Show Us Your Mojo – Guitar Builds by Chuck Chambers

I wanted to share some pictures of a couple guitars I built using Mojo bodies and pickup kits.  I wound the pickups with your PE wire.  All of the items were top quality and look, play and sound great.  Thanks for providing quality parts and trustworthy service!!!!

Chuck Chambers
Chambers Custom Guitars and Amps

Chuck Chambers / Chambers Custom Guitars and Amps

Wiring Your Speaker Cabinet

Now that you’ve received your new unloaded Mojo cabinet, it’s time to install a set of speakers to finish it up.  The following is a guide for wiring a speaker cabinet correctly to match the output impedance of your amp.

Impedance is an equivalent resistance that an inductor or capacitor produces in a circuit. Therefore, without delving into Ohm’s Law, from which our process for calculating total impedance is derived, we can start with the basic equations for calculating series and parallel resistance.  The difference between impedance and resistance can be disregarded for this application.

Loads that are wired together in series result in a total resistance (impedance) that is equal to the sum of all loads or resistances in the circuit.

Wiring loads together in parallel results in a total resistance that is equal to the reciprocal of the sum of all reciprocals of each load.

This will come in handy when a circuit has more than two loads in parallel, but by rearranging variables, we get a more accessible equation for calculating the total resistance of two loads in parallel.

This form can certainly be used for cabinets with more than two speakers.  Calculate the resistance of two of the speakers in parallel, calculate the resistance of the next two speakers in parallel (assuming the cabinet has four speakers), then calculate the total resistance of the two results in parallel.

If all of your speakers have the same resistance value, the calculation can be further simplified.  Notice above that four 16Ω speakers in parallel have a total resistance of 4Ω.  It is safe to assume that dividing the resistance value of the speakers by the number of speakers will yield the total resistance.  Remember, this is true only for loads in parallel with the same resistance value.

Calculating for Power

The big thing to consider regarding speaker installation is the power your amplifier outputs.  If the amp is rated for 100W, the cabinet should be able to accept more than 100W for safe operation.  So, if you have a 4×12 speaker cabinet and a 100W amplifier, four speakers rated at 30W would be safe.  The cabinet is rated at 120W.  Failure to plan for a safe cabinet power rating could result in blown speakers if the amplifier output is higher than what the cabinet is designed for.  If a voice coil fails, the resistance load of the cabinet can alter depending on the wiring method.  If the value falls below what the amplifier’s output impedance is set for, the output transformer is likely to fail.  So, avoid the expense of replacing your equipment and plan ahead.

The following is a set of wiring diagrams for the most popular speaker cabinet configurations.

Note: The series-parallel and parallel-series configurations function the same electrically.  The names for each are interchangeable which is apparent when searching for these configurations on the web.  We’ve labeled them in this fashion simply because they show up in other web resources more often than the other way around.  Furthermore, we know of no real proof that supports theories of tonal differences between the two.  However, if there is good scientific data to back it up, let us know about it; we’re eager to learn.  Please, no AB listening tests.  

Soldering 101

There are several types of solder, soldering irons, and iron tips for different applications.  Here we are mainly focusing on guitar and amplifier electronics.  Before learning the technique of soldering it is important to understand what to use for a particular job.

Choosing the Right Soldering Iron (avoid using soldering guns if you can)…..

25-30 Watt Irons
Great for delicate PCB work where less heat is good, though not recommended for hand wired electronics because it can require more time to heat up the bigger solder joints which may damage the component before the solder can melt.
35-40 Watt Irons
Ideal for most guitar and amp electronics, especially the hand wired components.  The higher wattage requires less time to melt the solder joint, so you reduce the risk of overheating the components.
Variable Heat Irons
These are the best because you can adjust the heat to handle almost any job.  You can reduce the heat enough to work on delicate PCB’s, or increase it enough to solder Humbucker covers or any large surface that absorbs heat and makes it difficult to solder.

