Editor’s Note: In the development of his highly respected digital audio components, Scott Berry of Computer Audio Design discovered the impact of High Frequency ground noise. Later, he found this signal ground noise also impacted on the performance of analogue components in an audio system. The result was the Ground Control range of high frequency noise reduction devices, including the mighty GC-R reference model tested in issue 185.
We spoke to Scott about ground noise, why it’s a problem, how the signal ground differs from the mains earth, and how this issue can best be resolved. While, of course, Scott’s focus is on his own GC and GC-R devices, it’s clear the resolution of high-frequency noise through the signal ground is becoming more of a universal concern among audiophiles and a plethora of products from different brands address the same concerns.
The CAD Ground Controls are aimed at reducing High Frequency “noise” on ground in an audio system. Can you start by explaining what ‘ground’ is?
‘Ground’ is the general name electrical engineers give to the reference against which a voltage is measured. In audio components, we call it ‘signal ground.’ Signal ground is the negative side of RCA, XLR, BNC etc. connectors on the back of audio components.
Signal ground is often confused with Mains Earth – on the mains power connection – that ‘third pin’ on a 13A UK or Type B USA plug.
In some audio component designs, signal ground and earth may be directly connected – but in most, they are not. For example, in many streamers and servers, and certainly in non-audio quality computer devices, the signal ground is typically directly connected to Mains Earth. However, in most higher-end audio components, there is typically either no connection, or a simple filter connection between Mains Earth and signal ground.
In a classic linear powered audio component design, mains power comes into the device and the power line and neutral go to a transformer, whereas Earth is typically directly connected to the chassis (case). The signal ground comes from the DC circuitry after the transformer – at which point, it has nothing to do with Mains Earth.
What is the purpose of Mains Earth in an audio product?
Mains Earth is there primarily for safety. Any electrical device that plugs into Mains power, and which has a conductive case (metal), must by law have that case connected to Mains Earth. And, the connection must be what is called ‘low impedance,’ meaning, easy for current to flow through.
This is to mitigate the risk of electrical shock if the device develops a fault. For example, if an internal wire becomes disconnected during shipping, and by chance touches the metal case, then if you plug that device in at the wall, the metal case will be live – if you touch it, mains current is going to try to go through you! By connecting a low impedance route to earth from the case, current will go through that route rather than going through you.
Mains Earth is also used by electrical designers to reduce high frequency noise within components. Attaching a ‘noisy’ part of circuitry directly to Mains Earth can reduce the noise within the product.
Computers are a good example of this. Computers produce a significant level of high frequency noise and the common method to reduce this noise (so that they will pass legal requirements) is to attach the entire signal ground of the device directly to Mains Earth. There are many other electronic components throughout our homes that are designed in a similar manner. The number of these devices has increased dramatically in the last fifteen years.
Unhelpfully, because of this, Mains Earth in many homes now contains a substantial amount of high frequency noise. This is a real problem for higher quality audio components! Attaching any part of an audio component to Mains Earth can actually increase the noise within the audio component instead of reducing it.
Do you think this is why Audiophiles talk a lot about the ‘noise’ on Mains Earth, and hammer copper rods into their gardens…..?
Yes, I think it is. For sure, as well as the high frequency noise that is created by the audio components themselves, there is also noise also coming “in from the outside world” via the Mains Power and Mains Earth. And in my opinion this high frequency noise is getting worse – there is more of it in this internet age.
I think we all experience our stereo sounding its best late at night, after everyone else has gone to bed. Of course, this may have something to do with the glass of wine or beer in our hands at the time! But it is mostly a result of the cleaner power on the grid late at night – your neighbours, all those TVs, computers, lighting systems, etc. – are being switched off. And many homes share the Mains Earth with neighbours. So late night listening really improves most systems, due to less high frequency noise on Mains Power and Earth.
And do you think that noise on Mains Earth is more significant than the noise on signal ground?
It all depends on the audio system and on the Mains Power environment of your home. Highly digital audio systems will produce a lot of their ‘own’ noise, all by themselves.
If your home contains a lot of digital equipment – I refer here to home automation networks, home offices, Wi-Fi etc, this will pollute your domestic electrical supply with high frequency noise. If you live in a densely populated area, then the Mains Earth will likely contain a substantial amount of high frequency noise from your neighbours. Earth can be shared across multiple dwellings.
The big issue with Mains Earth is that it must be directly connected to all metal casework, including the chassis of your cherished audio system: which means the chassis now contains this noise.
Since this connection must be low impedance to be compliant with safety legislation, it is very difficult to filter it. Power conditioners and regenerators are aimed at filtering power line and neutral, but they typically do not filter Earth.
Audiophiles are starting to talk a lot about ‘grounding devices.’ Can you describe what the CAD Ground Controls actually do?
The CAD Ground Controls do one thing: they reduce high frequency noise.
‘Noise’ in the context of audio components generally means any unwanted electrical energy. It can be in any frequency spectrum, and it can be found anywhere – on signal, on ground, on power, and on Earth.
First off, I think it is widely accepted that electrical noise in the audible frequency range (20Hz -> 20kHz) is a bad thing – it is audible and needs to be properly managed. All audio designers, myself included, invest a great deal of effort to minimise unwanted noise on signal and power.
In addition, I have focused on reducing noise on signal ground and at much higher frequencies. My research suggested that relatively few audio designs devote attention to noise on signal ground, perhaps because it’s assumed that signal ground does not have noise or because it’s believed not to be such an issue. But to me, Signal Ground – the reference to which the signal is being measured – is half the signal and it is crucial for it to be clean.
I also focus on noise in a much higher and broader frequency range, well above the audible range, up into the GHz range.
Why do you think this high frequency energy is important in audio components? Surely if it is above the audible spectrum, you can’t hear it….?
All electronic equipment has legal limits for the amount of high frequency noise it can produce. I am sure you are familiar with those signs in hospitals asking us not to use our phones near sensitive scanning equipment, and we switch our phones off for “take-off and landing”… these are just examples where high frequency energy affects electronics.
My experience is that this very high frequency, inaudible ‘noise’ also affects the sound quality of audio components.
Digital audio components themselves – CD players, servers, streamers, DACs – contain oscillators and digital circuitry that operate at high frequencies. This creates high frequency energy which can circulate throughout the entire audio system. And as I say, engineers take this into account with filters on signal and power circuitry, but typically little or nothing is done to clean up the noise on signal ground. But all the transistors, op-amps, integrated circuits etc., are all directly connected to signal ground, and these devices will perform differently as a result of this high frequency noise, and this in turn will impact the sound quality of the component.
What gave you the idea for the CAD Ground Controls?
The idea of an external device to reduce noise still further – the Ground Control – evolved from my work designing digital audio components. While my 1543 DAC and CAT (CAD Audio Transport) designs are as low noise as I can make them, these are ‘noisy’ digital devices. Faced with the issues I have outlined here, I realised that I had reached the limits of filtering on the signals and power supplies, and I really needed to focus on signal ground. I found that most filtering techniques, when used on signal ground, have secondary, detrimental effects on the music, particularly on rhythm and timing. So, I looked for a solution that was low impedance and somehow in parallel.
The GC1 was developed to address noise on signal ground and is flexible enough to be applied to just one or two components. The larger GC3, and the much larger GC-R are intended to reduce noise on Mains Earth. The extra mass helps – Earth is, after all, a big place.
The key to all of this, is that there is high frequency noise on the signal ground of audio components, and also on Mains Earth. The idea of ‘improving grounding’ is to reduce this noise.
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