Computer Audio Asylum

Posted by hfavandepas (A) on January 26, 2017 at 10:32:22

In Reply to: RE: Common Mode Noise posted by Mercman on January 24, 2017 at 10:56:04

Hi Mercman,

Thankx for posting this. It highlights a 'hidden' problem that I also had in my system and probably also many inmates may have in their sound systems without noticing. As for me, I only discovered this hidden problem when I made unplanned changes in power connections because I had too dismantle and re-install my sound system when my living-room needed some fresh painting.

In the end solving noise problems and solving related ground loop problems really paid off in my system!! So I definitely want too encourage other inmates too have a close look at their systems. May be similar sound quality improvements can be made in their systems.

On the other hand, finding and eliminating ground loops and suppressing associated noise problems was very time consuming and a lot of work. I spend much time on reading tutorials and papers, much on experimenting, buying parts, installing them, etc, etc.

So I decided Mercman's post is a good reason for writing down this very, very loooong post about what I tried in my system. Hopefully it will give other inmates an impression if 'hunting' for ground loops and associated noise problems in their system, might be worth the trouble.

* But first some considerations when I red your post.
While your friends solution focuses on suppressing these noise currents through filtering, you also focus on the pathway these noise currents flow. You point at a video https://www.youtube.com/watch?v=sMmdDLFP4So where Juergen Reis (MBL) discusses the 'back door leakage currents' that are found in complete systems which can have a negative impact on the sound of our systems.
Don't know why Juergen Reis (MBL) calles them 'back door leakage currents' but these 'back door leakage currents' are also better known as: ground loops. Don't know why Juergen chooses too call them: 'back door leakage currents'. (Probably just too make him look smarter and make the problem look more mysterious)

While adding filters too suppress noise is one solution, I was very happy that you also considered pointing at the pathway's these noise currents may use. Changing or eliminating these pathway's may be much more effective than putting a filter on it.
And what to think of: not creating those pathway's in the first place? (through prober system design and/or proper balanced interconnection)

However avoiding or eliminating those pathway's is easier said than done. Especially since many inmates nowadays will have sound systems that are (inter-)connected too:
1. a computer, TV-set, cable-box, streaming device, wired internet, etc, etc.
These consumer grade devices mostly use noisy PSU's and use (potentially problematic!) unbalanced connections.
2. coax-cables from cable-companies or antenna-systems that may introduce an extra (potentially problematic) pathway too the electrical safety ground.
3. consumer equipment that has a build-inn design defect also know as the 'Pin 1 problem'.
Combining all 3 points together make an ideal situation for creating (unintentionally) all kinds of ground loops causing minor (or bigger) sound quality problems.

Like me, most inmates probably will assume that a sound system has no noise problems caused by ground loops, as long there is no 50/60 Hz hum coming from the speakers. But unfortunately ground loops ('back door leakage currents') come in all sorts and can have all kind of (U)HF noise frequencies having negative impact on the digital parts of the sound system.

In his tutorial 'A Ham's Guide to RFI, Ferrites, Baluns, and Audio Interfacing', Jim Brown (vice chair of the AES Standards Committee working Group on Grounding and EMC Practices) makes a bold claim. He suggests that the most common way hum, buzz, and noise enters the circuit board of our music equipment are caused by design defects. Somehow, somewhere the cable shield has a (unwanted) connection too the circuit board ground. On page 5 Jim Brown writes: "Nearly all consumer equipment, including even the most expensive "high futility" gear, is built with this problem. Virtually all computer sound cards have these problems. So do most RS-232 interfaces and nearly all HAM equipment".
Although focused on HAM equipment Jim Brown's tutorial was a must read for me. It helped me a lot. It can be downloaded from: http://audiosystemsgroup.com/RFI-Ham.pdf

Just like you discovered, I also discovered that Jim Brown was right. The sound coming from my system could be improved by a significant amount when attention is paid not to create unwanted ground loops in the first place and/or put filtering on those loops if they can't be avoided.


As already suggested by Soundcheck, cleaning up the cable mess, is a good starting point. But that did not do anything in my system. My system setup is fairly simple and there are not a whole lot of cables.
System setup:
Coax cable -> cable box -> HDMI -> HD TV -> HDMI -> HTPC -> Cat 6 cable -> Merging Hapi -> XLR AES/EBU -> PMC TwoTwo.8
- the HTPC has two network interfaces. One NIC is connected to the Merging Hapi. One NIC connects to a wired LAN cat 5e cable for internet connection.
- With help of a Neutrik impedance transformer the cable box RCA S/Pdif output is connected to the AES/EBU XLR input on the Merging Hapi.
(I use this connection when watching movies on TV. I like too hear the movie sound through my sound system)
- At the cat5e cable which connects too the internet I use a Baaske internet isolators.