Choosing the Right Tip…

Chisel Tip (L), Pencil Tip (R)

Chisel Tips – These come in all sizes. They have a flat head which helps to better disperse heat across bigger surfaces.  A small chisel tip is good for most hand wired components that have solderable lugs.  Medium to large sized tips are great where high heat is needed, such as soldering Humbucker covers to a base plate, or soldering directly to a chassis.

Pencil Tips – These are pointed and designed to focus heat directly to one central point.  Pencil tips are ideal for PCB’s or any smaller solder connections.  They can also be great for crammed wiring where a chisel tip won’t reach without burning surrounding wires or components.

Choosing the Right Type of Solder…

This should be pretty self explanatory.  Just use a rosin core solder, like 60/40 or 66/44 which are most common.  The thinner the solder the better it is to work with.  You do not need to use flux with rosin core solder since the rosin is the flux.
Kester ”44” Rosin Core Solder .062 Core 66 Flux 44
Item No. 1000015a***SPECIAL ***

Let the Soldering Begin…

If there has ever been any mysticism or uncertainty about soldering, let us clear it up for you today.  While doing it right means less chance of a bad connection between components, there is nothing about it that should cause apprehension.  Follow these steps, practice practice practice, and commit them to memory.  You’ll be great at soldering in no time.
Step 1: Plug in your soldering iron, and wait for it to reach a good operating temperature.  For most applications, you’ll know you’re good to go when you can melt solder with the tip.
Step 2: Make sure the surfaces of the components are clean and clear of any debris. The only way for soldering to work is if metal is being soldered to metal.  If you are soldering a component to a PCB for example, you may have to scrape a bit of the PCB’s overlay coating from a trace to make a good connection.
Step 3: Secure the components together. More specifically, make sure the components are contacting each other at the point at which the connection should be made, and that they will not move when you apply the iron and solder to them.  This is important because you stand a good chance of creating a cold solder joint if the components move around during soldering.  A cold solder joint occurs when one of the components is heated enough to receive a good solder bond, but the other component is not heated enough due to an aforementioned movement or bad iron placement.  This is a failed solder connection.
A good way to stabilize everything together is through the use of alligator clips or a set of helping hands.

Step 4: Is your soldering iron ready?  Here is the key to a proper soldering technique:
  • Touch the iron to the area to be soldered.  Make sure the iron touches all of the components including the PCB if applicable.  This may take a few approaches at different angles before you get it right.
  • A few seconds later, touch the area with solder.  When it begins to melt, move it around the components for even coverage− no globs.
  • When everything is covered, take the solder away while keeping the iron on the area.
  • A few seconds after that, remove the iron while making sure nothing moves in the process.
  • After the solder hardens, give all the components a tug to test the bond.  Nothing should seem loose.
Your process should not deviate from this order.  Apply heat, apply solder, remove solder, and remove heat.  Practice this, and you will become a soldering master.
Now, what’s a good way to insure you’ve soldered properly?  Test it with an Ohm meter. Take a reading with the black probe on one side of the connection, and the red probe on the other side.  A good connection will read 0 to 10 Ohms max.  A connection needing attention will read O.L. (an open circuit) or some high resistance.
Need something to solder?  Try one of our Amp Kits or a Guitar Kit.
Pre-tin your leads with solder before making the connection.  This is most important with stranded wire because the strands need to be completely penetrated with solder in order to make a solid connection.  In summary, tin the wire, tin the part, heat both parts and join them to you will insure a better connection every time.

Click Image to Enlarge
Be careful not to overheat components, especially solderable lugs.  Remember that lugs are an extension of a contact point of a switch, jack, tube socket, or potentiometer. Overheating can make the solder to run down into the contact point causing it to fail or seize. When you see the solder start to “flow” onto the connection, then immediately remove the iron. This will prevent solder from “overflowing” into the contact point.
Always wear eye protection and solder with adequate ventilation. You never want to have solder smoke billowing around your face. Solder smoke is toxic and absolutely bad to breath. Use a fan or something to pull the solder smoke away from you. Also hot solder can fling or spit rosin which may damage surrounding finishes, or injure you, so always wear eye protection and protect the surfaces around your area.

