You’ve probably already heard about the possibility of grounding a turntable. In this article, we’ll first look at the background of why this makes sense and, in the second part, we’ll focus on how to ground a turntable properly.
What does the term grounding actually mean?
There are two different types of grounding in electrical engineering. When considering how to ground a record player, it is important to distinguish between these two terms.
Protective grounding
We speak of protective earthing when we connect a metal housing to the protective conductor of the mains. The aim is to discharge dangerous currents from the housing in the event of a conductor break and thus trigger a fuse. Very high demands are placed on this protective conductor connection and its design. At least in Europe this conductor has to be green / yellow. For safety reasons, we do not make any changes in this connection. But more on that later.
Functional grounding
As the name suggests, functional grounding is all about function. Since it doesn’t have to take any protective measures, you can deal with it quite relaxed. Function generally means that a technical device can work properly. In our example, for example, this is the turntable that should hum less. When we look further into how to ground a turntable, we are always dealing with functional grounding. If you are not sure whether your problem is hum, noise or distortion, I recommend this article.
The myth of the ground loop
You read again and again that you have to struggle with ground loops on turntables and that you can only reduce the hum if you solve these ground loops. Let’s take a look at a diagram that shows a very simplified representation of a turntable and its connection to an amplifier.
In the illustration we can see the amplifier on the right, which is connected to the mains via a three-pin power plug. The protective conductor connects the metallic housing for safety measures, which in turn also represents the ground potential for the signal. On the left we see the record player. The supply via a two-pin power plug only leads to the drive (regardless of whether it’s direct drive or belt drive). The cartridge generates the signal without a separate supply and leads its signal to the amplifier via an audio cable. For reasons of simplicity, I drew only one channel of the cartridge. For a stereo cartridge there are actually two coils, each of which generates a signal and passes it on to the amplifier.
As a prerequisite for a ground loop, the record player’s housing would also have to be grounded via a protective conductor connection. Since the two-pin power plug has no connection to the protective conductor, no ground loop can arise here. A ground loop is therefore out of the question as a possible culprit for hum.
Why turntables can still hum
As we have seen, there is no ground loop in this common turntable-to-amplifier connection. And yes, in theory there shouldn’t be any hum. Unfortunately, in this case the theory and reality are far apart. Through capacitive or inductive coupling, small currents still arise in the signal cable. As you can see from the illustration, the shield also serves as the return conductor of the signal. It usually consists of thin wire mesh and depending on the structure and length, the cross section and therefore the electrical resistance is relatively high. Often at least so high that the low interference currents already create significant voltages. Since these interference signals superimpose the desired signal (which has a pretty low level, as we already know from this article), they lead to more or less annoying hum in real life.
What does the ground wire do?
We can clearly see in the picture that the ground wire represents a parallel connection to the shield. Therefore it can help to reduce its resistance and thus the voltages for a given interference current. The prerequisite is of course that the ground conductor has a proper cross section.
Does it even matter how to ground a turntable?
This question is certainly legitimate and easy to answer. As described above, we implicitly ground our turntable via the shielding of the audio cables as soon as we connect them. In many cases, grounding via the shield is sufficient to suppress hum. If that’s not the case, we can simply help with an additional ground wire. Simply put, as long as you don’t have a problem with hum there is no absolute need to ground the turntable additionally. However, experience shows that we invest a lot of time and energy in optimizing the entire playback chain. Since grounding requires very little effort, it’s still advisable to think about it.
How to ground a turntable in practice
The ground wire
Of course you can buy a ground wire ready-made. Since the requirements are very manageable, there is nothing wrong with making your own cable. As described above, the cross section should be sufficiently high, usually any 0.5 to 1mm² (approx. 22 to 18 AWG) stranded wire is sufficient.
How to connect the ground wire
Before we work on the ground connection, we turn off all affected devices. If you want to be on the safe side, you can also pull the power plugs. We connect the ground wire to the turntable and the amplifier via either a threaded bolt or a screw terminal. Since all affected devices are switched off, there is no preferred order when connecting.
Further measures to reduce hum
As you can probably imagine, an additional ground wire cannot solve all problems with hum. It is undoubtedly a good measure to reduce hum, but there are other options that can help prevent hum in the first place.
Keep your system compact
It is always easier for interference to couple into the signal cable if the conductor loops are large. That’s why we lay our cables over a short distance between the individual components and place the components as close to each other as possible. A good practice is, for example, to roll up cables that are too long and secure them with cable ties.
Prevent actual ground loops
Even if the turntable itself does not form a ground loop with the amplifier, ground loops can still arise elsewhere. We should always be careful when several components are connected via three-pin power plugs. In order to reduce the risk of ground loop-related hum in such cases, it is a good idea to plug all components of the system into a common power strip.
Be careful with ground lift
With the ground lift you separate the connection from ground to the housing. While this of course makes no sense with a phono cable, there are cases in which Muggles disconnect the protective conductor connection to their device. As described above, the protective conductor has a protective function, which is why it must not be manipulated or even disconnected under any circumstances. Something different are special switches that some amplifiers offer. These allow you to perform a ground lift without putting yourself in danger.