Conference napalm::commusic_v1

    Sure, plug it in, but watch your levels. Chances are your D-50
    will subject the speakers to more than they're used to.
    
    I used a stereo amp for a year before I bought my (powered) board.
    
    Edd

    
    Seems stereo amps are fine. 

    Its the speakers that take a lickin and stop tickin.
    
    At low levels you will sound great with no danger.
    
    Just *try* and resist crankin it up and rokkin....
    
    rr.

    I don't necessarily recommend this but, FWIW....
    
    My 'studio' speakers are loaded with Radio Trash 8" full range
    speakers. I regularly run them at ear-shattering volumes. They
    break-up and distort but they *don't* fry...
    
    Edd

    A stereo system is almost ideal for keyboards (broad, flat frequency
    response), but understand the possibility of extremely high levels
    and extremely high bass content.  This is an unprocessed (specifically,
    no compression or limiting like on records or over the radio) source.
    
    len.
    

Due to the advent of CD technology, I imagine that most recent high-end 
equipment could handle moderate practicing (certainly not gigging or serious
partying on the instrument, though).  From what I understand, CD's are not
compressed, and my equipment is all very high current which is necessary for
handling transients.  I don't plan to use my system for my instruments, 
though.  It's not worth the risk.  There is a low filter on my preamp, and 
that's a fairly common feature from what I undrestand, so maybe no harm 
would be done if you had a high-end or "CD-ready" stereo system.


				Mark

    I fail to understand the concerns here. Certainly a Radio Shuck
    15 watt per channel setup with 4" woofers won't make it, but that 
    wouldn't make it for demanding 'consumer' listening anyhow.
    
    I have a 10-year old Marantz 75 wpch stereo amp, and some homemade
    speakers with Dynaudio components.. this was enough to fill the
    U of Az Planetarium at less than 1/2 volume.. 
    
    And I don't even PLAN to purchase a Compact Disk player.

    When I first set up my studio I used a 60 watt per Phillips
    reciever and the afore-mentioned RS loaded speakers.
    
    I soon learned that the stereo was to be the *LAST* item to be
    powered up and in any event *ALWAYS ABSOLUTELY POSITIVLY AFTER*
    the drum machine.
    
    As the drum machine powered up it would drive the speaker protection
    circuitry on the Phillips wacky, tripping the relays like there's
    no tomorrow. 
    
    I don't know why.
    
    Edd

    It's not the bass energy you need to worry about.  Your amp will
    most likely run out of gas before you can damage the voice coil
    of a bass driver.  It's the tweeters that are at risk.  Most tweeters
    will fry at very low RMS levels ( as low as a fraction of a watt
    with a sinusoidal waveform ) and a synth can certainly provide a
    sine wave as an input to your preamp!  This makes a synth much
    different from almost any other "music" source you are likely to
    connect to your system.  It will be a function of the robustness
    of your speaker's tweeters, the level you choose to play the synth
    and whether or not your amp clips the signals going to the speakers.
    If you send a high level sine wave or a clipped waveform to your
    speakers you can melt a voice coil in a heartbeat. Fusing the
    speakers is of possible help for the clipped signals but any
    reasonable-value fuse will happily pass a sine wave that will
    cook your tweeters.
    
    						Regards
    						Doug Dickerson
    

    Re: 828.3 by JAWS::COTE
    
    > My 'studio' speakers are loaded with Radio Trash 8" full range
    > speakers. I regularly run them at ear-shattering volumes. They
    > break-up and distort but they *don't* fry...
    >
    > Edd
    
    Well Edd, it seems you put a pox upon yourself.
    
    Friday night *both* speakers literally went up in smoke. Oh no,
    not just a little wisp like from a cigarette! We're talking clear
    the room and run for your life!!
    
    The story...
    
    I'm currently using a Peavey XR1200 powered mixer in my studio.
    200 watts per side output. I was driving a pair of homemade monitors
    loaded with RS drivers. This set up was served me well for some
    months now.
    
