Post by solderdude on Oct 19, 2013 7:43:38 GMT
Archimago bought himself a new receiver/cinema amp.
He did some basic MMAA measurements of the pre-amp section alone.
The numbers ain't that bad but it also has a power output stage which isn't going to improve things much.
As these things are designed to be connected to a shitload of equipment (DVD players, PC's, monitors, network players and what not) you are increasing the chance of groundloops which are caused by 'garbage' from switched mode power supplies (PC's, monitors, TV's, DVD players e.t.c. ALL have them)
When an amplifier has multiple types of inputs and LOTs of them it will be nigh-on impossible to design an adequate ground layout which would prevent those common mode noises to enter the audiopath.
I try to explain a simple groundloop HERE (you have to scroll down to part 6).
Imagine multiple common mode sources and what it can do to the signal.
IF you are bothered by groundloops depends on a lot of factors at the location the equipment is and depends largely on the used equipment itself too and HOW it is connected.
HERE you can see Archimago's results and further down in the article you can see what happens to his signal when a TV is connected via an HDMI cable (just connected is enough as the currents come through the ground/shield of the cable).
Of course he is doing RMAA measurements using a PC and external DAC. This 'common mode source' (the computer/DAC combo) + the receiver itself is already having a groundloop problem judging from the amount of hum (60Hz + all of its harmonics) and the TV adds a very typical SMPS noise spectrum.
The reason I link to this is because these are plots that manufacturers and testbench setups will NEVER show, and thus you won't see what happens in real life.
On a testbench care is taken not to have groundloops in order to only test the testsubject. Manufacturers are only giving you the impressive numbers (in general) and leave the bad ones out. They only measure at 1kHz for instance or give S/N ratios references to a max output voltage which is 'correct' but in real life that means the audio would be deafening and who listens to those levels ?
Anyway... these measurements show that groundloops (especially in home-cinema setups) are a very real thread and it doesn't hurt to break those ground loops when you can.
Common mode problems are very easy to get but can be difficult to avoid or remove.
He did some basic MMAA measurements of the pre-amp section alone.
The numbers ain't that bad but it also has a power output stage which isn't going to improve things much.
As these things are designed to be connected to a shitload of equipment (DVD players, PC's, monitors, network players and what not) you are increasing the chance of groundloops which are caused by 'garbage' from switched mode power supplies (PC's, monitors, TV's, DVD players e.t.c. ALL have them)
When an amplifier has multiple types of inputs and LOTs of them it will be nigh-on impossible to design an adequate ground layout which would prevent those common mode noises to enter the audiopath.
I try to explain a simple groundloop HERE (you have to scroll down to part 6).
Imagine multiple common mode sources and what it can do to the signal.
IF you are bothered by groundloops depends on a lot of factors at the location the equipment is and depends largely on the used equipment itself too and HOW it is connected.
HERE you can see Archimago's results and further down in the article you can see what happens to his signal when a TV is connected via an HDMI cable (just connected is enough as the currents come through the ground/shield of the cable).
Of course he is doing RMAA measurements using a PC and external DAC. This 'common mode source' (the computer/DAC combo) + the receiver itself is already having a groundloop problem judging from the amount of hum (60Hz + all of its harmonics) and the TV adds a very typical SMPS noise spectrum.
The reason I link to this is because these are plots that manufacturers and testbench setups will NEVER show, and thus you won't see what happens in real life.
On a testbench care is taken not to have groundloops in order to only test the testsubject. Manufacturers are only giving you the impressive numbers (in general) and leave the bad ones out. They only measure at 1kHz for instance or give S/N ratios references to a max output voltage which is 'correct' but in real life that means the audio would be deafening and who listens to those levels ?
Anyway... these measurements show that groundloops (especially in home-cinema setups) are a very real thread and it doesn't hurt to break those ground loops when you can.
Common mode problems are very easy to get but can be difficult to avoid or remove.