| Author | Message | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 4594 Registered: 6-2002 |
I had a gig this afternoon and used my Series I bass and the DS-5 portable power supply. During the gig there was some really loud low frequency feedback type noise coming through the PA/Monitors and of course because it was low frequency everyone looked towards me being the bass player. This came on and off during the first part of the gig and there was no earth lift button on the amp which is what I initially though might cure it as it sounded to me like mains hum. Any way this continued for a couple of songs and stopped when the lead vocalist pulled out the plug on one of the stage monitors. Now I played this particular bass for about 1/2 and hour at home before the gig which is what I normally do to ensure that everything works fine. Again I was reliant on the backline which was an Ampag B2R head and an amp cab of which I have no idea the model. I have included a drop box link to a recording that a friend made at the gig on an iPhone 6 so you can hear what the noise in. Maybe you can let me know where the sound may be coming from and whether it was indeed something to do with the monitor or whether disconnecting it was just a coincidence. I hope it's not anything to do with the bass. One time something similar to this happened was due to a dodgy DI box but again because it's coming from the bass player it makes the band feel that there is something unreliable about my gear. I'd like some confirmation please about what this may be. Here is a link, https://www.dropbox.com/s/wwl8n0ggis4zwei/IMG_1076.MOV?dl=0 (Message edited by jazzyvee on July 26, 2015) | ||
| mica
Moderator Username: mica Post Number: 8586 Registered: 6-2000 |
I got a 404 on the link. The description makes it sound like a ground loop. I may have posted this before but this article my dad wrote about ground loops may help you: In the old days we had equipment without the safety ground connection to the chassis, and the signal cables provided the only ground path. This is still the best approach except that it provides no safety if there is a fault in the equipment that would put mains voltages on the chassis. So we have to think differently and minimize the effect of the ground loop. Just having a ground loop doesn't ensure that you will have hum, the hum is caused by magnetic coupling into the ground loop. Let's look at where the ground loop is being formed. We have two mains cables going to either a wall outlet or to a plug strip. The safety ground wires are connected together at this point. The mains cables go to separate pieces of equipment. We make the ground loop when we connect a signal cable between the two pieces of equipment, thus creating a continuous connection around a "loop". A varying magnetic field can now induce a current into this loop, and create a voltage drop across the wires that form the loop. Even though the two pieces of equipment are grounded thru the signal cable shield and simultaneously grounded to each other thru the safety ground wires in the mains cables, in the presence of a varying magnetic field, the ground potentials at different points in the loop are different. To understand why you don't hear the hum when no instrument is connected, consider that the center signal wire of the cable between the amplifier input and the power supply doesn't connect to anything at the power supply end. If that wire weren't shielded, then we could induce noise into the center wire by electrostatic (or capacitive) coupling, and we would often describe the resulting noise as "buzz" since electrostatic coupling more readily couples high frequency components. The shield of the cable (and the metal boxes of both the amplifier and power supply) acts as a Faraday cage and shunts any potential electrostatic noise to the ground (or earth) and prevents this type of interference from being heard. The fact that the system is quiet with the instrument disconnected assures us that the electrostatic shielding is performing properly. Even though we still have the magnetic coupling generating voltages in the shields, it has no means of being sampled since the center wire is not terminated. When the instrument is plugged in we now have a means of listening to the magnetically induced noise (which is stronger at the fundamental frequency of the mains generator) so we perceive it as a "hum" sound. So how do we keep our safety grounds and minimize the hum? It might be easiest to first consider what we would do if we wanted to build a circuit to find a source of magnetic fields. We would take our “loop” and maximize the area and move the loop until it surrounds the source of the varying magnetic field. Our actual cable to the guitar is of no help to us in maximizing the hum since the signal conductors take exactly the same path as the outer shield and the area enclosed by this portion of the loop is zero. Thus you won't be able to move the guitar and its cable around to make a difference in the amplitude of the hum. So where is the area of the loop? It's that area between the mains conductors and the signal cable between the amplifier and the power supply, but also includes the metal chassis themselves. So