    Friday morning the whole she-bang was working fine. Friday night
    I went into the studio to do some work. The first item to come up
    in my power-up sequence has always been the board. With both mains
    turned all the way down I powered it up. As soon as I hit the switch,
    I heard 'HHMMMMMMMMMM....'.  Assuming a polarity problem, I powered
    down and threw the switch into the other 'on' position. 'HHHMMMMMM...'.
    Now, I've had hum before and just figured I'd find the cause after
    I had everything up, so I walked to the other side of the room to
    bring the synths up.  Within 5 seconds I realized this was not the
    wisest of decisions, as the smoke starts to POUR out of one of the
    monitors. ROCK 'N ROLL!!! I rush back to the board, shut it down,
    unplug it and leave th eroom to silence the smoke alarm in the hallway.
    
    A few minutes later I return, unplug the offending (offended?) speaker
    lead from the board and power up. No hum, and the remaining channel
    is working just fine. (My comment about "they don't fry" is now
    ringing in my ears.)
    
    Mistake #2. Assuming I had a case of SMDS (Sudden Monitor Death
    Syndrome) I move the good speaker lead to the output jack the fried
    speaker *used* to occupy. You see vhat I'm getting at, darlinks?
    Dopey me. This time however, I shut down at the first sign of smoke
    from the remaining good speaker....
    
    "A-ha!!! Board problem!!" I announce. (No shit, Sherlock.) Grabbing
    my trusty DVM, I measure across the 2 speaker leads connected to
    the bad channel. "What's this? 35 volts DC right to the speaker?"
    Argh....
    
    Saturday I make some frantic phone calls to anyone who may know
    anything about power amps. No luck.
    Argh...
    
    With nothing left to loose, I open up the board. (This is easy;
    remember February's Dr. Pepper story?) Luckily for me, when I 
    purchased the board I got a complete print set. Unfortunately, 
    I can't read a schematic to save my life.
    
    Anyhow, with the board opened up, I start to identify the various
    modules. Gut feeling tells me the problem lies in one of the 2
    power amps so I hunt those down first. Got 'em!! Each power amp
    is divided into 2 boards. One contains the 8 output transistors
    and some minor amount of related circuitry. This is mounted directly
    to a large heat sink. The second circuit board is refered to as
    a 'driver' and is attached to the previously mentioned board. 
    
    Following the output leads back I identified the 'bad side' and
    look for obvious signs of damage, burnt or melted parts. Nadia.
    Being an old FS engineer I quickly realize that the only thing to
    do is start swapping stuff out. (???) Not wanting to sacrifice my
    one remaining good channel I ponder which way to swap. Good side
    driver to bad side outputs or bad side driver to good side outputs???
    I opt for the later and move the board. Guess what!! The problem
    moved with it!!!! Feeling somewhat more confident now, I put the
    good driver on the 'bad' outputs and power up. The previously bad
    side now works, telling me I've isolated the problem to the board
    level.
    
    OK fine. If I had a spare driver board I'd be in business, but I
    don't so now we're stuck going down to the component level. I start
    testing all 43 resistors. The first 42 I find all seem within
    tolerance. Number 43 however, a big 1k 5w sucker, is dead open.
    Infinite resistance. I check on the schematic and discover that
    this component is the first thing on the +59V rail. All the outputs
    are 'down-stream' from here...
    
    Could this be the problem? Off to radio shock. Naturally, this is
    the one resistor they don't stock, so today we travel to Active
    Electronics and U-Blew-It looking for a replacement. Also included
    in the search is an op-amp. (At least I think it's an op-amp. It's
    got 8 legs so could be a spider...) This unit took the brunt of
    the Dr. Pepper violation and could be suspect. As long as I'm doing
    surgery...
    
    We'll keep everyone posted through this adventure. Copies of the
    schematic are available to anyone who wants to try trouble-shooting
    over the net.
    
    Edd

    re .9	Well, ain't that the trouble with these nu fangled
    semiconductive amplificaters ? 
    
    	Reg
    
    

    Did the resistor have scorch markes on it?  My suspicion is you
    had an emitter-collector short on an output transistor or some other
    failure that causes an output transistor in a complementary pair
    to be permanently on. So, when you install your new resistor, you'll 
    fry it as well as maybe some other parts.  If it is an output
    transistor from a complementary pair at fault, be sure to replace BOTH
    transistors.  Sometimes you have to replace a matched set, or the
    other may have gone out of spec as a result of stress.

