn’t be able to tell until after a few more steps. Here’s a pic with the progress so far:

New controls installed

I wasn’t sure how well the battery would fit in this little cavity, and I was right, it doesn’t fit. At the moment, I have it taped on the back of the guitar, but I’m hoping another little side project will permanently move the battery away from the guitar…

Here’s a picture of the top of the guitar:

New cables routed

At this point, everything was in place, all I had to do was cleanup all the wires and screw in all the screws to get it all put back-together. Here’s a pic of the final product:

Finished

I got it all put back together, and was amazed to find that it worked! It took me a minute to figure out the mono vs. stereo cable problem, but after that, it was all good. It does sound pretty good, it’s not drastically different, but you can definitely tell the difference before and after. The lows and highs are definitely more pronounced, and I’ve had to adjust some of my sloppy techniques because the pickups are a little more responsive.

Here’s one more pic:

Another finished pic

Thanks for reading this, and if you’re doing this yourself, I hope these posts might give you some good tips.

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EMG Pickup Installation in a Gibson Explorer (part 4)

Posted by Andy on November 20, 2007
Guitar / 4 Comments

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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EMG Pickup Installation in a Gibson Explorer (part 3)

Posted by Andy on November 19, 2007
Guitar / No Comments

EMG pickups require you to replace most of the electronics in the guitar, including most of the wires, the volume and tone potentiometers (“pots”), and the output jack. At this stage in the process, you basically rip out every part of the guitar, and replace it all with the shiny, brand-new, American-made EMG parts! America rules!

A potentiometer is basically a three-terminal variable resistor. Because there are three terminals, there are several different ways to wire it up. I must admit, in my original posting of this blog, I described how I thought it worked in a guitar, but I was dead wrong, so I have edited this post… Of course, I could still be wrong, but I just don’t have a huge desire to draw out the circuit diagrams and try to figure it all out completely, so please correct me if I’m wrong.

In a three-terminal pot, the two outside terminals are connected to each end of the internal resistor, and the middle terminal is tied to a sweeper that can be rotated to contact any point along the internal resistor. If you were so inclined to connect a signal path from one of the outer terminals to the center terminal (and leave the other terminal floating), you’ll basically just have a two-terminal variable resistor.

In a guitar, the volume pots work as a parallel “bleeding” resistor on the signal path. The signal current enters one of the outer terminals and exits the middle terminal, but the other outer terminal is actually tied to ground, which gives you a parallel, variable resistance path to ground. This parallel path acts to bleed current from the signal path, varying on how far you’ve turned the knob. In a guitar, to maximize the output volume, you turn the pot so that the signal passes from the outer terminal to the middle terminal with “no” resistance, and very little of the signal is bled to ground through the maximum-resistance parallel path. To lower the volume of the signal, you turn the pot so that some of the signal will pass through some resistance, and more and more of the signal bleeds to ground as the parallel path resistance is lowered. For zero volume, you turn the pot so that the signal path to the output jack faces a huge series resistance, and the parallel path to ground has no resistance, which causes all of the signal to bleed to ground.

With passive pickups, the potentiometer values for the controls are usually pretty high 250kOhm -> 500kOhm. Passive pickups have lower current outputs, so you have to be extra careful with power bleed as the signal travels from the pickup to the amp. As you bleed current, the signal power gets lower and lower, and more and more noise can begin to play a role in the signal. Active pickups, such as EMGs, normally work with with much lower-valued 25kOhm pots. There are probably many reasons for this, which I will attempt to describe… An EMG pickup is internally powered and the pickup output is boosted, so it can afford to work with a lower-valued bleed path because you’re not as concerned with losing precious signal current. With a passive pickup, you want a very large resistance in the bleed path, so that you bleed as little current as possible when you’re set to maximum volume. In an ideal world, using a huge resistor is great, but with real potentiometers, value tolerances and part “performance” can degrade as you work with parts of higher and higher resistance values. Most electronic components are manufactured with some sort of value tolerance, maybe 5% or 10%. With a resistor, this means that if the part is listed as 500kOhm, the resistance is actually some random value between 475kOhm and 525kOhm (500k plus/minus 5%). With an even larger value, like 1MegaOhm, the actual value will be somewhere between 950k and 1.5M. You can see that as the resistance value gets larger, the range of actual values gets larger as well. This might not seem like a problem, since we’re working with a variable resistor anyway, but the part “performance” can also degrade with larger resistance values. With a larger pot, the resistance sweep has a much wider range to cover, so there is a greater chance that the pot will will have undesired spikes, hot-spots, or undesigned variances in the value sweep. I also read somewhere that high-valued pots tend to have a spiky response to high frequencies. I’m not sure if that’s a specific characteristic of the pot hardware, or just a result of the inherent capacitance of any electronic component paired with a very large resistor.

