Nashville luthier and repair tech Dave Johnson from Scale Model Guitars leads you through a simple process to improve your guitar's playability by showing the steps to execute a neck adjustment, dial in your string action at the bridge, improve your nut slots, and lock down stable intonation.
Let’s build one of my favorite DIY guitar tools that I use daily in my shop. I’ll show you two versions and then explain how to put them into action.
Welcome back to Mod Garage. After receiving numerous requests to show more DIY tools for guitarists, today we’ll explore one of my favorites. For years I’ve used this one in the shop daily and I’m sure you’ll love it. It’s cheap and easy to build, but very effective for analyzing circuits of electric guitars and basses without opening the electronic compartment or lifting the pickguard. It’s a kind of adaptor or extension to measure a pickup’s DC resistance (DCR) from outside the guitar. After building one, we’ll discuss how to interpret the measurements.
The DCR of a pickup is by far the most common parameter you can read when reading pickup descriptions and often it’s used as an indicator of the output. The reason for this is that it’s easy to measure, but, sadly, it doesn’t tell us anything about a pickup’s output nor its tone. To quote pickup designer Bill Lawrence: “DC resistance tells you as much about a pickup’s tone and output as the shoe size tells you about a person’s intelligence.”
I’ve written about DCR as a pickup parameter in detail and you can read about it in “Mod Garage: Demystifying DCR.”
DCR is not a primary parameter in pickup design. It’s simply the result of the type and gauge of the pickup’s wire, the number of turns, and other parameters like the winding pattern, etc. But it isn’t completely useless, and we can use it as a good reference point for analyzing pickups both inside and outside a guitar or bass circuit. All you need for this is a digital multimeter (DMM). You don’t need an expensive calibrated precision DMM—any entry level DMM will work. You can get a simple digital DMM for $10, but if you want to invest in a better device, it can’t harm.
The easiest way to analyze a pickup is outside a circuit. Simply set your DMM to ohm and connect the two pickup leads to your DMM. If your DMM doesn’t have an auto-range function, set it to 20k ohm. Now you’ll get the DCR reading for your pickup. You can compare it to the factory specs of your pickup and it should be close. If your DMM shows “infinite” or “overload,” you know the pickup wire is broken. Let’s say your pickup should read 7k ohm, but yours reads around 2-3k ohm. Your pickup likely has a short circuit somewhere in the winding. Used this way, the DCR is always good to quickly check if a pickup is alive or not.
To quickly analyze a guitar or bass circuit with one or more pickups, you first need to build the DIY adaptor tool this column is about. There are two different versions, and you don’t need much for this:
- Version #1: This is the quick and dirty version. You need a standard 6.3 mm straight mono plug (the same type on all your guitar cables), some wire of your choice (preferably in two different colors), and two insulated alligator clips.
- Version #2: A more elegant version that you can also use with a scope if you have one. You need the same parts as for version #1, but instead of two alligator clips, you need two 4 mm banana plugs, and the two wires need to be longer than what you’d use for Version #1.
So, heat up your soldering iron and let’s get to building version #1.
- Solder one piece of wire to the HOT terminal of the mono plug and another one to the GROUND terminal. I prefer a red wire for the HOT and a black wire for the GROUND terminal (Photo 1).
- Solder an insulated alligator-clip to each end of the two wires, preferably a black one to the black wire and a red one to the red wire. Ready!
Version #2 is built the same way, but, instead of alligator clips, you solder a 4 mm banana plug to each end of the two wires, if possible, also in black and red. The two wires should be long enough that can place your DMM and/or scope at some distance from the guitar. In Photo 2, you can see version #1 on the top and version #2 on the bottom.
The difference between the two versions is that with version #1 you put the plug into the output jack of the guitar, connecting the two probes of your DMM to the alligator clips: the black probe of the DMM goes to ground (black wire) and the red probe goes to hot (red wire) as seen in Photo 3. With version #2, you need to remove the two probes from your DMM, plugging the two banana plugs directly into your DMM or your scope, also seen in Photo 3.
