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Amp gurus, I need your help!

Discussion in 'Recording' started by CombatWombat, Oct 12, 2007.

  1. CombatWombat

    CombatWombat Active Member

    I'm having an issue with my (new, chinese built) AC-30 CC2. It's got the standard Vox GHS speakers. So here's the issue:

    Recently, the amp started making a noticeable buzz/crackle in the left speaker when playing the bottom 5 notes of the guitar (and ONLY the bottom 5 notes). This problem is independent of volume (occurs at low and high volume) and independent of amp settings (tried all sorts of settings to see if it would change).

    My first assumption was a blown speaker as the crackle was coming from a single speaker. When I played the offending notes and applied pressure to the back of the speaker cone with my finger, the problem stopped occurring. So I took the whole damn amp apart to get the speaker out (most difficult amp I've ever seen to work on) and, to my surprise, no tear anywhere to be found. The speaker is in perfect condition.

    Could this be a tube issue? I really don't know much about amps and I don't want to go buy a whole new set of tubes if it's not likely to be the problem.

    Any help from the knowledgeable folks here would be greatly appreciated.

    Cheers,
    Tyler

    P.S. Sorry if this post is a bit jumbled. I'm quite pressed for time at the moment. Thanks again!
     
  2. Try it with a different cabinet and speakers.

    You should really never do that with a speaker.

    It's hard to tell which speaker it is, but if it's that one it sounds like a voice coil rub.

    It probably needs a recone.

    Those probably are not the best speakers around. I would look to replace them anyway.

    Rule of thumb for me is to replace new speakers and tubes. Why you might ask. Simple, the company is going to try and save money and those are the easiest ways.

    For instance I just talked to my friend who owns one and he replaced the speakers with Celestion Blues and now just put in Mercury Magnetic iron.....his response was WOW!!! Plus he has some NOS tubes, Mullard EL84 and JJ preamp tubes.

    They use the cheapest Chinese tubes and I would replace them with either some JJ or Russian or Nos type for better tone and more reliability.

    But back to the speaker, I think it a VC rub and it needs a recone, there are tricks to fix it by putting a wedge under one side of the magnet to straighten out the VC. I DO NOT recommend that.

    Call the place you got it and get a new speaker.

    If it's not the speaker it could be anyone of those crappy tubes. Which one can be tested with a chop stick and lightly tapping it to see which one makes the noise happen.

    It could also be a filter cap on you B+ rail. Or cold solder joint or any other electrolytic cap.

    My guess is the speaker.
     
  3. Space

    Space Well-Known Member

    It reads like a vibration is happening at that frequency and rattling the individual speaker.
     
  4. Davedog

    Davedog Distinguished Member

    Voice coil rubbing. The gritty sound is from the VC being out of alignment and those particular frequencies causing enough excursion to make it noticeable. Putting pressure on the cone and it stopping is the sign that this is the case. That speaker is cheapcheapcheap and its failure rate under real playing conditions is probably high . Its one of those things that makes retail so interesting. That amp comes with a couple of speaker options and why would ANY retailer order it with the worst speaker available??!! Any pro who is interested in that amp isnt going to buy it with those junky speaks....so why stock it?


    Because mom and dad will buy it for junior whos just starting out and since theres no knowledge, they get away with with this kinda crap.

    Inferior products simply PISS me off.


    Great call Bluesman.
     
  5. CombatWombat

    CombatWombat Active Member

    Thanks for the replies everyone. I've actually had the amp for almost 2 years now, so I guess it's probable that the cheap speakers are just ready to be replaced. The reasons I bought it with the cheapie speakers is 1) The price difference between the standard GHS speakers and the celestion blues is I think $600 retail. Maybe just 400, I can't remember. Either way, too much. I can replace them much cheaper myself. The other reason is I got this amp for a song as it was freight damaged because it had a little tear in the tolex.

    Anyway, I guess I look at buying some better speakers for it. Don't know if I can spring for a new set of tubes yet. Money's pretty tight.

    Thanks guys.
     
  6. CombatWombat

    CombatWombat Active Member

    Also!

    Can any of you folks make some suggestions on what speakers to get?

    When I bought this amp, I did a side by side comparison of the wharfdales and the celestions. They both sounded exactly the same to me when playing clean and at a reasonable volume. It wasn't until I turned the channel and master volumes way up that I could hear how much better the celestions sounded than the wharfdales.


    Also, could the messed up voice coil be a result of playing bass through the amp? If it is, I'm gonna make my roommate help pay for replacements as we share our basement studio and I know he's used it for that purpose a number of times.

    Thanks again and sorry again for the scatterbrained posts. I really need a vacation!
     
  7. Never play bass through a guitar amp unless it's on very low. Unless you know the parameters of your equipment don't do it, even then. The low notes make the VC extent past it maximum point and poof, blown or VC rub.

    Master volumes down everything sounds the same, squashed and compressed. Open up the amp and that's when it comes alive.

    Celestion Blue's are know to blow up, that's one reason they probably came out with the gold. Even 2 blue's probably can't handle the power.

    If you dig the celestion sound there are companies that make similar sounding speakers. One is Eminence the other is Webervst.

    Alnico speakers are more money than ceramic but may not sound better to your ear. Blues are Alnico.

    For $200, a pair of Celestion Greenbacks you can't go wrong.
     