what we want to do is to minimize the area by using a short signal cable, and by dressing the two mains cables, or even twisting them. In some cases this may be sufficient to make the hum acceptably low. Unfortunately, one of the hard things is that the source of the magnetic hum field is the power transformer inside the amplifier which is also part of the conductor path that makes the loop. So the entire loop is something like: one safety ground connection at one of the mains connectors, thru that power cable to the bolt on the chassis of the amplifier, thru that chassis metal and if the input jack is grounded to the chassis, to the input jack serrated washer that cuts thru paint, then thru the jumper cable to the power supply, which where the jack is grounded to the chassis, then up thru the cable to the instrument, thru the selector switch in standby, and back down thru the cable and to a bolt thru the chassis that connects to the safety ground terminal on the mains connector, thru the mains cable, and to the same safety ground connection we started from. So we can minimize some of the path, but other parts you'd have to smash by driving a truck over the chassis and bend them to minimize them and the equipment wouldn't work after you did that! So let's go back again to the concept of how to maximize the hum. And realize that if we make a coil out of the jumper wire between the amplifier and the power supply, say about 6 inches in diameter, then we can move the coil around and generate a larger or smaller ground loop current by positioning it closer or farther from the power transformer. Also, if we invert the coil by turning it over (or the same thing if we take the coil apart and wind it in the opposite direction), then the polarity of the signal that is picked up is reversed. So we can by trial an error, determine the winding direction to generate a signal polarity that is opposite that in the loop portion that we can't do anything about. And then position the coil or adjust its area by changing it from a circle to a narrow loop which changes the area which in turn changes the amplitude. If we can set the loop just right we can generate a current that is equal in amplitude to the one we can't do anything about, with the opposite polarity, and the hum is cancelled out. Quite frequently, the use of a short jumper and dressing the mains cables to follow the same path, and using a power strip so the mains connectors are side-by-side will make the hum sufficiently low. If that isn't effective, then building the loop as described above can work after a period of tedious trials to determine the number of turns and the area to be enclosed as well as the position that will generate the right "hum bucking" voltage to exactly cancel. Note also that sometimes instead of making the coil with the signal jumper, you can make it with one of the mains cables and position it under the amplifier chassis. The principle is simple, but since our eyes can't see magnetic fields, then we're blindly trying things. But understanding the fundamental nature of the problem helps us in our blindness. | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 4595 Registered: 6-2002 |
Sorry i put up the wrong video clip and was replacing it when you tried to connect. The right clip is there now. Wow that's some write up I will have to read a few times before I understand it. :-) Thanks Mica. | ||
| keith_h
Senior Member Username: keith_h Post Number: 2254 Registered: 2-2005 |
I can't really hear anything on the recording but I don't have a very good set of speakers. Just based on what took place it sounds like the monitor was the cause to me. I also have a question. Why are what appears to be the sound guys just sitting around on the side playing with their phones instead of trying to figure out what is going wrong? Were the monitors self powered? If they were they could be the source for a ground loop if they aren't an the same electrical branch as the rest of the PA. Not self power related but it could have had a wonky signal cable. Were they rung out correctly? Was it near a mike stand? Was it an active stage? These could point to a low frequency feedback loop. One thing that used to cause me problems were active stages and the old Atlas ball stands. The stands would pick up low frequency through the stage and form a feedback loop with the mic's and monitors. The fix was to use an equalizer to kill the offending frequencies and if I couldn't do that move the mic/monitor or try to isolate the one or the other from the stage. Was there any neon lighting or stage lighting near the monitor or on the same power branch? These are both noise injectors and depending upon the situation can come across as ground issues or low frequency noise. Keith | ||
| fc_spoiler
Senior Member Username: fc_spoiler Post Number: 1761 Registered: 5-2006 |
I don't think this is a ground loop problem (which is a constant low hum) I hear some "whoom" on the low notes which sounds like it is a problem with the eq settings in relation to the room and speaker (Pa?) setup. | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 4597 Registered: 6-2002 |
