Are you experiencing interference in your phono system?
It could be due to RFI, or radio frequency interference.
RFI can come from a variety of sources, including smartphones, nearby cell towers, and even high power transmitters from emergency services or airplanes.
The low amplitude signal from a phono cartridge makes it particularly susceptible to RFI.
But fear not, there are solutions!
From checking your earth ground connection to using specialized cables and filters, there are steps you can take to minimize the impact of RFI on your phono system.
In this article, we’ll explore the different types of RFI and how they affect phono systems, as well as some practical tips for reducing interference and improving your listening experience.
How Does RFI Affect Phono
RFI can have a significant impact on the sound quality of your phono system. The wires that connect the phono cartridge to the tonearm wiring are typically exposed and unshielded, making them a great antenna for receiving RFI. This can result in unwanted noise, distortion, and even complete signal loss.
The interference can come from a variety of sources, including smartphones, nearby cell towers, emergency services transmitters, and even wireless routers. The low amplitude signal from a phono cartridge makes it particularly susceptible to RFI, as it amplifies the extremely low amplitude signal from the cartridge.
RFI can also affect the phono stage, depending on how it’s constructed. This can further impact the sound quality of your system.
Understanding RFI And Its Sources
RFI, or radio frequency interference, is a type of electromagnetic interference that can affect the performance of electronic equipment. The tolerance of equipment to RFI depends largely on how well it is designed. Generally, symptoms will appear when sufficient RF energy reaches an active device-IC, transistor, tube-inside the equipment. The energy can arrive in two ways: radiation or conduction.
As it travels through the air, internal equipment wiring can act as a receiving antenna and deliver RF voltages directly to an active device. This is most common in equipment with plastic or wood enclosures that have no RF shielding ability. Because any wire can become a receiving antenna, RF energy can also be conducted into the equipment’s active devices via any wire leaving or entering the equipment. Interference can also arrive via any wire coming into the building.
Because power, telephone, CATV and even driveway intercom, landscape lighting, or outdoor loudspeaker lines also behave as outdoor antennas, they are often teeming with AM radio signals and other interference. The most troublesome sources, however, are frequently inside the building where the interference is distributed via the power wiring. At high frequencies, a building’s power wiring behaves like a system of mis-terminated transmission lines gone berserk, reflecting RF energy back and forth throughout the power wiring until it is eventually absorbed or radiated.
The RF does not just follow the green ground wire back to the earth ground rod and magically disappear. RF power line noise is coupled through equipment power supplies into system ground conductors. Therefore, significant noise voltage will inevitably exist between the chassis grounds of any two devices in AC-powered systems, whether safety grounded or not. This is the dominant noise source in most systems, not noise picked up by cables as is so widely believed.
When this noise flows in the shield of unbalanced signal cables, the voltage drop directly adds to the signal. Unbalanced interfaces generally use single-conductor shielded cable and two-contact connectors. Remember that RS-232 data connections are also unbalanced.
Sadly, most commercial equipment has never been tested for susceptibility to RF interference, whether arriving through the air or coupled to its inputs, outputs or such other outside world ports as its power cord. Of course, even well-designed equipment will misbehave if confronted with extreme levels of RF interference.
How RFI Interferes With Phono Systems
RFI interference can cause a range of issues for phono systems. One of the biggest culprits is interference from smartphones, which emit RF radiation and can interfere with the signal from the phono cartridge. This is especially true if your home is far away from the nearest cell site.
Another source of interference is emergency services transmitters, such as those used by fire or police stations. These high power transmitters can affect your phono system, particularly if your home is located nearby.
Even wireless routers can cause interference if they are positioned too close to your phono equipment. This is because the wires that connect the phono cartridge to the tonearm wiring are typically exposed and unshielded, making them a great antenna for receiving RFI.
The low amplitude signal from a phono cartridge makes it particularly susceptible to RFI, as it amplifies the extremely low amplitude signal from the cartridge. This can result in unwanted noise, distortion, and even complete signal loss.
It’s worth noting that RFI can also affect the phono stage itself, depending on how it’s constructed. This can further impact the sound quality of your system.
To mitigate RFI interference, some people recommend using ferrite beads or filters to reduce the influence of RFI or EMI. These can be placed at the input of both amplifiers and preamp phono inputs to block both RFI and EMI from entering the following circuitry.
Symptoms Of RFI In Phono Systems
If your phono system is experiencing RFI, you may notice a variety of symptoms. The most common symptom is unwanted noise, which can manifest as hiss, crackling, or popping sounds. This noise can be particularly noticeable during quiet passages in music.