    Steve

    Re .9
    
    Edd, I'd love a copy of the schematics. My Peavey 1200 has an
    intermitent chanel B monitor circuit problem (the PFL & meter stuff,
    not the 'mon' bus).
    
    Jimi. ( MKO2-2/D17 )
    
    p.s. while I'm in there i'm gonna fix the noisy reverb tank too!

    yo Edd. Reiterating that the resistor may be a symptom
    like the speakers....get a couple of em.
    
    Put one in and quick measure the DC volts INTO the
    power amp section. Cant say more without schematics.
    Either 1 or more transistors went and the remaining
    circuit pulls your big dc volts across the terminals
    
    OR, if the amp is "DC Coupled" (or an isolation capacitor
    has shorted!) , the preamp can be the problem as its 
    putting out some DC offset which is faithfully amplified
    to big volts. 
    
    Enjoy. Hey, at least they were RS speakers and not JBL's!
    
    rr
    

    re: .12   I'll get you a full set of prints in the mail tomorrow.
    
    re: others..
    
        Here's what we know so far....
    
               1. Side A is dead.
               2. Side B isn't.
               3. Moving the side A driver board onto the side B outputs
                  causes side B to behave like the bad side A.
               4. Moving the side B driver board onto the side A outputs
                  causes side A to work. (At least it worked for 2 or
                  3 minutes, I saw no indication of failure when I 
                  powered down.)
               5. Side A driver board has a bad 1K-5W resistor.
               6. There was no indication of impending doom during the
                  previous session 8 hours before. (No hiss, pops, etc.)
               7. The failure was noticed *immediately* on power-up.
               8. I moved the cabling from side A to side B and connected
                  a speaker to the *jack* labled A. (Note that jack
                  A is now driven by side B circuitry.) Everything was
                  fine.
               9. I didn't move the side B cabling to side A. 
                  
    
         I tend to agree with the concensus, that an output went sour.
         However, the outputs (8 per channel) are located on a separate
         board. My thinking suggests that (a) since the failure was
         immediate and (b) the driver board from the good side did not
         fail when placed on the bad side that (hence) the output trans-
         istors are OK. 
    
         Mind you, this thinking may be wrong!
    
    
               Driver Board                    Driver Board
           -----------------------        ----------------------
            |  Output          |              |  Output      |
        ----------------------------  ---------------------------------  
           |                   |             |                |
    ---------------------------------------------------------------------
    |         |      |       |         |      |        |         | 
    |         |      |       |   Heat Sink    |        |         |
    
    Output transistors (Big T03-type monsters) are mounted on the bottom
    side of the heat sink with legs extending through heatsink and onto
    output board. 
    
    I just got back from Active Electronics in Westbboro where I bought
    4 1K-5W resistors. Admittedly, it's probably not the source of the
    problem but it will have to be replaced eventualy.
    
    Keep those suggestions coming. Everyone who responds will recieve,
    FREE OF CHARGE, a schematic of the circuit so we can all talk about
    the same thing.
    
    Thanks!
    
    Edd 
      
             
    

    Installed resistor.
    Board works.
    I'm in Bedford with slow link.
    More Later.
    
    Edd

    amazing. 
    
    Mount it so that its OFF of the board.
    
    Do both channels resistors get equally hot? 
    
    Hope so, otherwise....
    
    Good thing you bought some extras to use while 
    you find out the REAL problem that blew the resistor....
    
    But what of the brand new speakers?   Active has some special
    ultra-fast blow fuses....
    
    rr
    

    Re: .13
    
    Yes, Edd, be glad they were not JBLs!  Back in my younger days,
    I blew the mid-range driver on our L100 Century loudspeakers by
    putting an unfiltered SQUARE wave through our stereo from my recently
    purchased synthesizer.  Square waves are more dangerous than sine
    waves because of their high frequency harmonic content.
    
    		Derek_who_now_knows_better

    Got the schematics, Edd.  Have you tried putting the new resistor
    in?  (Hope not, but thought I'd ask.)  As I recall, you said you
    saw DC on your speaker out and didn't see any other fried parts
    besides the resistor.  Looks like something on the load side of the 
    resistor (to the right on the drawing) probably shorted to ground,
    which caused the resistor to blow.  I would check C12 and C14, which 
    may both be electrolytic capacitors that have shorted over the years 
    (assuming this thing is old).  
            