Both versions work equally well. Version #2 is just easier to operate when you also want to use the adaptor for a scope.
For a quick check, you can also directly touch the hot and ground terminals with the probes of your DMM, but you need both hands or a second person for this if you want to play around with the controls or the pickup-selector switch.
Now we can easily check four things with this tool, assuming everything is connected the way it should be and your DMM is set to ohm and auto-range or the 20k ohm scale if your DMM doesn’t have an auto-range mode:
- Do you receive a reading on your connected DMM? If not, check if the volume pot is fully opened. Do you receive a reading now? If so, close the volume pot completely and see if you still receive a reading. No? Perfect, you just proved that the volume pot is alive and well.
- With a fully opened volume pot and a reading on your DMM, slowly turn down the volume and watch the reading on the DMM. If you receive some crazy reading, chances are good there is a treble bleed network on your volume pot. If the reading slowly goes down to zero, you know that there is no treble bleed network on the volume pot, and you can check if it’s an audio or linear volume pot (plus the taper it has, if it’s an audio pot). Let’s say we have a 500k volume pot. When you close the volume pot halfway and receive a reading around 250k, you know it’s a linear pot. An audio pot, depending on its taper, will result in a much higher reading on the first 50 percent of the volume pot. If you read 500k until the volume pot is almost fully closed, this means the pot has a 90:10 audio taper—exactly the kind of volume pot you don’t want to have. If you read something around 300k in the middle of the volume pot, you know it’s a 60:40 audio taper.
- If the volume pot is fully opened and you don’t receive a reading on your DMM, chances are good that your output jack is broken, not connected, or connected incorrectly. Please make sure there is no activated kill-switch in the circuit that can also cause this “problem.”
- Turning the tone knob(s) will make no difference in the reading you receive. If you receive a slightly higher reading with a tone pot fully opened compared to when it’s closed, you know it’s a no-load tone pot.
There is a lot to discover from just the outside of any guitar or bass. So, now let’s see what we can measure from outside the instrument starting with a Telecaster with a 4-way switch. The readings in all examples are the readings I received with guitars I had in the shop, but they can be different in your instruments:
- Bridge pickup only: 5.85k ohm
- Neck pickup only: 6.76k ohm
- Both pickups together: 3.18k ohm
- Pickup selector switch in position #4: 12.30k ohm
The readings for both pickups are within the factory specs and are in a typical range for a vintage-flavored Telecaster pickup set. With a reading of 3.18k ohm for both pickups together, you know that both pickups are in parallel. With the reading of 12.30k ohm, you know that both pickups are in series with each other.
Here is the simplified math behind these readings:
- Series connection: DCR pickup #1 + DCR pickup #2
- In our example, it’s 5.85k + 6.76k = 12.61k ohm, which is very close to the reading of 12.30k we received. The missing 0.31k ohm are eaten up by the resistance of the pots and the tolerance of your DMM. For this test, I chose the cheapest DMM I could find in the shop. A calibrated high-quality DMM will have much less tolerance.
- Parallel connection: (DCR pickup #1 + DCR pickup #2) divided by four
- In our example, it’s 5.85k + 6.76k = 12.61k ohm divided by four = 3.15k ohm, which is very close to the reading of 3.18k ohm we received.
Now let’s repeat this with a standard Stratocaster:
- Bridge pickup only: 7.07k ohm
- Middle pickup only: 5.88k ohm
- Neck pickup only: 5.70k ohm
- Bridge + Middle pickups together: 3.26k ohm
- Neck + Middle pickups together: 2.94k ohm
All three pickups are within the factory specs of this Strat. We have a slightly hotter bridge and two vintage-flavored pickups. The two in-between positions are in parallel.
