nola Posted February 10, 2008 Share Posted February 10, 2008 I have a technical Q. Speakers incl Klipschorns, LaScala's, Heresys, and Academy center. Since buying dedicated sub amps (2) I have GL Hum probs. Each sub amp has a 3 pronged plug. I actually don't have a 3 prong to 2 prong converter or cheater lying around and I do not want to mess with the new 1000w sub amps if possible. The prior Adcom stereo amps used in bridge mode were located in a different - but poor - position and the sub cable path and speaker wire path are also changed. On the prior non ideal placement and amp set up there was no GL hum - but, the prior amps only had 2 prong electric plugs. My Mac tube amp also is 2 pronged and my Outlaw 750 SS amp, well I can't see back that far... I found that by grounding the cable TV outer plug to a ground outlet plug of a 3 plug outlet strip hum is much reduced though still notable and bothersome. Changing outlets for the new amps and messing with the turntable ground wire does not seem to change anything. I do not know where the cable TV ground is located. The distance from cable TV splitter at home entry to sub amps is too far for the "lamp cord" speaker wire I have left now to attempt to ground to sub amp chassis. I will likely try that next. Each sub amp has a 3 prong plug. Other solutions I have found include getting 2 different 300/75 and 75/300 ohm tv converters and connecting them. May mess up TV signal, but a $5-10 solution. Also, getting an isolation transformer. Not cheap at $40-60 from Jensen Transformers. Parts Express 180-075 is about $11.00. As stated, the 3->2 prong cheater (which I really prefer not to do) and directly grounding the cable outer shell to my sub amps are also possible (with more speaker wire). Anyone have any other suggestions? Thanx from New Orleans Quote Link to comment Share on other sites More sharing options...
bhendrix Posted February 10, 2008 Share Posted February 10, 2008 Nola, Cable tv coax seems to be a common source of hum. If you disconnect the cable from the cable box, does the hum go away. Another thing to try is to connect the subs via three-prong extension cord to the same circuit the rest of the system is plgged into. I was able to eliminate the cable coax hum by grounding another "F" jack on the cable box to the ground of the power circuit. I couldn't eliminate it completely by grounding the outer ring of the F connenctor on the cable. Hummmmmmm . . . . . Quote Link to comment Share on other sites More sharing options...
mas Posted February 10, 2008 Share Posted February 10, 2008 Follow Bill Whitlocks Troubleshooting Guide attached here. And do not simply go adding grounds or lifting them! Creating a safety hazard is not really a solution! Good luck BWhitlock.GrdLoopTrblshtgGuide.pdf Quote Link to comment Share on other sites More sharing options...
nola Posted February 10, 2008 Author Share Posted February 10, 2008 Thanx for the advice Yes, the hum goes away when the cable TV line is disconnected, but then again, the TV goes away too Wierd how it did not occur with the prior amps which only had 2 prong plugs. I think I got about a 2/3 improvement by running a 2 foot long speaker wire from the cable ?shield to the strip outlet ground. If that is unsafe, I will undo it (still reading the pdf). The hum went away for seconds at a time, but always recurred. I also tried to determine the Ohm differential, but analog and digital multimeters gave very different results. 1-1.2 Ohns analog, up to 8 digital. (Cable TV wire to strip outlet ground). Is there some kind of Ohm balancer that Radio Shack would have? In the French Quarter of New Orleans, no telling where my cable box is. There is "a" cable box, rather mangled, about 100 feet from my slave quarter apt at the front of the main house. It is outside, so no ready way for me to ground that cable box to my inside ground. I have no way of knowing if the cable box and the house are grounded to the same spot(s). My wires could also be from a box on a neighboring property. That is not uncommon here. I do not wish to make any safety hazards. Quote Link to comment Share on other sites More sharing options...
nola Posted February 10, 2008 Author Share Posted February 10, 2008 oh, no difference which outlet (of the 2 reasonably available) I plugged the subs into - 1 was for the main stereo equipment. I was also afraid of overloading a circuit with 4 amps (about 3000w ttl), TV, preamp/processor, vcr, dvd, turntable, 2 tape decks, clock, etc.... Quote Link to comment Share on other sites More sharing options...
mas Posted February 10, 2008 Share Posted February 10, 2008 If the problem is simply due to the cable input, all you need is this, an inline isolation transformer: http://www.partsexpress.com/pe/showdetl.cfm?&Partnumber=180-075 Lifting grounds with 3->2 prong adapters is NOT a solution. Not really sure what is going on there, but 2 prong and 3 prong equipment is wired differently internally, so you do not want to go crazy just adding grounds!!! That IS unsafe...and you will create more ground problems. You want to resolve the differences between various ground path potentials - not create a few more with still different potentials! And as far as the load on a particular circuit, look at the current (amperage/amp) rating on each peice of equipment and add them. Ignore the wattage. Just do not exceed the current rating of the circuit (and that includes everything plugged into the different outlets on the particular circuit). You can determine what outlets are on that circuit by tripping the circuit breaker and checking the outlets with a light or radio (and be sure that any switched outlets are turned on!) You might also want to get a n LED ground/polarity checker for a couple of bucks at Home Depot to verify grounds and that polarity has been observed in the wiring of the outlets (just be sure to get one that also checks polarity). Quote Link to comment Share on other sites More sharing options...
nola Posted February 10, 2008 Author Share Posted February 10, 2008 Thanx. Maybe the partsexpress isolator is the thing to get. I will try looking into your circuit load advice during the week. Quote Link to comment Share on other sites More sharing options...
InnerTuber Posted February 11, 2008 Share Posted February 11, 2008 Thanks for the guide - handy. Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.