    Steve

    OK, I'm back from the land of incredibly slow links.....
    
    Monday night I installed the resistor (R18 for those with schematics).
    Voila! The board came up and worked like brand new! I ran the unit
    for about an hour before putting the skins back on, all the while
    testing the temperature of R18 against R16 and against the same
    resistors on the other channel. They all get real warm (hot?) but
    all are within the same range (as best as you can tell with a finger
    anyhow!)
    
    Since then, I've put 3-4 hours on the board with no ill effects.
    
    Re: .18 Is it 'normal' to expect an electrolytic cap to fail after
    n hours of use or y years in general? I've got no qualms pulling
    the board apart again for PM, but wonder if I should avoid fixing
    what's not broke.
    
    Also, (just a thought) is it possible the speaker could have failed
    and took the board out? Purely academic, I realize...
    
    Total cost to repair board ................................... $0.69
    
    Now all I have to do is finish reloading the drivers (3 way system)
    in the cabs and I'm back in business!!!
    
    Thanks to all for the help. (Don't throw those prints away!!! One
    never knows....)
    
    Edd

    
    Power resistors DO wear out sometimes, especially ones that are
    passing a good amount of current at all times during their life.

    They fail by opening up. Think of it this way, they're like a light
    bulb. There's a resistive wire inside the ceramic insulator. After
    a while the ceramic cracks from the repeated hot/cold cycling of
    use. When oxygen gets to the wire, it eventually burns out. If your
    headlight on your car gets hit by a stone, it will burn out real
    quick for the same reason.
    
    You did do right by checking to see if each resistor was at the
    same temp, though, because there might have been a semiconductor
    failure as well.
    
    Chris
    

    Precisely how it failed. Open. Infinite resistance.
    
    Edd

    re: .19  Ayup.  Electrolytics can fail over time.  Their values
    are often considered to be -20%/+100% what their markings are. 
    Often, you'll find they tend to fail in equipment that sits on the
    shelf for a while.  They rely on an electrolyte that forms a very
    thin layer of high impedance just along the face of one of the wads of
    foil inside.  After a while, especially when reverse biased or not
    charged up much, the electrolyte can break down and cause the thing
    to short.  Reverse biasing can cause the thing to literally blow
    its top, though there is such thing as an electrolytic that is not
    polarized.  One more thing, if you should ever have to replace one,
    make sure you replace it with one that has about the same voltage 
    rating.  A 100�F cap rated at 15V will NOT act the same as a 100�F cap
    rated at 100V.  For your circuit, I'd leave the board alone if things
    look cool.  If it is a bad cap, the problem won't go away and could
    cause the resistor to have a shorter life.  But, 69�....
    
    Steve
        

    re .19	Electrolytics have a bad reputation within dec.  As
    a service guy just check a few of our products to see which way
    the can is pointing in anticipation of whats going to come out of
    it when the electrolyte boils.  We don't seem to point the open
    end of big electrolytics at logic boards any more, though we used
    to.
    
    re .22	I think they also blow from age and latent defects,
    not just reverse biasing.
    
    	Reg
    

    Re: .23
    
    Oh thanks, I feel so much better now. :^(
    
    Should I bullet proof the studio? :^)
    
    Edd
    
    

    Ed,
    
         If it was a 1 watt resistor that failed due to over stress(or
    rated stress for a long time); then if you can fit it, why not replace
    the 1 watt resistor with a 2 watt resistor of the same value. You'll
    cut your stress ratio in half. How bout it you reliability folks??
    
    Frank

    re .23 and .24	I know of an upcoming product for which dec
    is considering adding fuses to some electrolytics, they are big
    ones.  Its a trade off between slightly earlier fuse failure vs
    slightly later exploded boiling acidic slime, not an easy choice
    the way decisions sometimes get made around here, eh ?
    
    	Reg
    

    re .25 Umm.  I'd rather replace a 69� resistor than a maybe 
    $2.00-if-I-can-find-a-replacement transistor.  So, I'd vote for
    leaving the resistor in and let it burn out every once in a while.
    
    Steve