Constellation Inspiration Stereo 1.0 power amplifier

I've found that some audio amplifiers have sonic signatures so subtle that they emerge only over weeks of listening; yet other amps sound so distinctive—more vivid, more transparent, more dynamic—that their signatures are immediately apparent. Can those latter qualities really be inherent in the recording, or are they colorations produced in the amplifier?

The question arose soon after I moved from New York to San Rafael, California. My New York listening room had been big—25' by 13', with a 12' semi-cathedral ceiling. I now listen to music in a room only 11' by 11.5', with a flat ceiling 8' high. My California room is less reverberant, with less bass extension and a shallower soundstage, but it's more revealing of instrumental timbres.

Which brings me to the first audio component I've reviewed in this new room: Constellation Audio's least expensive power amplifier, the 200Wpc Inspiration Stereo 1.0 ($11,000). I wondered if this amplifier would deliver the same excellent sonic qualities I've heard from costlier Constellations. The minute I heard the Stereo 1.0 play music, I had my answer.

From the front, the Inspiration Stereo 1.0 is a rectangular block of aluminum 8.5" high by 17 wide by 19" deep; it weighs 55 lbs. Its matte brushed-aluminum finish is relaxing to the eye and perfectly smooth to the touch—except for two ridges that gradually emerge from the surface as they ascend the height of the faceplate, then just as gradually disappear into the surface of the top plate as they run from front to back. The only control is a bar that runs most of the width of the front panel. This functions as a Power/Mute switch and has a single central LED. On each side panel are 9 rows and 22 columns of circular vents, offset from similar holes in a second panel under the first. This design creates a unique pattern of interlocking ports that provide ventilation for the internal heatsinks.

In the bottom plate below the internal heatsinks on each side is a row of rectangular vents parallel to its side panel, for convection cooling. Like the Mark Levinson No.585 integrated amplifier, the Stereo 1.0's heatsinks extend roughly half the length of each side panel. Each part of the case—top, bottom, and perforated sides—is tightly fitted around the heatsinks inside, making the entire case an effective radiator of heat. This allows the amp's exterior to resemble a smooth, uninterrupted, rectangular billet of aluminum that looks more like a sculpture than an exotic, high-end amplifier.


Sitting atop the rear panel at chassis center is a small black subpanel with a 20 amp IEC AC jack and the main power rocker switch. Near the center of the rear panel are two pairs of large, rugged speaker binding posts. Between and just above those are a USB service input jack, and a 3.5mm Trigger jack for a 12V DC on/off control signal from a preamp or a third-party control system. Also on the rear panel are a Mute On/Off toggle switch, a three-position toggle for selecting between Direct, Balanced, and RCA inputs, XLR jacks labeled Balanced and Direct, and an RCA input jack. The Direct XLR jack can be used only with Constellation's preamplifiers, all of which include the same line-stage gain module that comprises the Stereo 1.0's initial input stage. Plugging an XLR from one of those models into a Stereo 1.0's Direct jack bypasses the amp's input module.

Inside, the Inspiration 1.0 is divided into two compartments: the one in front houses a large toroidal transformer and switching relays, and in the rear are the circuit boards, electrolytic capacitors, output devices, and heatsinks. Putting the audio circuits in the rear makes possible the shortest route to the input and output connectors. The power transformer is shielded with aluminum plates, and a shielded channel brings the AC from the rear panel to the transformer. There's more point-to-point wiring between the circuit boards and transformer than I've seen in other high-end solid-state amplifiers, but these appear to be terminated in snap-on connectors, which should make for easy servicing. The back panel must be opened to replace the fuses; they're not easily accessible.

Like other Constellation amplifiers, the Inspiration Stereo 1.0 is built around single-ended, 125W MOSFET-based modules comprising discrete components. Identical multiples of this circuit are combined to scale up from the Stereo 1.0's 200Wpc to the 1.1kW of Constellation's flagship amp, the Reference Hercules II Mono (both outputs specified into 8 ohms). Each module represents a "single-end, fully-balanced amplifier" that employs carefully matched but floating (ie, not referenced to ground) pairs of N-channel MOSFETs connected to the speaker load, without an output filter network. The Stereo 1.0's power supply has an impressive amount of storage: 24 filter capacitors of 10,000µF each.The exterior of the Inspiration Stereo 1.0 exudes simplicity and purity of form, its rear-panel components are rugged and of high quality, and its internal build quality is superb.

With my reference Quad ESL-989 speakers at the repair shop—they were damaged during their journey across the US in an Atlas moving van—I placed one Revel Ultima Salon2 speaker to either side of my equipment rack. The Revels were 3.3' from the front wall, 6.3' apart (measured from the speakers' tweeters), and 6.3' from my listening chair.

Although the Inspiration Stereo 1.0 weighs only 55 lbs—half the weight of one Mark Levinson No.536 monoblock—its lack of handles and my own limited strength meant that I couldn't lift it onto a shelf. So I placed it on the floor, which made it easier to switch interconnects and speaker cables when comparing amplifiers.

The Stereo 1.0's shipping carton also contained a heavy detachable power cord and three fuses. There was no hard copy of the manual, so I downloaded it from the company's website. Following the instructions, I plugged balanced interconnects from my preamplifier into the amp's rear-panel Balanced jacks (not the Direct XLRs), set the Input toggle to Balanced and the Mute toggle to Off, and the master power switch to On. The LED on the front glowed a steady red, signaling that the Stereo 1.0 was in Standby mode.

Where it stayed. Despite my frantic pressings of the front-panel bar, the Constellation stubbornly remained in Standby. I remembered something similar happening in 1999, when I reviewed Mark Levinson's No.334 amplifier. Repeatedly pushing the No.334's Standby/Power button did nothing. Reading the manual revealed that I had to wait a full three seconds after switching on the No.334's main power switch, on the rear, before pressing the front-panel button to bring it out of standby. Could this be happening again?

Constellation Audio
Suite 1, Level 6, 580 Street Kilda Road
Melbourne, Vic 3004
(805) 201-2610

georgehifi's picture

I agree, but! it can be a problem if left open circuit (nothing attached) or used with un-shielded interconnects which many whacko's do, as then it is very susceptible to RF break through.

Also regarding wattage advertised, purposely understating the 8ohm wattage, this is starting to become a disturbing smoke screen trend these days, advertised 200Wpc into 8 ohms or 400Wpc into 4 ohms make this amp look as though it can double into each having of impedance load making it look as though its real current pusher into nasty speaker loads like the Wilson Audio Alexia.
When as you tested it gives in fact 340W into 8 ohms and only 480W into 4 ohms. Which is not a very good current pusher, pretty weak in fact and may not drive the Alexia's .9ohm EPDR load in the bass very well at all.

In a way Larry Greenhill heard what the circuit/topology limitations are in the bass EG: not much current.
"However, the Constellation didn't go as low in the deep bass. This meant that dynamic contrasts involving deep bass, such as sustained pedal chords from pipe organs, were more emotionally involving with the No.334, shaking my listening room more. When I played the Toccata of Widor's Organ Symphony 5, as performed by Jonas Nordwall and recorded by John Atkinson (24/88.2 AIFF file), the No.334 delivered more thunderous deep-pedal notes that pressurized the room"

Even though the ML334 is only a 125w amp it can push more current into the bass of his Revels than the 340w Constellation can.

Cheers George

dce22's picture

"Even though the ML334 is only a 125w amp it can push more current into the bass of his Revels than the 340w Constellation can."

Not really?
ML334 can do 240W squeaky clean sine to maxedout clipped 510W squarewave in 4 ohm,

The difference in low frequency performance comes from the subsonic filter that distorts the signal in Constellation.

CG's picture


First, I hope Larry Greenhill wasn't sitting in the listening position for hours during that 90 dB break in period. That's OSHA limit sound levels. Interestingly, with that listening position and those speakers with their efficiency performance, that sound level only requires about 3 (three!) watts in the bass region. That's assuming more or less monophonic source material in the bass and the measured roughly 4 Ohm speaker impedance down there.

I don't think any voltage source amplifier can "push" more power into any load resistance than another, based on Ohm's Law and basic physics. More current equals more volts (and vice versa). That's assuming that you're not into amplifier current limiting, of course. Since the Constellation can deliver 340 watts into 4 Ohms with relatively low distortion, you're not into current limiting up to that level. If one presumes that the (mostly) undistorted power output is limited by voltage clipping at higher load resistances (like 8 Ohms) and by current limiting at lower impedances (maybe even 4 Ohms), it only takes high school math and physics to determine the current limits of the amplifier.

So, do you think the lower bass impact is what's shown in figure 1? That is, the amplifier amplitude response being down by 3 dB at 20 Hz? Seems likely to me...

(Twist on usual disclaimer: I've never seen or heard any Constellation product. I don't think I've seen or heard any Levinson product since Harmon purchased Madrigal. Point is, I don't have a horse in this race. Wait - I have met people who are hearing impaired by exposure to too loud sound for too long periods. So, I'll stick to my one-sided bias of not playing music too loudly.)

dc_bruce's picture

Mr. Atkinson's measurements show this amplifier's amplitude response is about 2.5 dB down at 20 Hz. That seems to be audible, based on the review. A number of full range speakers will be flat in-room to 25 Hz or below, so this kind of response droop is more than academic.

