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boputnam
05-15-2003, 07:38 PM
Surfing the most interesting "Describe your HIFI System" sub-forum, and based upon some pm's I received from it, it occurred to me many of us are encountering the same problem: 60Hz hum from connecting consumer gear to pro audio.

Consumer gear is not grounded - it persistently has only the two-pronged plug, fat on one ear (for polarity purposes). Hooking audio outs from a consumer preamp, amp, etc. to pro audio gear (EQ, amp, etc.) typically results in a nasty 60Hz hum. VERY simply speaking, that hum is caused by the consumer gear "seeing" another possible ground path, and trying to ground through the pro audio gear.

I use two solutions:

First, and best, is a DI - Direct Injection box. These have "ground lift" switches, which alleviate the problem.

Whirlwind makes a great stereo model (the Direct2) which has 1/4" unbalanced inputs/bypass and balanced Lo-Z XLR outs. The added benefit of the DI is it converts the connections to XLR, which all pro audio gear takes. Come out of the DI with a short mic cord into the pro gear. Go into the DI from your consumer gear with a lead that converts RCA's to 1/4" unbalanced. Monster Cable makes some nice (and pricy...) ones.

Checking the Whirlwind site yesterday, I found they're now offering a VERY nifty DI (the "pcDI") that accepts 3.5mm (1/8") mini TRS plug AND RCA's in TWO SEPERATE INPUT SIGNALS in one DI. So cool. The mini would connect your PC to the consumer gear, and whipe out that hum! As well, you can use the RCA's, too. Check it out: http://www.whirlwindusa.com/dirbox.html

Whirlwind by email confirmed that FirstAudioUsa (http://www.firstaudiousa.com/page1.html) is a reputable dealer (I Googled to them...). I ordered some through brian@bigtimefans.com who has an "eBayStore" that hosts competitively priced Whirlwind gear.

Second - and a nearly as good cheaper alternative - is an odd little lead that Radio Shack makes. The "Audio System Ground Loop Isolator" - Part No. 270-054 http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F002%5F001%5F019%5F008&product%5Fid=270%2D054
This uses inductive coupling for the audio signal, so the interconnected gear cannot seek ground across them. The lead is RCA-to-RCA, so may keep your wiring needs simple (for now...). There is slight signal loss, but it is not anathema to the solution.

Hope this helps.
email with questions

boputnam
05-29-2003, 07:12 PM
At the risk of being recognized for suffering a pedantic focus on ground-loops (and JBL transucer polarity... ;-P ) I had a profound improvement in S/N tonight in rewiring some components.

My studio/den kit is plagued by a ground-loop hum that I worked-around by plugging the EQ and QSC (grounded AC) into the "switchable" outlet on rear of Onkyo P304 (un-grounded consumer AC), using an AC adapter to "lift" the ground. No hum.

On a lark, I inserted a pcDI into the audio path - P304 audio outs to pcDI to dbx EQ - and routed the AC for the P304 into the ETA Power Conditioner/Distributor (grounded AC) like it should be. Now the ETA switches on the entire rack. S/N was markedly improved. Simply cleaner.

Ground-loops are insidious things that suck on frequency response and compromise component efficiency.

If you have ANY consumer two-prong AC gear wired together with pro-audio grounded three-prong AC gear, you are suffering audio signal and imaging loss.

Mr. Widget
05-29-2003, 09:38 PM
Are you confusing AC grounding with balanced cabling?

I have owned quite a few pieces of unbalanced consumer hi-fi gear that had grounded three conductor AC power cords.

I certainly agree that mixing fully balanced and pseudo-balanced pro gear with unbalanced home gear can lead to ground loops.

In my home theater I am using 5 Pro EQs, 2 Pro Active crossovers, 4 consumer stereo amplifiers, 1 pro balanced amp, and a consumer processor being fed signal from a DVD player. I have spent hours chasing ground loops. If you put your ear near a speaker you can still hear a bit of hum, but at the listening position, 16' back you don't. I would love to be rid of it still but after spending the better part of a day lifting grounds, adding grounds etc. I am willing to put up with it. I would not tolerate it in my music system though.

boputnam
05-30-2003, 07:49 AM
Nope, didn't mean to, but my discussion(s) might have confused.

The problems arises through the audio wire connecting grounded with non-grounded components. Balanced cables cannot resolve this (completely) although in some cases cutting one end of the the shield wire (#1 pin) can help.

The ungrounded unit seeks an AC current ground through the audio path to the grounded unit. The only resolution is:

1) simply lift the ground of the grounded unit (i.e., unground everything). Never my first choice.
2) use an inductive ground-loop isolator wire - where the signal is transferred across a gap that cuts the ground-loop.
3) insert a DI into the signal path which will cut the ground-loop that the ungrounded component has established. That pcDI is sweet because it has RCA connections - most DI's have only 1/4-in inputs and XLR outs.

Of these, #3 is far superior, and I'd wager if you make another run at it, you can find/remove the hum, and improve that home theater S/N.

Mr. Widget
05-30-2003, 10:22 AM
" Of these, #3 is far superior, and I'd wager if you make another run at it, you can find/remove the hum, and improve that home theater S/N."

I am not terribly fond of adding direct boxes to an already very complicated setup... I am sure that you are right that it would be a quick fix but in addition to adding another have dozen active circuits to my setup the good ones are not cheap.



So I saw on another thread that you would refoam some speakers for beer... I am only 30 miles away from you, I have a case of Heineken with your name on it if you want to chase my groundloops... I guess I've gotten a bit lazy in my old age.

boputnam
05-30-2003, 10:49 AM
Ha! ROFL OL!

