Stellar M 700 monoblocks


#1

The monoblocks are being utilized in my weekend home. The system is in a relatively large room, about 24 x 28, with a 12.5 ft. ceiling. The speakers are the big line array Dali Megalines, which I’ve owned for seven or eight years. They have to be bi-amped. From the beginning they have been powered by Bel Canto 1000 Mk 1s, and then by the uprgraded Mk II class d amps. For about a year I’ve had the Direct Stream DAC and transport connected into a Class AV processor. Early on in my life with the Megalines I managed to purchase a second Dali crossover and a friend wired the system to provide balanced outputs to the amps. I’ve now completed two weekends of listening to the Monoblocks.

Out of the box, cold, the monoblocks sounded close to what the Bel Cantos sounded. Every night I ran the Purist Audio break in cd during both weekends. Towards the end of the first weekend music began to be more fleshed out in detail, being rather pleasant to listen to, but not at the level for which I had been hoping. Yesterday completed the second weekend (of non-stop playing). Music sounded even more detailed, refined and closer to what I imagine the live presentation would sound like. If I had not heard my main system in NYC, which also has the Direct Stream DAC and transport, I would be a happy camper. This system has a Vitus Integrated, which provides both incredible detail, but also control of the entire spectrum, especially at both extremes. I’ve never heard such controlled bass coming from my B & W 802 Diamonds. The second system, out in the country, using the PS Audio monoblocks is getting closer to what I hear in Manhattan. With only 100 hours on the monoblocks I concluded that they are not yet producing 100% of their capability. I should point out that the breakin for the Direct Stream DAC and the transport, took several hundred hours for the units to come completely into their own and sound their best, as they do now (I am listening as I write this).


#2

Excellent! Thank you!music-078_gif


#3

Can the M700s be stacked? If so, does stacking affect their sound quality?


#4

I hope so. I stacked mine. Haven’t noticed any problems but haven’t had them that long.


#5

Unless you listen at high SPL and have speakers that are known to be demanding loads, you’ll be completely fine stacking them. I stack my pair and even though I keep them on all day, they actually still run fairly cool.


#6

…the six 700’s that will be arriving soon are being stacked by two on three modular shelves…I have Magnepan speakers that demand power and I hope that this is ok…I am also awaiting the Dectet electric plugs device that the 700’s will be attached to…I have received the seven AC12 power cords for the six 700’s and the seventh for the Dectet to the wall outlet…if all this doesn’t cut it for me…the retirement home awaits.


#7

Yup. Perfectly fine. Send pics when it gets done.


#8

Cool re stacking…assuming adequate ventilation and ambient room temps. I have a second question. Pardon exposing my ignorance but it’s how I learn. If I 'scoped the M700’s output, would I see a signal (sinewave) more representative of a Class A or Class AB amplifier?


#9
Paul McGowan said

Yup. Perfectly fine. Send pics when it gets done.


Paul,

Your dealing with an old man of 75 (although I’ll never admit to it…wait…I just did)…I don’t have a camera nor do I have any knowledge of how to put pictures on this site…so…I’ll just have to write all the wonderful findings that I’m so looking forward to after spending many years with Bob Carver’s Grand Theater Amp which, through the Maggies, have sounded congested and harsh…I was thinking for a time that the sound was due to the speakers and/or the Audioquest cables, but I do not believe that they were the problem…it was only recently that I traded up from the 1.7 to the 3.7 models which reproduces the sound exactly as it receives it and exposed the Sunfire amp’s true limitations.


#10

I’m only a few years behind you “gramps” so don’t feel badly. 65_gif Have fun and let us know.


#12
n2djazz said

Cool re stacking…assuming adequate ventilation and ambient room temps. I have a second question. Pardon exposing my ignorance but it’s how I learn. If I 'scoped the M700’s output, would I see a signal (sinewave) more representative of a Class A or Class AB amplifier?


Hi n2djazz. On a scope the output of a class D amplifier looks different than a linear amp. On the M700’s, you would see a 500kHz signal which is a residual of the switching waveform of the amplifier after the LP filter. Adjusting for the correct time division on your scope would then allow you to see your sine wave or whatever the input signal is.

