Hum problem...

[W1GUH]

Here goes...

Got a problem with hum between certain audio devices. Some are OK, some aren't. My main power amp has the good ol', stander, 3 prong power cord..

Some devices that are powered with a wall wart cause a hum when plugged in, some don't.

Specifically..

CD player with a wall wart...OK
XM radio with a wall wart...OK
Phono preamp with a wall wart. OK

All three of those are clean as a whistle. No problema!

Laptop computer. HUM
New virtual studio with a wall wart HUM <--- that one hurts. Ouch!!!

Might be a clue there...the VS is basically a disguised computer?

Old virtual studio with the good ol' standard three wire plug was just fine.

I would like to ask for replies only from those who have experienced this. I've tried all the usual "ground loop" BS -- turning around the plug, and breaking the shield connection at one end. No improvement.

Anyone ever able to actually fix this with your own stuff? I'm thinking that if I can some how put a ground wire between the amp and the devices that might do it. Or it could blow something up. Stumped.

Further experience. I had a friend with a powered sub-woofer. It had a hum. I found out by chance that if I put my finger between the shield and the chassis, that worked. Not really being in a position to sit there 24/7 with my finger in the right place (huh-huh), I fashioned a jumper to do the job. Thinkin' I might try that here.

[W1GUH]

Closer...it's only the inputs to the VS that cause the problem...with them not connected all's cool. There's another route for that....trying it now.

[W1GUH]

Closer...it's only the inputs to the VS that cause the problem...with them not connected all's cool. There's another route for that....trying it now.

[W1GUH]

Operator error. Had inputs and outputs swapped. Using a tape swithch with ambiguouts marking! Move along, nothing to see here.

Slinking away in utter embarassment. Must be my long hair. Or the good, legal drugs I'm under the influence of!

Cheers!

[K7SGJ]

Glad it's working. Nothing is more discouraging than not being able to get new gear to work right, for any reason.

[W1GUH]

For sure. DUH!!!!!

The f'ing is hard enough to figure out without doing dumb things! Definitely NOT for anyone with a disdain for memories. They're bad enough when the terminology is familiar...but add new jargon & it's a very steep learning curve. But all seems well; progressing through learning OK. At least I'm not starting from zero -- been through the same process before!

Thanks for the encouraging words!

[WØTKX]

As an old school audiophool, fighting hum and noise floor issues have been quite amusing over the years.

Computer based studio equipment can really be a PITA... Can you say "Pin 1"?

http://www.rane.com/note151.html


The "Pin 1" Problem Many audio manufacturers, consciously or unconsciously, connect balanced shields to audio signal ground; pin 1 for 3-pin (XLR-type) connectors, the sleeve on 1/4" (6.35mm) jacks. Any currents induced into the shield modulate the ground where the shield is terminated. This also modulates the signal referenced to that ground. Normally great pains are taken by circuit designers to ensure "clean and quiet" audio signal grounds. It is surprising that the practice of draining noisy shield currents to audio signal ground is so widespread. Amazingly enough, acceptable performance in some systems is achievable, further providing confidence for the manufacturer to continue this improper practice -- unfortunately for the unwitting user. The hum and buzz problems inherent in balanced systems with signal-grounded shields has given balanced equipment a bad reputation. This has created great confusion and apprehension among users, system designers as well as equipment designers.
Similar to the "pin 2 is hot" issue, manufacturers have created the need for users to solve this design inconsistency. Until manufacturers provide a proper form of interconnection uniformity, users will have to continue their struggle for hum-free systems, incorporating previously unthinkable practices.
The Absolutely Best Right Way to Do It Clearly, the available literature prescribes balanced interconnection as the absolute best way to interconnect audio equipment. The use of entirely balanced interconnection with both ends of the shield connected to chassis ground at the point of entry provides the best available performance.
The reasons for this are clear and have been well-documented for over 60 years. Using this scheme, with high-quality I/O stages, guarantees hum-free results. This scheme differs from current practices in that most manufacturers connect balanced shields to signal ground, and most users alter their system wiring so only one end of the shield is connected. Due to these varied manufacturer and user design structures, an all-encompassing recommendation with proper coverage of both balanced and unbalanced interconnection is essential.
Conceptually, it is easiest to think of shields as an extension of the interconnected units' boxes (see Figure 1). Usually, metallic boxes are used to surround audio electronics. This metal "shell" functions as a shield, keeping electromagnetic fields in and out of the enclosure. For safety reasons, the enclosures in professional installations are required by law to connect to the system's earth ground (which in many systems is not the planet Earth -- an airplane is a good example).

[W1GUH]

Looks like good info. Will digest it when I'm not so swamped with hot projects. The infinite toys I've added to the menagerie here have an incessant, urgent call to action that I just can't resist! And since this one turned out to be nothing but a huge 'GUH DUH, it's background that I need to know...but too busy right now to digest it.

Thanks for the info!

Paul

[WØTKX]

I used to drive people nuts by fixing ground loops really fast.

Too many people thing "DC" when grounding. Hum ain't "DC". :lol:

[KC2UGV]

As an old school audiophool, fighting hum and noise floor issues have been quite amusing over the years.

Computer based studio equipment can really be a PITA... Can you say "Pin 1"?

http://www.rane.com/note151.html

Main reason I make all my own cables.

[W1GUH]

Main reason I make all my own cables.

Damn good move. And there's another reason, too. I've had numerous failures in coax jumpers I've gotten at hamfests. Now I only get them from people I know make good ones. And they cost no more than the others. And I've bought a bunch of connectors to fix the other ones.

Man! A relatively new coax jumper that opens up is be a BITCH to find when you're not expecting it!

[K7SGJ]

A good cable tester is your friend. I don't know what all cables you use but there are lots of testers, price and features, to choose from. You could even build a custom one to fit YOUR needs. They are perfect for testing continuity, shorts, polarity, and so forth. Great for doing a shake test for those intermittent little fu*kers. (that's a technical term)

Example here: http://www.bhphotovideo.com/c/product/304022-REG/Whirlwind_TESTER_Audio_Cable_Tester.html


This is the one I use. With adapters, you can test virtually any cable.

http://www.paladin-tools.com/view_tool.php?id=41

[W1GUH]

Thanks for the tip.

[n0iu]

Here goes...

Got a problem with hum between certain audio devices.
You know why it hums?








It doesn't know the words!

[W1GUH]

Absolutely nothing to say but...

OMG! Groan! ARGH!

And thanks for the chuckle. :rofl: