Conference napalm::guitar

    
    I have a friend who has the same model bass amp and has someone
    around the Milford, MA area do his repairs. I'll find out and 
    post the info here. You can also ship it back to Carvin for re-
    pairs, and although that sounds like the LAST thing you would
    want to do considering the horror stories we've all heard, Carvin
    has an excellent rep for doing the job right and getting your gear
    back to you. Whether or not your gear is still under warranty, give
    them a call first, they might have the answer. Call 1-800-854-2235
    for technical assistance.
    
    Neal
    

    Thanks for the information, Neal.  Milford is not too far
    for me.  Actually, I called the number you mentioned, and the
    person at the other end sounded very non-technical and did not
    offer Carvin repair service - at least now I know that I can
    ask for it if nothing else works out.
    
    I have been very impressed with the amp's features and sound,
    how about your friend ?  However, after looking at the internal
    construction, the amp should have a FRAGILE sign on it - all
    the front panel controls are mechanically attached to the
    pre-amp circuit board, instead of wired - pressure on a control
    can put pressure on the board.
    
    Looking forward to finding someone who has a technical
    understanding of the PB300.
    

    
>    I have been very impressed with the amp's features and sound,
>    how about your friend ?  However, after looking at the internal
>    construction, the amp should have a FRAGILE sign on it - all
>    the front panel controls are mechanically attached to the
>    pre-amp circuit board, instead of wired - pressure on a control
>    can put pressure on the board.

    Actually, most solid-state amps are built this way these days, for
    better or for worse.   The cost of wiring pots rather than using
    board-mounted pots is restrictive.  Most tube amps still use wired
    pots since they are still built on steel chassis.  Why do you suppose
    an SVT head costs $1700?

    
    	Bring it over to my place, I'll fix it - and charge you
    accordingly.
    
    	Joe Jas

    Maybe I'll take you up on this after I get the schematic from Carvin
    - thanks for the offer.  BTW, not having any experience with the
    cost of this kind of repair, and fixing things myself whenever I
    can, what are the typical charges for repairing large transistor
    amplifiers ?  I expect that I will need  replacement of a volume
    control, analysis of the pre-amp stage, and possibly replacement
    of an IC.  Since I got the amp used and at low cost, I would rather
    spend $100 on a new Mesa or Trace Elliot, than on repairing an amp
    that cost me only twice that.  Are there any standard rates ?
    

    As a side note not meant to be a rathole....
    
    I have two bassist friends who both own carvin bass amps.  Both
    have had repeated problems with them!  They sent theirs back to
    the factory, and both, on different occaisions, received a new 
    amp back...guess they thes that broke were pretty fried.

                    
    
    	
    		Soooooo.... that's why Mesa Boogie uses "wired" pots
    instead of Fender's Motherboard "implants".... hand wired=higher
    reliability....  Borrriss darlink iss dat you??  Dat iss you.. vee
    must get Moose and squeddell, daaaahlink!  
    
    
    Steve

    
    Actually hand wired is probably *lower* reliability from an electrical
    standpoint (maybe some reliability guys here would like to elaborate on
    this possible misconception?).  From a mechanical standpoint, well, the
    pots are bolted down to the front panel with a lock nut, how are you going
    to push it in and flex the board anyway? 

    
    
    
    		Right... I was speaking kinda tongue in cheek... <grin>.
     The issue for me is that the through hole pots should be more
    reliable, but the way most manufacturers (including Fender) mount
    them, they aren't.  Even with my Fender, the only thing supporting
    one side of the amp board is the pots.... so guess which joints
    take the torque when a professional musician loads and unloads his/her
    amp 5 or 6 hundred times with all the banging and dropping that
    goes along with it.   Boogie says that their stuff is made to take
    the road, and they point out stuff like hand wired pots as one of
    the examples... ironic huh??	That's the trouble with mechanical
    torque, one either tries to isolate it.. damn near impossible (see
    any pictures of the springs... not the water kind... at cheyenne
    mountain lately??) or ride with it...
    
