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Thread: Consumer and Pro-audio electronics: Connectivity

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    Consumer and Pro-audio electronics: Connectivity

    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.as...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
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    Last edited by boputnam; 05-15-2003 at 07:45 PM.
    bo

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    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.
    bo

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    Administrator Mr. Widget's Avatar
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    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.

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    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.
    bo

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    Administrator Mr. Widget's Avatar
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    " 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.

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    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.
    bo

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    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.
    bo

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    Re: Consumer and Pro-audio electronics: Connectivity

    Cable TV hookups can be notorious sources of ground loops.

  9. #9
    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    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.
    bo

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    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

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    Senior Member Steve's Avatar
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    ground loop fun

    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

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    Senior Member Steve's Avatar
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    Isolation transformer for CableA

    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

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    Moderator / Treasurer/Marketplace Czar boputnam's Avatar
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    "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)

    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).

    I think I made it...
    Last edited by boputnam; 08-02-2003 at 04:01 PM.
    bo

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    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.

  15. #15
    Your Memory Lives On RIP Tom Loizeaux's Avatar
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    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

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