I bought the 990 at first opportunity, and so far it has performed very well in my system. I have noticed a problem with the component video switching, and I was wondering if anyone else has experienced this.

With DVD source material, I see horizontal bands doing a slow roll up the screen. It is really easy to see in dark scenes, but it is going on pretty much throughout.

When I connect the Component cable directly to my projector I do not see this problem, so I'm assuming it is being introduced in the 990. I've tried switching cables, but the same thing occurs.

Any thoughts?

Greg

I haven't run into that in my setup, I'm afraid. I've run 480p and 1080i through the component switching without any problems. I assume you've verified that the extra component cables (presumably the ones going from DVD to 990, since the ones from 990 to projector are most likely a lot longer and were the ones you moved to the DVD player) aren't the culprit. Somebody else may have a more useful thought, but in the interim it couldn't hurt to quiz the Outlaws as well.

Sounds like "hum" bars. There's a difference in ground potential somewhere in your system. The most common cause is the cable tv input. Try disconnecting other inputs while the video is passing through you 990 and see if the bars dissappear.

Thanks for the advice. I'll check it out when I get home.

The cable run to the projector is admittedly pretty long, but when I connect that same cable directly to the DVD player the picture is pristine.

I'll try disconnecting the other sources and see what happens.

Thanks!

Greg

I support what Lawrence thinks. This is a classic "ground loop" symptom, that manifests it self as "hum bars", which look like what you are seeing.

Sorry to be ignorant here, but does that mean it is a power supply/line conditioning issue? I mean, if I disconnect the cable box and the bars disappear, how do I fix it so that I can leave the cable device connected and eliminate the bars?

You can certainly fix this by connecting everything to an all-in-one line conditioner (with phone and coax cable pass thru, that is). If you already have a line conditioner and don't want to spend the scratch, you can get in line coaxial products to add to your cable (like this one.

greg099: it is a subtle problem that is difficult to explain to non-technical people (and is often mis-explained by sales types). :-( It is not a simple power supply/line conditioning issue.

Google for "ground loop", and "hum bars" for more information.

Basically, you have two pieces of equipment with different ground references (because of different resistances to ground on each of them), and a ground connection tying them together that is part of a signal line, e.g. the shield on an interconnect. This forms a circuit with one big loop that tends to pick up 60 Hz "hum" from the 60 Hz power distribution system. That "hum" is effectively added to the signal. No amount of filtering will remove it -- you have you "break the ground loop".

This is why most audio equipment is doubly-insulated with two-pronged plugs, instead of three-pronged plugs. If a safety ground (the third prong) is present, it must be connected to the chassis, to which the signal ground is usually conencted as well. Without that safety ground, there is no opportunity for a loop, since the power transformer "breaks" any possible loop. It's when you have two grounded pieces of equipment that trouble can start with a ground loop between them. The cable feed, by law, has it's shield grounded, and so, is a common culprit. Computers are another. Of course once a piece of equipment picks up ground loop hum, it will pass it along, even if there is no ground loop between it and anything downstream of it.

The first step is to try to find where the loop is. Remove all pieces of equipment, particularly, those with cable, satellite, or computer connections, and those with three-pronged power cords, one by one. When the hum bars go away, you've identified one end of the loop.

Fixes all revolve around breaking the ground loop. For RF sources, like cable TV, you can use two 75 to 300 ohm RF transformers back to back (this won't work for satellite systems which need a DC path from the STB to power the LNB. You can try replacing analog audio interconnects with optical ones (coax ones may or may not have a transformer to break the loop). You can try audio transformers specifically designed for this purpose on analog audio lines. But, be warned, good ones are expensive, running several hundred dollars.

There is one thing you should not do, no matter how tempting: remove the safety ground from a piece of equipment. That is, do not be tempted to get a three-prong to two prong adaptor and use it to remove the loop. While fine, for temporary testing, to help isolate the loop, this is very dangerous as a permanent solution.

The purpose of the safety ground (third prong) is to short-circuit any "hot" power connection coming lose and touching the metal chassis. If you touched the chassis, and were grounded (also touching the chassis of a grounded piece of equipment, or a cold-water pipe, or standing on damp concrete (in a basement), you'd get a shock, which could be fatal. When the chassis is grounded, back to the electrical panel, via the third prong, the short-circuit will blow the fuse, or breaker, before you can get shocked. Remove the safety ground and you lose this protection.

One technique I have used in the past, was to wire up a small utility box with an ungrounded GFCI, and ran the offending equipment through that. This removed the safety ground, but offered safety in another way: if there was a short to chassis, and an alternate path for the power return current (e.g. your body), the GFCI would trip. The problem with this, is that shield in the interconenct to the other offending piece of equipment: a high current can flow in that path, causing heating and a fire, before the GFCI, or fuse or breaker can blow. Some consider that a small enough risk. But, I would not advise it if you are not comfortable with it -- a safety ground is really the best.

If you unhook the cable box and the problem disappears, then the problem is coming from the cable TV. You can further verify it by only disconnecting the RF cable from the cable box (leaving it completely hooked up otherwise). If the problem is related to the grounding on your cable TV service, there are several products that you can buy to put in line with the cable TV signal to alleviate the problem. I did a search through some old threads in the forum and came up with a few ranging from the expensive side to the very reasonable: MIT ISO-LinQ (probably on the pricy side), Mondial Magic Box (also pricy at $100), Dayton isolator (at $10 or so from Parts Express, this is an excellent thing to start out with if you do determine that you have a ground problem), and the Jensen VRD-1FF Cable TV RF Isolator (available from Markertek for $50).