Even better - I drive up to Marin every day through San Francisco, so there may be times when the distance is much less than 30-miles!

I'd love to have a look (and do some resurrounds, too...) at your set-up - it sounds much more complicated than anything I'll attempt. And, I could raid my trailer and bring along a basket of DI's and wires to run some tests. I have bunches I've accumulated from decades of pro audio (aka band) gear.

Relooking at, and trying to decipher, your signal path, two likely positions for ground-loops are:
1) the connection between the DVD / consumer processor and the "pro" balanced amp - I stuff a pcDI there for starts.
2) the 4 consumer amps - maybe isolate these grounds by running all to the same AC strip and lift that ground.

Whether really audible or not, there is S/N degradation when ground-loops develop.

boputnam
05-30-2003, 11:08 AM
Rethinking about my last #2 suggestion - I'm not sure that will do much. Those 4 consumer amps aren't able to find ground through that strip, anyway. But, I'd still give it a try - I'm constantly surprised by the solutions we find to these persnickety hums.

One other (but elegantly costly) solution: swap those 4 consumer amps for one QSC 4-channel amp - maybe the CX254 (http://www.qscaudio.com/products/amps/cx/cx4/cx4.htm). The inputs/outputs on this line (QSC's contractor series) are not as convenient as their PLX series, but this 4-channel solution seems brilliant for your application.

Cheers.

4313B
05-30-2003, 02:52 PM
Cable TV hookups can be notorious sources of ground loops.

boputnam
05-30-2003, 05:48 PM
Bingo!

And, they can be very difficult to screen out. I've had the best success with that (crummy) little Radio Shack inductive ground-loop isolator by there mere fact that its inductive. I have found this problem quite specific to the brand and age of the TV receiver and to the frequency (channel) being used. TV's are often lower quality in this area, but are getting better.

Charley Rummel
05-30-2003, 09:48 PM
Hi, all:

I've been making my own cords for many years, and a good portion of the cords in my main system are of my own construction. For anyone interested (though I don't have the contact info immediately at hand) a number of pro sound design guide books and web sights contain information on how to construct cords for various applications, ranging from the simple to the complex.

One scenario I've come across more than once is a ground loop between a power amp offering both low-Z balanced and hi-Z unbalanced inputs on a consumer pre amp hi-Z unbalanced feed. Here is a solution which is in many publications:

Using a single conductor cord for each channel with the ground shield open at the power amp end (the shield in the cable is not soldered to the connector ground at the power amp end) is an easy way to prevent a ground loop in that part of the circuit. Be sure to use shielded connectors on the cable; the pre-amp's sheilding effect is in the cable, and the power amp sheilding encompasses the connector housing at that end, which contains the small length of conductor between where the cable's shield ends and the connection to the power amp circuit is made. This approach has been a proven success many times over.

I had another problem once with a Crown open reel tape deck. I had it connected to a mixer, and no matter what I tried, there was a hum in the entire system - not just on the feed from the tape deck. After extensive troubleshooting I tried the following:

The AC interlock on the deck was a typical male grounded interlock which would accomidate a standard 3-conductor extension cord. I unplugged the cord from the back of the deck, turned it over and reconnected it leaving the ground prong exposed, and the problem was solved. This approach defied logic, since the line phase in all the power sources measured correctly.

In spite of all the science we can through at grounding on sound systems, there are still the logic defying scenarios out there......

Anyone want to share?

Regards,

Charley Rummel

Steve
05-31-2003, 01:25 PM
Aloha
We had a real wicked ground loop problem in my son's studio in our home and my sub amp (Altec 9440A) for my AV set up.
We did all the "normal" stuff, ground lifts, dedicated lines etc.
What was about 99% of the culprit was the cable supplying tv and internet to the house. When I physically disconnected the cable from the house.... the ground loop dissapeared. Found out that the cable company had not installed the grounding block and ground the cable because of the bars and lines that appeared on the tv. Interesting, lazy and potentially dangerous solution.
Ended up putting in isolation transformers on the cable into the house and at each connection.
While searching the internet for information on ground loops, there was a lot of information on the cable causing the ground loop because of diffferent ground locations etc. At least for the home problems with ground loops.
I called the cable company, they came and said I had AC current coming from the house into the cable, The electric company came and tested our house and said it was the cable companies fault etc. etc. etc.
Anyway, disconnecting the cable solved all the ground loop problems except for one we solved by running a ground cable from the computer to one of his mixers.


Steve

Steve
05-31-2003, 01:38 PM
Aloha
I forgot to mention, in my previous message, where I got the isolation transformers....in case someone wants to search or purchase any. Being isolated on a rock in the middle of the ocean, our selections are very limited. I found that Parts Express had ones that would work and do a better one than Rat Shack (as I was told ). Rat Shack was out of them here anyway and were more expensive. I wanted to address the cable issue at the source also.
Parts express has the ones I used.
Part # 180-075 for $12.80 or so each.
Operating frequency: 100 MHz to 1 GHz...
I didn't want to slow down my cable modem too much.

Hope this helps some....
No I don't own any stock in Parts Express etc....

Steve

boputnam
08-02-2003, 03:57 PM
"Cable TV hookups can be notorious sources of ground loops. and...

"Found out that the cable company had not installed the grounding block and ground the cable..." got me thinking.

I previously had the GL hum sorted-out, but lately had a whopper GL hum arrive un-invited, and have not been able to source it. I had made a number of changes to the rack and broadband, and couldn't figure the culprit.