The circuitry in the EMGs is probably tuned very carefully to work with a specific output “load,” so they probably try to use the lower pot values to get the better value tolerances, and maybe a “smoother” sweep from zero to maximum resistance. Another thing I learned is that pots can have different “sweep” (or “taper”) characteristics. You can get a pot with a linear sweep, where the resistance value increases linearly as you turn the knob, or you can also get an “audio potentiometer,” which has a non-linear  (logarithmic) sweep, which gives you more fine-grained control as you get to higher volumes. For example, with a linear pot, when you turn the knob to 50%, you’ll get 50% of the volume. With an audio pot, there is a logarithmic sweep, which means if you turn the knob to 20%, you might actually get 50% of the volume, but the remaining 80% of the pot turn is available to finely adjust the upper 50% of volume.

Anyway, I hope that wasn’t too boring, but I thought it was interesting. Here are a few more pictures. This one shows the control cavity. You can see the wires coming in from the pickup cavity – the cable from the toggle switch, and the two braided cables from the pickups.

Old controls closeup

The Explorer has 2 volume knobs (one for each pickup) and a “master” tone knob, which affects both pickups. The pot on the left is the neck volume, the middle one is the bridge volume, and the right one is the tone control. The tone control is another pot, but instead of a bleed resistor, it acts as a simple low-pass filter with a variable resistor and a capacitor. The capacitor sits across one of the resistor terminals and ground – it’s that round, orange thing soldered on the right pot.

Here’s a closeup of the left side:

Left control (neck volume)

The Explorer control placement is a little confusing in terms of the signal path. The pickup signal comes down through the braided wire through the volume pot, then gets routed back up to the toggle switch, and if the switch is in the right position for that pickup, the signal comes back down from the toggle switch, through the tone filter and finally out the output jack. One other interesting thing in this picture is the “string ground” wire. Near the top-right of the picture, you can see a silver wire that goes up into a little hole. This wire is tied to the ground of the controls (which are ultimately grounded by the amp, via the guitar cable), and apparently is connected somehow to the screws that hold the bridge piece. The bridge piece connects to the strings, which effectively grounds the entire guitar, strings and all. I read that if the strings are not grounded like this, there is a potential electric shock hazard. EMGs are internally grounded, so the EMG instructions say that you shouldn’t connect this ground wire when you replace the controls. To be honest, I don’t completely understand this, but oh well… I ended up just taping the wire up to the inside of the cavity with electrical tape when I took out the controls.

Here are some blurry closeups of the middle and right controls:

Middle control (bridge volume)

Here’s the tone control:

Right control (tone)

The black cable near the bottom connects down to the output jack.

That’s definitely enough for one post, thanks for reading!

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EMG Pickup Installation in a Gibson Explorer (part 2)

Posted by Andy on November 19, 2007
Guitar / No Comments

Here’s my first real post on my project to install EMGs in a Gibson Explorer. I got this Explorer a few years ago after my apartment got broken into. I got some insurance money for the stuff that was stolen, so I figured I’d get a new guitar, rather than replace crappy DVDs. I’d always wanted a Gibson Explorer, mostly because of James Hetfield of Metallica, and more recently Claudio Sanchez of Coheed & Cambria, but also because it’s a frickin’ sweet axe! I got kind of a low-end Explorer model, which meant that the included hardware wasn’t exactly high-quality. After a few years of playing, the volume knobs started getting a little scratchy, so this was as good a guitar as any to overhaul.

I got the EMG “Zakk Wylde” pickup pack, which includes an EMG-81 and an EMG-85. People usually put the 81 in the bridge position and the 85 in the neck position. I could pretend like I know exactly why these two pickups are different, but alas, I guess I just don’t care enough to delve down to that level of detail. I did read that the 85 actually has a higher overall output than the 81, but produces a “warmer” tone, possibly because the pickups use different types of magnets. On a guitar, the neck pickup “slot” produces a warmer tone anyway, because of its positioning further down the string, so the 85 is a good fit for the neck spot. The 81 has a high output as well, but has a “less warm” frequency response (mid frequencies filtered out a bit more) which is good for boosting the highs and lows of the more “focused” string vibrations over the bridge spot. A lot of people go with this 81/85 combination, but I’ve also heard of people using two 85s, or two 81s instead. Since this is my first time, I figured it wouldn’t really matter because it’s all new to me.

