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Hum problem w/ Soundcraft Ghost

Discussion in 'Pro Audio Equipment' started by erockerboy, Jun 14, 2001.

  1. erockerboy

    erockerboy Member

    (hope this is an appropriate place for my query... if not please advise!)

    Just replaced my ancient Mackie 24x8 with a new(er) Soundcraft Ghost in my MIDI room at the house. The Ghost is one of the 32-channel models, with the mute automation and the meter bridge. According to the factory it is less than 4 yrs old and appears to have been impeccably maintained. All good, right? Read on....

    The damn thing has what sounds like a ground hum on the 2-bus. With all inputs muted, nothing connected to the console, nothing else powered up in the room, and a pair of headphones plugged directly into the Ghost for monitoring purposes, there is a pleasant 60-cycle hum, fairly quiet but definitely not cool, coming out of the master stereo bus.

    At first I thought it might be a problem in the Ghost's CR output section... but the 2-trk returns are dead quiet. The hum seems to ONLY be present on the 2-bus. And it is present at all points downline (i.e. the inputs to my DAT machine, outboard, etc.), not just in the Ghost's monitor section.

    My entire rig is plugged into an Equitech balanced power box. The Equitech is powered from its own isolated 20-amp circuit, and is grounded directly to a 10-foot copper ground spike in my back yard. I've experimented with ground lifts everywhere in the chain, and with the Equitech both in and out of the chain. No difference.

    The Mackie was DEAD QUIET, in the same room with the exact same setup. I was so freaked out that I actually brought the Mackie back into the room and plugged it in next to the Ghost. With no audio equipment plugged into either console, nothing else powered on in the room, all inputs muted and all faders down, listening thru a pair of headphones, the Mackie's 2-bus was dead silent (except for the residual hiss of thermal noise way down there). The Ghost, OTOH, was hummin' like a contented grandma. (?)

    I've worked with a local studio tech in the past. Here are the theories he's kicking around regarding my hum problem:

    1. The Ghost's power supply is built in the UK. It can run on our American 120v/60Hz AC but it REALLY wants to see Brit-style 240v/50Hz. Thusly, the supply isn't doing as good a job of hum rejection at 60Hz as it would at its native 50Hz, and we should mod the supply to run on American juice. (Or run a 240v line into my room.) My tech sez he's had similar issues with a couple of other British-made consoles in my neighborhood (most recently a hum-laden Trident 65 whose noisefloor magically cleaned up with a new custom-built power supply).

    2. We may be dealing with some airborne EFI in my neighborhood. There is a big ol' electrical substation 2 blocks from my house. In the past, I've noticed while recording vocals that I can pick up a NASTY ol' 60Hz buzz depending on how I orient the mic cable in my room. I've tried replacing everything, and I do mean EVERYTHING, in the mic chain in an attempt to eliminate the problem. But it comes down to moving the friggin' cable to just the right angle, while chanting in Urdu and swinging a dead wallaby around my head(ha ha... U know what I mean). So my tech thinks I may need to build a Faraday cage in my little room. Aaargh. All I know is that the Mackie was clean as a whistle, and it seems counterintuitive to me that I need to build a copper box around my room just to get a decent noise floor.

    3. Final theory: my tech postulates that for some reason the Ghost's stock caps in the output section are doing an inadequate job of rejecting AC hum. Ergo, we should up all the cap values by an order of magnitude and replace the existing caps. (And while we're at it, my tech wants to maybe do some re-chipping... anyone done this? TL072's OK in a Ghost or ???) This may be something I want to do regardless of whether it helps my hum problem, just to get the damn thing sounding as beefy as it possibly can.

    I am at my wit's end with this stupid problem and would be eternally grateful if any of you lovely, lovely people could help solve it. Winner gets a bottle of Porfidio Plata fedex'ed to their door, on me.

    Anxiously awaiting a word from the pro's,

    -e
     
  2. PaulStory

    PaulStory Guest

    Hi,

    This won't be a final solution, but have you tried moving the console to a friend's (or neighbors) house? This would clear up the power supply issue and the power station issue (if you can get further away from your house)....if the hum goes away at your next door neighbor's house, it's in your house...if it's still there at a close neighbor's house, but not a distant one then it's the power station. I know it's a pain in the ass to drag that thing around, but at least you'll know what you are up against. Good Luck!!!!!
     