Today I went back to the rack, and unplugged all inputs into the preamp. One-by-one I reconnected, and then disconnected each, testing only one input into the preamp at a time. Findings:

1) The tuner alone (i.e., no cable or antenna connected) had a slight GL with the preamp. Odd. Both are Onkyo, high-end Integra. Whatever. I side-stepped it with a RadioShack "Audio System Ground Loop Isolator" - Part No. 270-054 (Radio Shack Ground Loop Isolator Link (http://www.radioshack.com/product.asp?cookie%5Ftest=1&catalog%5Fname=CTLG&category%5Fname=CTLG%5F002%5F001%5F019%5F008&product%5Fid=270%2D054))

2) Then, connecting the cable coax to the tuner revealed the whopper GL. The cable is grounded outside, and I even re-ground it as a test. No improvement. Since I have no idea, nor control over what is going into that coax from the rest of the neighborhood, I peeled-back the ground/shield on the coax into the tuner, and slid-in only the center (signal) lead. No GL, and fine signal. So, I saved $12.80 over the proper Isolation Transformer (Parts Express 180-075 Link (http://www.partsexpress.com/pe/pshowdetl.cfm?&DID=7&Partnumber=180-075)).

I think I made it...

JohnH
08-10-2003, 10:10 AM
Check the white papers at:

http://www.jensen-transformers.com/

Their is a wealth of info there on ground loop issues and solutions. Some of their solutions involve buying Jensen transformers, of course, which are expensive. But they are very high quality. But at least they can guide you to a systematic approach for analyzing the problem, rather than a hit-or-miss route.

Tom Loizeaux
08-26-2003, 07:50 PM
Maybe I'm just lucky, but I run my unbalanced sources into power amps or active crossovers and use either unbalanced 1/4" phono connectors or unbalanced XLR connectors, and have no hum problems! Eventhough I have the X-mods for my Crown PS power amps, I don't use them but run these amps in unbalanced mode - and I can hear NO hum from any of this.
To me, this "balanced line" concern does not necessarily seem important in a home or studio setup.

Tom

scott fitlin
08-26-2003, 10:17 PM
Originally posted by Tom Loizeaux
Maybe I'm just lucky, but I run my unbalanced sources into power amps or active crossovers and use either unbalanced 1/4" phono connectors or unbalanced XLR connectors, and have no hum problems! Eventhough I have the X-mods for my Crown PS power amps, I don't use them but run these amps in unbalanced mode - and I can hear NO hum from any of this.
To me, this "balanced line" concern does not necessarily seem important in a home or studio setup.

Tom Same here! My system is completely Unbalanced wiring! No hum here, either!

boputnam
05-03-2004, 02:58 PM
Anybody know this...? Looks like a clever solution to a problem many of us do know...

http://www.rane.com/bb44x.html

Mr. Widget
05-03-2004, 03:11 PM
During my college years, over a couple of decades, I moved quite a bit. I found that residential suburban and semi rural areas gave me no hum problems. Today living in an urban commercial part of San Francisco I have a constant battle with hum regardless of cable length. Most of my systems have a low level of background hum even after hours of changing cables and trying different circuits.

I recently went completely balanced in one system and for the first time in years heard absolutely no hummmmmm!:cool:

boputnam
05-03-2004, 03:18 PM
...and that was using this preamp, right?

http://www.adcom.com/preamplifiers/gfp750.htm

Did sound mighty fine.

If I could only recall the active crossover you were using - sweet! ;)

Mr. Widget
05-03-2004, 03:32 PM
I have one on it's way! Paid a bit more than you did... thanks for the taste test and the tip! I hope I like it as much when my head clears.:D

Widget

PS. Yep that's the pre-amp.

JuniorJBL
05-03-2004, 10:04 PM
I have been in the car audio install buis for 15 years and an electrician for about the same. Cars are more difficult then house's but you should use the same stratagies. First try to use only one circuit ( this means one ground/neutral) try to make sure that there are no motors on that circuit i.e. fridge ( if you need lots of current try a higher amp dedicated circuit to a single location. one high current outlet. more than one outlet can create this as well) use a good power filter/conditioner ( I use monster hts 5000's pluged into the same circuit on a single outlet 30A 10awg) I have also found that puting a transformer in-line with a signal cable can reduce signal-to-noise ratio somtimes very badly.
I also make sure to stay away from ALL lights and motors and such when running power. Try not to make sharp bends in ANY cables or power lines.

If you still have hum then you should look at your equipment to see if your RCA/XLR connectors have broken the solder joint on the PC board. Also some units are just badly designed and will have noise no matter what.

I would not say I am an expert in this field but I have had a lot of experience. I hope this helps!:)
Shane

JuniorJBL
05-04-2004, 02:30 PM
Originally posted by boputnam
...and that was using this preamp, right?

http://www.adcom.com/preamplifiers/gfp750.htm

Did sound mighty fine.

If I could only recall the active crossover you were using - sweet! ;)

I use that pre as well and it is a great piece!!:bouncy: :thmbsup:

I also use the ashley 1001 for my sub 1500's
Shane:D

whgeiger
05-04-2004, 06:32 PM
BP,

Quote: “Consumer gear is not grounded - it persistently has only the two-pronged plug, fat on one ear (for polarity purposes).”

The neutral (white) wire (fat ear) is at ground potential (except for a small intervening resistance imposed by the wire run from the building entrance ground to the connected equipment). As a result, except for some improperly wired, unsafe equipment, all consumer gear is grounded when connected to ‘house power’.

The third (green wire) protective ground replicates the neutral (white wire). Both are terminated to ground bar(s) in the service panel. When the green wire is present, it is used as a (protective) chassis ground; otherwise the neutral ground becomes the ground source. As both have some resistance and share a common cable sheath or conduit with that of the black (hot) wire, induced AC hum and line noise will be present at the chassis connection. For best results, a separate isolated, low impedance (signal) ground terminated directly at the building entrance (ground) should be used. If a UPS or isolation transformer is used to provide power to the technical load, then a local grounding system may be installed that is tied to the transformer secondary and provides separate signal, chassis and protective ground circuits that are free from noise resident in utility power circuits. This type of power and grounding system is typically used in well-designed computer (server) centers, telephone switch rooms, recording studios, process control rooms and other facilities that present technical loads that require a noise-free ground.

