Question Calling all Cambridge Audio AXR85 owners

[walterandbruges]

I have a simple question, but a long ramble: Does your AXR85 amp have a slight hum? I presume it's a power hum in the casing, because it's not coming through the speakers. You do have to get your ear really close up to it, on the left-hand side, to hear it. I have other modern amps that don't hum this loud. It's not the most high-end system, so I wonder if it is just how it's meant to be and I'm being pedantic. My Arcam has a very faint power hum, but that is putting my ear against the casing. I have an Onkyo mini-system on the bedside table next to my pillow and that one is quiet, but if the CA AXR85 was in the same position it would be annoyingly noisy. Fortunately, my listening position is usually far enough away, but I wonder if there is a quality issue with my particular amp. With quiet music, if you were sitting next to the amp, you could hear a subtle hum and that seems wrong to me.

 

[walterandbruges]

I have a simple question, but a long ramble: Does your AXR85 amp have a slight hum? I presume it's a power hum in the casing, because it's not coming through the speakers. You do have to get your ear really close up to it, on the left-hand side, to hear it. I have other modern amps that don't hum this loud. It's not the most high-end system, so I wonder if it is just how it's meant to be and I'm being pedantic. My Arcam has a very faint power hum, but that is putting my ear against the casing. I have an Onkyo mini-system on the bedside table next to my pillow and that one is quiet, but if the CA AXR85 was in the same position it would be annoyingly noisy. Fortunately, my listening position is usually far enough away, but I wonder if there is a quality issue with my particular amp. With quiet music, if you were sitting next to the amp, you could hear a subtle hum and that seems wrong to me.

I'll answer my own question with a potential set of solutions from Cambridge Audio:

When two or more devices are connected to a common ground through different paths, ground path noise, or a ground loop can occur. A potential difference between these two grounds can cause unwanted noise voltage in the circuit paths. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum/buzz.

This can be eliminated in one of two ways:

1. Remove one of the ground paths to convert the system to a single point ground.
2. Isolate one of the ground paths with an isolation transformer, common mode choke, optical coupler, balanced circuitry, or frequency selective grounding.

Please Note: While this article addresses a very common ground loop problem, there are plenty of ways in which system buzz and hum can enter into a setup.

Common Problem 1: Check to see if you have a heavy power supply or an outlet in the wall that is worn out and will not grip. If the hot/neutral/ground prongs on the plug and the ground are making intermittent or light contact with the tang on the inside of the outlet, it can cause a hum through the system. The best solution for this is to replace the outlet with an industrial version. Industrial outlets have better gripping and will hold power cables more securely.

Common Problem 2: Check the polarity of the outlet - it may be wired backwards. This is one of the first things you may want to check if unplugging the cable box does not remove the hum (and in some cases, the reverse polarity may still be the culprit.)

Common Problem 3: Light dimmers, fluorescent lamps, and other appliances that share the same circuit or common ground with your equipment can cause hums.

 

[Gray]

I'll answer my own question with a potential set of solutions from Cambridge Audio:

When two or more devices are connected to a common ground through different paths, ground path noise, or a ground loop can occur. A potential difference between these two grounds can cause unwanted noise voltage in the circuit paths. Currents flow through these multiple paths and develop voltages which can cause damage, noise or 50Hz/60Hz hum/buzz.

This can be eliminated in one of two ways:

1. Remove one of the ground paths to convert the system to a single point ground.
2. Isolate one of the ground paths with an isolation transformer, common mode choke, optical coupler, balanced circuitry, or frequency selective grounding.

Please Note: While this article addresses a very common ground loop problem, there are plenty of ways in which system buzz and hum can enter into a setup.

Common Problem 1: Check to see if you have a heavy power supply or an outlet in the wall that is worn out and will not grip. If the hot/neutral/ground prongs on the plug and the ground are making intermittent or light contact with the tang on the inside of the outlet, it can cause a hum through the system. The best solution for this is to replace the outlet with an industrial version. Industrial outlets have better gripping and will hold power cables more securely.

Common Problem 2: Check the polarity of the outlet - it may be wired backwards. This is one of the first things you may want to check if unplugging the cable box does not remove the hum (and in some cases, the reverse polarity may still be the culprit.)

Common Problem 3: Light dimmers, fluorescent lamps, and other appliances that share the same circuit or common ground with your equipment can cause hums.

Where would you start with all those variables eh?
Easy:
You need to take them out of the equation.
Take your amp to someone else's house, in a different part of town if possible.
With nothing else connected, plug it in and listen close to the casing as you did before.
Can you hear the same hum?
The answer to that that question determines your next move.

 

[Deleted member 116933]

You're forgetting one thing you haven't mentioned, some/all transformers hum, Naim are notorious for it my nap 200dr I could hear across the room when quiet. Same with my dac V1 and uniti 2 before that. The more powerful they are the louder they are.

My sugden has a hum with my ear up against it (don't recommend its very hot)

Speakers buzz and fuzz with your ear 2cm away from them,

If you can't hear from your listening position don't worry about it. You will know if you have a ground loop its very obvious this doesn't sound like that to me.

 

[Gray]

some/all transformers hum

Indeed they can.
Seems like the one possibility CA omitted in their detailed list strange

 

[walterandbruges]

I appreciate the feedback and advice. And I do suspect I'm being overly precious here - looking for a problem that isn't really there. My vintage Sony hums like crazy, which is a known issue, and I can live with it. I just figured newer kit might be super-insulated or resolved in this regard. So good to know the high-end stuff has power hums to them. I was just curious because, although it was bought as brand new, the box had been opened and re-tapped, which could have just been to replace the power cord with a local version. I didn't want to feel I'd gotten a returned item or demo version with any kind of problem. There are those Japanese audiophiles who condition their power from the street. I do not want to go down that path! I think it would have been nice if CA noted their amps can have a small audible hum within a 30cm radius... don't sweat it.

 

[Deleted member 116933]

I appreciate the feedback and advice. And I do suspect I'm being overly precious here - looking for a problem that isn't really there. My vintage Sony hums like crazy, which is a known issue, and I can live with it. I just figured newer kit might be super-insulated or resolved in this regard. So good to know the high-end stuff has power hums to them. I was just curious because, although it was bought as brand new, the box had been opened and re-tapped, which could have just been to replace the power cord with a local version. I didn't want to feel I'd gotten a returned item or demo version with any kind of problem. There are those Japanese audiophiles who condition their power from the street. I do not want to go down that path! I think it would have been nice if CA noted their amps can have a small audible hum within a 30cm radius... don't sweat it.

30cm! I think you're being a little "precious" Once you've noticed it will be hard to forget though. But It will pass as you use it.

I have yet to come across an Amp that doesn't hum to some extent.

But if you have a real concern contact CA and see if its normal behaviour.

 

[Gray]

If you're bothered, do what I suggested, if not forget about it.

Just for the record, I've never noticed humming from 30 cm on amps from
Alba, Nad, Harman Kardon, Marantz and Cyrus.

If you put your ear on / within the casing though, you're likely to hear humming on any amp.

 

[gasolin]

It can be from the fan

 

[matthewpianist]

I briefly owned an AX-A35. It was, for the money, a capable and enjoyable amplifier, but it was marred by a louder than acceptable hum from the transformer, audible from my normal listening position. It went back.