The guys at the side of the stage are not the sound guys they are DJ's. I'm not sure if the monitors were powered or note but I did think it could be low frequency boom picking up from the mic's via the stage which was a hollow box. I did listen carefully to the other bands on the stage before we went on and the sound was virtually all bottom end and all top end, not much going through the mid range so the sound was boomy and painfully sharp at the top end. When we went on stage the first thing I did was turn off the graphic EQ on the amp because the last two faders on the left were maxed out and the next two were about 1/2 way up and everything else flat down to the bottom. I then set all tone controls to 12 o'clock which I assume was flat, then during sound check moved cut bass knob down to about the 10 o' clock position because the speaker sounded like it was flapping. So on stage it was fine. I spoke with the lead singer this morning and he said he'd experienced that a number of times before and he could hear that it was coming mainly from the monitor on stage and being picked up by the stage mics so he unplugged it because we couldn't hear any music from it fortunately that seemed t cure it for the rest of the gig. | ||
| ed_zeppelin
New Username: ed_zeppelin Post Number: 10 Registered: 2-2010 |
I hope you don't mind the suggestion, but a Real Time Analyzer saves tons of time and does a far better job of setting up your gear than our ears ever could. I've been using them since the early 80s. Literally plug 'n play, especially with today's technology. In case you're not familiar with them, the best ones feed "pink noise" through your system (including amps, so they do double duty by tailoring everybody's amps to the room) and tailor the sound to the room. In the old days we had to use special mics and then adjust the EQ manually. In my opinion, the best "idiot-proof" (I'm proof, in fact) version ever made was Peavey's "Autograph 2" MIDI graphic EQ. You can find them for less than a hundred bucks, usually. Like here: http://www.ebay.com/itm/Peavey-Autograph-2-Computer-Controlled-MIDI-Graphic-Equalizer-/371391117482?hash=item5678a2b8aa "28 Band Graphic Equalizer Constant EQ Filters on 1/3 Octave ISO Centers Real Time Analyzer Automatic Room Equalization Built-in Pink Noise Source Easy to Read 40 x 2 Character Display Non-volatile Storage of 128 EQ Curves Non-destructive EQ Curve Addition EQ Curve Compare Combination XLR/1/4" Phone Inputs Electronically Balanced Inputs and Outputs Feedback Finder MIDI Controllable Switchable 40Hz Subsonic Filter Dimensions - 19" x 1 3/4" x 9" Weight - 6.25 lbs." I have absolutely nothing to do with that auction, by the way. It's just an example of what's out there. There are even free RTA apps out there, though compared with the real thing they're strictly "better than nothing." | ||
| sonicus
Senior Member Username: sonicus Post Number: 4387 Registered: 5-2009 |
Agreed ! I have been making use of since RTA 's since the 1970's I currently still have a few . In my main live room I use a Goldline DSP 30 RM . I also have others in other rooms . They do the job ! It is imperative to use a calibrated microphone and know how to use it or the process is utterly useless ! Wolf | ||
| bigredbass
Senior Member Username: bigredbass Post Number: 2414 Registered: 9-2002 |
+1, Wolf. I once watched a 'sound man' who was 'educated above and beyond his intelligence' shoot the room with an SM58, connected, 'because that's what most of the mics onstage are!'. It was a long night . . . . Joey | ||
| sonicus
Senior Member Username: sonicus Post Number: 4389 Registered: 5-2009 |
Joey , yes, thanks . That mic has to be right for the job , as you know . . | ||
| ed_zeppelin
Junior Username: ed_zeppelin Post Number: 11 Registered: 2-2010 |
Goldline still makes the DSP30: http://www.gold-line.com/dsp30.htm I used to play in a band that had a volunteer sound man, an old geezer who had worked for everybody from movie studios and radio to Alabama (the band). What a great guy. He said any sound man without headphones and an RTA was an idiot. The headphones had two uses: when you're setting input gain on a board, it's like the singer is singing directly in your ear. Once it's set for the "hotness" of that mic or instrument, that's it. Everything else is sliders and EQ. The other reason for headphones is even more important: nobody messes with you when you're wearing them. Otherwise there's always some moron yelling; "more bass!" or; "turn up the singer!" He's the one who told me about Tom Dowd's theory that it's a lot easier to hear what sounds bad and turn it down than it is to decide what sounds best and turn it up. Tom Dowd engineered everything from Ray Charles and Bobby Darrin's "Mack The Knife" Aretha ("Respect") to "Disraeli Gears," Allman Brothers, BB King, just too much to list. http://rockhall.com/inductees/tom-dowd/bio/ Believe me, that changed everything, because he's absolutely right. With an RTA (especially that Peavey unit) and headphones you can set up in a few minutes. No guesswork, done. On EQ, crank the level, sweep to find the crap, turn the level down until the crap goes away, and you're done. Everything else takes care of itself, it seems. | ||
| sonicus
Senior Member Username: sonicus Post Number: 4390 Registered: 5-2009 |
