Interesting, very interesting

[stephen]

http://www.ebtechaudio.com/findloop.pdf

I only gave it a quick glance, but I wanna check this out some more.

[kewlpack]

OH cool - I need some of these... well, maybe not because we will be moving (probably) in the next few months and hopefully the new place won't have bad electrical issues...

Of course, if the ground loop is due to naughty components, I'll have to find a better solution.

[prscustom24]

If you have rack-mounted gear, first try something like HumFrees -- plastic tabs that isolate each chassis from the rack rails and from each other. The Ebtech Hum Eliminator owner's manual recommends this anyway, so you might as well try it first and maybe save a couple hundred $$.

[kewlpack]

No rack gear here... All I have is in my sig. Very very straightforward setup. No metal connecting to any other metal other than the usual 1/4" cables.

[prscustom24]

No rack gear here... All I have is in my sig. Very very straightforward setup. No metal connecting to any other metal other than the usual 1/4" cables.

Boss site is short on technical detail for the GT8, so no idea if its outputs are balanced or single-ended. If the latter, and since the output is line-level, I would think a couple 1/4"-to-XLR converters and a mic cable could handle the interconnect from the GT8 to the amp, for much fewer $$, iff you have a ground loop issue (which I tend to doubt, if the GT8 is powered by a wall wart).

[kewlpack]

I believe they are unbalanced 1/4" outs (I am pretty sure I read that in the User Manual). It does have it's own power supply.

I sometimes also have to plug the Variax in via the special stomp that comes with it... So I can have the V500, GT8 and Amp all plugged into a $15 power strip/surge protector. I've tried running things plugged into different outlets, but the ground noise is pretty much the same (low hum). :hissyfit

So those XLR to 1/4" converters would work??? Do I just need them in one spot or what? Doesn't that degrade the signal?

Never have tried this so I don't know.

[prscustom24]

With line levels and short runs -- up to about 30' -- you can make impedance transformations all day long with negligible effect on the spectral content of the signal.

Are you sure it's ground loop that you're chasing? It could just be the intrinsic hum/noise of the unit. The most likely culprit will be your amp. What's it sound like by itself, with volumes all at 0? When I was doing amp repair as a business I gained experience with a broad array of brands, and they all have residual hum & noise, but some of the latter-day Fender designs I found to be among the worst.

Ground loop is typically high volume relative to the signal, and keeps essentially the same ratio of signal to noise with increases in volume. This is because the voltage amplification stages detect the voltage standoff that a ground loop creates as a signal itself. Other noise sources tend to be swamped by the signal as the signal volume comes up.

If I understand your guitar, its output is line level and low impedance, as is the output of the GT8. Interestingly, the Variax ships with a TRS cable, implying a balanced output. If you plug the guitar straight into the amp with this cable, what happens to the hum/noise?

[kewlpack]

If I understand your guitar, its output is line level and low impedance, as is the output of the GT8. Interestingly, the Variax ships with a TRS cable, implying a balanced output. If you plug the guitar straight into the amp with this cable, what happens to the hum/noise?
Hmm, I usually just use a standard instrument cable to plug into my gear and run the V500 with NiMH batteries (6xAA). I wasn't sure if the "special cable" that came with the V500 would be okay to plug into anything but the V500 stompbox (it is essentially a DC power supply and XLR to 1/4" router in a box). Do you think it would work to plug it into the amp?? I guess I can try when I get home.

What do you think prs? By the way - nice to chat with a guru. ;)

[prscustom24]

If I understand your guitar, its output is line level and low impedance, as is the output of the GT8. Interestingly, the Variax ships with a TRS cable, implying a balanced output. If you plug the guitar straight into the amp with this cable, what happens to the hum/noise?
Hmm, I usually just use a standard instrument cable to plug into my gear and run the V500 with NiMH batteries (6xAA). I wasn't sure if the "special cable" that came with the V500 would be okay to plug into anything but the V500 stompbox (it is essentially a DC power supply and XLR to 1/4" router in a box). Do you think it would work to plug it into the amp?? I guess I can try when I get home.

What do you think prs? By the way - nice to chat with a guru. ;)

If 'guru' is somebody who has spent a lot of time making the usual mistakes and only learning from some of them -- perhaps I are one. :lol:

So the stompbox is also an external power supply for the guitar? I did not comprehend that before. In that case. . . the question becomes: is the ring connection dedicated to supplying DC to the guitar? If so, the output is likely an unbalanced, low impedance, line out.

In which case, nothing to be gained by fiddling with the TRS cable -- and I would want to be certain the battery voltage was not present on the ring before plugging into the amp. What Line6 _should_ have done is diode-isolate the batteries from the cable.