Thanks again for the education, gents. I will be going through the troubleshooting tonight.

Greg

I have experienced the same thing with the 'crawl' on the TV screen, and yes, this is definitely ground-loop-borne. Furthermore, if I turn the gain way up on the 990, I can hear the line noise (60, 120, 180 etc Hz) whereas if the cable is disconnected from my Motorola DVR (but all connections left intact from the DVR to the 990) the hum immediately disappears (completely) and the screen crawl stops. After $inking what I have into amps, speakers, pre/pro, HDTV etc, the thought of just 'living with' the hum and crawl just doesn't cut it.

One simple fix that I have used is to take two 300 Ohn to 75 Ohm 'baluns' (Radio Shack or equivalent) and wire them back to back. That is, solder the two pair of 300 Ohm terminls together, resulting in two 75 Ohm screw connectors. This effectively isolates the grounds but lets the signals pass through. With this in place there is neither screen crawl nor hum from my system...and the fix costs all of about $9.00 to implement.

However...what I have noticed is that there is definitely a loss of signal to noise ratio on the 'lower' tier of cable channels (and regrettably, I seem to have made a rather effective notch filter for channel 7 in the process), though those above 100 or so don't seem to be adversely affected one iota. Fortunately for me, I don't watch those channels much (and more importantly, neither does my wife...), so that really doesn't bother me. Another plus here is that the HD channels don't seem to be affected at all either....so I'm willing toi live with the lower S/N on the channels I seldom watch. Compromises...

Cool thread though...I'll have to check out what some of the others have proposed. Maybe I can eliminate the ground loop hum and crawl, and not lose as much signal (on the lower channels) in the process.

One last bit...can anyone here say how good the proposed isolators are in terms of maintaining signal to noise ratios on aALL channels?

Mark

In my case I had a ground loop problem once with a satellite feed.

There was no opportunity to use the dual 75 to 300 ohm balun trick because the LNB requires power from the satellite STB. Even if one uses a powered multiswitch, for DirecTV systems, the STB uses different DC voltages to select the LNB polarization. Dish systems use DiSeQ switching control which uses a 20 Khz carrier, which would not pass too well through a balun pair. I used a different trick.

At first, I ran a heavier #6 ground lead from the dish ground rod to the main house grounding point, but this only helped a little.

In my case the loop was between the satellite feed and my subwoofer which had a third prong on the power supply. Rather than break this safety ground to break the loop (potentially very dangerous), I build a little extention cord, terminated in a single gang utility box with a GFCI mounted in it. Thus, I could safely lift the ground, and still have some fault protection via the GFCI. This worled well.

I would not encourage others to do this though, unless they thorougly understand what they're doing: there is a danger of the GFCI not tripping even if there is a short to signal ground, which can travel back on an interconnect shield, possibly causing a fire. It's unlikely, but not a risk that exists with a real ground in place. In my case I consider it about as likely as a "real ground" working itself loose and thus gone, so I accepted the risk.

Another possiblity is to break the loop at the output of your cable STB: use optical digital audio interconnects, and video baluns on the video lines (one, two, or three, for composite, svideo, or component outputs). This won't help digital video signals, though, on DVI or HDMI connectors, unless you use a paid of electrical/optical DVI converters, typically used for long runs. That can get expensive. (Even video baluns can run several hundred dollars each, for good ones).

I love it when stuff just works out...

So, I perused this thread and some other sources (including some of the Outlaw manuals) and found a 'reasonably' priced isolator readily available - the Jensen VRD-1FF ( www.jensen-transformers.com ), bought it (around $50 or $60), and took delivery a few days later.

So, I installed it between the service point and the cable TV amplifier / distribution box. I then removed the cheesy home-made variant (that I reference in one of my prior posts in this thread) and connected the cable directly to the Motorola DVR.

Result?

Absolutely ZERO hum and ZERO video crawl. Works like a champ. Also, the lower tier channels that suffered poor S/N at the hands of my cobbled isolator are now much, much lower (video) noise (though I doubt I'll watch many of them anyway).

I should say that theoretically, putting one isolator between the cable service point and the cable amplifier / splitter block (for those who have them) may not completely solve hum and crawl for all systems. This is because (and I think others have pointed this out) all of the cable shileds are tied to one point (the splitter or distribution system), so theoretically, a ground loop could still result by virtue of the cable referencing ground in another part of the house.

I think it's fair to say that no two installations are exactly alike, and this goes for potential found at the ground at a given location. However, I think it's also fair to say that the difference in potential between the cable at the service point and the house ground are considerably greater than what's likely to result from the grounds all being tied together at the splitter or cable TV amplifier / distribution point.

All I can say is that I installed the isolator where I did, and there are three other TVs in the house in various rooms connected to the cable at their repsective locations. None of them have hum or crawl.

So, I'd say try 'going cheap' first by trying it the way that I did. If you still have problems then if you were to install them on each cable send (or at each TV / /DVR / Cable box / audio system) I think the chances are very good that you'd kill any and all hum / crawl at every location (because seperately-isolated feeds would ensure isolation on each cable, and therefore, from each other).

Oh, and the folks at Jensen give you a nice short F to F cable with the isolator, so no trips to the store or having to crimp your own. In less than 1 minute my problem was solved.

Life is good.

Mark
PS: Indeed, this will not work for Satellite systems, but it worked wonders on my cable.

Outlaw Audio has some suggestion about the "ground loop" problem in the manual of their new amplifier 7125 on page 8 and 9.

RW