For further information on grounds, shields and interconnecting cables, references to the following AES articles are provided:

Regards,

WHG

Title: Grounding, Shielding, and Isolation
Author: Arthur Davis
Publication: AES-J, Vol. 1, No. 1, p. 103 (1953)
Abstract: none

Title: Considerations in Grounding and Shielding Audio Devices
Author: AES-J, Vol. 43, No. 6, p. 472 (1995)
Publication: Stephen R. Macatee
Abstract: Abstract: Many audio manufacturers, consciously or unconsciously, connect balanced shields to audio signal ground. This is the source of many audio interconnection hum and buzz problems. The options available to manufacturers who follow this improper practice are …

Title: Fundamentals of Grounding, Shielding, and Interconnection
Author: Kenneth R. Fause
Publication: AES-J, Vol. 43, No. 6, p. 498 (1995)
Abstract: The ultimate performance of modern audio systems may be significantly constrained by signal contamination introduced by inappropriate grounding and interconnection practices. Fundamental principles of electromagnetism and linear circuits are reviewed.

Title: Grounding Systems and Their Implementation
Author: Charles Atkinson
Author: Philip Giddings
Publication: AES-J, Vol. 43, No. 6, p. 465 (1995)
Abstract: The isolated star ground system is the most popular implementation of technical founding for the purposes of grounding sensitive electronic equipment. This approach has been in practice for many years, and while it is not the perfect solution, it is the …

Title: Differential Technology in Recording Consoles and the Impact of Transformerless Circuitry on Grounding Technique
Author: Author: Thomas M. Hay
Publication: AES-P, No. 1723, Cnv. 67 (Aug-1980)
Abstract: Possibly the least understood problem encountered during the construction of a recording studio is the powering and grounding of the equipment. While the arts of acoustics, monitoring, and equipment design have been studied extensively, it seems that the …

Title: Differential Technology in Recording Consoles and the Impact of Transformerless Circuitry on Grounding Technique
Publication: AES-P, No. 1748, Cnv. 66 (Mar-1981)
Author: Thomas M. Hay
Abstract: Possibly the least understood problem encountered during the construction of a recording studio is the powering and grounding of the equipment. While the arts of acoustics, monitoring, and equipment, design have been studied extensively it seems that the …

Title: Technical Ground Systems Versus the Electrical Code
Author: Philip Giddings
Publication: AES-P, No. 3181, Cnv. 91 (Oct-1991)
Abstract: Electrical codes impose rigorous restrictions on the equipment ground conductors that accompany 120-VAC power circuits feeding audio and other technical equipment. Many facilities and systems are in breech of the code. The issues surrounding requirement …

Title: Considerations in Grounding and Shielding Audio Devices
Author: Stephen R. Macatee
Publication: AES-P, No. 3916, Cnv. 97 (Nov-1994)
Abstract: Over the past decade, the declining cost of professional audio equipment has facilitated its use in more home studio environments. As home studios incorporate professional, balanced equipment into their systems, the unbalanced and balanced worlds collide

Title: Grounding Systems and Their Implementation
Author: Charles Atkinson
Author: Philip Giddings
Publication: AES-P, No. 3931, Cnv. 97 (Nov-1994)
Abstract: The isolated star ground system is the most popular implementation of technical grounding for the purposes of grounding sensitive electronic equipment. This approach has been in practice for many years and while it is not a perfect solution, it is the …

Title: A Transformerless Ground Loop Isolating Preamplifier-Introducing Current Balanced Circuit Technology
Author: David Fiori, Jr.
Publication: AES-P, No. 4849, Cnv. 105 (Sep-1998)
Abstract: Current BalancedŞ technology is described with a circuit that achieves extraordinary isolation and CMRR characteristics without a transformer. The circuit is DC coupled, connects to unbalanced equipment, and provides signal gain without compromising CMRR. Like a transformer, it implements two-port audio signal isolation that is characterized by a balance in the currents flowing in and out of each port.

Title: Amplifier-Loudspeaker Interfacing
Author: R.A. Greiner
Publication: AES-J, Vol. 28, No. 5 pg. 310 (1980)
URL: http://www.aes.org/journal/search.html
Abstract: Loudspeaker cables are investigated to determine if they exhibit transmission-line characteristics. Lumped representations of cables are suggested with consideration of the effects cable parameters might have on the audio signal being transmitted.

Title: Effects of Cable, Loudspeaker, and Amplifier Interactions
Author: Fred E. Davis
Publication: AES-J, Vol. 39, No 6, pg. 461 (1991)
URL: http://www.aes.org/journal/search.html
Abstract: Loudspeaker cables are among the least understood yet mandatory components of an audio system. How cables work and interact with loudspeaker and amplifier is often based more on presumption and speculation than on fact. The literature on loudspeaker ...

JuniorJBL
05-04-2004, 06:39 PM
Originally posted by whgeiger
BP,

Quote: “Consumer gear is not grounded - it persistently has only the two-pronged plug, fat on one ear (for polarity purposes).”

The neutral (white) wire (fat ear) is at ground potential (except for a small intervening resistance imposed by the wire run from the building entrance ground to the connected equipment). As a result, except for some improperly wired, unsafe equipment, all consumer gear is grounded when connected to ‘house power’.