The input impedance of the GT8 is a megohm, so it doesn't make sense that it would be loading your signal. I would guess many of the amp models try to emulate the natural compression & sag of that particular amp, and that may be what you're hearing. Clean patches would tend to have less of it, I would expect.

[kewlpack]

The noise is present when the amp volume is at 0 whether the modeling is actually enabled or not.

If I plug in my tiny second amp (crate gfx15) and run everything in stereo (the GT8 Right output to the crate, the GT8 Left output to the Stage 1000), the Crate amp has the noise BIGTIME even when volume set to 0 on everything. I just remembered that I tried this a while back.

Also, this behavior popped up when I tried running 2 individual stompboxes in the Stage 1000's FX Loop. Nothing else was hooked up and the ground noise was quite loud even at volume 0 on the amp. If I unplugged one of the pedals from the chain, the noise VANISHED.

The only thing I can think of is that it is a grounding issue or something similar.

[seagullplayer]

I don't know that this has anything to do with anything but;

On the VERY few and far between times I plug in, I almost always had a hum in the system. I use an active guitar pickup (factory Ovation) into the PA system. This week I tried a "Direct Box" unit inline, wow. What a differance, no noise, and I thought a much better reproduction of the sound signal.
It was a "passive" direct box (no battery), and had a "ground lift" switch? I really can't tell you how I had the switch, whatever way didn't hum, I guess.

Sorry if this didn't belong here, I just had to tell somebody!

[kewlpack]

I was wondering about the ground lift too... I am going to Guitar Center tonight - maybe I can find something.

[prscustom24]

[quote="kewlpack"]The noise is present when the amp volume is at 0 whether the modeling is actually enabled or not.

Next, unplug the GT8 from the amp input with the amp volume still zeroed; does the noise level change?

If I plug in my tiny second amp (crate gfx15) and run everything in stereo (the GT8 Right output to the crate, the GT8 Left output to the Stage 1000), the Crate amp has the noise BIGTIME even when volume set to 0 on everything. I just remembered that I tried this a while back.

Classic ground loop situation. Try a cable that has the shield lifted at one of the plugs. Plug the lifted end into the GT8, the normal plug into the Crate. Also try this with just the Fender amp. This does NOT create a shock hazard.

Also, this behavior popped up when I tried running 2 individual stompboxes in the Stage 1000's FX Loop. Nothing else was hooked up and the ground noise was quite loud even at volume 0 on the amp. If I unplugged one of the pedals from the chain, the noise VANISHED.

I would guess the pedals did not employ true-bypass switching.

The only thing I can think of is that it is a grounding issue or something similar.[/quote

[stephen]

. . . the question becomes: is the ring connection dedicated to supplying DC to the guitar? If so, the output is likely an unbalanced, low impedance, line out.

In which case, nothing to be gained by fiddling with the TRS cable -- and I would want to be certain the battery voltage was not present on the ring before plugging into the amp. What Line6 _should_ have done is diode-isolate the batteries from the cable.

The input impedance of the GT8 is a megohm, so it doesn't make sense that it would be loading your signal. I would guess many of the amp models try to emulate the natural compression & sag of that particular amp, and that may be what you're hearing. Clean patches would tend to have less of it, I would expect.

:shock uh, what did he say? :dunno Are you guys tryin to build a rocket or somethin?

[prscustom24]

:shock uh, what did he say? :dunno Are you guys tryin to build a rocket or somethin?

Why, yes, yes we are, and we want it to to be verrrrry quiet.

[kewlpack]

Okay - did some quick testing last night.

The hum must be coming from somewhere in the house because last night, when I had everything set up and turned on, the hum was much quieter. To the point I had to lean in to hear if it was there (it was late and I couldn't turn it up too loud). There have been times in the last few months where it was fairly prevalent.

I checked all the cables. The computer monitor was on (just like always - but the Variax doesn't suffer feedback or interference noise like that) and stuff was going on downstairs.

It was pretty quiet though...wonder what was different. Something must not have been on downstairs or on my circuit in the breaker (???).

I had a Crate V30 for a few days and MAN did it ever have noise problems. I was picking up radio stations and all manner of pink/white noise. The Line6 stomps were just about as bad. Yuck.

Maybe it just magically decided to go away.

[prscustom24]

Maybe it just magically decided to go away.

And, like magic, it'll probably come back. Assuming it's not just the difference in overall volume (recall the F-M curves) in the wee hours.

Power line noise and level variations used to drive me nuts. The worst is playing outdoor gigs on portable power. But, heavy loads and/or "southern-engineered" house wiring can cause headaches in buildings too.

Again, this is why I run an ac line regulator. The one I use is the Furman AR1215. Street price around $400. To me, worth every centavo.