Perhaps this amplifier's virtues are best appreciated with a stand-mount speaker, most of which fail to reproduce much below 40 Hz.

Still, for $11,000, I think a buyer would reasonably expect flat response to 20 Hz, on the off chance that he or she might some day replace that bass-shy stand mount speaker with something bigger and more powerful in the bass.

georgehifi's picture

dce22 "Not really?
ML334 can do 240W squeaky clean sine to maxedout clipped 510W squarewave in 4 ohm,"

This show the ML334 can do the doubling into half the impedance far better that the Constellation can, which means it's far better at supplying current.

Cheers George

dce22's picture

"Doubling into half the impedance far better that the Constellation"

Yes ML334 can drive lower resistance without brownout but by the time your in 400 watt you are crunching deep into the voltage rail its all gone wrong, while Constellation is squeaky clean up to 410 watts and bearable at 510 watt while ML is fully flatlined,

So the current is not a problem into these speakers its the distortion ML is pristine into the lower frequency while Constellation distorts the low end creating that light sound

Example - Figure 1 and Figure 6 blue line

ML334 has lower voltage rail more stability at 2ohm, 1ohm load,
on these 3,5 ohm Revels Constellation amp has 3db more dynamic range that will never come to play normal levels are maxing out at 10 Watt with some peaks at 100 Watts

Its easy to fall into the trap of
It sound like this because of that (Current ability in this case)

Myself did the same when designing a tube amp for a friend,
trying to fix a specific sound quality issue focusing on one fancy thing that seems logical when infact its something less sexy and more simple.


georgehifi's picture

These ML2's at only 25w per channel will drive "to a given volume" the Wilson Alexia better than the Constellation can, and even the ML334 as well. As they will stay flat and not act like a tone control like the Constellation and to a lesser degree the ML334 will.

This is why I'm so against manufacturers understating the 8ohm wattage just so it looks like it's doubling into 4ohms, to give the impression that their amp has massive current ability.

Cheers George

dce22's picture

Constellation amp from the fig 4 and 5 looks like is designed to double from 200 watt 8ohm to 400 Watt 4 ohm but the designer upped the voltage rail to give it more dynamic range into 8 ohms,
Nelson Pass does the same thing in his Pass Labs Amps.

This is ok when you see the same shape in 8,4,2 ohms just shifted in the THDvsWatt curve like on this amp on PassLabs and on ML334,
alright there is no curve for 2ohms on this one.

If the 2ohm curve starts to bend up early then it will wimp out on Alexia's

On 4 ohm load it is actually cleaner than ML334 because ML will crush the signal into the rail and the current window will close
(maximum at 100% distortion is 510 Watts),
Constellation will continue to deliver clean current up to 410 Watts and 3% distortion at 510 Watt so it can do more current into 4 ohm even if it has weaker Transformer then ML334.

Specs dont tell jack, audio manufacturers need to print a graph so you can see if it starts to distort up more (gain accounted of course) into low resistant loads or stay idential, does not matter if it double up on power if distortion spectrum is stable aka identical into 8,4,2 ohms then it will sound fine.

The messed up tone control is indeed what damages the sound.

georgehifi's picture

The end result is this amp was never going to get the best out of the Revel Ultima Salon2 impedance curve, the ML334 did a better job. All you have to do is look at the remarks from the reviewer (below) and then draw a conclusion from the tests results.

Larry Greenhill
"However, the Constellation didn't go as low in the deep bass. This meant that dynamic contrasts involving deep bass, such as sustained pedal chords from pipe organs, were more emotionally involving with the No.334, shaking my listening room more.
The conga drum that begins "Hotel California," from the Eagles' Hell Freezes Over was well defined and tight through the Stereo 1.0, but more 3D and room-shaking through the No.334.
The heartbeat that opens "Breathe (in the Air)," from Pink Floyd's The Dark Side of the Moon was a well-defined, dense, solid, pitch-perfect pulse with the Stereo 1.0, but not as ominous or as room-shakingly massive as with the No.334."

Cheers George

dce22's picture

Constellation can push more current into Revel Ultima Salon2 then ML334 its Ohm's law
If you turn up the volume so that 11 Amps flows to the Revel's

Constellation Will sound a bit distorted
ML 334 Will sound like screeching noise (more current capability blocked by voltage rail to delever less)

ML will sound better at 1 ohm speakers,
you need voltage so that current flows thru the wire
Constellation has more voltage and at Ultima Salon2 curve will not runout of current at clipping.