The third (green wire) protective ground replicates the neutral (white wire). Both are terminated to ground bar(s) in the service panel. When the green wire is present, it is used as a (protective) chassis ground; otherwise the neutral ground becomes the ground source. As both have some resistance and share a common cable sheath or conduit with that of the black (hot) wire, induced AC hum and line noise will be present at the chassis connection. For best results, a separate isolated, low impedance (signal) ground terminated directly at the building entrance (ground) should be used. If a UPS or isolation transformer is used to provide power to the technical load, then a local grounding system may be installed that is tied to the transformer secondary and provides separate signal, chassis and protective ground circuits that are free from noise resident in utility power circuits. This type of power and grounding system is typically used in well-designed computer (server) centers, telephone switch rooms, recording studios, process control rooms and other facilities that present technical loads that require a noise-free ground.



A much lengthier (and better!:cool: ) description than I was willing to write last night.:yes:

This is the case! You are well versed in this area!!:cheers: :yes:
Take heed all, You SHOULD try this at home!:thmbsup:
Shane:D

boputnam
05-05-2004, 06:46 AM
Hey, Bill...

Thanks for the tome! Extra effort, dood... :thmbsup:

In addition to your references, there frequently are sections on this topic within many of the Pro sound "Technical References" on the eponymous Thread. In-particular, the "Pro Audio Reference" by Bohn of Rane Corp. has a fairly exhaustive treatment of this, and includes some wiring / soldering charts cor creating proper cables.


induced AC hum and line noise will be present at the chassis connection. which is why it is recommended to drop the shield at either end of a balanced cable interconnect.

Too often "users" resort to dropping the AC ground, in hopes of stopping the hum. :scold: Bad behavior... All that is needed is proper cabling.

boputnam
05-05-2004, 05:48 PM
Hey, Bill (II)...

I had to await return home to dig these out, but figured these would be a worthy addendum to your post...

Muncy, N.A., 1994, Noise Susceptibility in Anaolgue and Digital Siganl Processing Systems: presented at 97th AES Convention of Audio Engineering Society in San Francisco, CA.

Muncy, N. and C. Perkins, 1994, Grounding, Shielding and Interconnections in Analogue & Digital Signal Processing Systems: Understanding the Basics: workshops presented at 97th AES Convention of Audio Engineering Society in San Francisco, CA.

boputnam
05-11-2004, 07:35 AM
Originally posted by boputnam
...it is recommended to drop the shield at either end of a balanced cable interconnect. Pretty lonely when one quotes his own posts... :rotfl:

But, this needs be remedied.

It is common practice in pro audio to drop the shield on one end of balanced interconnects. However, in contrast to the convention adopted by Rane (ibid), it make more sense to drop the INPUT end. Why? The partially disconnected shield will likey act as an RF antenna. If the shield is dropped at the OUTPUT end (Rane convention) this leaves the shield connected at the INPUT and any RF can find it's way into the INPUTs. Makes more sense to drop the shield at the INPUT - that way the RF cannot enter the INPUT, resulting in lower noise floor.

And remember, be consistent throughout your entire system interconnects.

Always seeking a quieter quiet,

Charley Rummel
05-11-2004, 07:54 PM
Hi, everyone:

More than once in my life I've seen (and heard) installations where everything appears to be by the book in cable settup, and then there's a very faint but present "strange voices" phenomenon comming out of the house mains and/or monitors.

I haven't read the other posts in the string in depth, but the fact is any unsheilded conductor of any length (maybe longer than an inch or so for practical reasons) may serve as an RF antenna. Also, by shielding it - and from the INPUT side - the conductor has no opportunity to receive RF and feed it into the input circuit; capacitance in the input sheilded conductor cancels it to ground in the input device, whereas this is ability is absent if the sheld is grounded by the output device (and therefore introduces "strange voices" into the signal). This comes from first hand practical experience. (Defective guitar chords are a good source of RF).


Regards,
Charley

Altec Fan
05-19-2004, 08:48 AM
Perhaps this has been cited before but I've found it to be a useful reference when dealing with interconnection woes:

Rane Note 110 (http://www.rane.com/note110.html)

Later . . .

John Nebel
05-19-2004, 09:26 AM
Rane's last shot is great!

* Use balanced connections whenever possible.
* Transformer isolate all unbalanced connections from balanced connections.
* Use special cable assemblies when unbalanced lines cannot be transformer isolated.
* Any unbalanced cable must be kept under ten feet (three meters) in length. Lengths longer than this will amplify all the nasty side effects of unbalanced circuitry's ground loops.
* When all else fails, digitize everything, use fiber optic cable and enter a whole new realm of problems.

John

boputnam
10-31-2004, 04:16 PM
Two things:

Rane makes a thingy called Balance Buddy: Rane Balance Buddy (http://www.rane.com/bb44x.html) which by description sounds like the perfect device. It DID NOT work for me. It apparently does not isolate the Pin1 / shield from the chassis - so when rack mounted this bad boy GL's bad.

Radial has a newbie: Radial Twin-Iso (http://www.radialeng.com/pr-radial-twin-iso.htm) that has the right idea. There isn't much on this on the Radial site - only that press release. Maybe Oldmics has some experience with these... :hmm: I'm presently employing Radial's JDI in these same positions and it works superb, but is over-engineered for this application.

