They have some reasonable wide frequency response models over at Edcor in several impedances. The circuit is simple enough but I'm seeing several different impedance recommendations.
AUDIO GROUND LOOP ISOLATOR SCHEMATIC TV
Simple, effective, yet shouldn't present a compromise to your TV picture.I'm getting a parts list together for a headphone amp that I'm working on and would like to incorporate an audio source ground loop isolator using a couple of matching transformers. But, even with all grounding up to code, I always use a capacitive isolator in my CATV line. If in doubt, call a licensed electrician and/or your cable TV company.
A CATV isolator should not be used as a band-aid to cover up a potentially dangerous situation caused by improper or failed grounding of your CATV line or your house electrical system (I once saw a difference of 50 VAC due to a failed cable TV ground!). It only takes a small difference in potential to cause hum in your audio system, but if the difference is more than a few volts, I suggest finding the root of the problem. I suggest checking the AC voltage difference between your cable TV ground and power line ground before adding the isolator. For those who can't build one themselves, Jensen Transformers offers an excellent capacitive isolator, VRD-1FF ( It's actually the only product Jensen makes that isn't a transformer. That way, your A/V system is also isolated from your cable modem.
Insert the isolator between the cable TV outlet in your A/V room and your CATV or DVR box. A 630 VDC / 400 VAC version is also available, Digi-Key #495-1318-ND. I used Epcos metallized polypropylene, Digi-Key #495-1279-ND. The capacitors should be film types with a rating of 250 VDC / 140 VAC, in countries where the line voltage is nominally 120 VAC. The F-connectors and capacitors can be housed in a small plastic project box, such as a Hammond 1591L, Digi-Key #HM100-ND. When terminated with a 75-ohm load, the isolator provides a low-loss signal path in the RF region while appearing very high-Z at the line frequency and the low-order harmonics likely to cause buzz. All you need are a pair of 2.2nF capacitors - one in the signal line and one in the ground line.
Reader Gary Galo came up with a better solution, one that does not come with such a price to pay.ĬATV grounding can be a menace to audio systems and, as you point out, isolation transformers can be a problematic solution due to the losses involved.Ī better solution is to use a capacitive isolator. Most CATV isolation transformers have a price to pay because of their limited bandwidth: poorer picture quality for higher speed HD signals. I typically recommend a CATV isolation transformer but I also make that suggestion with a cautionary note. Remedying it at the source is the best way to solve the problem. If you have satellite TV like Direct it's not a problem, but if you're connected to the cable and that is connected in your system at any point, chances are good you have a ground loop. I mentioned one of the biggest offenders of hum creation in our systems through a ground loop comes from the cable TV connection.
0 kommentar(er)
