Conference napalm::guitar

    
    I'm not sure why you would want to disconnect the speaker while
    the amp is on, but in Fender amps anyway, going to standby disconnects
    all power from the tubes *except* the heaters so it *should* be
    safe.
    
    Most modern solid state amps have no problem running into an open
    circuit such as a disconnected speakers. 
    
    

    As far as transistor amps go, be careful that you don't short the
    speaker connections (this can happen if you plug the speakers in after
    the amp is turned on, depending on which connection you are making at
    the time. To cover yourself, turn that amp off then make changes. I'd
    suggest this with tube amps also, just to be safe.

    I remember that I had a A$$ kicker EMC bass guitar amplifier back in
    the late 1970's that had a transistor output stage on it, it was also
    fuse protected in the output stage. I blew that transistor stage 4
    times and never once damaged the fuse (the fuse was certainly protected
    alright - it was the correct value, according to the info on the back
    ofthe amp). My solution was to take a bunch of 10 ohm 20 watt resistors
    (4 actually) and put them in parallel (comes out to 2 1/2 ohms) then
    connect those in series with the output jack - never blew them after
    that. These parts are still available from Radio Shack.

    I also have an old Standell power amp that some ingenius desiger solved
    the short cuircuit problem by putting a 12 volt car light bulb (like
    the ones found in your average car turn signals) in series with the
    output. Well, it did indeed add a very unique distortion to the sound,
    tho not very desirable (sounded awful!!) - I got this amp for 50 cents
    a flea market - it also had a blown output stage. With resistors (as
    described above) it worked a lot better. Seems that everyone uses
    2N3055 output transistors (I know that the Shure Vocal Master does,
    along with 2N2955's - Since I've fixed one of these recently).

    The moral of the story is never swap speaker connections when things
    are powered up. You'll save a lot of headaches.

							Jens

    G.K. AMPS SEEM TO BE VERY SUSCEPTABLE TO OUTPUT STAGE DAMAGE FROM
    HAVING THE LOAD DISCONNECTED----SEE REPLIES TO TOPIC ON G.K.
    RELIABILITY.I DONT UNDERSTAND WHY YOU WOULD WANT TO TAKE CHANCES
    WITH ANY OF YOUR EQUIPMENT-I WOULDN'T--MY STUFF'S LIKE MY CHILDREN
    ALMOST!
    

    
    	What happens on tube amps is that the output transformer works
    like a big inductor, without the speaker load. Accidently put a
    signal into it and it will "react" with a very big voltage. The
    voltage is sometimes enough to arc across the primary windings of
    the output transformer, leaving a carbon trail. Once this happens,
    it takes less voltage to get across the carbon trail, and (why do
    I type this all in?) you'll get an arc even with the speaker connected!
    You've successfully blown your output transformer!!
    
    	On standby, B+ is disconnected from the output tubes, hence
    they cannot put a signal into the output transformer; it cant react,
    etc. You only open yourself to a possible mistake; OOPS! I hit the
    standby and a "power chord" - forgot to plug in the speaker...
    
    	Some amps short the output at the 1/4" jack to avoid this.
    
    	I learned about "what happens" when I was using a tube hifi
    amp as a distortion generator - without any loading for the speaker
    at all. Whatzat Smell?
    
    	Joe Jas
      

    This seems like an appropriate topic...
    
    I just purchased an EV Amplified Bass Module. Basically, it's a 
    12" long throw woofer driver in a ported plastic cabinet with a 
    built in 400 watt class-D digital amplifier and crossover unit.
    
    I have a few questions about this unit...
    
    1) I've read about class A, class B, class AB type amps. What is a
       class D. I presume the D means digital, but how a digital amp works,
       I have no idea. What is it's expected reliability? Any shortcomings?
    
    2) My Peavey Special 130 guitar amp states 300 watts at the input
       and 130 watts maximum output. The back panel of this unit states 
       "400 watt Class-D Digital amplifier" but at the A/C (110v) power 
       inlet it says "100 watts", and the power cord is not as heavy gauge 
       as I would expect for a 400 watt unit. I can understand the Peavey
       requiring 300 A/C watts to make 130 watts RMS, but how can this
       amp use 100 watts to create 400 watts RMS? Are the EV folks using
       some "new math" to figure their specs?
    
    3) The A/C plug does not have a ground pin. 
       The mains consist of a (grounded) Peavey CS-800 (stereo mode) into 
       (2) TOA 380-SE. I fear that if the EV module goes searching for a 
       ground, It'll go back through its signal input line, into and
       through my mixer, out the other mixer outputs to the CS-800 and it's 
       ground. 
       BTW: All components are connected either directly ot through 
       power-strip to a (grounded) Furman power conditioner. 
       Could this lack-of-ground in the bass module create some difficulty 
       with the rest of my system? Could the above nasty actually happen 
       and cause to blow/cook some equipment (or perhaps myself) at a gig?
    
    Any answers and discussion are welcome.
    
    Larry Brooks