DC leakage from power amps
I am hoping to get some advice on how to check for dc leakage from my power amps. I have a pair of Bryston 28B SST2 mono blocks, powering a pair of Wilson Maxx2's. The Wilsons drivers are protected by resistors, acting as fuses. I have been blowing quite a few of the mid driver resistors, valued at 5.8 ohms. Last night I lost another mid resistor cluster on my left channel ( there are 4 wired in a series/parallel configuration), and what I thought was a tweeter resistor, but upon replacing that single resistor (4.2 ohm) with a fresh one, still no tweeter. I was fed up, and did not investigate further, but fear that I may have a dead tweeter, or worse, crossover issues. I am no tech expert, but am concerned that I may have DC leakage from my Brystons. I live about a 4 hour round trip to the Bryston facilty in Peterborough Ontario, and have lots of warranty left, but don't want to pack up the beasts and have them inspected if I can confirm on my own, if there is a DC issue. How do I go about checking the amps at home, and confidently knowing if there are amp issues, or not. If the amps are faulty, I will return them for repairs, but would like to eliminate/confirm the issue at home. Any help will be greatly appreciated.
@gs5556 I may need to add that I never power down any of my solid state gear. Only when I go away on extended holidays. My tube gear goes off after every listening session, and upon powering up, is given at least 45 minutes to warm up. The Brystons really help keep my heating bill down in the winter!!! LOL Great for toasting marshmallows too :) LOL |
This problem is **not** caused by DC!! The speaker has crossovers that prevent the midrange and tweeter from seeing any DC- even if the amp had a serious failure that put out so much DC that the woofer was fried, the midrange and tweeter would still be OK. The woofer is always the part that fails due to DC, but a few millivolts is not going to harm it in any way. It has to handle a lot of power from the amp and a few millivolts of DC is nothing. IOW, that's not the problem. What is going on is that the amplifier is not making enough power to make the desired volume. So as a result, it is being overdriven pretty hard, and the harmonics of the distorted bass notes are at frequencies that the crossover allows into the midrange and tweeter. Since these drivers normally don't have to handle such large amounts of power, they get burned up. The solution is either get a bigger amp (start out with at least twice as much power) or put fuses in series with the midrange and tweeter drivers to prevent damage. Or don't turn it up so loud, or get a speaker that is more efficient, so you don't have to clip the amp. |
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@crazyeddy, What are you feeding the two amps with? I assume each amp has its’ own 120V 20 amp dedicated branch circuit. Roughly what is the distance, length, of the wiring from the electrical panel to the wall receptacle outlets? What are you using for receptacles? Did you use #12awg bare minimum wire size or increase the wire size to #10awg? Are you using the stock power cords that came with the amps? If you are using after marker power cords, made by who, model? It would appear these amps need plenty of mains power if you are pushing them hard. If the mains voltage is dropping due to VD (Voltage Drop) on the branch circuit wiring it may be having an impact on the amp’s ability to deliver their full rated power. You can check the mains voltage at the wall receptacle with your multimeter. First check the voltage with the amps at idle. Check the voltage again playing music at a moderate level. Check the voltage playing music loud at the level you like to hear it at. Is the voltage lower but holds steady? Is the voltage lower, bouncing around, with the beat of the music? Specs http://bryston.com/PDF/brochures/SST2_875HT_BROCHURE.pdf https://www.youtube.com/watch?v=TOof73b60E0 Review https://www.stereophile.com/solidpoweramps/108bry/index.html You may find these posts of Charles Hansen of interest concerning "fully balanced from input to output". https://www.audioasylum.com/forums/amp/messages/22/220523.html Jim |
