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Crackling, Rattling and Popping

“Snap, crackle, pop.” Great for cereal, but not what you want to hear from your amp. But what if you do? Let’s look at the causes of crackling, rattling and popping and find out what you can do to make them stop.

Crackling

Crackling is like static, only more severe and with more pop.

Troubleshooting
You can find the source of crackling as you would with static. It often has same root causes. It can also result from absorption of humidity by the resistors, from an arcing transformer or socket or from a broken component.

Rattling

Rattling takes two forms - electronic and acoustic. Each comes from a different source.

Electronic

This rattle often originates with the amp speaker, a power tube or the rectifier tube.

Troubleshooting
Use the same methods you would to find the source of static or popping.

Acoustic:

Acoustic rattling is almost always cabinet-related. It can come from loose panels, name plates, mounting screws, or even from fractures in the cabinet body.

Troubleshooting
The best way to locate the source of acoustic rattle is by close inspection of cabinet. Check all joints, screws and other parts that might come loose. Also, inspect the cabinet for hairline fractures or other cracking.

Popping

The sound of popping is similar to crackling, but distinct and intermittent. It can originate from the rectifier arcing, a socket arcing, bad connections or bad sockets, and arcing of components.

Troubleshooting
The best way to isolate the cause of popping is to use stage isolation. You do this by methodically removing and replacing your pre-amp tubes, beginning with your phase inverter tube. You can find more about this technique here.

Rattling, crackling and popping are not unusual in an amp that gets a lot of use. Like any piece of equipment, it will suffer from wear and tear. However, you will save time and money by learning how to isolate the causes of these problems yourself, even if your technician is the one to fix it.

Good luck. Next week is the final installment of this series.

You turn on your amp only to hear a hum coming from it that you weren’t expecting. What can you do?

Hum in an amplifier comes in two types:

60 cycle hum

This type of hum more often than not originates outside of your amplifier. However, it can also come from the filament supply, a burnt bias pot or resistor or from the filament and grid wires being too close to one another.

In a fixed bias amp, 60 cycle hum usually comes from a bad bias supply filter cap.

120 cycle hum

Unlike 60 cycle hum, this type of hum does originate within the amplifier. It most likely comes from bad filter caps or a coupling cap becoming conductive.

Troubleshooting

Rob Hull Custom Guitar Cable

To determine if your amp hum has an outside cause, unplug your guitar cable from the amplifier. If the hum stops, you know the amp isn’t the problem. Instead,  your cable or input jacks and plugs could be the culprit.

If this is not the cause of the hum in your amp, you can do a visual inspection of the components to look for burnt resistors or bias pots.  Also, check the filament and grid wires proximity to one another.

If the hum is 120 cycle, you can find out if a coupling cap has become conductive by checking the plate voltage of the tubes. One of them will be noticeably low compared to the others.

Disclaimer: Unless you are an experienced amp technician or trained in electronics, please do not attempt to make repairs on your amplifier yourself due to risk of serious injury, including electric shock and burns.

Source: Weber, G. (1997). Tube Amp Talk for the Guitarist and Tech, p. 17-25. Kendrick Books: Texas

You want to use your tube amp at this weekend’s gig, but when you sit down to practice or jam with friends, you get a horrible popping noise. The noise goes away and comes back, but no amount of adjusting the knobs or cables gets rid of it. What you have, is a static problem.

Causes of Amplifier Static

Tube Amp

Some of the causes of static in your amp may include:

• Loose connections
• Bad solder joints
• Arcing capacitors
• Bad resistors
• Faulty ground
• Arcing between components

Of course, other causes may exist.

How do you find the cause of static?

The two best ways to find the source are the same as those used to find the source of hum.

The process of elimination

First, you can use the process of elimination. You do this by methodically removing and replacing your pre-amp tubes, beginning with your phase inverter tube.

The chopstick method

Begin with a visual inspection of the components. Sometimes that is enough for you to see if a resistor is burnt or a capacitor is damaged. If you don’t see anything upon visual inspection, you can use the chopstick method. This method allows you to find the source of the problem without the risk of shock or burn. It is also simple and inexpensive to do.

To conduct this test, remove the chassis from the cabinet. Hook up a speaker and turn the amp “on” and set it to “play” mode. Turn the volume controls up all the way. Using a wooden chopstick to probe, gently poke the components at their joint, wire and component connections. If a component is loose, you will hear noise when you poke or tap the resistor.

