4ohm & 8ohm speaker set up for NAD M33 - is it harmful?

[TobyJ]

Hi folks

I have another ignorant tech question that I hope you'll be able to help me with...

I am lucky enough to have a NAD M33 and a pair of Martin Logan Motion 40is. They make a very cool pairing - all sorts of lovely.

But I like the whole thing even more when I add a second pair of speakers - a pair of Monitor Audio Bronze 5s. (Nowt special on their own, but when bass port plugged, they add considerably to the sense of wide soundstage for the whole shebang.)

My question: am I doing any long term harm to the amp by running both pairs of speakers simultaneously? The MLs are 4 ohms, and the MAs are 8. I ran them both together for a couple of weeks and kept watch on the handy temperature readings that the NAD has. It didn't seem to be stressing the amp (at least in temperature terms).

But then I took out the MAs, cos various reading that I did suggested that the setup could be harmful to the amp in some way.

So, could you help me understand: (a) am I doing harm by having that 4 ohm/8 ohm combination running simultaneously? (The NAD has plenty of power - 400w into 4 ohms, it claims). And (b) if I am, could you help me understand what that harm is? (I have no real understanding of the physics or engineering involved, but I'm a reasonably quick learner...)

My best guess was that putting that load on the components would cause them to wear out more quickly. Is that right?

Does it make a difference that the NAD is a class D amp? Does that make it any more/less likely that I'll be doing it harm?

Thanks for any increase in my dim understanding that you can help to create...

 

[TobyJ]

Bumping this, in case anyone with engineering experience has eyes on this time around!

Any help gratefully received.

 

[TobyJ]

This may be helpful... Here's an article on the NAD website claiming that their amps are good down (up?) to a 2ohm load (which should make the 4ohm plus 8ohm parallel setup ok, right?)

https://support.nadelectronics.com/hc/en-us/articles/360000158988-NAD-Full-Disclosure-Power

Oh, and in my attempts at further reading, I have found various articles saying that the other potential danger of this setup is overloading the 4ohm speakers. Aside from the obvious (sounding distorted, drivers moving significantly) how would I tell if the MLs are suffering?

Thanks again...

 

[Koeitje]

Why not just buy better speakers? Those Martin Logan's aren't great.

 

[Vladimir Filevski]

Whatever Monitor Audio says, the Bronze 5 is nominally a 6-ohm loudspeaker, because its impedance drops below 5 ohms in the 130 - 300 Hz region. Hence, the danger of very low impedance load is real with paralleled Motion 40 and Bronze 5, although NAD declares 2-ohm compatibility. Actually, NAD declares "dynamic power rating" at 2 ohms load - in other words, not continuous power rating at 2 ohms!
Not dangerous if played at not too high levels, though.

 

[TobyJ]

Whatever Monitor Audio says, the Bronze 5 is nominally a 6-ohm loudspeaker, because its impedance drops below 5 ohms in the 130 - 300 Hz region. Hence, the danger of very low impedance load is real with paralleled Motion 40 and Bronze 5, although NAD declares 2-ohm compatibility. Actually, NAD declares "dynamic power rating" at 2 ohms load - in other words, not continuous power rating at 2 ohms!
Not dangerous if played at not too high levels, though.

Thanks Vladimir. (And for my guidance, your definition of "not too high levels" would be what?

Also - was I correct in thinking that the temperature readings of the amp are a good indicator of it being too stressed? (Or are the temperature readings irrelevant?)

Thanks again....

 

[Vladimir Filevski]

NAD M33 is very powerful, so no problem driving Motion 40 plus Bronze 5 - if pushed too high, you will fry the speakers, not the amplifier. But according to Stereophile test of NAD M33 ( https://www.stereophile.com/content...3-streaming-integrated-amplifier-measurements ): "amplifier's protection circuit operated intermittently at powers above 400W", indicating stiff current protection. In 2-ohms load amplifier wants to push double amount of current than in 4-ohms load, hence the possibility of trouble. All that is very surprising because NAD M33 is built around the very capable Purify Eigentakt power amplifier modules. Maybe the power supply section of M33 is the limiting one here.
Definition of "too high levels" is deceptive and very subjective, in absence of actual measurements.
Don't know anything about the temperature reading of the NAD M33.

 

[AdamG]

In race car analogy, your pushing into the red too much. Running on the raggedy edge. I would not do it myself to my gear. Just asking for problems. You asked for opinions.

 

[Kal Rubinson]

I would suggest getting another amp for the MAs and run it from the analog outputs of the M33.

 

[TobyJ]

I would suggest getting another amp for the MAs and run it from the analog outputs of the M33.

ooh, that's an interesting idea. So treat the NAD as a pre-amp for the second set of speakers. (I'll have an explore of how to do this... I might have further questions about how to make this work!)

 

[TobyJ]

I would suggest getting another amp for the MAs and run it from the analog outputs of the M33.

Fetched an old amp out of the loft, and took the "pre out" signal from the M33 to that. Sounds great - exactly what I was hoping for.

Began with a slight hitch - it turns out that the pre out of the M33 is really (really) quiet, so I had to turn the volume up very high on the second amp to hear it. (It took about 15 mins of experimentation to find out that was the problem!) But once that hump was negotiated, it's all good.