SteveW
11-01-2004, 10:23 AM
I struggled with all the interconnect issues for years. When rigging up some 50 pcs. of gear things get interesting real quick. You get something optimized and it all starts over as soon as you repatch. The tool kit included Jensen tranformers, Balance buddys and the like, Tascam LA's, wood racks, lifts, aux chassis grounds, star grounds, cable tricks of all sorts - it keeps going, along with a zillion if's, ands, or but's.....
The fix: one Equitech balanced power supply. All the AC grounds and signal grounds (unbalanced too) are directly referenced the center tap of an isolation transformer that is referenced to earth ground. Neutral and hot become +60v and -60v (out of phase). Interconnect schemes are WAY easier to deal with. The 60 Hz. issues are gone along with audible noise floor.
Soapbox statement: The whole problem starts with unbalanced power, and the only way to eliminate all the resultant problems is to balance it.
You still have to deal with +4/-10 issues but that's easy. Not to sound like an Equitech rep, Furman sell these things too. A good explanation of why this works can be found at www.equitech.com
These things will cure everybodys headaches (heartaches?) except for maybe Bo's.

scott fitlin
11-01-2004, 10:48 AM
For years now, I have been looking at EquiTechs boxes! I have been told by a few who do electrical work for recording studios it works, and its ( balanced AC ) is also supposed to sound better. Not just lower noise, but also better sound.

What are your findings, besides getting rid of GL,s and lowering your noise floor?

EquiTech makes nice, big commercial boxes for people like me!

boputnam
11-01-2004, 11:20 AM
Hey, Steve...

Thanks for the referral, and testimonial. Sounds like the proper solution. I actually saw a few one of these in the racks of Charlie Daniels' Band at the Grand National Rodeo on Friday.

Got a source for them?

SteveW
11-01-2004, 12:36 PM
I bought the rack mount 5Q model. 40 amps continuous. Got it with the OFC and meter option. Also got an upgrade (not referred to on their site) that gets you a bigger transformer for more headroom and cleaner power yet. That gets you about 50 amps worth. It added another rack space to the height of std unit too. Wall mount versions are functionally the same. Didn't go that way cause I could get the juice needed in a rack version and be able to move it if desired. That was the plan anyway, but not anytime soon..... it took two guys just to lift it off the ground, and four to raise it up high enough to stick it in the wall. Some of the outlets on the back are filtered (HF) for power amp feeds too. It indeed does all the things they say it does.
If your starting with a complex and/or poorly grounded system to begin with it would do wonders. Benefits realized obviously depend on the system complexity and ones ability to address issues. Some lucky guys with playback only systems might get away with just proper attn. to grounding and be happy. I started with a system in a control room that had every worthwhile band-aid know to man applied - starting with isolated power grounds at same lengths....all that stuff. Everytime you get another toy, the first thing you gotta do is figure out which one of 14 ways of interconnect your gonna try first. Not having to do that bit anymore is better than a recording that mixes itself.

My observations: Started with all as it was. Then fed entire system with balanced power. Console and amps on '10' was same noise floor as it used to be on '5'. Started pulling bandaids one by one. Before balanced, doing this just increased noise. Balanced, it only got quieter. After optimising the grounding for balanced power, which was more fun than it should be - I could barely hear the noise floor when full up. Gear was Neotek series 2 to bridged Crown K1's to JBL 4435's (the ones Giskard is fixing - because the noise floor was so low I didn't know it was full up).
They make some audiophile stuff too, but that may be for those folks that feel the need.....

SteveW
11-01-2004, 01:43 PM
Sorry, can't help with source. Got mine through a one man Internet gear house called Calipso music over a year ago. I searched and came up empty.... like as if he's gone away. No wonder, he sold me the unit for 2800.00. The guy said his markup was something like 50 bucks. Equitech drop-shipped it to me. They (Equitech) said they would sell to me direct, but wanted about a grand more than this guy did. At the time I was just window shopping, wasn't really convinced yet - it seemed like a good idea but was leary about the value-add thing in regards to the overall scheme of things. Couldn't pass on the deal, took the chance and gee wiz... it paid off (for once). Good at twice the price!

Alex Lancaster
11-01-2004, 02:47 PM
Hi:

Apparantly it is a 6 KVA isolation, center tapped transformer, what else does it have?

SteveW
11-01-2004, 04:05 PM
Ummmm....well, it's not an Isolation tranformer if that's what you mean. It does not supply a regulated voltage either. The unit I have is fed 240 V. If regulated final supply is desired then you need to feed the unit with an 'isolation transformer' that does just that. Personally, I don't care if my voltage swings from 118 to 122 V. If your question is in regard to what it has that's different than an iso transformer - that's easy.... Iso doesn't provide balanced power. Equitechs web site is chuck full of the particulars.

boputnam
11-05-2004, 07:37 PM
As I now better understand it, these balanced power supplies must be used in complete power isolation - that is, if your system incorporates, say, audio from a TV with cable or PC with modem, you're toast. The cable and modem open to different ground source(s), and the balanced power supply cannot be used.

Hopeful I was - wiser I am... :slink:

jkc
11-06-2004, 05:40 AM
For those of us in countries with 230 Volts where lifting the ground is a definite no no mains isolating transformers seem to do the trick. I have 5 of them stashed under the house with the amps.

The transformer laminations can hum and buzz away to their hearts content and keep the noisy amp fans company.

The 9 amps stashed in the basement make quite a racket even before they start pushing electrons up to the speakers.

It is also possible to lift the amp circuit boards from ground with a resistor or diodes if you know what you are up to and the amp case can still be at ground for safety’s sake.

I recently was able to cure hum bars on my TV by making the power cable and video cables the exact same 10 meter length, works on the theory that the very small current flow is equal in all cables so no “loop”

However something must be a bit loopy when you have 10 Kw’s driving a JBL surround system.
:smthsail:

Infredible
03-11-2005, 03:34 PM
Surfing the most interesting "Describe your HIFI System" sub-forum, and based upon some pm's I received from it, it occurred to me many of us are encountering the same problem: 60Hz hum from connecting consumer gear to pro audio.