Here’s the first step in the process – remove the pickguard:

Remove the pickguard

Here’s a closeup, you can see the toggle switch and its wires, and the braided wires coming from the old pickups:

Remove the pickguard closeup

Here’s the step I probably should have done first – remove the rusty old strings:

Remove the strings

With the strings off, the tailpiece and the “tune-o-matic” bridge aren’t attached to anything, so they might just fall off if you flip the guitar over. Be careful with the screws that hold the tune-o-matic, if these are mistakenly screwed up or down, your string height/action will change, which will create for some annoying adjustments later. Speaking of the tune-o-matic, there’s actually something you can do with this thing if you’re having intonation problems with your guitar, which was the case for me. If your string lengths are not set correctly, the guitar may sound out-of-tune at higher frets, even if you have the open strings tuned perfectly. For example if you tune an open string correctly, and then press down at the 12th fret and find that you’re sharp or flat, it means that your string is either too short or too long. This can be easily adjusted with a tune-o-matic – each string has its own “saddle” that can be moved back and forth with a little screw. In my case, I was having the “sharp-at-the-12th-fret” problem, which meant that my string was too short. I moved the saddle as far as I could to lengthen the string, but unfortunately, I hit the limit on how far I could move it back, and the string was still sharp at 12. Luckily, the saddles are shaped like a little angled wedge, and the factory setup is for the wedge to slope up from the bridge towards the neck. (I hope that makes sense.) Anyway, I found that you can flip the saddles around so that the wedge slopes up from the neck towards the bridge. Flipping the saddle basically moves the string contact point back 2mm or so, and gives you a little more room to screw the saddle back even further, if the 2mm change is not enough. Here’s a nice, blurry picture showing a few of the saddles flipped around. I don’t know if it’s really clear, but it actually helped, in the end, I was able to achieve better intonation.

Tune-o-matic closeup with flipped saddles

It’s hard to see, but the two on the left have been flipped around, and the 3rd one from the left is screwed all the way forward – I’m about to take it out to flip it around. This was just a little side-thing to do while I had everything dismantled.

This is probably enough for one post, but I’ll post a few more blogs with more pictures.

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EMG Pickup Installation in a Gibson Explorer (part 1)

Posted by Andy on November 19, 2007
Guitar / 1 Comment

A few days ago I wrote a blog about wanting to get a new guitar, but seeing as how my credit card bill has gotten a little out of hand with skiing stuff this past month, I decided to do something that wouldn’t cost as much money.

Rather than buying an entirely new guitar, I thought it would be fun to try a maintenance-type project on one of the guitars I already have. A lot of my favorite bands use EMG pickups in their guitars, and I’ve always been curious to try them out, so I decided the time had come! I’d never really done much work or maintenance on a guitar, but I did do some soldering in college, so I figured it would be a good weekend project to undertake.

For those who might not know, a guitar pickup is basically a magnet with a long, thin wire coiled around it. When you pick a string, it vibrates over the magnet and affects the magnetic field, which induces a current (the guitar signal) to flow through the coil of wire.  The signal is sent out of the pickup and travels through some passive components (volume/tone filters) in the guitar, and is finally sent out to the amp. This basic type of pickup is known as a “passive” pickup because it sits there passively and produces a signal directly related to the physical characteristics of the magnet, coils, and the vibrating string.  In other words, there are no active (i.e. powered) components that affect the signal, only passive electronic parts. EMG pickups are “active” pickups – they have a powered circuit within the pickup that can pre-process the signal produced by the magnet/coil before it gets sent out through the guitar. The active circuitry serves to boost the signal and apply some equalization (e.g. boost the highs/lows, cut the mid frequencies). It might also apply a noise filter to cut out a lot of the “hum” that might be produced by a passive pickup. A lot of the guitar “purists” probably look down on active pickups because they cut out a lot of the “organic” sound of the guitar, but if you use a lot of distortion, boosting the guitar signal to get a better frequency response might be more useful than preserving the natural sound of the guitar.

I read a lot of forums and tips before I started, but I never really found a good walkthrough of the whole process, so I figured I’d take pictures along the way; maybe I can help someone else undertake something like this. I’ll post a few separate blogs about this to try to break it up a little.

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