Instrument Flight Rules?

I very recently purchased a Sanders Magtech amplifier to feed my Magnepan 3.7i speakers.  I have a 30 day trial period so I have been diligent in my efforts to “exercise” the Magtech to see if it fits my needs.


I have lamented the lack of useful dB meters or even dB LEDs on the front of the Magtech.  This may seem childish until one has a problem. Twice in two days it seems as if one (right hand side) speaker cut out. My hand held dBa meter tells me I was always under 90 dBa and my Rotel RC-1590 pre-amp tells me it was set at 70% of full power; so I will argue that I was not hammering on it.

 I’ll turn the pre-amp down to 40%, take a short break, return and when I do both speakers are working perfectly. It could be a source problem, a pre-amp problem, a power amp problem or a speaker problem.

Tuesday morning I called Josh at Sanders and his idea was that sometimes the power amplifier fuses do not travel well.  "So remove and replace and the problem may go away."  Maybe circuit breakers reset, in my experience AGC glass fuses don’t heal on their own.

 When I mentioned that some indicators might be helpful he mentioned that Sanders internally uses “American Audio LED dB Level Displays ” ($80 on Amazon) which, I am advised) are sonically transparent, I could place one before and another after the Magtech.  So I purchased two.

 I could also put an ohm meter across every RCA cable, search for an intermittent open cable? No one was anywhere the cables when this happened twice. I've purchased "audiophile"  RCA cables that were bad out of the box.

 My Rotel pre amp lacks the ability to swap L&R channel output.  In general making an equipment configuration more complex, or adding 3rd rate auxiliary junk, is not how one best diagnoses complex problems. I have mixed feelings about this approach.

 I own a Samsung Galaxy S9+ phone. I found a RTA app for my phone named “Audizr Pro” which cost me 99 cents and so far I think it was money well spent. When my furnace fan kicks on I get a 260 Hz noise that is -70 dBa; it can detect it with the room other wise silent. I also have a very large Levoit air Purifier in an adjacent room that the Audizr can detect in an otherwise silent room.  There may be other RTA apps for android devices if you have some experience I would like to benefit from your experience.

 I own an inexpensive “American Recorder Technologies Sound Pressure Level Meter” which cost me $50 five years ago and is still on the original batteries. I would argue that it is not OSHA calibrated but it is better than nothing, or better than guessing.  Without it I would not know that I seldom have 90 dBa listening levels, I would have guessed I was above 100 dBa.

 Other than educated ears, what instruments do you use in your listening room?  I had some very inexpensive thermometers I used to position on the shelf beside or on top of my power amplifier.

Hi OP,

None of these tools are particularly good at diagnosing amp / speaker on/off problems, but assuming you had a working system might help you find a speaker not performing closely to another.

I suggest you investigate a DC/AC analysis class first, followed by learning how to build speakers.

Then you'll know what tools you want/need.
The problem did not repeat last night, I was listening at lower sound levels.
@mike_in_nc  I'll have to keep a 1.5 mm hex handy, required to change speaker cables on Magnepan at the speaker.
I like the song I was listening to today, when bumped up the volume I lost the right channel again.
Today I lost both channels. When I returned an hour later I have sound but no lights on the front of the pre amp. I think I may know where the problem is.
This has not made me a fan of Rotel.