Consumer gear is not grounded - it persistently has only the two-pronged plug, fat on one ear (for polarity purposes). Hooking audio outs from a consumer preamp, amp, etc. to pro audio gear (EQ, amp, etc.) typically results in a nasty 60Hz hum. VERY simply speaking, that hum is caused by the consumer gear "seeing" another possible ground path, and trying to ground through the pro audio gear.

I use two solutions:

First, and best, is a DI - Direct Injection box. These have "ground lift" switches, which alleviate the problem.

Whirlwind makes a great stereo model (the Direct2) which has 1/4" unbalanced inputs/bypass and balanced Lo-Z XLR outs. The added benefit of the DI is it converts the connections to XLR, which all pro audio gear takes. Come out of the DI with a short mic cord into the pro gear. Go into the DI from your consumer gear with a lead that converts RCA's to 1/4" unbalanced. Monster Cable makes some nice (and pricy...) ones.

Checking the Whirlwind site yesterday, I found they're now offering a VERY nifty DI (the "pcDI") that accepts 3.5mm (1/8") mini TRS plug AND RCA's in TWO SEPERATE INPUT SIGNALS in one DI. So cool. The mini would connect your PC to the consumer gear, and whipe out that hum! As well, you can use the RCA's, too. Check it out: http://www.whirlwindusa.com/dirbox.html

Whirlwind by email confirmed that FirstAudioUsa (http://www.firstaudiousa.com/page1.html) is a reputable dealer (I Googled to them...). I ordered some through brian@bigtimefans.com who has an "eBayStore" that hosts competitively priced Whirlwind gear.

Second - and a nearly as good cheaper alternative - is an odd little lead that Radio Shack makes. The "Audio System Ground Loop Isolator" - Part No. 270-054 http://www.radioshack.com/product.asp?catalog%5Fname=CTLG&category%5Fname=CTLG%5F002%5F001%5F019%5F008&product%5Fid=270%2D054
This uses inductive coupling for the audio signal, so the interconnected gear cannot seek ground across them. The lead is RCA-to-RCA, so may keep your wiring needs simple (for now...). There is slight signal loss, but it is not anathema to the solution.

Hope this helps.
email with questions

Hi Bo,

Last sunday I got my satellite system installed and of course since then I have a nasty ground loop hum that I can't get ride off.
I was reading you recommandations in the above thread and was wondering about something. I'll describe my system connection:
Everything is consumer gear except my EQ which uses XLR in and XLR out. My receiver has only a two prong plug. I was thinking about ordering the pcDI which looks like a good solution. But here's is my question. My receiver is a big Yamaha which has a preOut/mainIn that output the preamp signal for external amplification and the mainIn to use the internal amplification from another external source. So I insert my EQ in the the preOut/mainIn loop and everything gets EQed. If I insert a pcDI in between PreOut and EQ in will it work? Since the EQ out goes back to the receiver for amplification. I guess the ground will still seek is way toward the EQ?
Hope you get the picture.

Fred.

Infredible
03-13-2005, 01:12 PM
Ok, a trip to RadioShack just solved the problem. I plugged the EQ to the amp with a ground lift prong and an isolation transformer in between the amp and EQ just cleaned the signal to a 0 background noise. Thanks Bo!:applaud:

Fred.

Don Mascali
03-14-2005, 08:52 AM
The Cable TV isolation transformers work but not for Broadband signals. I have Comcast Digital TV and a cable modem. I lost the DTV signal strength and quality with the inline isolation types at the converter. The internet connection also causes problems with my PC connected to the audio gear. My CATV tech friends tell me most of it comes from the signal amplifiers up the line having a different ground potential than at the house.

My solution was to go outside and drive a ground rod halfway between the cable and the power entrance and bond all three stakes together with 6 ga copper wire using NoOx compound on all connections. It has been the best so far, but still not perfect.

If I unplug the cable all of my stuff sounds great. I use a wide range of Pro and consumer and a lot of it is that lowly regarded Behringer stuff.:D

boputnam
03-14-2005, 11:09 AM
I plugged the EQ to the amp with a ground lift prong and an isolation transformer in between the amp and EQ Hey, Fred...

Try this without "floating" the EQ ground. What you're doing is not as bad as floating the ground on an amp, but if you can avoid it is better. The isolation transformer alone should be enough (unless there's another source of GL).

You did not have a GL until the satellite, right? How is the satellite connected to the Yamaha - RCA's (single end'ers)? If so, that is where the isolation transformer needs go - between the satellite and the amp.

boputnam
03-14-2005, 11:12 AM
My CATV tech friends tell me most of it comes from the signal amplifiers up the line having a different ground potential than at the house.

My solution was to go outside and drive a ground rod halfway between the cable and the power entrance and bond all three stakes together with 6 ga copper wire using NoOx compound on all connections. It has been the best so far, but still not perfect.

Don...

Try peeling-back the shield on the coax, preventing it from connecting to the preamp input. I only use the signal lead, and the hum "left the building". Your friends are at-least partially right - grab a volt meter and measure across the shield and signal wire - you will be astounded at what is travelling that coax...

---------------------------------

And, Don - I'm sorry for beating you up on the Behringer boxes. They are wonderfully priced, but realize that at those price points reverse engineering alone will not afford the top-quality filters that make for good, audiophile listening. That was my point. I was paying your acoustic tastes a compliment and suggesting you move-up the cost curve a bit - you will be rewarded. :yes:

Don Mascali
03-14-2005, 02:58 PM
No offense taken, Bo. I know it's not the best stuff, but, beer budget and all that. Until I win the Lottery, it will have to do. Someday...