Make sure you check every component, because the noise may come from the resistor you are tapping, but one close to it. Go through the components in the same systematic way you did with the pre-amp tubes.

Next steps

Once you are absolutely certain you have found the source of your static problem, you can fix it.

If you cannot find the source of the static in your amp, or if you are a novice, take it to a reputable technician for repair.

Source: Weber, G. (1997). Tube Amp Talk for the Guitarist and Tech, p. 17-25. Kendrick Books: Texas

Hissing Noise

This noise usually occurs whether or not there is signal to the amplifier. Additionally, it rises and falls as the volume is raised and lowered. This type of noise can have one of two causes:

Pre-amp tube problem

If you suspect that the problem originates with a pre-amp tube, the best way to rule it out is to exchange the pre-amp tube with one you know does not hum. Be careful that you aren’t simply using a low gain tube, however. Good pre-amp tubes have good gain, good tone and do not hum.

How can you know if it might be the pre-amp tubes?

Start by having the amplifier on and in play mode, then remove the phase inverter tube. This is the pre-amp tube closest to the power tubes. If you no longer hear the hum, it likely originates with your phase inverter tube or other pre-amp tubes. Now, you want to use a process of elimination. Replace the phase inverter tube and remove the pre-amp tube next to it. If the noise continues, it is your phase inverter tube. If not, keep removing and replacing the pre-amp tubes in order to discover which one is creating the noise.

Plate load resistor problem

Begin with a visual inspection. An arcing plate load resistor may look charred or burnt.

The Chopstick Test

If you cannot visually detect the bad resistor, you can use the “chopstick” test. To conduct this test, you first remove the chassis from the cabinet. Then you hook up a speaker and turn the amp “on” and set it to “play” mode. Turn the volume controls up all the way and using a wooden chopstick to probe, gently poke the components at their joint, wire and component connections. If a component, such as a resistor, is loose, you will hear noise when you poke or tap the resistor.

Check every component, because the noise may not originate with the exact resistor you are tapping, but the one closest to it that is reacting to the shock. Go through the resistors in the chassis systematically as you would the pre-amp tubes.

These two methods should eliminate the hum in your amp.

Source: Weber, G. (1997). Tube Amp Talk for the Guitarist and Tech, p. 17-25. Kendrick Books: Texas

Resistors have specific values which are indicated using a series of colored stripes on the body of the resistor. Each color is assigned a value, and each stripe position determines its purpose. It takes some practice to learn how to read the values quickly, but here is a guide you can use to help you.

Begin by holding the resistor so that the multiple colored rings are at the top of the body. The picture below is one example.

The first stripe is the first number in the value of the resistor.

The second stripe indicates the second number of the resistor value.

For example, in the picture below, the first stripe is orange, which equals 3 and the second stripe is black which equals 0. So the complete number is 30.

The third stripe color indicates the number of zeros that follows the first two. In the case of the pictured resistor, that value is 0, so no additional zeroes will follow the 30.

This means that this resistor has a value of 30 ohms.

The last stripe, which is usually separated from the others,
indicates the tolerance. In our picture, the resistor has a tolerance of 5%.

30 Ohm Resistor

The Gold or Silver band should always be to the right as you read from left to right. If there is no tolerance band, the side with a band closest to a lead is the first band.

If you cannot distinguish the colors of the bands on a resistor, the only way to read it is by using a multi-meter across the leads.

Do you have any special tricks you use to help you read resistor values? Please feel free to share.

by Robert Hull

Liquid RMA (Rosin, Mildly Active) flux or equivalent … designed for electronics work.
I call this the secret solder juice. Solder flows best when all the surfaces are clean. That means all wires are clean, all terminals are clean, the solder itself is clean and the soldering iron tip is clean. The nemesis of any soldering job is oxide buildup. Oxides develop on any bare metal when exposed to air…it is a natural process. We could spend lots of time cleaning every component and terminal before soldering but there is a quicker solution…flux. Flux is a multi-chemical mixture that when strongly heated, creates a mild acid that dissolves the top oxide layer of metals. With the oxides removed, the bare metal underneath allows the solder to adhere quickly and solidly. This is exactly what we want.