Current capability in this case does not limit the low frequency sound quality its the circuit design is it subsonic filter or is it overactive DC servo you need circuit schematic to tell the tests say that is something like that nothing to do with current.

You are attributing the cause of the problems to something unrelated.


Edit : By "push current" i mean capable of current flow without bending out of shape, distorting in irregular fashon different that higher impedance.

georgehifi's picture

Sorry, you can't see the forest through the trees, I'm not talking loudness WATTS for rave parties!! If I want that I'll get a 1000w Crown. I'm talking the abilty to best drive (to a certain volume) the review and test comments back it up.

Would you think a pair of 25w ML2 monoblocks would drive the Revells better (to a given volume) than the Constellation can, yes, because they can do current better, just like the ML334 can.
Yes these are only 25w into 8ohms

Cheers George

dce22's picture

Not denying that 25 watts good amp can sound better,
you are mixing current capability with distortion, if you design in same front end distortion mechanism that is in Constellation into ML334 it will sound alike

Fig. 6 blue line 12Watts 8Ohm you can see the distotion mechanism in action

Does not matter the load impedance, current, loud or quiet it will sound the same.

Trying to tell you that Constellation can do more current/power more dynamic range into the revels and the sound is not connected to your misguided opinion that its because loads or currents.


dce22's picture

Take ML 334


and change the transformer to the same core just change the winding to output higher voltage and you will get


The same amp....

does that means that now the ML 334 sounds different, not really.

Pass Labs does this Constellation does this not doubling on power is not precursor to bad sound you need to look at the distorion curve does it change into higher load if the shape is the same just shifted all is good.

georgehifi's picture

"you are mixing current capability with distortion,"

No you sorry are mixing high loudness distortion with quality normal listen level that has better everything dynamics included. And the ML2's and ML334 will do it better. End of story.

Cheers George

dce22's picture

If the amp is more capable at high power it will not brake a sweat at normal listening level.

ML2 25/50/100 Watt vs Constellation 300/400/200* Watts

*Let's say for the sake of argument that it can do at least 200 at 2ohm

Costellation has better dynamics any way you slice it, its all in signal distortion.

You are behaving like a conspiracy theorists even in the light of clear evidence you are clinging on that the earth is flat.

Just trying to help people get a better reading of the Measurement graphs not to change your mind really, people that does not know much can easy be steered in a wrong way and snowball your lie that the heavy amp with lots of metal that goes 5/10/20/40 watts at 8/4/2/1 ohm is more dynamic than Class D ncore KW amp,
and it sounds better because its big and heavy and uses lots of power not because it distorts less or in a different manner.

No hard feelings or anything personal i just think you are not informed enough recommending Bob Cordell's book "Designing Audio Power Amplifiers".


georgehifi's picture

Sorry you can understand what I said therefore you can't see the forest through the trees.

The proof to you is, the 25w ML2 will sound and drive better "to a given level" the .9 ohm load of the Alexia and also to a degree the Revells here than the 380w Constellation can. As the Constellation will act like a bit of a tone control because of the Alexia's impedance variations from 20hz to 20khz. Where both the ML's will stay flatter. End of story.

Cheers George

dce22's picture

"ML2 will sound and drive better "to a given level" the .9 ohm load of the Alexia"

Yes you are correct

"As the Constellation will act like a bit of a tone control because of the Alexia's impedance variations from 20hz to 20khz. Where both the ML's will stay flatter."

Yes you are correct and on that "Tone Control" Constellation has another "Tone Control" on the frontend of the amp that creates the bass discrepancy between the ML334 and Constellation on Revel's because the Output stage has no problems driving the Revel Ultima Salon2 as good as ML334

Constellation output stage is better at driving the Revel Ultima Salon2 than ML334 by virtue of higher output voltage

ML334 is voltage limited on Ultima Salon2
Constellation is current limited on Alexia

The Measurments confirm that low frequency impact on Constellation is caused by the amp front end distortion not the output stage so more transistors and bigger transformer to drive 1ohm at kilowatts will not change the bass performance of the amp it will still sound the same.

You get what im saying.


georgehifi's picture

a 25w ML2 will sound and drive better "to a given level" the .9 ohm load of the Alexia than the Constellation, so will the ML334.
I don't care about party levels, it was all about picking the right speaker to do an amp review with, and in this case it wasn't, as the reviewers comments and tests bore out.

"Yes you are correct"

That all I wanted to say. By

Cheers George