1. Please take 30 seconds to register your free account to remove most ads, post topics, make friends, earn reward points at our store, and more!  
     
    TalkBass.com has been uniting the low end since 1998.  Join us! :)

HELP!! SVT4PRO cutting out

Discussion in 'Amps and Cabs [BG]' started by carpedebass, Apr 18, 2009.


  1. carpedebass

    carpedebass

    Jun 10, 2006
    Texas
    Endorsing Artist: Basson Sound
    Hi everyone. Been a member for a while, but just do not have much time to post due to hectic radio schedule and equally hectic gigging schedule.
    Here is my trouble...
    I run an Ampeg SVT4PRO bridged mono into a Basson 8X10 cab through a BOSS GT6B effects board and X2 Wireless system.
    Lately I have been having issues with my signal cutting out. I checked the cables first, then wireless and effects with no joy. I noticed that the wireless was getting signal and I was getting signal into the SVT4PRO as well, because it would show to be clipping when I would crank it up, but no sound was coming forth. I removed the top from the SVT4Pro and began to notice that the fan was running pretty much full bore.
    Now I have heard the stories of 4PROs having cooling issues when rack mounted, so I left the top off and turned it off to let it cool. Switched back on and thought I had it fixed because I played for another twenty or so minutes and it happened again. Now prior to this, I have played outdoors in heat with no issues, in hot rooms with no a/c and never have I had an issue.
    I started paying closer attention and it seems to be happening at random intervals (sometimes after 5 minutes of playing) with nothing really to do with heat at all.
    Last night i had it in a cold air conditioned room actually fairly close to the a/c discharge with the top off and I noticed that there would be a clicking sound and the fan would rev up really high. A couple of minutes later another click and the fan would operate at normal speed and I had sound again.
    I switched the unit off and let it sit for a minute then back on and played for another hour until the gig was over with no problems.
    What gives here? Could there be something that is falsely telling the thermal senors or whatever that it is getting too hot when it is not? Can anybody help me?
    Thanks.
     
  2. BassmanPaul

    BassmanPaul Gold Supporting Member

    Aug 25, 2007
    Toronto Ontario Canada
    Taking the top off a fan cooled amp and operating it is probably not the wisest move. This would be akin to taking off your radiator cap in your car and then driving it. Fan cooled amps need to move air across the heatsink fins to remove heat from the output devices. Very often the lid is part of that system. Check if the fan blades are dirty. This would indicate that the cooling system is clogged and needs to be vacuumed out.

    What I think is happening is that the output stage is getting too hot and the amp goes into protect. This switches off the speakers or shorts the input to allow the output stage to cool down. Once this happens the speakers are reconnected and the amp operates normally.

    When you bridge any amplifier it's going to be working flat out and getting hot is normal. If it gets too hot the amp will fail.

    What is the nominal impedance of your cabinet? your amp should be able to bridge into 4Ω for 1200W. I seem to remember a post about Bassoon cabinets that their impedance can dip below the nominal impedance of the cabinet. That could well be wrong, I simply don't remember well enough.

    Paul
     
  3. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Perfectly possible there is a bad solder joint telling the amp it is hot. or it could BE hot.

    If the fan speeds up, that suggests something in the thermal sensor that is either actually hot, or is claiming to be.

    To do ALL that, fan and thermal shutoff, the fault, if there is one, would have to be right around the thermal sensor, and disconnect it from circuit common, That's one of about a half dozen solder joints at most.

    maybe it really IS heating for some reason..... did you feel it for heat, or just assume it was Ok cuz it was by the A/C?

    On the other hand, random shutoff seems more like bad connection........
     
  4. carpedebass

    carpedebass

    Jun 10, 2006
    Texas
    Endorsing Artist: Basson Sound
    Thanks for the replies. I only operated with the top off for a little while. It has since been placed back on.
    Today at rehearsal, it started this right away. As soon as I turned on the unit, the fan went to high speed and no sound. I cycled the power off and back on and it worked for a little while and shut back down.
    It does not seem to be getting overly hot. Jerrold, i think you may be onto something. I am going to drop it off at a friend's house that works on these things. He is more likely to find the cause than Ampeg's designers. He is really electrically a genius.
    One thing though, he will want an electrical diagram or schematic or whatever they are called. Does anyone have one perhaps in a .pdf file they could send me by chance?
    By the way, the Basson cab is 4 Ohm.
     