  3. erockerboy

    erockerboy Member

    This won't be a final solution, but have you tried moving the console to a friend's (or neighbors) house?

    Haven't tried this, and you're right, it would certainly tell me whether the problem is specific to my location. The problem is, this thing won't exactly fit in the trunk of my Civic, ya know? And ultimately, there's no option... I HAVE to be able to work at the house, one way or another. (Even if it means going back and buying a 32-ch Mackie, God forbid.)

    Nonetheless, thanks for the reply. :) In the interest of science, I may try and snag a minivan or something, and spend a day totin' the console around town.

    More advice???
     
  4. mixdude1

    mixdude1 Guest

    I had the same problem. One of the ground wires was not attached to the screw in the channel strip inside the console. It was an easy fix but was a pain to diagnose.

    I really like the Ghost, but I don't think the quality control is that great.
     
  5. erockerboy

    erockerboy Member

    Steve, can you describe the physical whereabouts of this particular ground wire inside the console? I'm gonna have my tech give it the once-over anyways, but thought I would get in there first and have a look around......
     
  6. mixdude1

    mixdude1 Guest

    Its been a while so I might be off a little. It's pretty easy to spot though. If you take off the bottom panel, There are screws with about 4 or 5 wires coming off it by the xlr connectors. There are about 8 screws running along the back with wires connecting to each channel.The wires have a hoop that goes on the screw. If you are looking for it, It should be obvious.

    With my console, one of the wires was not attached to the screw. Just sitting next to it. I attached it and 2 months of frustration disappeared.

    BTW, I am not a tech. Good luck,
    Steve
     
  7. mixdude1

    mixdude1 Guest

    Let me know on any upgrades you do. I asked John Curci (A tech in Dallas who works with some of the bigger studios here)and he didn't seem to think any upgrades were worth doing. He thought the chips in the Ghost were pretty good.
     
  8. MPlancke

    MPlancke Member

    Originally posted by mixdude1:
    Let me know on any upgrades you do. I asked John Curci (A tech in Dallas who works with some of the bigger studios here)and he didn't seem to think any upgrades were worth doing. He thought the chips in the Ghost were pretty good.

    I have a whole list of upgrades for this board from Don Petty. It *can* be improved, thank God.
     
  9. erockerboy

    erockerboy Member

    I have a whole list of upgrades for this board from Don Petty. It *can* be improved, thank God.

    Well for God's sake, Mark my man, don't be a tease! Spill all the juicy details!!!

    BTW, Steve, thx for the info... am opening up the board this PM. Will let ya know what I find.

    -e
     
  10. erockerboy

    erockerboy Member

    Welp, took the board apart over the wk-end, and couldn't find any obviously non-attached ground wires internally. My tech is giving it the once-over this week, so guess I'll keep my fingers crossed 'til then. What a PITA tho.

    I am still keen on hearing from anyone who's successfully modded their Ghost. Mark P, if you're out there... love to hear from ya.

    :)
     
  11. MPlancke

    MPlancke Member

    Originally posted by EJolson:
    I am still keen on hearing from anyone who's successfully modded their Ghost. Mark P, if you're out there... love to hear from ya. :)


    Okay, let me see if I can find it.
     
  12. realdynamix

    realdynamix Well-Known Member

    I have an A&H board that gave me the same problem, thinking the caps might be bad in the supply, I replaced them all. No good. Mine would hum in the bus as well, but very evident in the pre-fader solo section. I said what could this be coming from? So I disconnected everything from the board, except monitor out, and just sat and listened. The hum increased and decreased in level, then spike back on, then go quiet, then up again, then modulate. I said what the h*** is this cr**? Sometimes it would not do it for weeks. Next, I did a current draw check on the power panel. That was it! there was an imbalance in my power system on that rail, AC units, Fridge, etc. More current was required on that rail, and when it was loaded up, it transmitted (Radiated the 60hz/120hz,) etc. into the very line I was using. Problem solved, I balanced the circuits, to more evenly distribute the power use on the panel.

    --Rick
     
  13. erockerboy

    erockerboy Member

    That was it! there was an imbalance in my power system on that rail, AC units, Fridge, etc. More current was required on that rail, and when it was loaded up, it transmitted (Radiated the 60hz/120hz,) etc. into the very line I was using.