To use flux, dab a little onto the wire or connection just prior to applying the soldering iron tip and solder. A small amount goes along way so don’t put in too much. When the heat of the soldering iron contacts the connection with the flux, the flux will boil quickly. This is the prime point to apply the solder. With the solder applied, the flux then turns into fumes (avoid breathing). What should be left behind once the soldering iron is removed is a clean, solid solder connection and a small amount of dark amber residue.

Now, what every bottle of liquid flux needs is a:

Flux dispenser bottle with needle(s)

These plastic bottles are the best for delivering just the right amount of liquid flux. Some bottles come with multiple sized needle tips to choose from which is very convenient. I’ve recently started using the flux pens and I’m impressed. They are a terrific way to deliver flux without spillage. I think we should have both in our arsenal of flux choices.

Isopropyl Alcohol
Once a soldered connection has been made, there may be some small amount of flux residue left behind. This comes from either the rosin core solder or any added flux. In most cases, this residue will not cause any trouble, however it is a good idea to remove it. Isopropyl alcohol is the best choice for this task. Isopropyl alcohol is not the same as rubbing alcohol found in drug stores. Rubbing alcohol is often 50% water and added oils where as Isopropyl is made with no water and leaves no residue when it evaporates, which is important when cleaning.

Isopropyl alcohol, being a mild solvent, is excellent for washing out dirty tube sockets. It gently dissolves most contaminants and won’t damage the socket.

I use this solvent for cleaning all the time and consider it a “must have”. There are a few other solvents I use as well (such as Acetone - an aggressive solvent, removes paint, and Naptha - a milder solvent, great for greases) but Isopropyl is what I use most often.

Now, what every bottle of Isopropyl alcohol needs is a:

Pump liquid dispensers
These bottles make dispensing liquid solvents a big time saver while conserving overall usage. Not to mention, they don’t spill. With a light pump action and top reservoir, these bottles allow quick and timely delivery of a solvent to a cleaning brush, all with one hand. I keep three of these on my bench, one for alcohol, one for naptha, and one for acetone.

by Robert Hull

It is really fun building electronic stuff. Especially building useful stuff like audio amps and audio effects; robotic arms, high powered lasers and anything with blinky LED lights. Soldering these sorts of things together should be fun. However, soldering can also be frustrating when that “simple” soldering job doesn’t want to solder correctly. Solder flow problems can often be cured with the use of a few good specialized tools. This discussion will be about what tools make soldering like the professionals possible.

Temperature controlled soldering iron running at a proper temperature.
The first and most important tool is a good soldering iron. A temperature controlled soldering iron is preferred because these units will sense when the tip is cooling down and will send more power to the tip heating it back up again. In this way the tip always stays at a constant temperature making solder flow easily and quickly into connections. This constant heat is also beneficial as it allows connections to be made quicker and, with less prolonged heat, thereby protecting wire insulation and components from overheating.

The best temperature I have found to have a soldering iron set at is around 650 degrees. This is adequate to quickly melt solder yet still provide great life out of a soldering iron tip. A soldering iron tip running at a properly set temperature will last many, many years. An indication that a soldering iron tip is running too hot is if the tip turns blue when the solder is applied or after being wiped clean. That blue coloration indicates oxides burning on the surface of the tip. These contaminant oxides will eventually bake into the surface and will not come off, making soldering nearly impossible. At this point, the tip must be replaced.

Soldering iron tip cleaner (sponge)
As a hot soldering iron idles in its holder (even for a few seconds), it quickly builds up oxides on the surface of the tip. These surface oxides interfere with the efficient transfer of heat from the soldering iron tip to the connection. This makes for frustrating soldering as the solder will not flow smoothly (if at all). A simple moist sponge can remedy this problem and improve all solder connections.

By wiping (not dousing) a hot soldering iron tip gently across the surface of a moist sponge, the outside oxide contaminant layer will solidify and wipe off into the sponge. This action will leave a shiny, clean surface on the tip. A clean, shiny tip will accept solder readily and transfer heat efficiently to a connection. In this way, you will be able to make better, cleaner connections. Talk about happy soldering!

I do encourage every technician to have a couple of extra sponges on hand. Sponges get worn and it is a good idea to have an immediate replacement close at hand so your work doesn’t have to slow down because of a sponge.