Lastly, let’s try a vintage PAF-loaded Les Paul:
- Bridge pickup only: 7.77k ohm
- Neck pickup only: 7.09k ohm
- Both pickups together: 3.74k ohm
Both PAFs have the typical vintage DCR and are in parallel in the middle position.
That’s it. Next month we’ll take a deeper look at changing wires on pickups, which is something I’ve been asked about a lot, so stay tuned!
Until then ... keep on modding!If you want the maximum tones out of an HSS-configured guitar, here’s how to wire the switching and eliminate two pet peeves from a basic auto-split wiring.
Welcome back to Mod Garage. This month we’ll have a deeper look into auto-splitting pickups on an HSS-configured Strat and similar guitars. We covered this a long time ago, exploring the basic version of this wiring in “Stratocaster Auto-Split Mod.” Today we’ll take it one step further with a pro version and discuss what can be done with it.
The HSS setup with a bridge humbucker plus two traditional single-coils is the perfect combination for many Strat players, but it’s not limited to Strats. With the bridge humbucker you have a powerful pickup for soloing and rocking the crowd, while the two single-coil pickups give you traditional sounds and everything in between. When you choose a bridge humbucker with 4-conductor wiring, you can even split it for more possible sounds and to also get the famous in-between “quack” tone with the bridge and the middle pickup together in parallel. That’s exactly where the auto-split wiring comes in when you want an easy-to-operate setup. Let’s have a look what can be done with such an HSS pickup configuration and a 5-way pickup selector switch.
Some players may not need the in-between pickup position with the bridge plus the middle pickup together in parallel. Maybe they can’t use this tone in their musical context, or they simply don’t like these slightly hollow tones with less output. Even Leo Fender himself never liked this tone that he called “out of phase” (which is technically incorrect). These players are fine with a standard 2-conductor bridge pickup and standard Stratocaster 5-way switching.
- Both coils in series (standard humbucker operation with full output)
- Both coils in parallel (a kind of hum-free, single-coil-like tone with less output)
- One coil shut down to ground (real split mode with only one coil engaged)
- With a simple 2-way toggle switch you can shut down one of the coils to ground to get an additional single-coil-like tone from the bridge pickup. This can also be used to get the in-between sound together with the middle pickup. You can also use any standard push-pull or push-push pot, or the Fender S-1 switch, for this operation, so you don’t have to alter the appearance of your guitar.
- If you want more, you can use a DPDT on-on-on switch like the DiMarzio “multi-sound switch” to get all three sounds from your bridge humbucker. This operation can’t be done from a push-pull or push-push pot—you need an additional 3-way toggle for this.
- If you want all four possible sounds from your bridge humbucker, an additional rotary switch is the way to go. We discussed this just a few months ago in “Mod Garage: How to Triple Shot Your Humbuckers.”
That’s where the pro version kicks in, replacing the standard 5-way switch with a “super switch” that has four individual switching stages instead of only two, eliminating the two peeves from the basic auto-split wiring.
Please note: This is only possible with a humbucker sporting 4-conductor wiring. You can’t do this with a humbucker with traditional 2-conductor wiring!
Of course, there are players who don’t need all the gadgets. They simply want a powerful humbucker tone in the bridge position and the typical traditional Strat tones from all the other switching positions, including the in-between position of the bridge plus middle pickup. The auto-split wiring is perfect for these players because it’s a set-and-forget situation.
What will happen without the auto-split wiring when dialing in the bridge humbucker together with the middle single-coil pickup in parallel? You won’t hear a big difference in sound compared to the bridge humbucker alone, simply because usually the bridge humbucker is a lot louder compared to the single-coil and will dominate the tone by out-acting the single-coil. To combat this problem, the auto-split wiring will automatically (hence the name) split the humbucker into a single-coil by shutting down the other coil to ground for a traditional in-between sound of both pickups, like we all know from a regular SSS-configured Strat. The switching matrix of the auto-split wiring looks like this:
- Bridge humbucker with both coils in series for full humbucker operation
- Bridge humbucker split + middle single-coil in parallel
- Middle single-coil
- Middle + neck single-coil in parallel
- Neck single-coil
Deciding what coil of the humbucker will be sent to ground leaving the other active could easily be the subject of a whole column. Depending on the winding direction and polarity of both pickups, you usually don’t want to end up with an out-of-phase tone when both pickups are engaged and when your middle pickup is RWRP (reverse-wound, reverse-polarity), you also want to have the hum-cancelling function this switching position can provide. So … choose carefully!
