ATC SCM150 Amp and Preamp recommendations

@lonemountain 

Hi Brad,

Thank you for the detailed and thoughtful response. I appreciate your insight as the U.S. importer and certainly respect ATC’s engineering philosophy—especially the precision and integration of their active systems. The technical points about phase coherence, component tolerances, and amp-driver calibration are well taken and valid from a design purity standpoint.

That said, I chose the SCM150 passives very deliberately, not as a compromise, but because they allow me to shape the sonic outcome exactly as I want it. My priority is extracting a harmonically rich, dynamic, and lifelike presentation—qualities I’ve been able to enhance by pairing them with an ultra-high-current Class AB amplifier and a well-matched tube preamp. The transient performance and low-end authority I’m getting now are exactly what I was seeking.

While I understand the argument about passive crossovers and inductor wire lengths, in practice, the performance delta depends heavily on system synergy and listener priorities. The subjective gains I’ve achieved through amplification choice—particularly in tone density and spatial realism—outweigh the theoretical drawbacks of the passive network in my setup.

Regarding power: you’re right that +3 dB isn’t a night-and-day difference on paper, but in dynamic music like large-scale orchestral works, the added headroom of an 800W+ amp translates to more effortless macro- and microdynamics at live-like levels, especially with complex low-frequency content. For me, it’s not about listening at 115 dB, but about having total control and composure when the music demands it.

Ultimately, this comes down to different paths to musical satisfaction. I fully understand the merits of the active approach, but I’ve found that the passive route—with the right amplification—gives me the flexibility and sonic character I value most.

I sincerely appreciate the dialogue and hope we can stay in touch as I continue refining the system.

Rotel Mitchi M8 is a nuclear weapon when it comes to power. Stereophile has a review on these monos. I have heard the stereo version of the M8.

@ei001h 

You’ve put forth the only argument that wins.  It for this reason that we still build passives as many in the hi fi hobby love the ability to "craft their own" so to speak.  The technical virtues of "the lowest distortion way" dont always win as we can easily see with those that love tubes.

My experience is that when active is chosen, it does not diminsh this "craft your own" part of the hobby and actually strengthens it.   Once the distortion of so much wire is removed, and phase is now linear, the items IN FRONT of the actives take on new meaning and greater dimensionality.  Cables, turntables, line level cables, streamers all become more different, more obvious than before. I ahve found that changes in front of the actives are now even more significant than before.

All that being said what most people focus on is tone, how a trumpet sounds, a piano, a vocal; in this the active and passive are remarkably similar.  the times I have done this comparison, many in the room cannot tell the difference or just take a wild guess.  What does affect choice that is easy to miss is tiny differences in level, comparing two things; this can make a dramatic impact in perception of which one sounds more full or warmer.  Slight differences in level appear as better bass or less bass, more treble or less (thank you Fletcher Munson curve). 

The source material can also influence this choice as many records or albums have more or less bass or more or less treble than another record.  IF I play Led Zeppelin you’ll be convinced there is less bass  (these LZ records are notorius for no bass).  If I play Patricia Barber you will be convinced there is more bass and better midrange (I know the engineer who records her and he uses very expensive hand made tube microphones i sold him many years ago that have tremendouos definition) . 

The casual or rough demos we expereince in trade shows or at someones’s house can really lead you astray, as many factors influencing perception are hidden: look no further than continuously variable gain controls on preamps which are impossible to match or repeat from one source to the other.  A tiny 1 dB level difference will make you 100% certain one of the two things has more bass or treble.   Often we attribute differences that we hear to something other than level as level alone is tough to hear. 

For example, conviction that the 800W amp vs the 300W amp is signitificant   enough to hear the differences in dynamic range may not be true depending on just two factors: the efficiency of the speaker you are comparing them on and the "sound" of the amp itself on that particular pair of loudspeakers.  I think those two factors could sway your choice one way or the other, regardless of which one has the larger power output.  SO if you are actually listening at 85dB SPL on a 90ddB 1w/1m speaker, it may not show that a 800W amp as better than a 300W amp dynamically.  O a 80dB 1w/1m speaker, it may show this easily. 

Brad      

@lonemountain 

I actually remember when I first reached out to you during my decision process between active and passive SCM150s. You strongly recommended going with the actives, and I took that advice seriously. I spent time listening to them—really trying to connect—but while they were undeniably impressive in terms of clarity and control, I found myself oddly unengaged. Something about the presentation just didn’t draw me in.

So I went with the passives—and as you’ll recall, you kindly arranged to have them shipped directly to my home. That moment marked the beginning of a very different journey. With the passives, I was finally able to shape the sound in a way that felt personal. Pairing them with an ultra-high-current Class AB amp and a tube preamp brought out the harmonics, tone density, and transient realism I’d been chasing. The system came alive in a way the actives simply didn’t.

I do understand and respect the technical benefits of actives—better phase coherence, reduced component variability, and so on. But in my experience, the real-world gains of external amplification—especially in bass authority, dimensionality, and tonal nuance—have made a bigger musical impact. For someone like me, who listens primarily to large-scale classical and acoustic recordings, that nuance is everything.

You also made a great point about how level differences and source material can color perception. It’s something I try to control for when I’m evaluating gear. But those same small differences don’t invalidate what we feel when we’re genuinely moved by a system. At some point, it’s not about which one measures better—it’s about which one connects.

So while I completely respect the elegance of the active design, for me, the passives were never a compromise. They were the doorway to shaping a system that feels uniquely mine—and that makes music feel more human, more alive. Edward 

@lonemountain thank you for participating.  Perhaps ATC will pickup my suggestion of an outboard active crossover?

I imagine the OP made the best choice for his specific situation.