View Single Post
Old April 23rd, 2004, 12:01 PM
DMXtools DMXtools is offline
Senior Team Emeritus
 
Join Date: Oct 2003
Location: Elgin, IL, USA
Posts: 367
Thanks: 0
Thanked 0 Times in 0 Posts
Send a message via AIM to DMXtools
Default Re: Tech crew blowing speakers too frequently...

Quote:
Originally Posted by Mayhem
You could also use "polyswitches" which do a similar job.... The bonus here is that unlike the globe that needs to be replaced, backing off the power will cool down the polyswitch, allowing the gig to continue.
The problem with polyswitches is excessive hysteresis - once they trigger, you have to cut the power down to almost nothing to get them to reset. The lamp, as long as it doesn't blow, acts more as a compressor/limiter, with the resistance dropping rapidly as the power falls below dangerous levels.

Quote:
Also, Mosfet power amps are prone to oscillation at higher frequencies whcih also will take out speakers. This is a lot harder to detect as it is past the audiable range. I do not know all that much about it but I am lead to belive that the polyswitches can offer protection from this as well.

John - are you able to add to this?
Not really, most of my experience has been with bipolar power stages.

Quote:
Another point regarding clipping - this actually means that you are sending DC or direct current to the speakers which is bad. The reason that I mention this is that you may hear someone suggest "checking if an amp has DC at the outputs". This is what they are checking for.
Actually, not true. DC at the outputs is generally the result of the failure of one or more transistors in the amplifiers. Also, being that it's a two-channel amplifier driving a pair of speakers with passive crossovers, DC is effectively blocked from the tweeters by capacitors in the crossover. Such a fault is much more likely to smoke the woofers.

Quote:
Originally Posted by TimoteusR
He thought the monitor wedge was possesed by demons...
ROFLMAO!

John
Reply With Quote