  8. CombatWombat

    CombatWombat Active Member

    I was just listening to some mp3 comparisons of different celestion speakers. The greenbacks actually sounded the best to me. If I can find a set for $200 or less, I might have to go that route. There is simply no way I'm gonna pay $540 for a set speakers to go in an amp I only paid $800 for. :lol:
     
  9. They usually sell for that, but you can get them used for a few bucks less. they do retain their value.

    $109.00 at Musicians friend with free shipping.

    (Dead Link Removed)

    Make sure you get the correct impedance(Ohmage).
     
  10. CombatWombat

    CombatWombat Active Member

    Thanks bluesman. You've been very helpful. Any suggestions for where/what to look for new tubes should I decide to spend more money than I have.
     
  11. If you want new tubes call my friend in Texas, he will also have those greenbacks for you. Tell him Noah sent you, that's my name.

    http://www.jmimusic.com/

    If you want NOS.

    http://www.kcanostubes.com/content/

    Do not buy JJ GZ34 rec tubes if you have a rec tube, use the Russian Sovtek one. I and many other people have had issue's with the JJ GZ34. 5AR4 and GZ34 are the same tube. I pay a little extra for the GT 5AR4 which is a Sovtek. I don't like Chinese tubes all that much, I've had issues with them.

    http://www.tubedepot.com/index.html is a good place to get tubes.

    I think JJ makes some ok El84's but I would do some searches for people who use that amp or that tube.

    Since you are short in the money department I think NOS Mullards are out of your league, but those are the best. They have been reissued and are probably nowhere near as good as the originals, but may sound OK. Reissued in name only, it a whole story.
     
  12. If you want new tubes call my friend in Texas, he will also have those greenbacks for you. Tell him Noah sent you, that's my name.

    http://www.jmimusic.com/

    If you want NOS.

    http://www.kcanostubes.com/content/

    Do not buy JJ GZ34 rec tubes if you have a rec tube, use the Russian Sovtek one. I and many other people have had issue's with the JJ GZ34. 5AR4 and GZ34 are the same tube. I pay a little extra for the GT 5AR4 which is a Sovtek. I don't like Chinese tubes all that much, I've had issues with them.

    http://www.tubedepot.com/index.html is a good place to get tubes.

    I think JJ makes some ok El84's but I would do some searches for people who use that amp or that tube.

    Since you are short in the money department I think NOS Mullards are out of your league, but those are the best. They have been reissued and are probably nowhere near as good as the originals, but may sound OK. Reissued in name only, it a whole story.
     
  13. CombatWombat

    CombatWombat Active Member

    Cool. Thanks for the recommendations. I know very very little about tubes. I went and looked at the innards and there is one big Sovtek 5AR4, 4 electro harmonix EL84s and 3 Chinese 12AX7s that plug into the circuit board.

    Seeing as I don't know anything about tubes, I don't know what each of these tubes do or whether they need replacing or not. I went googling, but didn't find a whole lot that helped me understand.

    Thanks again for all your help. Much appreciated.
     
  14. Well you seem to already have some good tubes in there.

    I would change out those 12AX7's eventually.

    There's plenty of info on the net about tubes. You have to search.

    Go to Webervst forums and ask questions there.

    There are 2 basic 12ax7's, long plate and short plate. The long plate are good for high gain sounds but can get microphone especially in a combo.

    The original amp used all Mullards and the 12ax7's were long plates.

    Maybe the JJ ECC 803 or 83 might be a good choice for your amp. Tube depot explains a lot on their web site.
     
  15. cathode_ray

    cathode_ray Active Member

    Try this on speaker; remove from cabinet, lay on flat surface facing upwards. With a small paint brush paint lacquer thinner on the spyder - it will soften and "maybe" re-center within magnet gap. What have you got to loose(beside brain cells from the thinner).
    Tubes:http://www.eurotubes.com/index.htm. Guys in Pacific NW and can't be beat.
     
  16. CombatWombat

    CombatWombat Active Member

    Thanks for the reply...but I don't even know what the "spyder" is...so I don't know how qualified I am to perform that work. :lol:

    Nevertheless, I will find out and give that a try before I spend any money.

    How bad of an idea would it be if I just replaced one speaker with a greenback, left the other as is and replace it later when I have more money?
     
  17. moonbaby

    moonbaby Mmmmmm Well-Known Member

    Greenbacks are known to break up a bit "earlier" than most of the other Celestions. They are great in a cab, they are fine in a combo. Using one now, and replacing the other one later is no problem, many folks have FINALLY discovered that unmatched speakers can deliver great- in fact, killer - tone. You might even want to leave it that way! Just be sure you use the right impedance model. Also, observe and follow the speaker wiring very carefully.
    And despite what some people on this forum have suggested, bass guitar can, like BD stated, kill a guitar speaker fast. Tell your buddy to pony up.
    Even if some guitar speakers can take low-dosages of bass, those Chinese-made Celestions can't.
     
  18. Buy one at a time. No problem there....

    Some people like to mix speakers.
     
  19. Davedog

    Davedog Distinguished Member

    One of my main recording cabinets in my past lives was a 1971 Marshall slant 4-12.....It had one original celestion, one HiWatt Fane speaker, one Fender stamped basket, and one JBL D120. It was wired so I could use any ONE speaker or two, or the whole flippin thing. Thing was, when they were all cranked up together that cabinet sounded incredible.


    Again.......way ahead of the times...............
     

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