Thanks very much for your help folks. Much appreciated.

 

[Kal Rubinson]

Began with a slight hitch - it turns out that the pre out of the M33 is really (really) quiet, so I had to turn the volume up very high on the second amp to hear it. (It took about 15 mins of experimentation to find out that was the problem!) But once that hump was negotiated, it's all good.

Ok but this highlights an advantage of the separate amp: You can adjust the relative levels of the two sets of speakers.

 

[TobyJ]

Ok but this highlights an advantage of the separate amp: You can adjust the relative levels of the two sets of speakers.

Just checking - there's no way to adjust the "pre out" signal level, is there? (The M33's signal is so quiet that I have to have the second amp at 80% volume to get any kind of sound from it)

Or (it occurs to me now...) am I asking the wrong question? I've plugged the RCA lead from the pre out of the M33 into the CD input socket of the second amp. (I've also tried it in the Aux socket, and the MP3 single socket input (via RCA to 3.5 mm). None of those other options created a greater sensitivity on the part of the second amp). I can't see any other input options. Should I be trying to find a different input socket?

(The second amp is an old Cambridge Audio Topaz SR10).

 

[Vladimir Filevski]

"Pre out" volume usually is fixed.
All inputs (CD, DVD and Aux) have the same sensitivity, so it is irrelevant where are you connecting the Pre-out signal from M33. But do not use MM Phono input!
I didn't object before, but I have to ask now - are you aware that playing the same stereo signal through two completely different pairs of loudspeakers in the same room is a big no-no, audiophile-wise?
Playing the same stereo signal through two identical pairs of loudspeakers is no much better, though.

 

[TobyJ]

"Pre out" volume usually is fixed.
All inputs (CD, DVD and Aux) have the same sensitivity, so it is irrelevant where are you connecting the Pre-out signal from M33. But do not use MM Phono input!
I didn't object before, but I have to ask now - are you aware that playing the same stereo signal through two completely different pairs of loudspeakers in the same room is a big no-no, audiophile-wise?
Playing the same stereo signal through two identical pairs of loudspeakers is no much better, though.

Thanks Vladimir - that's pretty much what I thought - useful to have it confirmed by someone who knows!

And yes, I had always presumed that adding a second different pair of speakers would sound terrible. But then I tried it, and I preferred it. I don't get the same tight stereo image as with only two speakers, but I get a much bigger soundstage, and a much reduced sense that the music is coming from "over there" (I.e. from the direction of the speakers). If the choice is a tight stereo image or sense of a room full of music, I choose the latter!

 

[Kal Rubinson]

Just checking - there's no way to adjust the "pre out" signal level, is there? (The M33's signal is so quiet that I have to have the second amp at 80% volume to get any kind of sound from it)

Makes sense because the audio output is affected by the volume setting in the M33. Theoretically, the connected amp should have the same gain with its VC full up to match the level from the speaker output of the M33.

And yes, I had always presumed that adding a second different pair of speakers would sound terrible. But then I tried it, and I preferred it. I don't get the same tight stereo image as with only two speakers, but I get a much bigger soundstage, and a much reduced sense that the music is coming from "over there" (I.e. from the direction of the speakers). If the choice is a tight stereo image or sense of a room full of music, I choose the latter!

What you do in the privacy of your own home should be of no importance to others.

 

[TobyJ]

Makes sense because the audio output is affected by the volume setting in the M33. Theoretically, the connected amp should have the same gain with its VC full up to match the level from the speaker output of the M33.

What you do in the privacy of your own home should be of no importance to others.

Ah, I see! The volume control of the second amp is effectively as a percentage control for the volume of the M33. (I have just verified this through experimentation).

Thank you very much for taking the time to increase my understanding. It is much appreciated.

Also, my M33 and MLs thank all the other contributers to this thread for extending their lifespans...

 

[Vladimir Filevski]

I get a much bigger soundstage, and a much reduced sense that the music is coming from "over there" (I.e. from the direction of the speakers).

If you are craving for a big soundstage, than you have to consider "omnidirectional" type of loudspeaker. One pair only!
There are plenty of second-hand Mirage Omnisat and Ohm Walsh (old models only!), plus the new kids (and elders) on the block like Duevel (https://www.duevel.com/home/loudspeaker.shtml), German Physiks (https://www.german-physiks.com/unlimited-ultimate-carbon-loudspeakers) or MBL (http://www.mbl.de/products/laudspeaker/?lang=en).
I would suggest Mirage Omnisat.

Vintage Ohm Walsh loudspeaker:

 

[TobyJ]

Thanks Vladimir. I was thinking similar things myself. I was reading a review of the duevel omni directional speakers just the other day.

I think I'll try to audition some for my next speaker purchase. (It will take a couple of years to save up for that though!)

(The resemblance of those vintage Ohm Walsh speakers to traffic cones does take be back to student days...)

 

[Kal Rubinson]

If you are craving for a big soundstage, than you have to consider "omnidirectional" type of loudspeaker. One pair only!

They're still at the mercy of room acoustics. If you are craving a big soundstage, go multichannel (with room correction).