How hot should a McCormack DNA-225 get?

Hi Mike -

I confess that I am puzzled by the fact that your breaker continues to trip when turning the amp on. The DNA-225 has a fairly large power supply, but tripping circuit breakers has never been more than a rare thing. I can't really imagine anything that could be wrong with the 225 that would 1) cause the breaker to trip, and 2) not show-up in some other obvious way - fuse blowing, amp not working, etc. Did the electrician check your AC system Earth ground? Problems with your power system ground might cause some sort of seemingly unrelated issues like this. I do feel that something unusual must be at work because this is just not a problem normally.

For what it's worth, the "ARC-2" upgrade option does have the effect of being a sort of "soft-start" circuit (even though that is not its intended function). This might eliminate the problem if you decide to have the upgrade work done, but otherwise I don't know what to suggest.

Please give me a call if you want to talk this over.

Best regards,

Steve McCormack
www.SMcAudio.com
760-732-0352

Getting on this topic late so maybe you have looked at or have already been advised of this. Since you have a dedicated line to your equipment you probably don't have this, but on the newer houses, I guess for newer codes, some of the circuit breakers are now equipped with a quicker shut off. Even though they are rated at the 15-20 amp constant load they will flip when seeing a real quick spike, this especially holds true in the high lightning storm areas. I have my listening room on a dedicated circuit line and when I had my electrician install my line he told me he had to use this type of breaker to stay within code, if/when I wanted to change it he would supply me with the breaker but would not install so as not to jeopardize his licence.

I have two amps that are doing just what you are complaining about, a vintage Krell KSA 100 and a highly modified little 2A3 SET amp. The krell I can understand why it is tripping the circuit, it has no protection circuit and goes right to the very large capacitors. The 2A3 amp has had a lot of bi-pass capacitors added to the power supple as well as in the signal path. When it is turned on it either trips the breaker or takes out one of its fuses. Issue 2, has you amp been modified? My solution was to have on outboard slow start for all of my amps and the problem was solved. I started with a variac but it degraded the sound so I modified a Welborne filter with a 3 step slow start circuit, problem solved. I leave the amps switch turned on all the time (saves the amps switch) flip the first switch on the out board filter wait about 10 seconds, flip the second switch wait for the bias to build (2A3 amp) (about 30 seconds) flip the third switch which than is direct and enjoy. This has worked for me for the past 4 years, a little trouble but well worth the effort...............

Again, if this has already been suggested sorry for the redundancy......Bob

I'll make the assumption you bought your 225 used. If so, have you checked the main (externally accessible) fuse? Perhaps the amp developed (or always had) some kind of internal problem on power-up that kept blowing the line fuse so he simply replaced it with a MUCH bigger slo-blo fuse. Cheaper to flick a circuit breaker than keep replacing fuses. Checking the main fuse obviously doesn't fix the problem, but could be a clue to something amiss internally and/or something the previous owner never told you...

DNA 225 fuse rating at 5A..is it fast or slo blo

Hello Hi5 -

I presume you are referring to the AC mains fuse for 220-240VAC, and these are always slow-blow. The fuse will read "T5A" where "T" stands for time-delay. FYI, the internal DC rail fuses are 10A fast-blow (F10A).

Best regards,

Steve McCormack
SMc Audio