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.


timothywright
I use OmniMic when I'm doing sensitive work.  For your average HT measurement and calibration the cheapest band best tool I know of is the Dayton Audio iMM-6.  I use it with AudioTools on Android.

https://amzn.to/2LkvTl4

One of the most popular combinations I know of is Room EQ Wizard, with a mic from miniDSP.

However, turning to your specific problem, those Magtech amps when they are functioning well can handle any load. They are not delicate then it comes to speaker load or volume.  If the amp is cutting out, you definitely have to have it looked at.


Given the construction quality of Magnepan loudspeakers (no offense, I own a pair), it is more likely the 3.7i than the amp.
Last night I ordered 6 pair of new RCA cables.  Of course they are on back order for a week.  The speaker only goes away after hours of playing.

I'll replace the one right side pre-amp to power amp cable. It could also be a the right side speaker cable; also brand new.

@bdp24 no offense taken, thank you.
@erik_squires  I just ordered the Dayton microphone you pointed to. and today I'll look into "Room EQ Wizard" and I suspect I will buy it.  Thank-you.
Have any experience with Behringer brand equipment?

Their analog gear is cheap, noisy crap not fit for anyone but the desperate.
The digital gear is remarkably bland sounding.  I'd recommend miniDSP products over theirs any day.

@erik_squires  Thank you for that assessment of Behringer.  It seems expensive and not geared for my needs anyway.

Also in my listening room equipment list is a laser pointer/ruler.  It will give me distances from walls, or speakers quickly when I am alone.  Mine is a Bosch, 5  years old, still works on original batteries.  New ones cost only $30. It is a great way for one person to size things up.
I wanted to mention that my phone is a model with an extra large battery. It could go a whole day or 3 with out recharging and features a quick CPU.  That is relevant in that using a phone as a RTA  is both CPU and battery demanding.
Larger than my phone would be a tablet or ipad.  Is anyone running a RTA app on such a devise?  Tablet? windows or ipad  or android?  Any experience out there to advance my learning curve?
Hey Timothy,
It may be better to try to help you by understanding what it is you are trying to achieve first.  What do you need this gear for?

Best,
E
Good question, easy diagnosis of problems when for example a speaker quits making noise.  But I also have an intellectual curiosity.

Last night I was sorting out frequencies and sound levels of background  noises. 

Thank you for asking. I have one of those personalities that first gather's data then finds uses and patterns later on.  40 years ago I pioneered identifying types of coal deposits, and BTU content based on E-log signatures.
I also use the OmniMic. A bit simpler to set up and use than REW, in my experience.

But since I own a UMIC-1 (for use with a miniDSP SHD), I’ve installed REW as well, and the parts I have used are quite good. That would be a cheaper combination than the OmniMic, and if you don’t mind a little learning curve (with a LOT of online support), it is a great way to go.

I suppose you don’t have a spare pair of speakers you could use to help troubleshoot this problem?

Mike

P.S. I also find a laser measure invaluable in audio setup.

P.P.S. Switch the wires between speakers and see if the problem moves with the wires (upstream problem) or not (speaker problem).

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.