While the basic version of this wiring works great, it has some peeves that some players complain about:
- It’s not possible to freely arrange the dual tone controls. They are fixed to one for the middle and the other for the neck single-coil, leaving the bridge humbucker without any tone control, like in standard Strat wiring.
- You’ll have to use individual tone caps for each tone control.
That’s where the pro version kicks in, replacing the standard 5-way switch with a “super switch” that has four individual switching stages instead of only two, eliminating the two peeves from the basic auto-split wiring.
Good idea, but unfortunately the road to hell is paved with good resolutions.
The super switches are physically a lot larger compared to the standard version, so take care that they’ll fit into your guitar. Recently I had to upgrade an Ibanez HSS guitar with this wiring, and it was impossible to put a super switch in without extensive routing to make space for it. I had such problems before with Yamaha and Fender guitars. The PCB-based versions of this switch require less space, so often this is the way to go.
Often such extended auto-split wirings are trying to also handle what I like to call the “resistance paradigm.” Fender used 250k pots for their guitars with single-coil pickups in the early days, while Gibson used 500k pots for their humbucker-loaded guitars. I don’t think the resistance values were chosen for any tonal reasons. We’re talking about the 1940s and ’50s, when they simply didn’t have the choices we have today. Especially Fender used whatever was available in large quantities for a low price, and it’s likely that Gibson had a similar approach.
Today you can still find unfounded rumors all over the internet that single-coils sound best with 250k pots and humbuckers with 500k pots. While the basic idea behind this contains some truth (500k pots still leave some high-end with a humbucker while 250k pots prevent the single-coil from sounding too harsh), such rules are not set in stone and usually such debates totally neglect that we’re talking about a passive system.
Often 500k pots are used for an auto-split wiring, incorporating some additional resistors to “convert” them to 250k for the single-coil pickups. Good idea, but unfortunately the road to hell is paved with good resolutions. Digging deeper at this point is too much for this column but may be a good subject for a follow-up. My personal recommendation: Forget about it. In more than 20 years, I have tried every variation of such jack-of-all-trades wirings and not a single one really worked in a useable way. Here are my two cents regarding such a wiring:
- A good and useful distribution of the tone controls is one 500k pot for only the bridge humbucker and the other one 250k for the two single-coils.
- Using two tone caps (one for each tone control) is simply perfect for this wiring, i.e., I really like to use a small cap value for the humbucker to control the warmth of it plus a traditional value for the two single-coil pickups.
- Using a 250k master volume works excellent because in a passive system like a Strat, you can benefit from the much better taper regarding evenness compared to a 500k pot. The loss in high-end compared to a 500k pot is marginal: measurable, but not audible. Using a treble-bleed network is a matter of choice and up to your personal preferences.
The wiring layout seen in the diagram at the top of this page is what I recommend and that most players will be happy with, so here we go. I assume that the middle pickup will be a RWRP type, and as usual, I used the Seymour Duncan color code for the humbucker. If you have a humbucker from a different company, you’ll have to convert the shown color code with one of the converting charts online. The bare wire of the humbucker always goes to ground, no matter what type it is. I tried to keep the illustration as clean as possible by leaving out all ground wires, so, as usual, they’re shown with the international symbol for ground. Solder all these connections to the back of a pot of your choice.
That’s it. Next month we’ll build a cool and simple yet very effective diagnostic gadget for electric guitars and basses. I use it in my shop daily and you will love it for sure, so stay tuned!
Until then ... keep on modding!