Related Items:

Philips JAN 6080WC OTL Amp Project

Tired of listening to output transformers?  Make your next project an OTL amp using the military-grade Philips JAN 6080WC output tube.  This NOS U.S.A. made tube was subjected to the most rigorous vibration tests for military use, and as a result, should prove to be less microphonic than the Russian versions, and last longer too.

For the low-budget builder, a simple cathode-follower or a common cathode resistor bias will push both sides of the tube in the output section.  This is due to a low plate resistance (280-300Ω), well-matched triodes, and the tube’s ability to pass a lot of current.  These are also great for low impedance headphone drivers in the studio. Compared to other dual-triode configurations, the 6080 is more rugged than the 6AS7G, and much more affordable than the 2A3.
Check out some examples of the 6080/6AS7 used in OTL audio amplifiers:
Then, if you find yourself reminiscing about your days with output transformers, keep our 15W SE transformer in mind.

Related Items

Vacuum Tubes
Amp Kits

DIY Guitar Pickup Winder Counter

David Shepherd
David Shepherd Mojo Guitar Parts Manager Custom Wound Pickups

David Shepherd of Custom Wound Pickups shows how to make an inexpensive pickup winder counter using a $1 calculator and a $5 magnetic reed switch. This particular counter method is perfect for someone who is learning how to wind pickups as well as the occasional rewind in a busy repair shop. I recommend this counter to be used with a variable speed hand drill for the most economic and easiest way to wind pickups. It is however very limited on how fast you can wind before the calculator stops counting. My guess would be around 400-500 rpm’s max before it can’t keep up, but you will clearly see it stop counting after a certain speed and learn the limit. Speed should not be important anyway if you are learning. That said, I give this calculator counter idea a big thumbs up for getting started. The calculator counter idea has been around for quite some time so I do not take credit for this. I chose to describe this method because it is very inexpensive to make and easy to use. I also had to look at how available the parts would be locally. There are tons of other counter ideas that work great too and are inexpensive, but finding the parts locally can be challenging or impossible for some. The parts for this counter are conveniently available at most electronics stores or hardware stores and calculators are just about everywhere. I hope you will find this information helpful and good luck with your success!

Tools you will need

  • Basic calculator
  • Magnetic reed switch with wire leads
  • Soldering iron and solder
  • Razor blade
  • Small drill bit or file
  • Hand drill
  • Screwdrivers

(click thumbnail images to make larger)

  1. Remove the back from the calculator.

  2. Remove the battery if possible.
  3. Using the razor blade, carefully scrape the two (2) holes on the PCB pathways over the “=” button of the calculator until bare copper is exposed.
  4. Drill a small hole into the side of the calculator for the reed switch wires to feed through. All calculators are different so use your best judgment on where to drill a hole. On small thin calculators you may find using a small needle file to set a groove for the wires to feed into the calculator is best.
  5. Feed the 2 wires from the magnetic reed into the calculator through the hole. You may want to use silicone caulk or glue to hold the wires secure in the hole or you can get fancy and use a rubber grommet.
  6. Solder the 2 leads from the reed switch to the PCB holes over the “=” sign. It doesn’t matter which wire goes to which hole. Do not bend the wire or move the solder joint once your connection is made or you will risk breaking the pathway on the board.
  7. Re-install the battery
  8. Put the back on the calculator
  9. Turn the calculator ON and press + 1.
  10. Now move the magnetic assembly across the reed switch (approximately 1/8” to 1/4” space between the magnet assembly and reed switch) and watch it count up after each pass of the magnet. You will need to orient the magnet correctly for the switch to work which is immediately apparent. It will either work or it wont, depending on the direction of the magnet. Just flip it if it doesn’t work.