    	BTW... wicked nice explanation of effects pedals (in response
    to another note) meant to tell you then but forgot until now.. very
    helpful....

    re: .8 
    
    I don't know how you do it, but I did it with my little Fender practice
    amp a couple of years ago!  And it didn't even get dropped or any
    rough treatment.  Had a very difficult time finding a new pot for
    the thing too, as the ones they used had a small body which it appears
    few other companies use.
        
    BTW:  It didn't break the circuit board, but the little board the
    Pot is mounted on.
    
    Greg

    
    	Reliability is the outcome of deeper factors, one of which is
    called "robustness" or simply how "beefy" something is put together.
    Obviously, if the controls are bolted to a front panel which is
    part of the chassis, this is more "beefy" than if the shafts just
    stick thru clearance holes and any support is rendered via the soldered
    connections to a PC board.
    
    	It is debatable whether the reliability of a wire wrap connection
    exceeds that of a soldered-to-PC-board connection or not. Turns
    out it's a matter of how well the wrapping and soldering process
    is controlled, at the factory. If done correctly, either connection
    will last "forever".
    
    	My repair offer still stands...
    
    	Joe Jas
    

    I'm sure that part of Reliability is usage environment, which for
    a bass amp is full of vibration.  The amp head actually fell off
    a single 15" open back cabinet during normal use, while also insulated
    from the speaker by carpeting.  Unfortunately, after travelling
    about 20 inches, the volume contol touched down first - the probability
    of this happening again is low, and I would not expect most
    manufacturers to design for this problem.  However I do wonder,
    I am better off securing the amp to the speaker where it will get
    a lot of vibration, putting on the floor where a kick to the front
    panel could really hurt, or am I slowly discovering why rack mount
    is a good option ?
    

     One improvement you can make is only use a closed back cabinet
     with your bass head. The amp has to work alot harder to reproduce
     lower frequencies because the spkr becomes "unloaded". That means
     that at lower frequencies, the pressure on the rear of the cone 
     equals the pressure on the front of the cone and they cancel out.
     you may find yourself cranking up the bass knob on the head, which
     stresses the amp and the spkr because the efficiency is so low.
     Open back guitar amps are a different story; they don't have to
     be efficient below 100 Hz or so. 
    
     Neal
    

    
    
    	Greg, this is kind of an aside, but when I needed a pot for
    my Fender, I called them directly and they sent me the pot at no
    charge.. I've documented the whole conversation here somewhere.
     Seems like the person I talked to didn't want to be bothered with
    end customers, and sent me the pot so that I'd get off the line..
    <grin>.. neat deal, huh???   I should have asked for a strat while
    I was at it.   I used a HART desoldering machine here at the plant
    that worked great, but it was an easy enough job that it could have
    been done with a 15watt iron and a Radio Shack solder sucker.

    Thanks Steve, that happened to me about three years ago.
    
    Since I started reading this notes file, I've seen several people
    say that Fender sent them little parts like that free.  Unfortunately
    I wasn't working for Digital then, so I had to have a music store
    special order the thing.  It cost me about $8.00, too!  That's way
    over twice what the 'normal' price was, but I couldn't use the amp
    without it.
    
    Mine was also an easy replacement job.
    
    Greg

    
    Bill,
    I spoke with my friend Ronnie and he said that he always sends
    his head back to Carvin if he needs to get it repaired, except
    for one time when they sent him the circuit board and he had a
    Tech friend of his install it.
    	Ronnie also said that the guy to deal with at Carvin is
    Neil. If you call again, ask for him. They might be willing to
    send you what you need to make the fix. Then again it might be
    worth your while to have Joe Jas take a look at it, especially
    if it's out of warranty.
    
    Neal
    

    Neal, thanks for looking into repairing the PB300.  Carvin sent
    me the schematic.  Aside from the destroyed volume control, I still
    think there is either a broken solder connection or a broken portion
    in the board - which I will look over very carefully before using
    someone else's time; hate to have the mechanic tell me that the
    car was out of gas !  Meanwhile, of course, I have to endure the
    wrath of the other band members, who have been pretty good about
    the substitute 40 watt amp I have fallen back on.  But isn't this
    all part of " playing in the band " ...
    
    - Bill