Although my sound system is quite simple, I only discovered by accident that my system could sound significantly better. Here's how. For many years I powered my HTPC from a separate power socket across the room. I feared the noise that the ATX computer PSU might throw back into the power line thus spoiling the power input of the amplifiers in my Klein & Hummel O300 active speakers. Only by coincident, I found out that my system definitely sounded much better when the noisy ATX computer PSU was plugged into the same power strip that also powers the active speakers and the Merging Hapi.
Looking back, I know now that I made a huge beginner mistake. Like most computers, also my HTPC has a 'Pin 1 problem' by design. With help of this design defect I had created a massive ground loop that added more noise than the ATX PSU would do by itself.
So now the ATX computer PSU, the active speakers and the Merging Hapi unit are all powered from the same power strip. However, I've added an Epcos power line filter into the ATX PSU power cable. The Epcos power line filter suppresses the noise that the ATX PSU throw's back into the power strip, which again improved the sound by a significant amount !

Because of this success I got heavily infected with 'ground-loop-hunting fever'.
I began reading many internet papers/tutorials on ground loops. Beside Jim Brown's tutorial, I would also recommend reading:
'Understanding, finding & eliminating ground loops in audio & video systems' written by Bill Whitlock, (http://web.mit.edu/jhawk/tmp/p/EST016_Ground_Loops_handout.pdf)
Although it's more of an advertorial (and not exactly a white paper) it still provides in-depth high quality information

After reading Bill Whitlock's paper, I now looked suspiciously at the coax-cable connected too my TV and cable-box. This coax-cable is also connected too the earth's safety ground in my breaker panel closet, possibly creating another ground loop (with help of the unbalanced connections on the TV and the cable box). But unplugging the coax-cable did not improve sound quality.
Also completely disconnecting and removing the TV and cable-box from my sound system (power + interconnects) and running my computer 'headless' did not improve sound quality.

Because Jim Brown also looks at cleaning 'Ethernet trash' in his tutorial, I also tried cleaning 'Ethernet trash' in my home. First I installed a Baaske LAN isolater, but that did not have any impact on sound quality (waste of money). So like Jim Brown suggests I tried too suppress the noise coming from the PSU's that power my LAN network equipment.
In my breaker panel closet I have five cheap switch-mode wall wart style PSU's that power: a cable-internet-router, a managed Netgear ProSafe switch, a WiFi-acces point, a Philips Hue bridge and a NAS.
I decided too install a whole new 6 outlet (earthed) power strip. Onto the strip's power cord (AC side) I installed an Epcos power line filter too suppress noise that those 5 cheap wall wart style PSU's will throw back into the 230 V AC power line.
On the DC side I installed the same common mode choke coils like your friend also installed.
Unfortunately, the sound quality only improved marginally. I don't think this slight improvement was worth the trouble.
But I just red Ryelands tip on removing connections on/to pin 4&5 and 7&8. Ryelands always has tips that work very well. 50% less wires that can create a ground loops and/or provide a path for noise, And also 50% les antenna's to pick up noise. So I'm going to try Ryelands tip ASAP


So what did I learn from this 'ground loop hunting'?
Computers do not only cause problems because they come with a noisy (ATX) PSU. Computers also come with a build-inn design defect: the so called 'Pin 1 problem'.
I don't know which one of the two is more worse. But when combined together (Pin 1 problem + the noisy PSU) it can have serious negative impact on sound quality.
Especially in systems that use unbalanced connections. Ground loops introduced by using unbalanced connections will create noise and also allow noise too travel almost system wide.

Happy 'ground loop' hunting.

I'm curious how other inmates eliminated ground loops and suppress associated noise.
So please do report your findings here on the audioasylum.

Mark

Mac (with Audirvana + ARC2 Acoustic Room Correction plugin) -> Cat 6 cable -> Merging Hapi -> AES/EBU XLR Vovox SD -> PMC TwoTwo.8

• Understanding, finding & eliminating ground loops in audio &   (Open in New Window)