I have been using a pair of Nc400s on a pair of Magnepan 3.7s recently and at high dB levels they shut down. I have not been able to find anything about this on the forums
If I shut them off and turn them back on in about 10 minutes they work fine. Is there some type of circuit breaker in the NC400 that resets?
From the Magnepan website (FAQ section):
A new type of amplifier (Class D) has become more popular because it is a "green" design and uses less power plus it is smaller in size compared to conventional amplifier designs. We have heard reports of Class D amplifiers shutting down when driving 4 ohm loads or sound quality that is less-than-desirable. Quite frankly, some sound very poor on Maggies. However, more recent designs of high-end models are much better. Because we do not have the time to determine which models of Class D designs are compatible with Maggies, we must take a conservative approach. Direct-coupled, Class A/B designs with high current capability have proven a good choice for many decades.
So that was some funny reading at least for me
, I am curious. What is high dB levels to you? Are you using an SPL meter and if so, what level is it when your amp shuts down (measured from your listening position)? How far are you from each Magnepan 3.7 (please measure accurately!). What is the cubic feet of your listening room, or alternatively the LXWXH in feet?
Judging from the spec sheet on the NC400, and knowing that your NC400 is mounted in the incredible Aluminati cases, they should be getting enough heatsinking if built properly and as long as there is heatsink compound between the NC400 and the chassis (I am going to assume so).
The spec sheet on the NC400 and the graphs seem to suggest that 400-500 watts at 4 and 3 ohm loads is really about the limit for this amplifier. They don't give a max specification, just a typical specification. And the graphs seem to agree with this. Yes, the NC400 can put out gobs of current.
The Magnepan 3.6
is a pretty resistive load of 3 to 4 ohms judging by the last Stereophile review. I haven't seen any accurate, repeatable and verifiable measurements on the 3.7. I'm going to hazard a guess that it will also be about 3 to 4 ohms, and the sensitivity is really 83.5 to 84dB at 2.83V input (at around 500Hz
). So if you are seated about 10 feet from each speaker (and I know the speaker is a QUASI line source), then you will achieve about 107dB PEAK, at the listening position
, at 400-500 watts; this might be an instantaneous
output since the average spl might be about 10-15 dB lower, i.e. 90dB (depending on how compressed your particular song you are playing is, how much bass content there is, etc...).
There are a lot of SPL calculators on the internet. However, the one I found to be the closest to real world simulation is this one (make sure you state that the speakers are IN phase):http://www.doctorproaudio.com/doctor/calculadores_en.htm#calc_spl
If you find that your NC400 build is not suspect, ie. everything is wired correctly and there is plenty of cooling provided by the Aluminati case, then there are only a few options.
Turn the volume down
Get more sensitive speakers
Get a larger amplifier
Move closer to your speakers