We cover a lot of amplifier and guitar electronics projects in our DIY features. Perhaps we take it for granted that everybody knows how to solder – but even those of us who have been soldering for decades may be able to learn something new.
This guide is divided into two parts. In the first part, I’ll be sharing some pro tips on soldering equipment and good practice. In the second part, I’ll be applying this info to a simple project, showing how to make a high-quality guitar cable.
There are various types of soldering iron and it’s important to choose the right one for your needs. Pencil-style irons are integrated units with the iron at one end and a wall plug at the other. Most come with a stand, which holds the hot iron while you’re in between tasks. This comes in handy if you hope to avoid burning holes in your workbench, carpet or yourself. Don’t ask me how I know… I just know.
Pencil irons are either on or off, and their operating temperature is fixed. In contrast, soldering stations include an iron and a stand that may or may not be integrated, but the station lets you set the operating temperature of the iron. Some interact with a sensor in the tip, to maintain that temperature.
Soldering guns are another option. They heat up rapidly, but can get too hot and aren’t really suitable for delicate work. Gas-powered soldering torches are also available, but they’re better suited to fine metalworking and if you’re inexperienced, you may end up setting something or somebody on fire. For guitar and amp work, I’d recommend a soldering station with temperature control.
Different soldering jobs require differing amounts of power from a soldering iron. You don’t need much power to solder through-hole components onto a printed circuit board, but soldering a ground connection onto an amplifier chassis is beyond the capability of most soldering irons. Common jobs in guitar DIY that require higher power include soldering ground wires onto potentiometer cases and Stratocaster spring claws. In amp building, a fair amount of power will also be required for eyelet and turret-board assembly.
If you have a 15- or 20-watt soldering iron, you probably won’t be able to do these jobs, because larger metal parts act as a heatsink, dissipating heat from the iron. When the iron cannot maintain a sufficient temperature, solder cannot melt and flow properly to form a solid joint. You’ll also end up holding the iron in situ for a long time and despite there being insufficient heat for soldering, you can still melt plastic parts and damage delicate electronic components.
All irons can reach a temperature high enough to melt solder, and higher power doesn’t necessarily mean the iron will get hotter; it actually means it can maintain its temperature even when heat is being dissipated. As a rule of thumb, more power is always better and a 50-to-60-watt iron should be sufficient for most jobs.
Right, to the wire
Solder for electronic applications comes in two varieties – lead-based and lead-free. Increasing awareness of the health dangers associated with lead have resulted in legislation restricting the use of lead-based solder in manufacturing.
Leaded solder is usually a 60/40 mix of tin and lead that melts at around 190°C and it would have been used in all vintage guitars, pedals and amps. It’s still widely sold and it’s the best option for restoration work. 63/37 leaded solder is also available and its faster transition from liquid to solid can reduce the risk of ‘cold’ solder joints – where parts move before the solder has solidified.
Lead-free solder has a higher melting point, so it’s a bit harder to use and you’ll need a powerful soldering iron. It’s an alloy of tin, silver and copper, and although lead-free solder joints can be stronger, they can be more brittle, too.
The law requires manufacturers to use lead-free solder and you may opt to do the same on health grounds. On the other hand, if you do relatively little soldering and much of it involves maintenance and repair of older equipment, you may choose to stick with leaded solder. I’ve used both and since I prefer leaded, I often use a small extractor fan that draws solder fumes into a carbon filter.
Electrical solder has embedded rosin flux, which dissolves metal oxide, helps the solder to flow and promotes bonding with metal parts. Plumbing solder has acid flux and it’s unsuitable for electronics. Various solder-wire gauges are available, but I find 0.7mm fine for most applications.
Better-quality soldering irons allow you to change tips. This is important for two reasons – firstly, tips wear out and secondly, different tip shapes can be used depending on the job at hand.
Fine and sharp conically shaped tips are ideal for precision work, such as soldering PCB sockets. Some tips look more like small chisels and others look more like flathead screwdrivers. When soldering onto potentiometer casings, where you need to distribute the heat over a wider area, a flatter tip is preferable.
Whichever tip you use, it’s advisable to keep it in good condition. When you’re struggling to make solder joints and molten solder falls off the iron, it indicates that the tip has become oxidised. If it looks dull and black rather than silver and shiny, that’s almost certainly the case. Contaminants on the tip can also get into the solder joint and cause it to fail.
Get into the habit of cleaning solder tips as you work. Most iron holders have a tray section that contains a sponge that should be dampened with water before you start work. Wiping the tip on the damp (not wet) sponge after each solder joint removes excess solder from the tip. Some prefer to use brass or stainless-steel wool to clean iron tips to prevent oxidisation.
After every few joints, it’s advisable to wipe the iron clean, apply fresh solder to the tip and wipe off the excess. This prevents the tip from oxidising and it should also be done at the end of a job before you switch the iron off. The process is called ‘tinning’ and a healthy iron tip should look shiny. You should also tin new tips before using them.
If you feel your tip is no longer working properly and cleaning and tinning doesn’t help, you have a couple of options. You may try treating it with tip activator, or simply replace it. Tips are relatively inexpensive, but you must get the right one for your iron.
Don’t blow it
Solder shouldn’t be considered ‘metal glue’, which is simply wiped on with the iron and allow to set. Solder needs to flow onto the parts to make a good joint and this requires proper soldering technique.
Whether it’s a resistor leg sticking through an eyelet or a hole in a printed circuit board, or capacitor leadout wires wrapped around a turret or tag, the iron should be used to heat the area where the joint is being made. With the area pre-heated and iron tip still touching the work, bring the solder into contact with the joint.
It should melt and flow almost instantaneously and the key here is that the solder flows into the joint rather than forms a blob on the surface. Do not try and melt solder onto the iron tip and then transfer it onto the joint, because the flux that helps the solder to bond will have evaporated before doing its job.
Knowing what temperature to set and how long to preheat the area comes with experience. Leaded solder melts at around 190°C and lead free at around 200°C. With printed circuit boards, an iron temperature of about 325°C should be a safe starting point, because it’s imperative not to damage the board. If you find it isn’t sufficient, then up the temperature to 350°C and try again.
Higher temperatures are needed for potentiometers, turrets and eyelets and there’s no harm in starting at a low temperature then increasing it if the solder is taking a while to melt and flow. Experienced solderers often prefer to work with irons set at 400°C or above, to get in and out in a couple of seconds.
Once the solder has flowed, remove the iron and allow the joint to cool naturally. Resist the temptation to blow on the solder to hasten the process. When soldering transistors and op-amps, try attaching a crocodile clip to the legs. It will act as a heatsink, to draw heat away from delicate components.
Test your new-found soldering skills by making your own guitar cable.