RFI can also cause distortion in the audio signal, resulting in a loss of clarity and detail in the music. You may notice that instruments or vocals sound muddled or indistinct.
In severe cases, RFI can cause complete signal loss, resulting in no sound at all from your phono system. This can be frustrating and may require professional assistance to fix.
It’s important to note that RFI can be difficult to diagnose, as the symptoms can be subtle and may vary depending on the source of the interference. If you suspect that your phono system is experiencing RFI, it’s worth experimenting with different placement of your components and cables to see if it improves the sound quality. Additionally, investing in high-quality cables and components that are designed to reject RFI can help mitigate the issue.
Solutions For Minimizing RFI In Phono Systems
Fortunately, there are several solutions for minimizing RFI in phono systems. One option is to shield as much of the phono leads as possible. This can be achieved by replacing unshielded wires with properly shielded ones or wrapping delicate leads from your cartridge with shielding. Another solution is to switch cartridges to see if the problem persists or changes. Isolating the frequencies of the FM signal can also be helpful in identifying the source of the interference.
To suppress RFI, filtering circuits can be installed across the noise-producing terminals of electronic devices. A 10nF COG/NPO ceramic capacitor with very short leads or ferrite beads can also be used to reduce RFI. It’s important to note that using an electronic filter may have an audible effect that is more pernicious than the original problem, so experimentation is required.
Another effective solution is to reduce the RF getting into the phono stage. This can be done by winding all cables a few turns around a form that is an inch or two in diameter close to your phono stage. Using heavy wire for ground cables and bundling signal leads with grounds can also help, along with using signal leads with very good shielding, such as braid over foil.
When shopping for a new phono stage, it’s important to ensure that it’s designed and fully tested for RF interference resistance. If you’re experiencing RFI from a CW station, which are mostly ham transmitters, politely asking them for help may be effective. However, extreme conditions such as being near a medium wave (AM) broadcast antenna or a FM antenna radiating 40KW may require designing and building replacement preamps that do not have the problem.
Importance Of Proper Earth Ground Connection
One of the most important factors in reducing RFI in your phono system is ensuring that you have a proper earth ground connection. When two points of a circuit are intended to have the same ground reference potential but instead have a different potential between them, this is known as a ground loop or earth loop. Ground loops are a major cause of noise, hum, and interference in audio systems, including phono systems.
Proper grounding ensures that all vulnerable signal circuits are referenced to one point as ground, which helps to eliminate ground loops. This can be achieved by attaching a grounding wire to your turntable chassis and amplifier. This wire puts the turntable and the amplifier at the same ground potential, which helps to prevent a ground loop from occurring.
It’s important to note that the preamplifier reference ground is the most crucial ground in your phono system, not metaphorical earth or the electrical safety ground in the electricity supply. Therefore, it’s essential to check for continuity between the grounding wire and the headshell, finger grip, and body of the tonearm. In some cases, the tonearm body ground is integral to one of the signal grounds and not a separate wire.
In a well-sorted cartridge/tonearm/preamp setup, only a tiny bit of low pass broadband noise should be audible with the gain (volume) control at maximum. Any discernible 50/60Hz hum or any 100/120Hz ripple, buzz, sizzle or crackle is indicating less than ideal wiring or screening from an engineering standpoint. Proper grounding can help eliminate these unwanted noises and ensure that you’re getting the best possible sound quality from your phono system.
Using Specialized Cables And Filters To Reduce RFI
Fortunately, there are specialized cables and filters available that can help reduce RFI in your phono system. Shielded cables with a grounded shield can be used to minimize the amount of interference that is picked up by the wires. These cables have a conductive layer that surrounds the wires and is connected to ground, effectively blocking RFI from entering the signal path.
In addition to shielded cables, RFI filters can also be used to protect against unwanted interference. These filters contain passive components such as capacitors and inductors that block both conducted and radiated RFI. They are designed to reject specific frequencies or types of interference within a power line or signal.
There are various types of RFI filters available, including white goods filters for home appliances, single-phase filters for smaller electronics, three-phase filters for larger equipment, medical-grade filters for sensitive medical equipment, and military application filters for aerospace and military communications applications. Choosing the right filter for your specific needs is important in ensuring optimal performance of your phono system.
It’s important to note that while specialized cables and filters can help reduce RFI, they may not completely eliminate it. Proper grounding and shielding of your system can also play a crucial role in minimizing interference. Overall, taking steps to reduce RFI can greatly improve the sound quality of your phono system.
