I have a pair of B&W DM2a speakers that are delightful, but have a dark, evil side. A few years ago these were my main shop speakers. But they have killed or crippled four amplifiers. A Sansui B3000, Denon POA-2200, Rotel RA-1412 and a Yamaha AX-930. This process takes a few weeks, it does not happen at once – thus causing me to check or replace everything in the chain but the actual speakers. Rather taking them out back and shooting them, I shelved them but now it is time to give them one last chance for rehabilitation. They both meter at 6.5 ohms, both sound identical, both sound fine, but ONE of them is able to quietly fry internal amplifier components WITHOUT putting them into protection mode. I had the Rotel repaired and it was not the main outputs but the BIAS & DC Offset transistors that let their factory smoke out & had to be replaced. I am thinking something in the crossover is to blame? Will a bad cap cause impedance issues under a load? Can anyone confirm such? Should I replace all the components in the crossovers? Even the inductors? Or just the resistors and caps? Anyone with gooder knowledge than me have any insight?
Are you sure it’s not your speaker cables?
Depending on how old those speakers are the caps and resistors could’ve drifted. If possible I would flip the middle inductor on the right so it’s perpendicular to the nearby chokes. Maybe refresh all solder joints.
Wasn’t the wire - that was my first check. And I now have different speakers on that same wire. I guess my actual question is if I were to replace the resistors & caps and there really is no measurable way to check them, I’m taking a risk testing them, so can a bad coil cause the symptoms I’m experiencing? I took them out today and see there were 2 caps & resistors already replaced with a pair of +/ - 10% ones - not exactly audio grade… And sadly - I don’t remember which speaker was causing the grief…
Coils don’t go bad. Talk to B&W for the crossover circuit. Update caps and resistors. If you don’t feel comfortable doing it then find an electronics repair shop to do it. Better than fixing amps.
I used to sell and service B&W back in the 70’s and 80’s. B&W were good in not using electrolytic caps; however I would be suspicious of the replaced capacitors as well as insuring the switch contacts are in good shape.
Cool - I used to work at a Radio Shack that also sold B&W - a million years ago… Do you have a recommendation for caps? Parts Connexion here in Canada has a multitude of options - I think I will go with Jantzen Mox for the resistors - but for caps, there’s 36 different manufacturers with dozens of sub categories… I’d like to use something as close as the originals without spending a ton of money…
I have the circuit & have been repairing electronics on a hobby level and soldering is a daily event in my job so I’m good with the repair part - just trying to narrow down replacement parts at a reasonable price now and ensuring I don’t kill anymore of my vintage inventory…! A guy can easily spent a thousand bucks on top notch caps & resistors… for ONE crossover!! Yikes. But thanks, I’m reassured that the inductors should not require any attention.
On the lower cost side I would recommend ERSE caps. Miflex makes really nice copper foil caps if you want more refinement. I would even add a 0.1uF Miflex copper cap as a bypass for any caps in the tweeter circuit.
I have found Solen caps to be a good price/value replacement. Dunlavy used them in their speaker line and my pair has lasted 20years without issue.
Have you measured the individual parts with a DMM? A decent DMM should have Capacitor measurement, and its worth checking each inductor for simple resistance.
I noticed the inductors are in the same plane so the three that are closest to each other are inducing into each other. The easiest fix is to place the middle one on edge so the fields are at 90 degrees.
Foil inductors are actually not that expensive and I have found they provide a big improvement for the cost. Start with the inductors that are in series with the woofers.
Over the years I’ve moved up the price point with crossover parts and have found that speakers can be improved very dramatically (assuming the rest of the system is higher quality).
I’ve narrowed it down to Claritycaps & Jantzen ($100 in all @ Parts Connexion) or Dayton Audio & Lynk Metal Oxide ($70 @ Solen) (Damn shipping) to keep price reasonable, as I’m also rebuilding the crossovers on my currently used main soundroom MG-IIIs, I’ll spend a bit more on those. The B&Ws are not being used, it’s just that ‘next project’ drive in me & the need to save yet another vintage bit of gear…
Thanks for your help!