I remember in the studio when near field monitors did exist and all we had were ALTEC 604's for the mix in the studio . Later AURA TONES , showed up for the so called dirty car radio mix . SO now Ya'll all know how old I REALLY am ! (old as dirt ) Wolf | ||
| bigredbass
Senior Member Username: bigredbass Post Number: 2415 Registered: 9-2002 |
I went to NAMM in Anaheim in the 80's. The store I worked for was a Yamaha dealer, and we wrangled an invite to Yamaha's recording studio. We got a tour of the place (and saw a programmer for the then-new DX's, something we weren't actually supposed to see, along with a bunch of home-market axes). One room ran thru one of their big PM mixers, one of the big live-sound boards that were big sellers in the day. The other room had a real recording board (maybe a Harrison or MCI, can't remember now), and along the top were the usual Auratones and the then-new, white-cone NS10's, which went on to become so common in studios. Except the labels were missing. When we inquired if this was because these were special or prototypes, etc., the tech required ashen-faced that late one night in an inspired dose of humor, some wag had cleverly altered the script to read YAMAMA instead of YAMAHA; this had been left that way . . . . until a recent visit by Yamaha's Japanese CEO who had noticed this revision to the company logotype, and was NOT impressed at this gaijin humor ! Joey | ||
| dfung60
Senior Member Username: dfung60 Post Number: 614 Registered: 5-2002 |
jazzyvee - The feedback definitely sounds acoustic to me. I would look to see if they have a mic that your band wasn't using that's still turned on. They may have a house PA mic that they didn't completely mute when you were playing and it's feeding back from the PA, especially if it's in physical contact with the stage. The DJ-style EQ (max the bass) doesn't help. Just to be sure, you didn't bring a second bass, did you? It's unlikely that you would plug it in to your amp and not fully mute it, but that would be another possibility. David Fung | ||
| ed_zeppelin
Junior Username: ed_zeppelin Post Number: 12 Registered: 2-2010 |
I was a repairman at Daddy's Junky Music (then the world's largest dealer of used instruments) and one of the reps came back from NAMM with a bunch of weird stuff, some of which he said was odds 'n ends exhibitors had piled up at the end of the show for anybody who wanted it. I snagged an Ovation Adamas carbon-fiber top, Monster cables, etc. ... And two dust caps off what I assume were huge Yamaha speakers. My bench was known as the "Inner Sanctum," and I'd lined the walls with headlines and articles from World News Weekly ("Batman Tribe Found In Jungle!" "Space Alien Backs Clinton!" "Severed Leg Hops To Hospital!" etc.) Word got around about the Inner Sanctum and visiting dignitaries would stop by to read my walls. So I instituted a policy that if you wanted to hang out, you had to don a "YAMAHA YARMULKA" as a mark of distinction. Thus I have in a box somewhere snapshots of Hartley Peavey, Eddie Van Halen, Joe Walsh, Paul Reed Smith and a bunch of other celebrities and rock gods in YAMAHA YARMULKAS. Coincidence? I always wondered where they came from. I don't remember when they showed up and Daddy's is long gone, but perhaps a little part of the mystery is solved. We'll never know. By the way, the story about the Batman tribe is absolutely true. A trader came through with a battery powered TV/VCR and showed Adam West to the tribe (none of whom had ever seen TV, and thought little gods were inside the magic box) and the next thing they knew, guys dressed as Batman were running around the jungle. The Brazilian government had to step in when they killed a shaman from another tribe because he painted his face white, and they thought he was the Joker. You can't make stuff like that up, not even World News Weekly | ||
| edwin
Senior Member Username: edwin Post Number: 2089 Registered: 5-2002 |
Jazzyvee, this has been a great discussion about RTA's etc (and you can get a very good one to run on your iPhone with AudioTools by Andrew Smith that even includes a version of SMAART Live as one of the in app purchases. Very good for telling a sound man what's going on or even analyzing the performance of your own rig), but they depend on a sound person knowing what they are doing and spending the time to get it right before there's an audience in the room. No one wants to subject an audience to 110 DB of pink noise. SMAART Live and a few other systems (I have SpectraFoo by Metric Halo) will accomplish the same thing using music as a source and give you a real time output of the difference between the source and the actual sound in the room, along with myriad other information presented in a variety of visual forms. Lots of fun, but what does it mean for the gigging bass player? Not much, because unless you have a sound person who knows what their doing, if you are telling them how to do their job at this level, it's already too late. If they know what they are doing, it wouldn't come to this. It sounds like you are suffering the slings and arrows of outrageously bad sound people. For ground hum issues, I always include a mic splitter, an Ebtech Hum Eliminator and a three prong to two prong adapter for the mains (not useful in the UK and messing with the ground with the voltage you use over there is not recommend. Tasting 120V is one thing, but tasting 220V is entirely another). Good luck! Edwin | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 4601 Registered: 6-2002 |