    Rick, thanks for the response. There are a few things that I don't understand as this applies to my situation, though.

    First of all, do I understand correctly that your console was sharing a *circuit* with other appliances? Or are you saying that your stuff was merely on the same *rail* in your breaker box, and *not* sharing a circuit? My studio is powered from two isolated 20-amp circuits, with a dedicated ground wire run out to a copper ground spike in my yard. The *only* EFI that could be coming in from other appliances in my house would be via the shared rail in my breaker panel, since all the studio stuff is on its own circuits.

    Second, shouldn't the console's power supply do an adequate job of rejecting precisely this kind of interference? And even if the console PS didn't do it, what about my Equitech? Seems like there are enough conditioning and line filtering stages in my setup to eliminate any junk coming down the AC line....

    The thing that still bothers me, is that my Mackie 8-bus was DEAD QUIET in this room. Nothing has changed except the console. I even set up the Mackie and the Soundcraft side by side, and sure enough: Mackie = quiet, Soundcraft = hummmmm. WTF?!?

    So I'm still in hum nirvana over here. Sounds like from what you're saying, recapping may not be a solution. Man, I am running out of ideas......
     
  14. Rader Ranch

    Rader Ranch Member

    not that it'll be any help, but a place i worked at 5 years ago tried to switch one room from a couple Mackies to a larger Soundcraft console and had the same problems. the room had a star grounding scheme with balanced power from an Equitech. i can't remember if it was Soundcraft folk themselves or techs from the sellers, but a few guys came out and scratched their heads for quite awhile (days) before giving up and hauling the thing away. told you it was no help, anything but encouraging :(

    you've already tried powering the console with normal unbalanced ac, bypassing the Equitech? not that it could be a permanent solution of course...just sussing...
     
  15. realdynamix

    realdynamix Well-Known Member

    -e; Yes, the breaker panel was unbalanced, one leg of the 220, that comes into the building, was drawing a much larger load (many amps more). I do share circuit, with some minor lighting, but nothing else. My mackie didn't do it either, I only noticed the noise with the A&H and it's seperate power supply (which also lives near the concrete floor). I am sure you tried another circuit in your facility, with the exception of the 2 you mentioned. The move to test was not an option for me, as my board's weight is 141 pounds. I also tried the direct ground here, 14' of copper into the water table, but that didn't help me, the circuit balancing, was my cure. Don't worry, I trust you wil find the source, it's just frustrating as hell eh,?
    --Rick
     
  16. erockerboy

    erockerboy Member

    Well, I am still beating the same ol' dead horse with this hum problem. My tech's latest idea is to build a new power supply to run at 60Hz/117VAC American power (as opposed to the British-made Soundcraft supply, which presumably duzn't have the same hum rejection at 60Hz as at the UK's native 50Hz). Does this sound like a harebrained scheme to you guys?

    BTW - Mark P, still would love to hear 'bout those Soundcraft mods... any news?
     
  17. exdc

    exdc Member

    humming ghosts

    ever get this fixed?
    i assume you unloaded the console instead, right?
    or did it get fixed?
    exdc
     
  18. Davedog

    Davedog Distinguished Member

    The OP is over seven and a half years old. Curious is one thing. Ancient history is another.
     
  19. audiokid

    audiokid Staff

    hehe, good eye Dave.
    Here's the good thing about 7 year old topics getting posted on. Since I've been working on our new software, and doing a little SEO with google optimizing, RO is getting indexed even better.

    When we launch our new site ( very soon!... ), the entire forum is going to get more traffic, God willing... , thus, old topics will re surface and folks from around the world will be coming here. This is a good thing and hopefully we will be able to answer some of the questions without being puzzled by this..

    This simply means, people are searching google for answers and finding those topics here. It means our google indexing is working and they are asking questions on already opened topics rather than starting a new one. :cool:
     
  20. Tom Fodor

    Tom Fodor Active Member

    Why would you bother switching out the 8 bus for a Ghost? Seem like a step sideways instead of up. The ghosts are renowned for being noisy, and inconsistent. The Mackie is just clean and colourless. You probably have a rack full of outboard colour going on anyway.
     

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