  5. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Um, you do realize that Jerrold was one of those designers for Ampeg, right? Chief designer, I believe.
     
  6. carpedebass

    carpedebass

    Jun 10, 2006
    Texas
    Endorsing Artist: Basson Sound
    Wow. Talk about ways to make friends and influence people...
    *removes foot from mouth*
    My goodness...that was tasty.

    Sorry Jerrold, did not mean any offense. I was just trying to say that this guy is good at what he does. Stupid statement on my part. Guess I've blown it for myself on this forum, huh?
     
  7. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Eh, I'm sure he'll get a good chuckle out of it. I wouldn't worry.
     
  8. pbd

    pbd Commercial User

    Jul 17, 2003
    Metro Detroit
    owner Procables N Sound
    You wouldn't be the first person to put foot in mouth on a chat forum, don't sweat it and keep hanging with us.

    Todd :)
     
  9. carpedebass

    carpedebass

    Jun 10, 2006
    Texas
    Endorsing Artist: Basson Sound
    Thanks for your understanding guys...just hope Jerrold does too. Still in need of a wiring diagram, schematic or whatever in .pdf if anyone by chance has one...please?
     
  10. Jaco who?

    Jaco who?

    May 20, 2008
    Basson seems particularly proud that that cabinet requires 1500 watts. Maybe 1200 Ampeg watts really is still just 1200 watts? I'm just sayin.........
     
  11. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    Laughing right now!

    If you PM me an email you can carpe schematic.....

    JT
     
  12. rbonner

    rbonner

    Sep 25, 2008
    There's several problems in SVT-4PROland.

    The first is racks that are too tight. If you don't provide lots of room on the left and right sides the hot air trying to get out of the amp has no place to go. There's nothing you can do about this design except accommodate it adequately. Heat will build up inside and cook stuff.

    Also taking the top off removes the cooling path as has been stated.

    If the cooling vents are blocked it only takes 1 minute of playing to trip the amp to high fan and only a couple to trip it offline.

    I had an amp in a SKB Roto-X for 1 day. the side got hot and sagged IN blocking both the intake and outlet.

    Once these amps get COOKED really good they will not function right after that. I recommend a trip to Factory service to get it sorted back out, not your buddy the genius. One of my amps I purchased off eBay had been worked on by an electrical engineer who thought he had it figured out and the repair bill was $760 to get it UN-BOOGERED.

    Obviously Jerrold is right on stuff and it might just be a simple solder joint. Apparently according to the techs, these things suffer from overtightened SCREWS retaining FET's and voltage regulators that break off during shipping. Jerrold might confirm if this is BS or not. But with parts not screwed down to heat sinks, things will overheat REALLY FAST.

    I have a small experience with 4PRO's. You can never move enough air around the outside of these things. The best racks are the Shock mount ones with open inner racks and a fan blowing in to supply air to the rack.

    AMPEG recommends three inches of space on each side of the amp for cooling air. This is nearly impossible except for a couple models of rack.

    Mine is rather large and has 1" of side clearance, so I have two fans supplying air to the bottom and two pulling warm air out of the top. SO far so good. BOB
     
  13. rbonner

    rbonner

    Sep 25, 2008
    Oh and the other problem is the Basson cab. It uses 250 Watt speakers and these things inductively KICK BACK at the amplifier apparently. This is why Basson recommends a minimum of 1500 watts worth of amplifier to power the cabs.

    I have heard of a lot of people using 4PRO's with the 810 cab, but i have also heard of problems... There is no solid state amp that likes problems in its output.

    This cab you have will take ALL THE POWER the 4PRO can dish out and more. However if you are playing your amp at anything more than about 5/8th - 3/4 full wide open on the master and just flashing on the input side, the amp will trip offline due to current.