Thanks for all the info guys. Understanding it is a bit of a challenge and taking a lot of re-reading but it seems like the issue was not a fault with my bass which is my main concern. Usually with Musical Youth we have our own FOH sound guy who is also superb at mixing reggae. He does loads of the big festivals, teaches sound at university degree level here and also is a bass player. But this time it was an unknown person driving the desk and throughout the afternoon the sound was bad even when there was a guy doing a PA set with a backing track all you could hear was bottom end, extremely high top end and hardly anything in the mids at all so not much in the vocals either. Well that gig is out of the way and hope to have our regular sound guy back for the next gig. | ||
| jazzyvee
Senior Member Username: jazzyvee Post Number: 4602 Registered: 6-2002 |
Thanks for all the info guys. Understanding it is a bit of a challenge and taking a lot of re-reading but it seems like the issue was not a fault with my bass which is my main concern. Usually with Musical Youth we have our own FOH sound guy who is also superb at mixing reggae. He does loads of the big festivals, teaches sound at university degree level here and also is a bass player. But this time it was an unknown person driving the desk and throughout the afternoon the sound was bad even when there was a guy doing a PA set with a backing track all you could hear was bottom end, extremely high top end and hardly anything in the mids at all so not much in the vocals either. Well that gig is out of the way and hope to have our regular sound guy back for the next gig. | ||
| ed_zeppelin
Junior Username: ed_zeppelin Post Number: 13 Registered: 2-2010 |
I want to apologize for derailing this discussion. On March 29th I accidentally cut my right big toe off, and staring at the ceiling above my sofa for months has made me even more loopy than usual. Plus, I'm a bassist. That factor alone should excuse a myriad of eccentricities. | ||
| terryc
Senior Member Username: terryc Post Number: 2401 Registered: 11-2004 |
ed zeppelin.....lawnmower accident ?? | ||
| growlypants
Intermediate Member Username: growlypants Post Number: 142 Registered: 3-2011 |
No biggie. (Ya' get it??!) Ouch. Hope you're OK. | ||
| ed_zeppelin
Junior Username: ed_zeppelin Post Number: 14 Registered: 2-2010 |
I tripped (as in "stumbled," the distinction being important because IS Alembic, after all) down stairs. My toe became lodged between the juncture of the tread and the bottom rail of the bannister, but my bulk continued falling - flailing madly - to the landing below, leaving my toe behind (to my surprise). We're bassists, so I'm sure most of you want to see pics, right? WARNING! Not for the squeamish! http://m.imgur.com/44DU2Ls (Sorry about the dreadful foot hygiene, but I had just chased my Golden Retriever through the backyard, barefoot, so we could take a bath together - an event that still hasn't occurred, come to think of it) The gods smiled upon me, though. I looked down, once, and decided not to do that again. I went to my "happy place" to avoid shock, and my toe and I went to the ER (I told the EMTs the ambulance was now a "toe truck"), where we were reunited by the state's leading orthopedic surgeon, who happened to be operating on another clumsy oaf at 8 A.M. on a Sunday morning. Within fifteen minutes I was off to wherever Michael Jackson went, while the surgeon stitched me back together. His work is worthy of Michelangelo. The nerves grew back. I have 100% nerve function. The toenail grew back. The only sign of the injury is a tiny, barely visible scar and a very stiff joint (I mean "toe-knuckle." There's that distinction again).  | ||
| sonicus
Senior Member Username: sonicus Post Number: 4393 Registered: 5-2009 |
(double post correction) (Message edited by sonicus on July 29, 2015) | ||
| sonicus
Senior Member Username: sonicus Post Number: 4394 Registered: 5-2009 |
Dear Sir , I am so sorry for your plight. Some years back ago I had an accident with a hedge trimmer and the pinky on my left hand and it is still all there now after having been pealed back like a banana. I also lost the finger nail and it also grew back . Now it is all back to the way it was before the accident ,with just a small scar . Wolf | ||
| terryc
Senior Member Username: terryc Post Number: 2402 Registered: 11-2004 |
Having been in the medical profession for longer than I can remember , that wasn't too bad as I have seen some extreme limb injuries that are caused by the most simplest of tasks performed by men and women. Garden forks through feet, carving knives through hands usually with the vegetable or piece of meat they were cutting attached the hand, drill bits in knees, percussion nails which have nailed all four fingers together, oh yes , a plethora of ghoulish mental pictures although I have a very sedate job now (but miss that part of it at times!) |