Water Bottle (for Wetting the Cleaning Sponge)
It may seem silly to include this on a list of soldering tools and supplies, but over the years I’ve found having a filled water bottle close at hand for wetting the sponge a big help. It is time saver to wet the sponge at the work bench vs. walking to the bathroom and wetting the sponge and returning. My bench water bottle is a recycled plastic drinking bottle with a screw cap. It works great and is good for the environment, too.

-by Robert Hull

This post is the third installment of our Solder Series. You can read Part 1 here and Part 2 here.

Now we come to the gauges. I have found that the most effective gauge of single core solder to use is something close to .031″ dia. which equates to a 21 gauge. This is a great size and delivers adequate solder and flux for most connections. The smaller gauge of .02″ (gauge 25) is excellent for discrete and IC components and PCB use. The larger gauge of .04″ (gauge 19) is best for large connections and ground planes. When it comes to multi-core solders, .032 is the standard size but it takes a lot of feeding into the connection to get enough solder. This is where a higher gauge (.04″ / 19 gauge) comes in handy.

Soldering Station

To wrap everything up, the solder you choose to use will become very personal. There are many suppliers, all at different qualities and costs. You will eventually get the “feel” of a particular brand. Therefore I encourage trying several to find the one that works best for you. Additionally, it is good to have a few gauges on hand so that you can cover just about any situation. And, above all, keep lead safety high on your list of practices.

Hopefully this has been helpful, and if there are any comments you would like to offer, you can do so below. We look forward to hearing from you.

-by Robert Hull

This post is the second installment of our Solder Series. You can read Part 1 here.

Soldering Iron

That brings us to the lead free solders. There are many lead free solder choices today made from alloys containing silver or copper in addition to the tin. These solders are the choices for environmentally sensitive requirements or concerns. The challenges are that these solders tend to melt at much higher temperatures which can create concerns for component safety. Additionally, they require that the surfaces be very clean for proper solder flow. Otherwise, these solders function equally well (if not better in the case with the silver bearing solders) albeit at a higher cost as compared to the lead solders.

Solders today are rarely solid. They are usually hollow along the full length, with the center chamber filled with a chemical to make the alloys flow easier when heated. This chemical center is known as “flux” and is most often made from tree resin. Tree resin is a very good flux but it is often necessary to clean the connection afterward to remove the resin residue. If this residue isn’t properly removed, there is an increased chance of corrosion that can damage the connection. Thankfully, there are other fluxes that don’t require cleaning and I strongly recommend using these as it removes the cleaning step in the construction process.

In addition to being hollow, and filled with flux, often solders will have either a single chamber or multiple parallel chambers. The more flux that is applied to a connection, often the better the substrate metals (the copper and steel of the components and terminals or PCB traces) are able to bond with the solder. As a personal choice, I will often choose a multi-core solder over a single core. However because there is less solder per thickness, the usable gauge has to be increased. Handling the larger gauge of solder is sometimes a problem for small connections. As well, the multi-core solders tend to be much more expensive.

-by Robert Hull

You finally have all the components together. The transformers, the capacitors, the resistors, the wire and sockets. You’ve picked the best pieces within your budget and the time has come to assemble your creation. Joyous music will soon burst forth from these once diverse parts and the world will be filled with love. But, before you start to conjoin all these to make the circuits, the one item that all these components share together is the solder.

Roll of Solder

Solder is the “glue” that makes it possible for the electrons to flow between the components. It connects all the pieces, holding them fast together. And successful completion of your masterpiece is fundamental on using good quality solder.

So what makes a good solder verses a bad solder? As you have probably discovered, there are many types and sizes of solder. So many to choose from and which is best? For our purposes, we will only concentrate on the types used for electronics servicing. And will pick from these.

Most leaded solders today are made from a combination of lead and tin. The most common ratio is 60% lead and 40% tin. This ratio melts at a reasonable temperature for component safety. You will sometimes come across “eutectic” solder which comes in a slightly different ration of 63% lead and 37% tin and melts at a slightly lower temp. Either of these is fine, my personal choice being the eutectic ratio but it is more difficult to find.

As with any contact with lead, it is advisable to be cautious regarding fumes and residues. Wash hands often, use a venting system to pull the fumes away when soldering, and consuming any food at the workbench is strongly discouraged.