So its similar besides the switching waveform and its related harmonics. This is why when we measure the THD+N of a switching amplifier, we must apply a digital brick wall filter that has a bandwidth of 20Khz. This allows the analyzer to capture the THD+N that’s within the window of human hearing.

Why not just filter more of the switching waveform?

I get this one a lot. Filtering more of the switching fundamental requires moving the pole of the output filter lower in frequency. As we move that pole down in frequency, it starts to actually interact with the audio band, meaning output impedance and phase shift at HF go up. One obvious solution is to create a higher order filter so that your filter rolls off more dB per an octave. I’ve found this to only cause more issues than it solves without any active feedback from the output to correct for the parasitic’s of the filter. Sonically, output filters that are to close to the audio band tend to “pancake” and smear the images in the soundstage. Overall separation of instruments and detail are also dramatically affected.

Although its extremely critical, the output filter is only one part of the puzzle that has to be optimized in order to design an excellent sounding switching amplifier.

Hope this answers your question.


#13

Hi Darren, thank you for the detailed explanation. It’s very interesting, at least to me, to hear what goes into designing an amplifier from the actual designer themselves. Again, thank you. michael


#14

Craig here… Thanks Darren, yes your explanation is fascinating to this amateur engineer. I did 3 years of electrical engineering and 50 years of audio listening and reading. I understand basic circuitry and amplifier design classes. I have enjoyed a PS Audio 200C class AB amp for 30+ years (Thanks Paul and Bob Odell). It’s great performance had persuaded me that massive current capability, fast slew rate and balanced design with low feedback are well worth the effort and the 75+ pounds of mass. I have read of the possible limitations of class D in past designs, but have also been attracted to the potential efficiency. So, it was with some trepidation that I opted to trade in my old 200C on a pair of new M700 monoblocs. I picked up the M700s last Friday and plugged them in with no load on the bench for 24 hours. Starting Saturday I swapped them into the system in place of the 200C. I had built a pair of dummy speaker loads (8 ohm, 100W) and began to run streaming sources through the amps 24/7 to help burn them in. I listened informally to them on and off over the weekend to various sources and decided that they need more time online, especially at lower volumes. Back onto the dummy loads for another day. Today, with only maybe 75 hours on them I listened more seriously and I must say they are beginning to sound beautiful. High freq sheen is fading, bass is solid, and the detail and definition of the mid and highs is great…the presence and dynamic weight is exceeding even the 200C. I really don’t know how (yet) that a class D output section can do that, but, I am now satisfied that it can and I am delighted. They are back on the dummy loads for the night…looking forward to much more music.


#15
edwardweinman said
Paul McGowan said

I’m only a few years behind you “gramps” so don’t feel badly. 65_gif Have fun and let us know.

...will do...

#16

After reading the recent review of the M 700 monoblocks I decided to follow the advice in the review.
I’ve had four of them since they first came out, as I am bi-amping my speakers. Two stacks of two
were how I listened. The advice in the review was a sonic improvement was heard by separating them, not
stacking them. Yes, indeed, all sonic measures, resolving power, detail, air around instruments and voices,
depth of stage, and most important bringing the timbre of voices and instruments to be heard closer to
what one hears in a live performance. Yes, indeed, remarkable. I did not stop there. Since hearing that I
decided to place each of the two amps per side on the Pangea (very solid and reasonably priced) stands.
This upped the level to a new high. Almost unbelievable. What is interesting is that the resolving power has
improved which now allows me to hear the differences among recordings, poor, average, high level. The average
and great recordings are now reproduced to a level that I have never heard in my home. I urge any one using
these amps to follow the advice herein. Lastly, following the review I have ordered the Iso Acoustics Indigo pugs,
which the reviewer said made an additionally heard improvement.
Happy listening!
Herb


#17

Thank you for pointing out the advantages of following the reviewer’s suggestions regarding stacking. I have very similar experiences and I will not stack them again.


#18

You are most welcome. Enjoy.


#19

I’m excited to see how they work for your amps. The Oreas did wonders for my SGCD and I plan to get more for my S300.


#20

That is great to hear. Eight of the Indigos are on their way to me which I will place under the

amps feeding the ribbons. If I hear further improvement I will order eight more for the amps

feeding the bass sides of the Megalines.