Don M

boputnam
05-28-2007, 11:14 AM
Revisiting an old thread...

One thing not covered here is the benefit of running on the same AC circuit. Intiuition sez it shouldn't matter in one's home, but since I run into the GL problem constantly in small clubs, when the band backline is on a different AC Edison plug than I am (for load reasons), I frequently encounter GL's. Since all gear is three-wire AC, most remedies require merely a DI between the snake and the stage gear. But for really testy gear that simply will not stoptheir quiet humming no matter what is tried, I plug them into my AC circuit and hope the breaker will hold - this always remedies the problem.

At home, I've been struggling a number of years with a GL between the TV and system. I've used various types of DI's, and have reduced the symptom, but the quiet hum wouldn't completely leave. I've gotten to kinda like it, but the wifey, not. The TV and system are on two sperate AC circuits :hmm: So, I tested running an extension cord to the amp rack and "bingo", hum gone. Noise floor remarkably reduced. So, I clipped one end of the 14 gauge extension cord, and ran it through the hole in the floor along with the system cable bundle that runs under the house, ending in the amp rack domain and am finally free of this hassle. This is exactly what is done at shows, where I must run the console on the same circuit as the amp racks to avoid GL's, so I run AC from stage along side the snake.

Clearly, even though the TV and system were on the same breaker box, by being on two different circuits there were two paths to ground, and the TV didn't like it.

moldyoldy
05-28-2007, 02:39 PM
Very important stuff, Bo. :applaud:

I'd add/clarify that while having everything on the same branch circuit will solve many problems, one really only needs to connect to the same "leg" or phase of the house wiring to enjoy all the benefits you mentioned, while not creating any overloading of a single circuit.

Mr. Widget
05-28-2007, 03:17 PM
I'd add/clarify that while having everything on the same branch circuit will solve many problems, one really only needs to connect to the same "leg" or phase of the house wiring to enjoy all the benefits you mentioned, while not creating any overloading of a single circuit.That's not always the case. The reason for the hum is the resistance in the neutral to ground connection... the ground potential has to be the same for each circuit... hence "star grounding"... in any event the easiest solution is to have a single circuit with a large current capacity and to plug the entire system into it. When everything has the same ground potential there is no hum and usually no RFI.

Using different legs is an even larger issue... It is interesting how many people, electricians included, who don't understand this. I have two "audiophile" friends who have wired dedicated circuits into their listening rooms. Both of them have used separate legs for each side of the room and plug one mono block into each leg... their idea is similar to that of the distortion reduction in a push pull amp... in this case, added noise is the result.


Widget

moldyoldy
05-28-2007, 04:09 PM
That's not always the case....

Good point, and entirely true. Should be a requisite for new construction/installs. From the frugal, Q&D POV of a lowlife renter (myself) or Head Roadie though, finding the right combinations of outlets to use quickly solves the big problems.

Slight variances in potential-to-ground between 'house legs' is a common noise source that begins outside at the xfmr, beyond our control. That leaves same-circuit as the solution for centrally-located gear, and same-phase the best option for scattered, remote gear.

Hadn't bumped into the "push-pull" crowd yet. Another reason I live in the sticks...;)

boputnam
05-28-2007, 04:10 PM
The reason for the hum is the resistance in the neutral to ground connection... the ground potential has to be the same for each circuit... hence "star grounding"... Yup. It matters SO much.

With my "current" current connection, the noise floor has dropped at-least -2 dB, likely more. It also seems to have cleared-up the Video sound, as if the GL was somehow muddying the FR.

I'm certain someone here could explain what happens to the signal when a GL is present...

macaroonie
05-28-2007, 05:22 PM
Estabish a technical earth or ground. Put a copper spike into the dirt under your house and connect all the relevant grounds to that with at least 6 mm cable. take a pee on the ground where the spike is .... salts connectivity etc.
There are loads of web sites that can give you chapter and verse on this.

just4kinks
05-28-2007, 08:45 PM
I know this is an old thread, but I'd like to chime in, because I recently fought through these problems myself. I have a coax cable line coming in, 3 consumer 2-prong units, 2 pro power amps, and a 3-prong projector for the TV. I was getting a nasty hum and lines in the TV image.

I researched ground loops for a while... I was about to spend a lot of money fixing the problem, but I decided to try the easy way first. I basically just got a bunch of 14 gauge wire, crimped some connectors on, and connected all the cases together. I also grounded into the coax cable, at a nearby splitter box. It worked perfectly, my system is now dead silent and the TV picture is perfect.

There might be situations where it won't work, but it's at least worth a try. Some of those ground loop isolators can get pretty pricey.

Audiobeer
06-10-2007, 07:29 PM
Hum that I had came from my components all of which are grounded and noise-free on their own. Then I brought my cable into the mix. My ground at the house should have zero volts AC and DC however, there's usually a very small amount of voltage present in a ground. This in itself does not necessarily cause hum, but if two devices are connected to grounds where there's a difference in electrical potential between them, current will flow through one ground wire to the other, developing a voltage whose flow is audible as hum.
When you connect different components to different circuits, you frequently get hum, since each circuit's ground will probably be just a smidge off of zero volts AC and DC. If everything is connected to a component that is grounded, you can sometimes "cheat" your grounded plugs on everything else and solve your hum problem. . That could be a recipe for disater. But that cable TV connection, what a piece of %$^&! . The coaxial cable that I have in my house is grounded via its shield and that's grounded at the cable provider's Box. Different circuits in the same house can have ground planes that differ in voltage. Do you that something grounded Down the street a bit from my house has the same potential? Not likely.
You can by a grounf isolater and in fact you can make your own. I copied a lot of the above theory from the internet to explain my problem.