    Just a little ditty. BOB
     
  14. carpedebass

    carpedebass

    Jun 10, 2006
    Texas
    Endorsing Artist: Basson Sound
    Great...now I have to either buy an amp that will supposedly support my Basson cab or buy a new cab...(Basson endorsement...so I will not go with the latter.)
    Any more good news? lol
     
  15. Jerrold Tiers

    Jerrold Tiers

    Nov 14, 2003
    St Louis
    No experience with Basson cabs.....

    On the other hand, unless the Basson cab is a lot lower impedance that it says, I don't know why it should be an issue with the 4PRO. The 4PRO amp is based on a PA amp that would drive almost anything....

    The inductive kickback issue is complex.... without going into boring details, there are two types of that.... one is a mass-based issue if the cones are heavy, that produces an "elliptical load line" (speaker mass shows up as inductance electrically). The other is a purely inductive during an event like clipping....

    If the speaker cones are heavy, the speaker may be less efficient, and might require a lot of power to hit full capability. If the magnets are huge, some of that is canceled, and efficiency can be increased.... but other things change.

    If the 4PRO is built right, it has a conical spring washer under each FET screw, to keep correct pressure. And a torque spec on the screw. Breaking off should not be an issue, and I have actually not heard of that, but I have been out of the loop on new ones for a couple years. ;)

    These days, with new ones, who knows?
     
  16. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Well, it looks like Chuck Liddell is going to retire from UFC ;)

    Yeah, Basson really means it with their suggested wattage ratings. I used to think it was a lot of horsecrap, but they use big giant speaker magnets that really require that kind of wattage to work. My question is what the heck do you do if you want to play quieter?
     
  17. mrkreuzschlitz

    mrkreuzschlitz

    Jun 30, 2008
    Dacula, GA
    Get a 2x10.
     
  18. rbonner

    rbonner

    Sep 25, 2008
    Well Jimmy it isn't playing quieter its the size of the power amp overhead that the thing is looking for.

    Ah... Think sitting on the Florida freeway with the A/C on full and the traffic stopped dead on a hot day and the car starts overheating. Standard mode around Orlando right?

    But the big old diesel truck with a massive radiator just sits there going, I wish I could just drive OVER THE TOP of all these cars waiting to turn into MOUSE. Other than that he doesn't care no overheating.

    Well this kickback from the speakers is a lot like that, if the amp has a lot of capacity it doesn't care. Also if a guy PLAYED the cabs quiet it wouldn't matter, but who does that? You buy a BASSON cab to hit the thing with a ton of bricks. The problem is the 4PRO is just on that ragged edge of dealing with this issue.

    NOW I do not believe this issue with his amp is the kickback issue. I think it is flat out internal at this point. The kickback would have taken out several FETS. Now Jerrold can pipe up here as he's so very knoledgable of the internals of the things. You take out a couple FET's and you will have problems just like whats happening here.. I think.

    BOB
     
  19. rbonner

    rbonner

    Sep 25, 2008
    My two that went in for service were the USA built models. Both "B" stock new, RIGHT!

    One had been worked on by a hack and had a half dozen mismatched FET's installed. They also told me the heatsink and voltage regulators were not bolted down. The first tech could have just given up and tossed all the parts back in the box.

    I had plugged it in to a cloud of smoke and looked at it and saw all the fried parts on the board and just shipped that one off.

    The other unit they said the thing had busted componant screws from shipping ALL OVER THE INSIDE.... But that one also needs to go back again as they didn't fix the problem.

    They maybe just flapping gums for warranty sake with the company and to keep the "Customer" inline.

    I was a heck of an electronics tech while in college. Worked on commercial two way and Ham Radio also a licensed broadcast engineer. Jumped from radio to computers in 1980. Worked on a heck of a lot of audio too all tube amps though but never for a job.

    I've done so many things when I talk about it all most people cry bullticky so I just discuss it usually a little at a time. It makes for an interesting story over a beer though.

    BOB
     
  20. JimmyM

    JimmyM

    Apr 11, 2005
    Apopka, FL
    Endorsing: Ampeg Amps, EMG Pickups
    Ah, I see. That makes much sense to me now. Basson cabs are really odd ducks in the bass cab world, and this whole insane wattage thing is a world I'm probably best to stay the **** out of, anyway. I did a classic/current rock gig last night with my B-15 stack :bassist:
     

Share This Page